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  • 1.
    Andersson, Evert
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Nelldal, Bo-Lennart
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Varför behövs Nya Stambanor i Sverige?2020Report (Other academic)
    Abstract [sv]

    Stora investeringar och omdaningar planeras i vårt transportsystem. Transporterna väntas öka starkt i framtiden och mera kapacitet måste skapas på ett hållbart sätt. Diskussionerna om vilka transportmedel som ska prioriteras, såväl som vilka objekt som vi ska satsa på, är livliga.

    En viktig fråga är satsningen på Nya Stambanor avsedda för snabba persontransporter i de redan idag hårt belastade stråken Stockholm‒Göteborg och Stockholm‒Malmö, med ett stort antal mellanliggande orter. Denna typ av järnvägar finns redan eller planeras i de flesta av världens ledande ekonomier. Syftet med att bygga nya stambanor är att öka den totala kapaciteten för person- och godstrafik på järnväg, öka punktligheten och öka tillgängligheten genom korta restider. Det ger också förutsättningar för större regionala arbetsmarknader och ökat bostadsbyggande utanför storstäderna samt en bättre miljö. Nuvarande stambanor avlastas och lämnar plats för bl a effektivare godstransporter.

    Denna rapport behandlar först järnvägens egenskaper. Järnvägen är det energieffektivaste transportmedel vi känner till, den tar liten plats och är mycket trafiksäker. Moderna tåg på modern bana är vårt snabbaste transportmedel till lands. Tåg kan bereda plats och komfort för arbete och avkoppling under resan. Enligt författarnas uppfattning bör dessa egenskaper göra järnvägen till ett förstahandsalternativ för effektiva och hållbara transporter i de segment där järnvägen är eller kan bli konkurrenskraftig.

    Prognoser och analys, samt erfaren­heter från utlandet, visar att trafikunderlaget i Sverige är tillräckligt för nya stambanor. Med de förslagna banorna väntas järnvägens totala kapacitet öka till mer än det dubbla i de mest belastade stråken. En viktig faktor är att den snabba och långsamma tågtrafiken separeras. Denna åtgärd ger ökad kapacitet, utöver vad de dubblerade spåren ger, eftersom tågen kan köra tätare efter varandra och störningarna i tågtrafiken minskar.

    Restiderna för orterna längs de nya stambanorna minskar kraftigt, i regel mellan 30 och 65%. Tillsammans med ökad turtäthet och minskade störningar ger det stora ökningar av tågtrafiken. De officiella prognoserna lider dock av ett antal allvarliga brister, varför både trafikökningen och den samhällsekonomiska lönsamheten beräkningsmässigt framstår som mindre än vad den enligt KTH:s prognoser och internationell erfarenhet borde vara.

    Författarna anser att anläggningskostnaderna är rimliga i relation till nyttorna och jämfört med vad andra omställningar i samhällets transportsystem kostar. Detsamma gäller den engångs ”klimatskuld” som uppkommer vid de flesta satsningar för framtiden inom alla trafikslag. Nya transportslag i ett tidigt utvecklingsskede (elflyg, magnettåg, Hyperloop etc) är mycket osäkra beträffande när eller om de överhuvudtaget kommer att bli tillgängliga för användning i stor skala. I flera fall skulle krävas stora tekniska genombrott som vi idag inte känner till. Vi anser att man rimligen inte idag kan besluta att satsa på helt nya tekniska system för vilka framtiden är mycket osäker. Vi kan inte heller ”vänta och se”, eftersom ytterligare kapacitet behövs redan idag och ledtiderna är långa.

    Sammanfattningsvis är de nya stambanorna ett samhällsbyggnadsprojekt och en del i transportsektorns nödvändiga omställning. De ger korta restider och effektiva transporter mellan våra största städer, liksom till och från ett stort antal mellanliggande orter, med omnejd. Godstransporterna kan också få plats på spåren och de kan utvecklas och effektiviseras. Det handlar om hållbar mobilitet för människor och gods i framtiden.

  • 2.
    Bottier, Mathieu
    et al.
    Eq. 13, Institut Mondor de Recherche Biomédicale, Inserm U955, Créteil, France.
    Peña Fernández, Marta
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Pelle, Gabriel
    Eq. 13, Institut Mondor de Recherche Biomédicale, Inserm U955, Créteil, France.
    Isabey, Daniel
    Eq. 13, Institut Mondor de Recherche Biomédicale, Inserm U955, Créteil, France.
    Louis, Bruno
    Eq. 13, Institut Mondor de Recherche Biomédicale, Inserm U955, Créteil, France.
    Grotberg, James B
    Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA..
    Filoche, Marcel
    Eq. 13, Institut Mondor de Recherche Biomédicale, Inserm U955, Créteil, France.
    A new index for characterizing micro-bead motion in a flow induced by ciliary beating: Part II, modeling.2017In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 13, no 7, article id e1005552Article in journal (Refereed)
    Abstract [en]

    Mucociliary clearance is one of the major lines of defense of the human respiratory system. The mucus layer coating the airways is constantly moved along and out of the lung by the activity of motile cilia, expelling at the same time particles trapped in it. The efficiency of the cilia motion can experimentally be assessed by measuring the velocity of micro-beads traveling through the fluid surrounding the cilia. Here we present a mathematical model of the fluid flow and of the micro-beads motion. The coordinated movement of the ciliated edge is represented as a continuous envelope imposing a periodic moving velocity boundary condition on the surrounding fluid. Vanishing velocity and vanishing shear stress boundary conditions are applied to the fluid at a finite distance above the ciliated edge. The flow field is expanded in powers of the amplitude of the individual cilium movement. It is found that the continuous component of the horizontal velocity at the ciliated edge generates a 2D fluid velocity field with a parabolic profile in the vertical direction, in agreement with the experimental measurements. Conversely, we show than this model can be used to extract microscopic properties of the cilia motion by extrapolating the micro-bead velocity measurement at the ciliated edge. Finally, we derive from these measurements a scalar index providing a direct assessment of the cilia beating efficiency. This index can easily be measured in patients without any modification of the current clinical procedures.

  • 3.
    Bouchouireb, Hamza
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Advancing the life cycle energy optimisation methodology2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Life Cycle Energy Optimisation (LCEO) methodology aims at finding a design solution that uses a minimum amount of cumulative energy demand over the different phases of the vehicle's life cycle, while complying with a set of functional constraints. This effectively balances trade-offs, and therewith avoids sub-optimal shifting between the energy demand for the cradle-to-production of materials, operation of the vehicle, and end-of-life phases. This work further develops the LCEO methodology and expands its scope through three main methodological contributions which, for illustrative purposes, were applied to a vehicle sub-system design case study.

    An End-Of-Life (EOL) model, based on the substitution with a correction factor method, is included to estimate the energy credits and burdens that originate from EOL vehicle processing. Multiple recycling scenarios with different levels of assumed induced recyclate material property degradation were built, and their impact on the LCEO methodology's outcomes was compared to that of scenarios based on landfilling and incineration with energy recovery. The results show that the inclusion of EOL modelling in the LCEO methodology can alter material use patterns and significantly effect the life cycle energy of the optimal designs.

    Furthermore, the previous model is expanded to enable holistic vehicle product system design with the LCEO methodology. The constrained optimisation of a vehicle sub-system, and the design of a subset of the processes which are applied to it during its life cycle, are simultaneously optimised for a minimal product system life cycle energy. In particular, a subset of the EOL processes' parameters are considered as continuous design variables with associated barrier functions that control their feasibility. The results show that the LCEO methodology can be used to find an optimal design along with its associated ideal synthetic EOL scenario. Moreover, the ability of the method to identify the underlying mechanisms enabling the optimal solution's trade-offs is further demonstrated.

    Finally, the functional scope of the methodology is expanded through the inclusion of shape-related variables and aerodynamic drag estimations. Here, vehicle curvature is taken into account in the LCEO methodology through its impact on the aerodynamic drag and therewith its related operational energy demand. In turn, aerodynamic drag is considered through the estimation of the drag coefficient of a vehicle body shape using computational fluid dynamics simulations. The aforementioned coefficient is further used to estimate the energy required by the vehicle to overcome aerodynamic drag. The results demonstrate the ability of the LCEO methodology to capitalise on the underlying functional alignment of the structural and aerodynamic requirements, as well as the need for an allocation strategy for the aerodynamic drag energy within the context of vehicle sub-system redesign.

    Overall, these methodological developments contributed to the exploration of the ability of the LCEO methodology to handle life cycle and functional trade-offs to achieve life cycle energy optimal vehicle designs.

  • 4.
    Casanueva, Carlos
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Dirks, Babette
    Trafikverket.
    Tohmmy, Bustad
    Trafikverket.
    Rail Vehicle Dynamics Simulation-based decision support for novel block brake material implementation in Sweden2019In: THE 26TH IAVSD INTERNATIONAL SYMPOSIUM ON DYNAMICS OF VEHICLES ON ROADS AND TRACKS, 12-16 August 2019, Gothenburg, Sweden, 2019Conference paper (Other academic)
    Abstract [en]

    . The application of TSI Noise in Sweden needs decision support that can objectively state system-wide benefits and disadvantages, as there are issues with the introduction of novel block brakes: reduced braking performance and increased equivalent conicity. The Roll2Rail Universal Cost Model (UCM) is used to analyse Life Cycle Cost (LCC), as it was also conceived so that it could be used within the decision making processes of infrastructure managers. The simulated characteristics are mainly track Rolling Contact Fatigue (RCF) due to the worsened dynamic train-track interaction.

    The full text will be freely available from 2020-04-30 21:46
  • 5.
    Ceccato, Chiara
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Barbier, C.
    BillerudKorsnäs, Grums, Värmland County, Sweden.
    Investigation of rolling contact between metal and rubber-covered cylinders governing the paper compaction process2019In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 163, article id 105156Article in journal (Refereed)
    Abstract [en]

    With the goal of partial or complete replacement of plastic components with paper-based products, 3D paper structures have seen a growing interest in industrial applications: from packaging to more complex daily life objects. However, the extensibility of paper has become a key issue within this context and is the main factor determining the formability of these products and determining the depth of the achievable shapes. The most effective way to increase paper's stretch potential is by subjecting the moist paper web to a compaction process, which can be achieved through an extensible unit that is located in the drying section of a paper machine, where the network experiences in-plane compression in the machine direction (MD), under out-of-plane lateral constraints. The objective of this work is to clarify the mechanisms governing the compression process and to evaluate the influence of various parameters on the final material properties to optimize the industrial production of extensible paper. The system operation has been simulated realistically and shows that paper experiences a compressive state passing through the nip, with plastic strains in MD direction being of the same order of the applied speed difference, which was expected experimentally in optimal conditions of compaction. Starting from an initial reference case, a sensitivity study has been performed to identify and address the following factors that may affect the compression state: (a) friction coefficients; (b) indentation level; (c) speed difference; and (d) rubber properties. The analysis of the numerical results gives an insight into the mechanisms governing the compaction operations and allows a better comprehension of the features controlling the process outcome.

  • 6. Dall'Ara, Enrico
    Palanca, Marco
    Giorgi, Mario
    Cristofolini, Luca
    Tozzi, Gianluca
    Precision of Digital Volume Correlation approaches for strain analysis in bone imaged with micro-computed tomography at different dimensional levels2017In: Frontiers in MaterialsArticle in journal (Refereed)
  • 7.
    De Mori, Arianna
    et al.
    School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth PO1 2DT, UK..
    Peña Fernández, Marta
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Blunn, Gordon
    School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth PO1 2DT, UK..
    Tozzi, Gianluca
    Zeiss Global Centre, School of Engineering, University of Portsmouth, Portsmouth PO1 3DJ, UK..
    Roldo, Marta
    School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth PO1 2DT, UK..
    3D Printing and Electrospinning of Composite Hydrogels for Cartilage and Bone Tissue Engineering.2018In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 10, no 3, article id E285Article in journal (Refereed)
    Abstract [en]

    Injuries of bone and cartilage constitute important health issues costing the National Health Service billions of pounds annually, in the UK only. Moreover, these damages can become cause of disability and loss of function for the patients with associated social costs and diminished quality of life. The biomechanical properties of these two tissues are massively different from each other and they are not uniform within the same tissue due to the specific anatomic location and function. In this perspective, tissue engineering (TE) has emerged as a promising approach to address the complexities associated with bone and cartilage regeneration. Tissue engineering aims at developing temporary three-dimensional multicomponent constructs to promote the natural healing process. Biomaterials, such as hydrogels, are currently extensively studied for their ability to reproduce both the ideal 3D extracellular environment for tissue growth and to have adequate mechanical properties for load bearing. This review will focus on the use of two manufacturing techniques, namely electrospinning and 3D printing, that present promise in the fabrication of complex composite gels for cartilage and bone tissue engineering applications.

  • 8.
    Eliasson, Sara
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Barsoum, Zuheir ()
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Wennhage, Per ()
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Development of fatigue testing procedure for unidirectional carbon fiber composites2019In: Procedia Structural Integrity, ISSN 2452-3216, Vol. 19, p. 81-89Article in journal (Refereed)
  • 9.
    Everitt, Carl-Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Öberg, Martin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    An imprint method to produce surface asperities for EHL and RCF experiments2020Report (Other academic)
    Abstract [en]

    A method was developed for creating single well defined surface asperities using an imprint technique. The proposed method can be used to create asperities of different heights and widths in the micrometre range. The technique for creating single surface asperities is based on rolling a hard disc with indents against a soft disc. The contact pressure will cause plastic deformation forcing material into the indents to create the asperities. The height of the asperities can be controlled by adjusting the applied force. After initial reshaping during the run-in process, the asperities were strong enough to survive more than 35 million EHL contact cycles. The method should thus be of great interest for the researchers investigating rolling contact fatigue experimentally. The method could also aid the research of the run in process by enabling tracing the development of specific surface defects. Since the method can produce high and strong asperities it might also prove useful for investigations of exactly how asperities deform under sever contacts conditions.  

  • 10.
    Gualtieri, P.
    et al.
    Dipartimento di Ingegneria Meccanica e Aerospaziale, 'Sapienza' University, Via Eudossiana 18, 00184 Roma, Italy.
    Picano, F.
    KTH, Superseded Departments (pre-2005), Mechanics. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy;.
    Sardina, G.
    Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome; UKE - Università Kore di ENNA Facoltà di Ingegneria, Architettura e Scienze Motorie, Via delle Olimpiadi, 94100 Enna, Ital.
    Casciola, C. M.
    Department of Mechanics and Aeronautics, 'Sapienza' University of Rome, Via Eudossiana 18, 00184 Rome, Italy.
    Exact regularized point particle method for particle-laden flows in the two-way coupling regime2012In: Proceedings of the Seventh International Symposium On Turbulence Heat and Mass Transfer, 2012, p. 1342-1351Conference paper (Refereed)
    Abstract [en]

    In this paper we present a new methodology which is proved to capture the momentum exchange between a carrier turbulent flow and thousands of sub-Kolmogorov inertial particles. The velocity disturbance produced by the disperse phase is described in terms of exact regularized unsteady Stokes solutions. The approach is validated by addressing the motion of a single particle in still fluid and by comparing data of actual turbulent spatially homogeneous flows against results provided by the classical particle-in-cell method.

  • 11.
    Hörberg, Erik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    An Experimental Investigation of Shape Distortions in Aerospace Composites2020Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Composite materials are increasingly used in primary structure of modern commercial aircraft. Its excellent material characteristics enables reduction of structural weight compared to traditional metal solutions and thereby offers reduction of fuel consumption and carbon dioxide (CO2) emissions. In the aerospace industry, carbon fibre reinforced plastics or CFRP is the most commonly used composite material, where the reinforcement is held together by a thermoset resin, often epoxy, referred to as the matrix.

    When manufacturing aircraft composite parts, the curing temperature is usually in-between 120°C to 180°C. As the constituents, i.e. fibre and matrix, have significantly different thermal expansion, the temperature difference from manufacturing of parts to assembly and in-service use results in shape distortions and/or development of residual stresses. With an increased size and complexity of structural parts used in modern aircraft, the development of efficient methods for shape distortion analysis are therefore becoming increasingly important. Shape distortions come from numerous sources and some of them like thermal expansion and chemical shrinkage during curing are fairly well studied and understood. The focus of this thesis is on less researched parameters such as the laminate bending stiffness and effects of moisture content.

    The bending stiffness of a laminate can be controlled by varying the thickness of the laminate, or by changing the layup sequence of individual plies. Paper A presents an experimental study on shape distortion were the effect of laminate bending stiffness is separated from that of the laminate thickness. The results show that it is possible to tailor the laminate layup in a way that is beneficial for in-plane loads, while still reducing the built-in stresses that occur in a composite component due to shape distortions.

    The second parameter investigated in this thesis is the laminate moisture content. Composite materials used in aircraft structures will be exposed to environmental effects such as varying temperatures and moisture. The exposure is seldom constant but varies over time, depending on seasonal change and geographical area of aircraft operation. In Paper B, the influence of laminate moisture content on shape distortions is experimentally investigated. It becomes clear that laminate moisture content has such a strong effect on shape distortions that it is important to control and predict for all composite structures.

    The results presented in this thesis show that both laminate bending stiffness and laminate moisture content have a great influence on shape distortions, and that further research and development is needed to improve the simulation methodology used within the aerospace industry. This is key to future cost-efficient production and assembly of large composite parts.

  • 12.
    Hörberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Nyman, Tonny
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Thickness effect on spring-in of prepreg composite L-profiles – An experimental study2019In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 209, p. 499-507Article in journal (Refereed)
    Abstract [en]

    This paper presents the results and analysis of an experimental study of laminate thickness effects on the springin and shape distortion of thermoset composite L profiles. The primary objective is to achieve a broader understanding of how shape distortion is affected by laminate bending stiffness and part thickness of L-shaped laminates whose thickness varies between 1 and 12 mm. The larger thicknesses in particular have not received much attention in previous research. This work further aims at distinguishing the pure (geometrical) thickness effect from that of the coupled laminate bending stiffness by comparing laminates with different lay-ups. The work is performed on test specimens subjected to both a standard cure cycle and post-cure heat treatment at elevated temperatures. In parallel, finite element (FE) analysis is performed to evaluate if variation in the bending stiffness or the laminate thickness affects the predicted spring-in angle. The results clearly show springin dependence on laminate thickness and bending stiffness, whereas this dependence is not well predicted by the FE approaches. It is concluded that both effects exist and that shape distortions are more strongly related to bending stiffness than to laminate thickness.

  • 13. Hörberg, Erik
    et al.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Moisture effect on shape distortions of curved prepreg laminatesManuscript (preprint) (Other academic)
    Abstract [en]

    The influence from moisture content on shape distortion of curved thermoset composite laminates is investigated experimentally. The particular objects of study are L-shaped carbon/epoxy specimens with a quasi-isotropic layup and the thickness varying between 1 and 12 mm. The effect on the shape distortion is quantified by means of spring-in angle measurements vs. accelerated moisture uptake utilising a climate chamber at 90°C and 95% relative humidity. The results clearly show a strong dependence on spring-in angles from laminate moisture content – the effect is in fact in the same order of magnitude as the spring-in from thermal and chemical shrinkage during curing. Moisture does thus not only affect shape distortions but also has to be taken into consideration and be carefully controlled when assessing spring-in due to other parameters. Finally, a model based on the experimental results predicting the spring-in angle is presented.

  • 14.
    Krishna, Visakh V
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hossein Nia, Saeed
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, Superseded Departments (pre-2005), Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    New Methodology to Estimate Costs Caused by Rail Wear and RCF Depending on the Type of Running Gear2020In: IAVSD 2019: Advances in Dynamics of Vehicles on Roads and Tracks / [ed] Matthijs Klomp, Fredrik Bruzelius, Jens Nielsen and Angela Hillemyr, 2020Conference paper (Refereed)
    Abstract [en]

    A new methodology to estimate costs for wear and Rolling Contact Fatigue (RCF) on rails that cause a major portion of track maintenance costs is presented. It is demonstrated for a standard UIC-Y25 bogie and a FR8RAIL bogie, a softer and cross-braced iteration of the former. The rail profile evolution and the surface-initiated fatigue on the rail surface for different track radii with progressive tonnage are calculated using multi-body simulations. ‘Fastrip’ is used to calculate tangential stresses on the contact patch. Various non-linearities in the vehicle and track models have been considered, based on running conditions on the Swedish Iron-ore line. A cyclic rail grinding procedure at fixed tonnage intervals based on recommendations from EN13231-5 is implemented, to also account for the effect of track maintenance on the rate of rail surface damage. The wear depths (W), worn cross-sectional areas (A) and the number of axle passes that carry a risk for RCF initiation (Nr) are presented and discussed for 100 Mega Gross Tonnes passage. In doing so, the methodology addresses ‘track-friendliness’ of the running gear considering both its design and the track maintenance strategies.

  • 15.
    KULKARNI, ROHAN
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Qazizadeh, Alireza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    FAULT DETECTION AND ISOLATION METHOD FOR VEHICLE RUNNING INSTABILITY FROM VEHICLE DYNAMICS RESPONSE USING MACHINE LEARNING2019In: Proceedings of 11th International Conference on Railway Bogies and Running Gears (BOGIE'19) / [ed] Prof. István ZOBORY, Budapest, 2019Conference paper (Refereed)
    Abstract [en]

    In this paper, a Fault Detection and Isolation (FDI) method is proposed for monitoring the vehicle running stability in a high-speed railway bogie. The objective is to detect and isolate the different faults of bogie components which are critical to vehicle stability, especially degraded yaw dampers and high equivalent conicity caused by wheel wear. The proposed method has two steps; firstly, signal features sensitive to the characteristics of running instability are extracted based on frequency domain and time domain analysis of lateral accelerations of bogie frame and axlebox; then these features along with vehicle speed are fed into machine learning based fault classifiers. The supervised machine learning based fault classifier are trained to identify the cause of observed running instability among yaw damper degradation and wheel-rail profile pair with high equivalent conicity. The Support Vector Machine (SVM) classifier with Linear and Gaussian kernels are trained by k-fold crossvalidation method and the hyperparameters are optimized with a bayesian optimization algorithm to minimize the classification error. These fault classifiers are trained and tested with an extensive database generated from numerical experiments performed by multibody simulation (MBS) software. The performance of Linear and Gaussian SVM fault classifiers is compared with each other to identify the best performing classifier. The results underline the ability of machine learning based fault classifiers to be used for FDI of vehicle running instability and outline the possibility of detecting and isolating bogie faults critical to the vehicle stability based on onboard measurement of vehicle dynamic response.

  • 16.
    Lind, Petter N.
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Augmented Single Loop Single Vector Algorithm Using Nonlinear Approximations of Constraints in Reliability-Based Design Optimization2019In: Journal of mechanical design (1990), ISSN 1050-0472, E-ISSN 1528-9001, Vol. 141, no 10, article id 101403Article in journal (Refereed)
    Abstract [en]

    Reliability-based design optimization (RBDO) aims at minimizing a function of probabilistic design variables, given a maximum allowed probability of failure. The most efficient methods available for solving moderately nonlinear problems are single loop single vector (SLSV) algorithms that use a first-order approximation of the probability of failure in order to rewrite the inherently nested structure of the loop into a more efficient single loop algorithm. The research presented in this paper takes off from the fundamental idea of this algorithm. An augmented SLSV algorithm is proposed that increases the rate of convergence by making nonlinear approximations of the constraints. The nonlinear approximations are constructed in the following way: first, the SLSV experiments are performed. The gradient of the performance function is known, as well as an estimate of the most probable failure point (MPP). Then, one extra experiment, a probe point, per performance function is conducted at the first estimate of the MPP. The gradient of each performance function is not updated but the probe point facilitates the use of a natural cubic spline as an approximation of an augmented MPP estimate. The SLSV algorithm using probing (SLSVP) also incorporates a simple and effective move limit (ML) strategy that also minimizes the heuristics needed for initiating the optimization algorithm. The size of the forward finite difference design of experiment (DOE) is scaled proportionally with the change of the ML and so is the relative position of the MPP estimate at the current iteration. Benchmark comparisons against results taken from the literature show that the SLSVP algorithm is more efficient than other established RBDO algorithms and converge in situations where the SLSV algorithm fails.

  • 17.
    Liu, Hailong
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Ahlinder, Astrid
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.
    Yassin, M. A.
    Finne Wistrand, Anna
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.
    Gasser, T. Christian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Computational and experimental characterization of 3D-printed PCL structures toward the design of soft biological tissue scaffolds2020In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 188, article id 108488Article in journal (Refereed)
    Abstract [en]

    Degradable porous polymeric structures are attractive candidates for biological tissue scaffolds, and adequate mechanical, transport, chemical and biological properties determine their functionality. Aside from the properties of polymer-based materials, the scaffold's meso-structure controls its elasticity at the organ length-scale. This study investigated the effect of the meso-structure on scaffolds' mechanical and transport properties using finite element analysis (FEA) and computational fluid dynamics (CFD). A number of poly (ε-caprolactone) (PCL) - based scaffolds were 3D printed, analyzed by microcomputed tomography (micro-CT) and mechanically tested. We found that the gradient (G) and gradient and staggered (GS) meso-structure designs led to a higher scaffold permeability, a more homogeneous flow inside the scaffold, and a lower wall shear stress (WSS) in comparison with the basic (B) meso-structure design. The GS design resulted in scaffold stiffness as low as 1.07/0.97 MPa under compression/tension, figures that are comparative with several soft tissues. Image processing of micro-CT data demonstrated that the imposed meso-structures could have been adequately realized through 3D printing, and experimental testing validated FEA analysis. Our results suggest that the properties of 3D-printed PCL-based scaffolds can be tuned via meso-structures toward soft tissue engineering applications. The biological function of designed scaffolds should be further explored in-situ studies.

  • 18. Lu, Xuekun
    et al.
    Peña Fernández, Marta
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Bradley, Robert S
    Rawson, Shelley D
    O'Brien, Marie
    Hornberger, Benjamin
    Leibowitz, Marty
    Tozzi, Gianluca
    Withers, Philip J
    Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography.2019In: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 96, p. 400-411, article id S1742-7061(19)30464-7Article in journal (Refereed)
    Abstract [en]

    Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. STATEMENT OF SIGNIFICANCE: This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.

  • 19. Mansour, Rami
    et al.
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Second-order reliability method based on Edgeworth expansion with application to reliability-based design optimization2019In: Proceedings of the ASME Design Engineering Technical Conference, 2019Conference paper (Refereed)
    Abstract [en]

    In the Second-Order Reliability Method, the limit-state function is approximated by a hyper-parabola in standard normal and uncorrelated space. However, there is no exact closed form expression for the probability of failure based on a hyper-parabolic limit-state function and the existing approximate formulas in the literature have been shown to have major drawbacks. Furthermore, in applications such as Reliability-based Design Optimization, analytical expressions, not only for the probability of failure but also for probabilistic sensitivities, are highly desirable for efficiency reasons. In this paper, a novel Second-Order Reliability Method is presented. The proposed expression is a function of three statistical measures: the Cornell Reliability Index, the skewness and the Kurtosis of the hyper-parabola. These statistical measures are functions of the First-Order Reliability Index and the curvatures at the Most Probable Point. Furthermore, analytical sensitivities with respect to mean values of random variables and deterministic variables are presented. The sensitivities can be seen as the product of the sensitivities computed using the First-Order Reliability Method and a correction factor. The proposed expressions are studied and their applicability to Reliability-based Design Optimization is demonstrated.

  • 20.
    Marin, Gustav
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. RISE Innventia.
    Nygårds, Mikael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Stiffness and strength properties of five paperboards and their moisture dependency2019In: Proceedings of the 2019 International Paper Physics Conference / [ed] Doug Coffin, Tappi , 2019Conference paper (Refereed)
    Abstract [en]

    Five folding box boards made on the same paperboard machine have been analyzed. The paperboards were from the same product series but had different grammage (235, 255, 270, 315, 340 g/m2) and different bending stiffness. The paperboards are normally used to make packages, and since the bending stiffness and grammage varies the packages performance will be different. Finite element simulations can be used to predict these differences. However, the stiffness and strength properties then need to be known. For efficient determination of the three-dimensional properties in MD, CD and ZD, it is proposed that the whole paperboard should be characterized with the following tests: in-plane tension, ZD tension, shear strength profiles and two-point bending. The stiffness and strength properties have with the proposed setups been determined at different relative humidity (20, 50, 70 and 90 % RH), and the mechanical properties have been evaluated as function of moisture ratio.

    The results showed a linear relation between mechanical properties and moisture ratio for each paperboard. The data was then normalized with data for the standard climate (50 % RH) and investigated as a function of moisture ratio. The results indicated that the normalized mechanical properties for all paperboards coincided along one single line and could therefore be expressed as a linear function of moisture ratio and two constants.

    Consequently, the study indicates that it is possible to obtain the mechanical properties of a paperboard, by knowing the structural properties for the preferred level of RH and the mechanical property for the standard climate (50 % RH and 23 °C).

  • 21.
    Peña Fernández, Marta
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Bodey, Andrew (Contributor)
    Parwani, Rachna
    Blunn, Gordon
    Barber, Asa
    Tozzi, Gianluca
    Full-field strain analysis of bone-biomaterial systems produced by osteoregenerative biomaterials after in vivo service in an ovine model2019In: ACS Biomaterials Science and EngineeringArticle in journal (Refereed)
  • 22.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Barber, A H
    Blunn, G W
    Tozzi, G
    Optimization of digital volume correlation computation in SR-microCT images of trabecular bone and bone-biomaterial systems.2018In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 272, no 3, p. 213-228Article in journal (Refereed)
    Abstract [en]

    A micromechanical characterization of biomaterials for bone tissue engineering is essential to understand the quality of the newly regenerated bone, enabling the improvement of tissue regeneration strategies. A combination of microcomputed tomography in conjunction with in situ mechanical testing and digital volume correlation (DVC) has become a powerful technique to investigate the internal deformation of bone structure at a range of dimensional scales. However, in order to obtain accurate three-dimensional strain measurement at tissue level, high-resolution images must be acquired, and displacement/strain measurement uncertainties evaluated. The aim of this study was to optimize imaging parameters, image postprocessing and DVC settings to enhance computation based on 'zero-strain' repeated high-resolution synchrotron microCT scans of trabecular bone and bone-biomaterial systems. Low exposures to SR X-ray radiation were required to minimize irradiation-induced tissue damage, resulting in the need of advanced three-dimensional filters on the reconstructed images to reduce DVC-measured strain errors. Furthermore, the computation of strain values only in the hard phase (i.e. bone, biomaterial) allowed the exclusion of large artefacts localized in the bone marrow. This study demonstrated the suitability of a local DVC approach based on synchrotron microCT images to investigate the micromechanics of trabecular bone and bone-biomaterial composites at tissue level with a standard deviation of the errors in the region of 100 microstrain after a thorough optimization of DVC computation. LAY DESCRIPTION: Understanding the quality of newly regenerated bone after implantation of novel biomaterials is essential to improve bone tissue engineering strategies and formulation of biomaterials. The relationship between microstructure and mechanics of bone has been previously addressed combining microcomputed tomography with in situ mechanical testing. The addition of an image-based experimental technique such as digital volume correlation (DVC) allows to characterize the deformation of materials in a three-dimensional manner. However, in order to obtain accurate information at the micro-scale, high-resolution images, obtained for example by using synchrotron radiation microcomputed tomography, as well as optimization of the DVC computation are needed. This study presents the effect of different imaging parameters, image postprocessing and DVC settings for as accurate investigation of trabecular bone structure and bone-biomaterial interfaces. The results showed that when appropriate image postprocessing and DVC settings are used DVC computation results in very low strain errors. This is of vital importance for a correct understanding of the deformation in bone-biomaterial systems and the ability of such biomaterials in producing new bone comparable with the native tissue they are meant to replace.

  • 23.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Black, Cameron
    Dawson, Jon
    Gibbs, David
    Kanczler, Janos
    Oreffo, Richard O C
    Tozzi, Gianluca
    Exploratory Full-Field Strain Analysis of Regenerated Bone Tissue from Osteoinductive Biomaterials.2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 1, article id E168Article in journal (Refereed)
    Abstract [en]

    Biomaterials for bone regeneration are constantly under development, and their application in critical-sized defects represents a promising alternative to bone grafting techniques. However, the ability of all these materials to produce bone mechanically comparable with the native tissue remains unclear. This study aims to explore the full-field strain evolution in newly formed bone tissue produced in vivo by different osteoinductive strategies, including delivery systems for BMP-2 release. In situ high-resolution X-ray micro-computed tomography (microCT) and digital volume correlation (DVC) were used to qualitatively assess the micromechanics of regenerated bone tissue. Local strain in the tissue was evaluated in relation to the different bone morphometry and mineralization for specimens (n = 2 p/treatment) retrieved at a single time point (10 weeks in vivo). Results indicated a variety of load-transfer ability for the different treatments, highlighting the mechanical adaptation of bone structure in the early stages of bone healing. Although exploratory due to the limited sample size, the findings and analysis reported herein suggest how the combination of microCT and DVC can provide enhanced understanding of the micromechanics of newly formed bone produced in vivo, with the potential to inform further development of novel bone regeneration approaches.

  • 24.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Cipiccia, Silvia
    Dall'Ara, Enrico
    Bodey, Andrew J
    Parwani, Rachna
    Pani, Martino
    Blunn, Gordon W
    Barber, Asa H
    Tozzi, Gianluca
    Effect of SR-microCT radiation on the mechanical integrity of trabecular bone using in situ mechanical testing and digital volume correlation.2018In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 88, p. 109-119, article id S1751-6161(18)30763-XArticle in journal (Refereed)
    Abstract [en]

    The use of synchrotron radiation micro-computed tomography (SR-microCT) is becoming increasingly popular for studying the relationship between microstructure and bone mechanics subjected to in situ mechanical testing. However, it is well known that the effect of SR X-ray radiation can considerably alter the mechanical properties of bone tissue. Digital volume correlation (DVC) has been extensively used to compute full-field strain distributions in bone specimens subjected to step-wise mechanical loading, but tissue damage from sequential SR-microCT scans has not been previously addressed. Therefore, the aim of this study is to examine the influence of SR irradiation-induced microdamage on the apparent elastic properties of trabecular bone using DVC applied to in situ SR-microCT tomograms obtained with different exposure times. Results showed how DVC was able to identify high local strain levels (> 10,000 µε) corresponding to visible microcracks at high irradiation doses (~ 230 kGy), despite the apparent elastic properties remained unaltered. Microcracks were not detected and bone plasticity was preserved for low irradiation doses (~ 33 kGy), although image quality and consequently, DVC performance were reduced. DVC results suggested some local deterioration of tissue that might have resulted from mechanical strain concentration further enhanced by some level of local irradiation even for low accumulated dose.

  • 25.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Dall'Ara, Enrico
    Kao, Alexander P
    Bodey, Andrew J
    Karali, Aikaterina
    Blunn, Gordon W
    Barber, Asa H
    Tozzi, Gianluca
    Preservation of Bone Tissue Integrity with Temperature Control for In Situ SR-MicroCT Experiments.2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 11, article id E2155Article in journal (Refereed)
    Abstract [en]

    Digital volume correlation (DVC), combined with in situ synchrotron microcomputed tomography (SR-microCT) mechanics, allows for 3D full-field strain measurement in bone at the tissue level. However, long exposures to SR radiation are known to induce bone damage, and reliable experimental protocols able to preserve tissue properties are still lacking. This study aims to propose a proof-of-concept methodology to retain bone tissue integrity, based on residual strain determination using DVC, by decreasing the environmental temperature during in situ SR-microCT testing. Compact and trabecular bone specimens underwent five consecutive full tomographic data collections either at room temperature or 0 °C. Lowering the temperature seemed to reduce microdamage in trabecular bone but had minimal effect on compact bone. A consistent temperature gradient was measured at each exposure period, and its prolonged effect over time may induce localised collagen denaturation and subsequent damage. DVC provided useful information on irradiation-induced microcrack initiation and propagation. Future work is necessary to apply these findings to in situ SR-microCT mechanical tests, and to establish protocols aiming to minimise the SR irradiation-induced damage of bone.

  • 26.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Hoxha, Dorela
    Chan, Oliver
    Mordecai, Simon
    Blunn, Gordon W.
    Tozzi, Gianluca
    Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography2020In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 10, article id 1035Article in journal (Refereed)
    Abstract [en]

    Accurate in vivo quantifcation of subtalar joint kinematics can provide important information for the clinical evaluation of subtalar joint function; the analysis of outcome of surgical procedures of the hindfoot; and the design of a replacement subtalar joint prosthesis. The objective of the current study was to explore the potential of full weight-bearing clinical computed tomography (CT) to evaluate the helical axis and centre of rotation of the subtalar joint during inversion and eversion motion. A subject specifc methodology was proposed for the defnition of the subtalar joint motion combining threedimensional (3D) weight-bearing imaging at diferent joint positions with digital volume correlation (DVC). The computed subtalar joint helical axis parameters showed consistency across all healthy subjects and in line with previous data under simulated loads. A sphere ftting approach was introduced for the computation of subtalar joint centre of rotation, which allows to demonstrate that this centre of rotation is located in the middle facet of the subtalar joint. Some translation along the helical axis was also observed, refecting the elasticity of the soft-tissue restraints. This study showed a novel technique for non-invasive quantitative analysis of bone-to-bone motion under full weight-bearing of the hindfoot. Identifying diferent joint kinematics in patients with ligamentous laxity and instability, or in the presence of stifness and arthritis, could help clinicians to defne optimal patient-specifc treatments.

  • 27.
    Peña Fernández, Marta
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Biomechanics. Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth, PO1 3DJ, UK.
    Witte, F
    Tozzi, G
    Applications of X-ray computed tomography for the evaluation of biomaterial-mediated bone regeneration in critical-sized defects.2019In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818Article in journal (Refereed)
    Abstract [en]

    Bone as such displays an intrinsic regenerative potential following fracture; however, this capacity is limited with large bone defects that cannot heal spontaneously. The management of critical-sized bone defects remains a major clinical and socioeconomic need with osteoregenerative biomaterials constantly under development aiming at promoting and enhancing bone healing. X-ray computed tomography (XCT) has become a standard and essential tool for quantifying structure-function relationships in bone and biomaterials, facilitating the development of novel bone tissue engineering strategies. This paper presents recent advancements in XCT analysis of biomaterial-mediated bone regeneration. As a noninvasive and nondestructive technique, XCT allows for qualitative and quantitative evaluation of three-dimensional (3D) scaffolds and biomaterial microarchitecture, bone growth into the scaffold as well as the 3D characterisation of biomaterial degradation and bone regeneration in vitro and in vivo. Furthermore, in combination with in situ mechanical testing and digital volume correlation (DVC), XCT demonstrated its potential to better understand the bone-biomaterial interactions and local mechanics of bone regeneration during the healing process in relation to the regeneration achieved in vivo, which will likely provide valuable knowledge for the development and optimisation of novel osteoregenerative biomaterials. LAY DESCRIPTION: Bone, being a dynamically adaptable material, displays excellent regenerative properties following fracture. However, the self-healing capacity of bone becomes more difficult with large bone defects. Those defects are common and occur in many clinical situations; hence, biomaterials are mostly used to restore both bone structure and function in the defect site. X-ray computed tomography (XCT) is a powerful tool to evaluate bone regeneration in critical-sized defects after the implantation of biomaterials, allowing to an improved understanding of the regeneration process following different bone tissue engineering approaches. This paper focuses on recent advancements in XCT analysis to characterise biomaterial-mediated bone regeneration in critical-sized defects. XCT supports three-dimensional (3D) analysis of biomaterials, scaffolds and regenerated bone microarchitecture, as well as bone ingrowth into the scaffold. As a nondestructive technique, XCT allows for a 3D characterisation of biomaterial degradation and bone regeneration over time. In addition, XCT combined with in situ mechanical experiments and digital volume correlation (DVC) provides a 3D evaluation and quantification of bone-biomaterial interactions and deformation mechanisms during the regeneration process. This remains essential for the development and enhancement of novel biomaterials able to produce bone that is comparable with the native tissue they aim to replace.

  • 28.
    Rosa, Anna De
    et al.
    Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy.
    Kulkarni, Rohan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Qazizadeh, Alireza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Gialleonardo, Egidio Di
    Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy.
    Faccinetti, Alan
    Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy.
    Bruni, Stefano
    Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy.
    Monitoring of lateral and cross level track geometry irregularities through onboard vehicle dynamics measurements using machine learning classification algorithms2020In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017Article in journal (Refereed)
    Abstract [en]

    In recent years, significant studies have focused on monitoring the track geometry irregularities through measurements of vehicle dynamics acquired onboard. Most of these studies analyse the vertical irregularity and the vertical vehicle dynamics since the lateral direction is much more challenging due to the non-linearities caused by the contact between the wheels and the rails. In the present work, a machine learning-based fault classifier for the condition monitoring of track irregularities in the lateral direction is proposed. The classifiers are trained with a dataset composed of numerical simulation results and validated with a dataset of measurements acquired by a diagnostic vehicle on the straight track sections of a high-speed line (300 km/h). Classifiers based on decision tree, linear and Gaussian support vector machine algorithms are developed and compared in terms of performance: good results are achieved with the three algorithms, especially with the Gaussian support vector machine. Even though classifiers are data driven, they retain the essence of lateral dynamics.

  • 29.
    Sedlak, Michal
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    A duplex oxide cohesive zone model to simulate intergranular stress corrosion crackingManuscript (preprint) (Other academic)
    Abstract [en]

    A finite element model with slip-oxidation is proposed for solving intergranular stress corrosion cracking (IGSCC) with duplex oxides. The purpose is to investigate the crack growth effect due to different rate, compositions and kinetics of the duplex oxide. The finite element model is based on a coupling between cohesive zone formulation, slip-oxidation model and a diffusion model. The cohesive zone formulation includes a degradation formulation which is linked to the slip-oxidation formulation. The environmental properties in the slip-oxidation were obtained from the diffusion modeled with Fick’s second law in onedimension. This was then coupled to the structural model by a segregated solution scheme. The mesh of the cohesive zone adapts to the oxide thickness of the duplex oxide during the crack growth. The duplex oxide has the mathematical form of a power law or a logarithmic form. The model showed matching results for all duplex oxide combinations in varying stress, but the inner logarithmical oxide gave higher crack growth rates than the power law. The power law with the thicker inner oxide showed good results for the change of stress intensity factor and gave the best results when the yield stress was varied. Grain misorientation effect was higher for the duplex oxides with thicker outer oxides

    The full text will be freely available from 2020-04-21 10:30
  • 30.
    Sedlak Mosesson, Michal
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Modelling of intergranular stress corrosion cracking mechanism2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When assessing nuclear power plant life, stress corrosion cracking (SCC) plays an important role. Stress corrosion cracking in nuclear power plants is well recognized and heavily researched. Still due to its complicated nature it is not completely understood. There are many different damage mechanisms behind SCC. The focus in this thesis is on the slip-oxidation model. In the slip-oxidation model, the aggressive ions are diffused to the crack tip. In the crack tip the aggressive ions act as a catalyst to slow down the repassivation rate of the oxide film. At the crack tip the localized anodic dissolution occurred until an oxide film was produced to repassivate the corrosion process. Due to the constant stresses applied, the oxide film ruptured, and new virgin material was exposed to be dissolved and finally repassivated. This process is consequently repeated.   The first part of the work introduces a new formulation of a cohesive element with extended environmental degradation capability, which is essential to create the later SCC models. The new degradation method was evaluated against a Hydrogen Embrittlement (HE) experiment showing improved agreement with the experiment compared to the literature. The effect of different susceptibility zones at the crack tip was also investigated, showing that a uniform degradation throughout the susceptible zone is more influenced by the χ parameter than a triangular susceptible zone.  In the second part a phenomenological SCC model was created with the purpose to model primary water conditions in pressurized water reactors (PWR). It used the slip-oxidation model for considering SCC in boiling water reactors (BWR) under normal water chemistry (NWC).   The PWR model was implicit, coupled with a segregated solution scheme including a diffusion equation based on Fick’s second law and a cohesive zone description for the fracture mechanics part. The degradation was modelled with an anodic slip-dissolution equation that uses the effective cohesive traction and concentration as the main parameters. The model was evaluated against experiments on the effects of cold work on intergranular stress corrosion cracking (IGSCC). The model showed good agreements for both shifting amount of cold work illustrated by only changing the yield stress in the bulk material and for shifting the stress intensity factor. The model versatility was also shown by simulating IGSCC in Alloy600, also with good agreements.   The BWR model was multi-physical including a slip-oxidation, diffusion model and had adaptive oxide thickness developed into the cohesive element framework. The oxide thickness was derived from the slip-oxidation model and updated in every structural iteration to fully couple the fracture properties of the cohesive element. The cyclic physics of the slip oxidation model was replicated. The model results agreed with experiments in the literature for changes in the stress intensity factor, yield stress representing cold work and environmental factors such as conductivity and corrosion potential. The adaptive model was also expanded into a duplex oxide model with an inner and outer oxide. The model showed agreeing results with literature and the model was used to simulate different oxide growth kinetics

    The full text will be freely available from 2020-04-21 10:55
  • 31.
    Sedlak Mosesson, Michal
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Simulation of intergranular stress corrosion cracking by mesh adaptivity in a cohesive zone frameworkManuscript (preprint) (Other academic)
    Abstract [en]

    A finite element framework with mesh adaptivity was developed to simulate the oxide growth of the intergranular stress corrosion cracking (IGSCC). In particular, the environment of boiling water reactors (BWR) in combination with austenitic stainless steel and constant stress was studied. The model is interdisciplinary, it is a combination of a cohesive element fracture model, electrochemical slip-oxidation model and Fick’s second law as the diffusion model. The cyclic physics of the slip oxidation model was replicated. In the model, the thickness of the oxide was taken into consideration as the physical length of the cohesive element. The cyclic process was modelled with oxide film growth. Oxide rupture occurred due to degradation of the fracture energy. The degradation is a result of both external traction and diffusion of aggressive ions. The rate of degradation is defined by a variety of parameters as material properties, electrochemical properties and diffusivity. Next, the re-passivation will be initiated by the mesh adaptivity framework. The model was solved with a staggered solution scheme and the mesh adaptivity was set every Newton-Raphson trial. The model results agreed with experiments in the literature for changes in stress intensity factor, yield stress representing cold work and environmental factors such as conductivity and corrosion potential. The model also shows cost effective predicting, which is useful for larger simulation or optimization situations.

    The full text will be freely available from 2020-04-21 10:24
  • 32.
    Staf, Hjalmar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Mechanical Modelling of Powder Compaction: Due to Corona is not possible to attend this defense in person, instead attend via this link: https://play.kth.se/media/t/0_mbkr2jhi​2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cutting tool inserts, for instance used in steel machining, have the requirement to be toughand are therefore most often manufactured out of cemented carbides, using powdermetallurgy. Manufacturing components with powder metallurgy has its advantages in highproductivity and good net shape. The powder is spray dried and compacted to half itssintered volume. Because of friction between the powder and the pressing tool, the densityafter compaction is uneven, leading to uneven shrinkage during sintering. To get the rightshape after pressing and sintering, the pressing tool must often be compensated, which isboth expensive and time consuming. By doing computer simulations of the manufacturingprocess, the shape after sintering can be predicted and used to compensate the pressing toolbefore it is manufactured, thus saving both time and money. Also cracks and porosity in thepowder blank can be predicted with such simulations.

    This thesis studies mechanical modelling of powder compaction in general and compactionof cemented tungsten carbide powders in particular. Because of the amount of powdergranules in a typical geometry, the mechanical behavior is modelled with a continuumapproach, using the finite element method (FEM). Accuracy is important in the presentapplication and therefore a detailed elastic-plastic material model with a density dependentyield surface of Drucker-Prager CAP kind is used.

    For accurate material modelling it is important to include relevant features and to excludeunimportant physical effects. In Paper A sensitivity studies are therefore performed inorder to conclude which properties in the material model that have a significant influence onthe result. The studies show that anisotropy can be disregarded in the current application.

    In Paper B the effects from creep and compaction speed are studied. It is concluded thatcreep has no influence on the density after compaction, which also is confirmed by densitymeasurements using a neutron source in Paper D. The compaction speed on the other handinfluences the friction coefficient between powder and pressing tool, lower at increasedspeed. In Paper C frictional behavior is scrutinized experimentally with the aid of aninstrumented die. The friction coefficient is determined and analyzed, and it is shown that itdepends on the normal pressure.

    The sensitivity studies in Paper A show that measurements of the local density are neededin order to determine and verify material properties. Since the analyzed powder containstungsten (W), which has a high atomic number, a polychromatic beam of thermal neutronsis needed. In Paper D it is shown that the local density can be measured with 3D imagingand a thermal neutron source.

    From the results and conclusions in the above-mentioned papers, a material description forpowder compaction is suggested. This description is implemented in FEM in Paper E andapplied to reverse engineering in order to determine important material parameters.Experiments in a pressing machine with a pressing method that includes multiple unloadingsteps is used. The material description with the determined parameters is verified withdensity measurements using a neutron source.

  • 33.
    Staf, Hjalmar
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. Sandvik Coromant, SE-126 80 Stockholm, Sweden.
    Olsson, Erik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Mechanical Characterization of PowderMaterials: A General Approach Detailedfor Cemented Carbides2020In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 364, p. 531-537Article in journal (Refereed)
    Abstract [en]

    Material parameter curves in an advanced material model describing compaction of spraydried cemented carbide powder are determined successfully based on a general approach formaterial characterization of powder materials. Pressing forces from a production machineand equivalent finite element (FE) calculations are used in inverse modelling. A pressingmethod that includes multiple unloading steps is used. The material model is of DruckerPrager CAP kind and friction between powder and pressing tool is modelled as a function ofnormal pressure. The results are verified with density gradient measurements using aneutron source. The method is proven to be robust and the results show good agreementbetween experiment and simulation. Effects that have not been captured numericallypreviously are captured due to the high accuracy of material characterization. The presentapproach is detailed for tungsten carbide powders but is valid for other powder materialswhen properly calibrated for constitutive and frictional effects in the same manner asoutlined here.

  • 34.
    Straub, Steffen
    et al.
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Forooghi, Pourya
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Marocco, Luca
    Politecn Milan, Dipartimento Energia, I-20156 Milan, Italy..
    Wetzel, Thomas
    Karlsruhe Inst Technol, Inst Thermal Proc Engn, D-76131 Karlsruhe, Germany..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Frohnapfel, Bettina
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    The influence of thermal boundary conditions on turbulent forced convection pipe flow at two Prandtl numbers2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 144, article id 118601Article in journal (Refereed)
    Abstract [en]

    Different types of thermal boundary conditions are conceivable in numerical simulations of convective heat transfer problems. Isoflux, isothermal and a mixed-type boundary condition are compared by means of direct numerical simulations (for the lowest Reynolds number) and well-resolved large-eddy simulations of a turbulent forced convection pipe flow over a range of bulk Reynolds numbers from Re-b = 5300 to Re-b = 37700, at two Prandtl numbers, i.e. Pr = 0.71 and Pr = 0.025. It is found that, while for Pr = 0.71 the Nusselt number is hardly affected by the type of thermal boundary condition, for Pr = 0.025 the isothermal boundary condition yields approximate to 20% lower Nusselt numbers compared to isoflux and mixedtype over the whole range of Reynolds numbers. A decomposition of the Nusselt number is derived. In particular, we decompose it into four contributions: laminar, radial and streamwise turbulent heat flux as well as a contribution due to the turbulent velocity field. For Pr = 0.71 the contribution due to the radial turbulent heat flux is dominant, whereas for Pr = 0.025 the contribution due to the turbulent velocity field is dominant. Only at a moderately high Reynolds number, such as Re-b = 37700, both turbulent contributions are of similar magnitude. A comparison of first- and second-order thermal statistics between the different types of thermal boundary conditions shows that the statistics are not only influenced in the near-wall region but also in the core region of the flow. Power spectral densities illustrate large thermal structures in low-Prandtl-number fluids as well as thermal structures located right at the wall, only present for the isoflux boundary condition. A database including the first- and second-order statistics together with individual contributions to the budget equations of the temperature variance and turbulent heat fluxes is hosted in the open access repository KITopen (DOI : https: //doi.org/10.5445/IR/1000096346).

  • 35.
    Xu, Johanna
    et al.
    Lulea Univ Technol, Mat Sci, Dept Engn Sci & Math, SE-97187 Lulea, Sweden.;Chalmers Univ Technol, Dept Ind & Mat Sci, SE-41296' Gothenburg, Sweden..
    Johannisson, Wilhelm
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Johansen, Marcus
    Chalmers Univ Technol, Dept Ind & Mat Sci, SE-41296' Gothenburg, Sweden..
    Liu, Fang
    Chalmers Univ Technol, Dept Ind & Mat Sci, SE-41296' Gothenburg, Sweden..
    Zenkert, Dan
    KTH, Superseded Departments (pre-2005), Aeronautical and Vehicle Engineering.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Asp, Leif E.
    Chalmers Univ Technol, Dept Ind & Mat Sci, SE-41296' Gothenburg, Sweden..
    Characterization of the adhesive properties between structural battery electrolytes and carbon fibers2020In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 188, article id 107962Article in journal (Refereed)
    Abstract [en]

    Structural batteries can simultaneously store electrical energy and carry mechanical load, being similar to both laminated carbon fiber composites and lithium ion batteries. The matrix in a structural battery must both conduct ions and transfer load between the fibers, made possible with a phase-separated combination of a solid polymer and a liquid electrolyte. This leads to a trade-off between the polymer contact creating adhesion and liquid contact creating ionic conductivity. Here we investigate the fiber-matrix adhesion between carbon fibres with different sizing and two different matrix systems, using microbond testing supported by transverse tensile tests. The results show that the mechanical adhesion of the fiber-matrix interface is lower than that of a commercial non-ion conducting polymer matrix but sufficient for structural battery applications.

  • 36.
    Zhang, Meng
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems. KTH Royal Institute of Technology.
    Ice load prediction for design of ice-going ships for inland waterways2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    With increasing interest in utilizing the inland waterways (IWW) in European countries, the design of IWW vessels gains attention both from a transport efficiency and an emission control point of view. However, unlike in western and central European countries, in Nordic countries, e.g. Sweden, IWW ships must deal with ice on the fairway during every winter. Usually, IWW ships are designed without ice concerns and are structurally weaker compared to ships designed according to ice class notification from the classification societies. Developing such ships requires particular concerns since there is no strict requirements regarding ice class notifications for IWW ships. A primary challenge is to estimate both the global and local ice loads acting on the ship hull structure. To consolidate the design problems for IWW ice-going ships, Lake Mälaren is selected. Ice conditions, i.e. ice type and concentration, and ice data, e.g. ice thickness and ice flexural strength, are extracted and analysed for the ice load estimation. The ice mechanical properties have great influence on the ice load. Ice characteristics are studied based on empirical formulae and properties are calibrated by reference data.

    The deterministic approach is widely used to predict the ice loads. It is suitable when all variables, i.e. ship geometry and ice properties, are known and refers to rule-based design hereby. For first year light ice conditions in Lake Mälaren, the Finnish Swedish Ice Class Rule (FSICR) is widely used. The thesis uses guidelines from the Finnish Swedish Ice Class Rules as a reference and compare the results with other methods.

    The probabilistic approach, on contrary, is useful when certain variables are unknow, which are interpreted as random variables, for instance ice breaking pattern. Here the probabilistic method and ice-hull interaction mechanism are studied. The probabilistic method simplifies the ice pressure in relation to the contact area between the ice and the ship hull. It predicts maximum ice pressure acting on the ship hull based on field ice test data and ice exposure conditions. Such semi-empirical method can be used regardless of ship type and size. For this, a numerical model is introduced based on ice-hull collision mechanisms and the essential ice breaking characteristics. The physical mechanism is studied for idealizing ship-ice impact model. The idealization model includes the ice failure process, ice conditions and ship geometry. The ice failure is assumed to be initiated by crushing ice and followed by breaking due to bending failure. Ice properties are set as constant values without any variations. The stochasticity in interact process is represented by randomness in collision location and number of pieces of ice floe formed after breaking. An energy method is used to calculate the ice crushing force, indentation displacement and contact area. The ice bending scenario is simplified as an infinite plate resting on an elastic foundation under a concentrated load. Ice impact load and critical load can be obtained for global and local structural assessment respectively. The structural responses and structural strength of a representative panel at linear and nonlinear contexts are investigated as well. Ship structure is commonly designed with material yield strength as limit. However, the study shows a lighter structure can be achieved if plastic deformation is allowed without causing failure. Therefore, the design can be optimized with regards to ice loading capacity and weight control.

  • 37.
    Zhang, Meng
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. 8910127185.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Zhou, Li
    A Numerical Ice Load Prediction Model Based on Ice-Hull Collision Mechanism2020In: Applied Sciences, ISSN ISSN 2076-3417, Vol. 10Article in journal (Refereed)
    Abstract [en]

    A simplified numerical model is introduced to predict ice impact force acting on the ship hull in level ice condition. The model is based on ice-hull collision mechanisms and the essential ice breaking characteristics. The two critical ice failure modes, localized crushing and bending breaking, are addressed. An energy method is used to estimate the crushing force and the indentation displacement for different geometry schemes of ice-ship interaction. Ice bending breaking scenario is taken as a semi-infinite plate under a distributed load resting on an elastic foundation. An integrated complete ice-hull impact event is introduced with ice failure modes and breaking patterns. Impact location randomness and number of broken ice wedges are considered in order to establish a stochastic model. The analysis is validated by comparison with the model ice test of a shuttle passenger ferry performed in May 2017 for SSPA Sweden AB at Aker Arctic Technology Inc. Good agreement is achieved with appropriate parameter selection assumed from the model test and when ice bending failure is dominant. This model can be used to predict the ice impact load and creates a bridge between design parameters (ice properties and ship geometry) and structure loads.

  • 38.
    Zhang, Wenliang
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics. School of Mechanical Engineering, Beijing Institute of Technology.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Nybacka, Mikael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Wang, Zhenpo
    School of Mechanical Engineering, Beijing Institute of Technology.
    Active camber for enhancing path following and yaw stability of over-actuated autonomous electric vehicles2020In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159Article in journal (Refereed)
    Abstract [en]

    Active safety systems contribute significantly to the safe driving of autonomous vehicles in hazardous circumstances. However, conventional active safety systems that mainly depend on braking intervention may not yield the desired vehicle behaviour in critical situations where the tyre forces tend to saturate. Over-actuation through individually cambering the wheels provides a possibility of overcoming this difficulty, as extra lateral tyre forces can potentially be produced. This paper presents active camber for improving the path following and yaw stability performance of over-actuated autonomous electric vehicles (AEVs). With a modified Dugoff tyre model, the camber effect on the lateral tyre force is modelled as an effective linear component. The modified tyre model, together with a double-track vehicle model, is utilised for active camber of the AEVs. The camber controller is developed in the framework of model predictive control (MPC), including both actuator- and safety-related constraints. The camber controller is investigated at different camber rates and road friction levels, in terms of path following, yaw stability and vehicle velocity gain.

  • 39.
    Zhang, Wenliang
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics. School of Mechanical Engineering, Beijing Institute of Technology.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Nybacka, Mikael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Wang, Zhenpo
    School of Mechanical Engineering, Beijing Institute of Technology.
    Exploring Active Camber for Path Following and Yaw Stability of Autonomous Vehicles2020In: Advances in Dynamics of Vehicles on Roads and Tracks, Springer, 2020, p. 1491-1499Chapter in book (Refereed)
    Abstract [en]

    This paper explores active camber for path following and yaw stability control of over-actuated autonomous electric vehicles (AEVs). The camber effect on tyre force is modelled with a modified Dugoff tyre model, where the influence of tyre slip on camber stiffness is considered. Additionally, a nonlinear vehicle model including the longitudinal, lateral and yaw motion of the vehicle and the rotational motion of the wheels is utilised. The control problem of the AEVs is formulated with model predictive control, where both actuator- and safety-related constraints are considered. Comparative studies show that with four-wheel camber control the path following and yaw stability performance of the AEV can be considerably improved.

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