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  • 11601.
    Östberg, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range-The wave-guide solution2011Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 13, s. 3222-3244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency: displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.

  • 11602.
    Österlind, Tomas
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    An Analysis of Machining System Capability and Its Link with Machined Component Quality2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Machining components out of tolerances is of no use in competitiveproduction. The machining system sets the limitations of dimensionalaccuracy and surface quality of a machined component. The capabilityof the machining system describes these limits in terms of specifiedvalues. This thesis deals with machining system capability analysismainly focused on machine tool static and dynamic stiffness.The influence of stiffness and flexibility on machining systemcapability is analytically and experimentally investigated. Theexperimental work presented in the thesis complies with the theoriesand shows the relation between machine tool capability and theoutcome on the machine component.The concept of capability analysis by elastic linked system andthe currently available tools for such an evaluation is presented anddiscussed. The basis of elastic linked system analysis is the use ofmeasurements under loaded condition. The machine tool is loadedwith a known force creating a test condition closer to real machining,compared to current methods of unloaded machine tools. Twomeasurement tools for elastic linked system capability analysis areexplained in the thesis: Loaded Double Ball Bar and ContactlessExcitation and Response System.The thesis consists of an analytical base and an experimental casestudy on spiral bevel gear face milling. The experiments are discussedand compiled with the given theories.

  • 11603.
    Österlind, Tomas
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Estimation of Machining System Dynamic Properties - Measurement and Modelling2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Dynamic characteristics of machining systems are analysed for improved understanding of both structural and process properties. The thesis stresses the use of testing methods under operational like conditions as these are more representative of closed loop systems, such as machining systems, as compared to conventional testing methods.

    The test instrument proposed is a contactless excitation and response system, developed for testing of machine tool spindles under load and with rotating spindle. The instrument uses electromagnetic excitation and displacement sensors for analysis of rotating milling tools subject to load. A graphical tool for displaying and analysing rotor displacement was developed in conjunction with this.

    A modelling procedure for both off-line and on-line estimation of dynamic properties of mechanical structure and process information is presented. The proposed auto-regressive moving average models enable calculation of operational dynamic parameters and they can be estimated in a recursive manner, thus enabling real-time monitoring. The discrimination between stable and unstable processes, both in turning and milling, was performed by analysing the damping obtained from the operational dynamic parameters.

  • 11604.
    Österlind, Tomas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Archenti, Andreas
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Daghini, Lorenzo
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Nicolescu, Cornel Mihai
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Improvement of Gear Cutter Dynamics by Use of Acoustic Imaging and High Damping Interface2012Ingår i: 3rd CIRP Conference on Process Machine Interactions / [ed] Shamoto, E, 2012, s. 17-21Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a study where acoustic imaging technology was employed for problem identification and high damping interfaces (HDI) were implemented in the machine tool structure to improve performance of process machine interaction, in bevel gear cutting, in terms of resistance to instability. Chatter marks at the gear root and tool fracturing represent a serious and widespread problem in the studied process. The acoustic image approach showed good agreement with modal analysis and also allowed to identify the chatter frequency. Once identified the problem, the paper also presents a novel approach for improving resistance to cutting instability by implementing HDI in the structure. The HDI consists of a viscoelastic composite material and is used to damp out the stick blade motion relative to the clamp block by transformation of vibratory energy, into heat. The primary contributions of this paper are the introduction of acoustic imaging for identification of chatter in gear cutting and employment of HDI for performance improvement for rotating tools.

  • 11605.
    Österlind, Tomas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Daghini, Lorenzo
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Archenti, Andreas
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Evaluation of tool steel alloy performance in a milling operation through operational dynamic parameters2017Ingår i: International journal of machine tools & manufacture, ISSN 0890-6955, E-ISSN 1879-2170, Vol. 114, s. 54-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic characteristics of machine tools and cutting tools have gained much attention from researchers and industry as it is one of the major factors limiting productivity due to excessive vibrations such as chatter during the cutting process. Numerous factors have to be taken into consideration when selecting material of the cutter body. This paper presents a comparison between two cutter bodies with the same geometry but made out of different alloys. Pre-hardened steel and conventional tool steel were investigated in order to highlight the advantages of selecting correct material to achieve high performance tools with respect of chatter resistance. The experimental part of this paper consists of impact testing, machining tests and surface integrity measurements. Operational dynamic parameters obtained through auto-regressive moving average model estimates from machining tests under stable and unstable conditions was used to characterise the performance. The findings are in correlation with material damping research and chatter analysis, thus giving a strong coupling to material selection in tool holders for enhanced process stability. The research also shows that operational dynamic properties obtained through indirect measurements is a valuable tool for process stability characterisation.

  • 11606.
    Österlind, Tomas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Frangoudis, Constantinos
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Archenti, Andreas
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Operational Modal Analysis During Milling Of Workpiece, Fixed On A Stiffness Controllable Joint2013Ingår i: Journal of Machine Engineering, ISSN 1895-7595, Vol. 13, nr 2, s. 69-78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibration in metal cutting processes has been studied to a great extent resulting in for instance stability lobe diagrams under which stable machining parameters can be selected. One limitation of accurately estimated stability diagrams is the change in process and dynamic characteristics of the machine tool under operation. The machine tool dynamic response is often analysed with experimental modal analysis under off operational conditions. One drawback with this approach is the large number of measurements required to fully describe a machine tool and workpiece in different positions and time of machining. Another drawback is that the change of dynamic characteristics under operation is excluded. Operational modal analysis has been applied in machining under different conditions resulting in successfully improved stability lobe prediction. This research includes operational modal analysis of the workpiece, fixed on a stiffness controllable joint and stability prediction to stress the importance of various machining conditions.

  • 11607.
    Österlind, Tomas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Nicolescu, Cornel-Mihai
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Analysis of stationary displacement patterns in rotating machinery subject to local harmonic excitation2017Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 389, s. 224-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rotor vibration and stationary displacement patterns observed in rotating machineries subject to local harmonic excitation are analysed for improved understanding and dynamic characterization. The analysis stresses the importance of coordinate transformation between rotating and stationary frame of reference for accurate results and estimation of dynamic properties. A generic method which can be used for various rotor applications such as machine tool spindle and turbo machinery vibration is presented. The phenomenon shares similarities with stationary waves in rotating disks though focuses on vibration in shafts. The paper further proposes a graphical tool, the displacement map, which can be used for selection of stable rotational speed for rotating machinery. The results are validated through simulation of dynamic response of a milling cutter, which is a typical example of a variable speed rotor operating under different load conditions.

  • 11608.
    Österlund, Jens, M.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne, V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Nagib, Hassan, M.
    Illinois insitute of Technology.
    Comment on "A note on the intermediate region in turbulent boundary layers" [Phys. Fluids 12, 2159 (2000)]2000Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 12, s. 2360-2363Artikel i tidskrift (Refereegranskat)
  • 11609.
    Österlund, Jens, M.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne, V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Nagib, Hassan, M.
    Massachusetts Institute of Technology.
    Hites, Michael, H.
    A note on the overlap region in turbulent boundary layers2000Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, nr 12, s. 1-4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two independent experimental investigations of the behavior of turbulent boundary layers with increasing Reynolds number were recently completed. The experiments were performed in two facilities, the Minimum Turbulence Level (MTL) wind tunnel at Royal Institute of Technology (KTH) and the National Diagnostic Facility (NDF) wind tunnel at Illinois Institute of Technology (IIT). Both experiments utilized oil-film interferometry to obtain an independent measure of the wall-shear stress. A collaborative study by the principals of the two experiments, aimed at understanding the characteristics of the overlap region between the inner and outer parts of the boundary layer, has just been completed. The results are summarized here, utilizing the profiles of the mean velocity, for Reynolds numbers based on the momentum thickness ranging from 2500 to 27 000. Contrary to the conclusions of some earlier publications, careful analysis of the data reveals no significant Reynolds number dependence for the parameters describing the overlap region using the classical logarithmic relation. However, the data analysis demonstrates that the viscous influence extends within the buffer region to y+≈200, compared to the previously assumed limit of y+≈50.Therefore, the lowest Reθ value where a significant logarithmic overlap region exists is about 6000. This probably explains why a Reynolds number dependence had been found from the data analysis of many previous experiments. The parameters of the logarithmic overlap region are found to be constant and are estimated to be κ=0.38, B=4.1 and B1=3.6 (δ=δ95).

  • 11610.
    Österlund, Jens M.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lindgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Flow structures in zero pressure-gradient turbulent boundary layers2003Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 22, nr 4, s. 379-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The near-wall region of zero-pressure gradient turbulent boundary layers was studied through correlation- and other two- point measurements over a wide range of Reynolds numbers. The requirements of high spatial resolution were met by use of a MEMS-type of hot-film sensor array together with a small, in-house built hot-wire probe. Streak-spacing and characteristics of buffer region shear-layer events were studied. At high Reynolds numbers the motions that are of substantially larger scale than the streaks have a significant influence on the near-wall dynamics. By removing such scales through high-pass filtering a streak spacing was recovered that is close to that found in low Reynolds number flows. The frequency of occurrence of shear- layer events was found to scale with a mixed time scale, in analogy with earlier findings in channel flow, again indicating the increasing relative influence of large scales with increasing Reynolds number.

  • 11611.
    Österlund Truedsson, Benjamin
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Ersätta OKG med förnyelsebar elproduktion2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Den nuvarande politiska osäkerheten kring investeringar i ny kärnkraft i Sverige leder till att kraftbolagen ogärna utreder möjligheten för nyinvesteringar i denna sektor. Detta medför att en framtida avveckling av reaktor O1 i Oskarshamn börjar bli lämplig då den börjar närma sig sin tekniska livslängd. En teknisk utredning utförs genom att analysera de olika förnybara energikällorna och deras utvecklingsmöjligheter rent tekniskt och juridiskt. Samtidigt utfördes en utredning i Oskarshamns kärnkraft för att fastställa ersättningsbehovet i elektriskt effekt. En jämförelse gav upphov till att ett biobränslekraftverk vore den lämpliga kandidaten för att ersätta O1. Vidare studerades huruvida elpriset skulle kunna utvecklas i framtiden då det är den huvudsakliga inkomsten. Detta gjordes även för bränslepriset för det valda bränslet för kraftverket.

    Den totala investeringskostnaden blev slutligen på 13,5 miljarder kronor med en årlig produktionskostnad på ca 3 miljarder kronor. Det lägsta bränslepriset för att klara en kalkylränta på 6 % och en ekonomisk livslängd på 20 år ligger på 213 kr/MWh. Detta bygger på antagandet att elpriset förväntas öka linjärt. De typiska emissionerna från den nya anläggningen beräknades bli på 29,4 Kg CO2, 650 g NO2 och 79,4 g SO2 per producerad megawattimme el.

    Då produktionskostnaderna är så höga jämfört med försäljningen av el, samt att elcertifikatsystemet kommer fasas ut anses investeringen inte vara lönsam. I detta arbete har lönsamheten för anläggningen beräknats då de endast säljer el. En ny kalkyl med utgångspunkt i att kraftverket säljer både el och fjärrvärme är därför nödvändig.

  • 11612. Österlöf, R.
    et al.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Temperature dependency of a viscoplastic constitutive model for rubber with reinforcing fillers2015Ingår i: Constitutive Models for Rubber IX - Proceedings of the 9th European Conference on Constitutive Models for Rubbers, ECCMR, CRC Press/Balkema , 2015, s. 149-156Konferensbidrag (Refereegranskat)
    Abstract [en]

    A material model is presented that captures the amplitude and frequency dependency of rubber with reinforcing fillers at temperatures between 23 to 85°C. It is a modification of the authors previous work and the basic principle is a smooth elastoplastic element in series with a viscoelastic network, implemented in the time domain. The rheological equivalence is based on the observation in literature that the frequency dependency of filled rubber is stronger for smaller strain amplitudes than for large amplitudes. Finally, the assumption that rubber with reinforcing fillers is thermo-rheologically simple is not always true for higher filler concentrations, resulting in discontinuous master curves for the temperature- frequency dependency. There as on for this discontinuity is that the amplitude dependency is temperature dependent. Therefore, material characterizations evaluated at a low strain amplitude could lead to erroneous results when a higher strain amplitude is of interest. Instead, it is suggested that a material model is fitted to a wide range of experimental data in order to enable realistic calculations of an actual component under operational conditions. To test the constitutive model, a double shear test specimen of natural rubber with 50 phr of carbon black filler is subjected to sinusoidal strains. The amplitudes are varied between 0.2 and 50% shear strain for frequencies between 0.5 and 20 Hz at 23, 60 and 85°C. The derived model needs only 5 material parameters to be fitted to experimental data and captures the storage and loss modulus for the entire range of strain amplitudes and frequencies, as well as non-sinusoidal loading conditions. Moreover, with the proposed modelling technique, it is expected that frequencies well above the available experimental data can be simulated. This is important, since the purpose of every model should be to make predictions outside of the range of available experimental data.

  • 11613.
    Österlöf, Richard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A finite strain viscoplastic constitutive model for filled rubber2015Ingår i: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    A phenomenological material model for carbon black filled natural rubber based on the multiplicative split of the deformation gradient is implemented for finite strains in three dimensions. This is a generalising of the authors previous work, where the uniaxial rheological equivalent is a smooth friction element in series with a generalized Maxwell chain. The aim of the paper is to demonstrate the advantage of this viscoplastic modelling approach. With only 5 material parameters, the storage and loss modulus is calculated for strain amplitudes between 0.2-50% strain and 0.5-20 Hz, with very encouraging results. These are reasonable ranges of interest when designing the reliability of load bearing components, such as vibration isolators for drivelines in the automotive industry. The Fletcher-Gent effect is well captured, where the strain rate dependency on the storage modulus is higher at smaller strain amplitudes. In addition, the storage and loss modulus are similar to measurements in literature, both in value and shape over the entire range of amplitudes and frequencies. It should be emphasized that capturing both the storage and loss modulus of a material is essential for a material model's capability to describe more complex loading situations than sinusoidal loading. A future implication of the developed model is that it enables realistic simulation of vibration isolators early in the design process whereby extensive physical testing can be reduced, saving both time and money.

  • 11614.
    Österlöf, Rickard
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Scania.
    Modelling the viscoplastic properties of carbon black filled rubber: A finite strain material model suitable for Finite Element Analysis2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    En ökad miljömedvetenhet, juridiska krav och den stora delen av de totala kostnaderna som kan hänföras till bränslekostnader är alla incitament för fordonsindustrin att minska bränsleförbrukningen. Den optimala drivlinan för att möjliggöra denna minskning beror på driftförhållanden och den tillgängliga infrastrukturen. Dessutom ställs höga krav på utvecklingen av drivlineisolatorer, eftersom kraven på buller och vibrationer (NVH) är desamma oavsett drivlina. För detta ändamål kan datorstödda beräkningar användas för att utvärdera ett stort antal konfigurationer. Dessa beräkningar är, i bästa fall, endast så bra som de använda materialmodellerna. Inom en överskådlig framtid kommer gummi med förstärkande fyllmedel användas i vibrationsisolatorer för att erhålla de önskade egenskaperna hos dessa komponenter. Men styvheten och dämpningen i gummi med förstärkande fyllmedel är kraftigt icke-linjära funktioner, och de tillgängliga materialmodellerna i kommersiella programvaror och i litteraturen är ofta otillräckliga. Därför är en viskoplastisk materialmodell för finita deformationer framtagen i tidsdomänen och implementeras som ett användardefinierat material i Abaqus Explicit. Modellen fångar töjningsamplitud- och frekvensberoendet av lagrings- och förlustmodulen för ett kimröksfyllt naturgummi. Den är korrekt över ett brett intervall av skjuvtöjningsamplituder och frekvenser, 0.2-50% respektive 0.5-20 Hz, och kräver endast 5 materialparametrar. Dessutom fångar modeller responsen från bimodala excitationer. Implementeringen i Abaqus Explicit gör att komponentegenskaper kan utvärderas tidigt i utvecklingsfasen, med materialparametrar som härrör från enkla provkroppar. Den förbättrade noggrannheten i simuleringar av dessa komponenter kan hjälpa ingenjörer att utveckla mer optimerade lösningar snabbare än med konventionella metoder.

  • 11615.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    An efficient method for obtaining the hyperelastic properties of filled elastomers in finite strain applications2015Ingår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 41, s. 44-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An efficient methodology for obtaining hyperelastic material parameters for filled elastomers utilizing unloading curves in uniaxial tension, pure shear and the inflation of a rubber membrane is presented. Experimental results from biaxial extension are crucial when fitting hyperelastic material parameters, and the bubble inflation technique is an excellent method of obtaining this data when specialized test equipment is unavailable. Moreover, filled elastomers have considerable hysteresis, and the hysteresis grows with increasing strain amplitudes. Therefore, the loading curve is in general comprised of both elastic and inelastic contributions, even at very low strain rates. Consequently, it is deemed more accurate to use experimental data from the unloading curve to describe the elastic behavior of the material. The presented methodology enables obtainment of parameters related to both the first and second strain invariant, which is required for a good fit between measurement and simulation results. Finally, it is essential that a chosen material model is accurate in all deformation modes when designing components subjected to a complex, multi-axial load history. An accurate material model enables more concepts and geometries of a component to be studied before a physical prototype is available.

  • 11616.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Diercks, N.
    Wollscheid, D.
    Constitutive modelling of the amplitude and frequency dependency of filled elastomers utilizing a modified Boundary Surface Model2014Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 19-20, s. 3431-3438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A phenomenological uniaxial model is derived for implementation in the time domain, which captures the amplitude and frequency dependency of filled elastomers. Motivated by the experimental observation that the frequency dependency is stronger for smaller strain amplitudes than for large ones, a novel material model is presented. It utilizes a split of deformation between a generalized Maxwell chain in series with a bounding surface plasticity model with a vanishing elastic region. Many attempts to capture the behaviour of filled elastomers are found in the literature, which often utilize an additive split between an elastic and a history dependent element, in parallel. Even though some models capture the storage and loss modulus during sinusoidal excitations, they often fail to do so for more complex load histories. Simulations with the derived model are compared to measurements in simple shear on a compound of carbon black filled natural rubber used in driveline isolators in the heavy truck industry. The storage and loss modulus from simulations agree very well with measurements, using only 7 material parameters to capture 2 decades of strain (0.5-50% shear strain) and frequency (0.2-20 Hz). More importantly, with material parameters extracted from the measured storage and loss modulus, measurements of a dual sine excitation are well replicated. This enables realistic operating conditions to be simulated early in the development process, before an actual prototype is available for testing, since the loads in real life operating conditions frequently are a combination of many harmonics.

  • 11617.
    Österman, Cecilia
    et al.
    Chalmers ChalmersUniversity of Technology,Shipping and Marine Technology,.
    Rose, Linda M
    KTH, Skolan för teknik och hälsa (STH), Ergonomi (Stängd 20130701).
    Osvalder, Anna-Lisa
    Chalmers University of Technology, Product and Production Development.
    Exploring Maritime Ergonomics from a Bottom Line Perspective2010Ingår i: WMU Journal of Maritime Affairs (JoMA), ISSN 1651-436X, E-ISSN 1654-1642, Vol. 9, nr 2, s. 153-168Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present paper reports a study composed of three research activities exploring the economics of ergonomics in a shipping context. First, a literature study aimed to review previous studies on the economics of ergonomics in general and within the maritime domain in particular; and moreover, to ascertain the key ergonomic factors addressed in contemporary maritime ergonomic research. Second, the concept of ergonomics was probed from a stakeholder perspective through nine semi-structured qualitative  interviews. Third, structured interviews were held with representatives of ten Swedish shipping companies to investigate if the shipowners are aware of and calculate the economic effects of ergonomics. The results show that severalmodels and methods have been developed to estimate costs and benefits of ergonomics in other industries, but no studies were found from the shipping industry.Whether these methods can be readily adapted to the shipping industry has to be investigated further. While contemporary maritime ergonomic literature showed a focus on physical ergonomic and health and safety issues, the results of the stakeholder interviews indicated a focus on organizational ergonomics. The Swedish shipowners calculate the costs of sick-leave, but do not estimate the economic effects of ergonomics on a regular basis.

  • 11618.
    Östevik, Agnes
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Örtengren, Alexander
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Stöldsäker insamlingsbehållare för blybatterier2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Blybatterier innehåller de miljöskadliga ämnena bly och syra och samlas därför in till återvinning. Dagens insamlingssystem utsätts för ett stort antal stölder på grund av den stora mängd stöldbegärligt bly som finns i batterierna. Blybatterierna har sedan hittats krossade i naturen där blyet utvunnits eller hittats i fordon på väg att transportera dem utomlands till försäljning. Till följd av stölderna kan en miljöriktig återvinning inte garanteras. På uppdrag av Stockholm Vatten AB har därför uppgiften att ta fram en stöldsäker insamlingsbehållare genomförts.

    Stockholm Vatten AB ansvarar för de anläggningar där insamlingsbehållarna står placerade. Anläggningarna består av miljöstationer, ofta placerade i relation till bensinstationer, och bemannade återvinningscentraler.

    Arbetet påbörjades med en informationshämtning i form av besök på återvinningscentraler och miljöstationer samt intervjuer med bland annat personalen på återvinningscentralerna. Kontinuerliga möten med Stockholm Vatten hölls där grundläggande information om problemet gavs. Problemområden definierades för att därefter lägga grunden till den idégenerering av lösningar och funktioner som därefter genomfördes. Idéer grupperades och utvecklades och slutligen valdes fyra koncept; Plinten, Vinkeln, Spiralen och Extern. Besök på återvinningscentraler gjordes åter för att utav personal få bedömning och synpunkter på de framtagna koncepten. Ett konceptval togs därefter, baserat på diskussion med Stockholm Vatten, inhämtade synpunkter och resultat från kriterieviktmetoden och Pugh’s matris.

    Spiralen lade grunden för det slutliga koncept som togs fram. Konceptets funktioner och konstruktion vidareutvecklades, material valdes och komponenter dimensionerades därefter. Fokus lades vid den stöldsäkra funktionen samt vid att skapa en säker inlämningsprocess. För

    att öka förståelse för funktion och användning av behållaren lades även stor vikt vid utformning och formspråk.

    Den huvudsakliga funktionen hos den stöldsäkra behållaren utgjordes av en spiralformad glidbana på vilken batterierna förflyttas ned i behållaren. Ett omslutande syrafast hölje skyddar både användare från syra och batterier från stöld och väder. En öppning i höljet med en skyddande skjutlucka möjliggör inlämningen av batterier.

    Den stöldsäkra insamlingsbehållaren anses uppfylla de i kravspecifikationen definierade krav och önskemål. Behållaren genererar till följd av sin spiralfunktion och sitt yttre hölje en stöldsäker funktion samtidigt som batterierna enkelt kan lämnas in med minskad risk för skador. I och med att fler batterier kan hamna i återvinningsprocessen med hjälp av den stöldsäkra insamlingsbehållaren reduceras utsläppet av miljöskadliga ämnen.

  • 11619.
    Östling, Erik
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Josefsson, Filip
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Nyttomaximering av en solcellsanläggning: En jämförelse mellan ett konventionellt- och ett smart solcellssystem.2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta kandidatexamensarbete utvärderar och jämför en befintlig solcellsanläggning med installerat energilager samt en smart växelriktare i Farsta, Stockholm. Jämförelsen ställer denna anläggning mot ett konventionellt solcellssystem med enbart solceller. Studiens syfte är att identifiera mängden egenanvänd solenergi, ta fram optimeringsförslag samt belysa eventuella kostnadsbesparingar. Den smarta växelriktaren har möjliggjort datainsamling via en webbaserad användarportal, portalen loggar och sparar anläggningens energi- och effektdata.

     

    Studien påvisar att systemet inte bidrar med en betydande ökning av egenanvändningen av solenergi, ty batteriets inställningar ofta medför att batteriet är fulladdat under dagens soltimmar. Det smarta systemets mest fördelaktiga funktion är att kapa fastighetens effekttoppar vilket skapar möjlighet till nedsäkring.

     

    Hur stor del av effekttopparna som kan kapas är starkt beroende av batteriets inställningar. Under studien har två olika scenarier testats. Det mest essentiella är att batteriet alltid kan kapa de högsta effekttopparna samtidigt som det aldrig laddas ur helt. Nyttan maximeras när batteriet aktiveras vid förbrukningar över 24 kW. Säkringsanalyserna från studien visar att fastighetens minsta möjliga huvudsäkringar som kan brukas är 35 A, dock rekommenderas nyttjande av huvudsäkringar om 50 A då en säkerhetsmarginal är önskvärd. Den rekommenderade nedsäkringen ger möjlighet att teckna ett billigare elavtal. Slutsatsen är att säkringsabonnemanget TID relativt effektabonnemanget L0,4S ger en kostnadsbesparing om 33 547 kronor per år.

  • 11620.
    Östlund, Jan
    et al.
    KTH.
    Damgaard, T
    Frey, M
    Side-load phenomena in highly overexpanded rocket nozzles2004Ingår i: Journal of Propulsion and Power, ISSN 0748-4658, E-ISSN 1533-3876, Vol. 20, nr 4, s. 695-704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The operation of rocket engines in the overexpanded mode, that is, with the ambient pressure considerably higher than the nozzle exit wall pressure, can result in dangerous lateral loads acting on the nozzle. These loads occur as the boundary layer separates from the nozzle wall and the pressure distribution deviates from its usual axisymmetric shape. Different aerodynamic or even coupled aerodynamic/structural mechanic reasons can cause an asymmetric pressure distribution. A number of subscale tests have been performed, and three potential origins of side loads were observed and investigated, namely, the pressure fluctuations in the separation and recirculation zone due to the unsteadiness of the separation location, the transition of separation pattern between free-shock separation and restricted-shock separation, and aeroelastic coupling, which indeed cannot cause but do amply existing side loads to significant levels. All three mechanisms are described in detail, and methods are presented to calculate their magnitude and pressure ratio at which they occur.

  • 11621.
    Östlund, Jan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. Volvo-Aero Corporation, S-461 SI Trollhättan, Sweden.
    Muhammad-Klingmann, Barbro
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Supersonic flow separation with application to rocket engine nozzles2005Ingår i: Applied Mechanics Reviews, ISSN 0003-6900, Vol. 58, nr 1-6, s. 143-176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The past decade has seen a qualitative advancement of our understanding of physical phenomena involved in flow separation in supersonic nozzles; in particular, the problem of side loads due to asymmetrical pressure loads, which constitutes a major restraint in the design of nozzles for satellite launchers. The development in this field is to a large extent motivated by the demand for high-performance nozzles in rocket engineering. The present paper begins with an introduction to the physical background of shock-boundary-layer interactions in basic 2D configurations, and then proceeds to internal axisymmetric nozzle flow. Special attention is given to past and recent efforts in modeling and prediction, turning physical insight into applied engineering tools. Finally, an overview is given on different technical solutions to the problem if separation and side loads, discussed in the context of rocket technology.

  • 11622.
    Östlund, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Residual stresses in paperboard and the influence of drying conditions2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The drying sequence in the manufacturing process for paperboard involves evaporation of water, primarily from within the fibres. The vapour is then transported out of the web by pressure or concentration gradients. As the moisture transport from the paper web to the ambient is quicker than the moisture transport within the fibre network to the surfaces of the web, moisture gradients develop through the thickness of the web. This work concerns effects on the mechanics of paper drying from the variation in moisture through the relatively thin structures of paper and paperboard.

    Distributions of inplane residual stresses through paper materials in the unloaded state after drying are believed to be caused by the varying moisture through the thickness during drying. The distributions in general exhibit compressive stress near the board surfaces and tensile stress in the interior of the board. This may be modified after drying and is also affected by structural variation in the material between different plies of multi-ply paperboards.

    The stress development during drying is important because it influences the resulting material properties of the paper and because it can lead to curl, which is a quality problem. The residual stresses themselves are an error source in simulation or evaluation of the mechanical behaviour of paper.

    In this work, residual stress distributions in paperboard were determined experimentally, to clarify the mechanisms of residual stress build-up. An experimental method for such tests was also developed. Based on the experimental findings, the mechanics of paper drying was modelled and the stress build-up simulated. Simulation offers a way of studying how the properties of paper develop during drying of wet paper webs.

  • 11623.
    Östlund, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Borodulina, Svetlana
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Östlund, Sören
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Influence of Paperboard Structure and Processing Conditions on Forming of Complex Paperboard Structures2011Ingår i: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 24, nr 6, s. 331-341Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments were made with a laboratory apparatus for forming paper sheets into double-curved structures. The purpose was to learn more about the design criteria for forming of paper materials into complex shapes. The influence of forming parameters such as moisture and temperature was studied, and the performance of some common pulps as raw materials for the paper sheets was evaluated. Papers made from short hardwood fibres performed worse than papers from other pulps, and the method of moisture application was more important than the amount of moisture that was applied.

  • 11624.
    Östlund, Stefan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Andersson, Evert
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Järnvägsteknik.
    Kottenhoff, Karl
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik.
    Efficient Passenger Trains for the Future1999Ingår i: Proceedings of the WCRR99, 1999Konferensbidrag (Refereegranskat)
  • 11625.
    Östlund, Sören
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Fracture modelling of brittle-matrix composites with spatially dependent crack bridging1995Ingår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 18, nr 10, s. 1213-1230Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In brittle-matrix composites cracking of the matrix is often accompanied by bridging of the crack surfaces. The bridging will reduce the net stress intensity factor at the crack tip and consequently increase the toughness of the composite material. The bridging mechanism is due to for example unbroken whiskers, fibres, ductile particles or interlocking grains.

    Analysis of the bridging mechanism in cracked structures is conveniently carried out using the concept of cohesive zone modelling. In this case the action of the bridging elements is replaced by a distribution of forces, so called cohesive forces trying to close the crack. The commonly used approach in such modelling has been to replace the action from individual bridging elements by a continuous spatially independent distribution of closing tractions whose magnitude is a function of the crack opening displacement only.

    In this paper the influence of the spatial distribution of bridging elements is considered for plane crack problems. The cross section of the bridging elements is assumed to be circular and the distance between the different bridging elements is determined by the volume fraction, the radius and the geometrical distribution of the bridging elements.

    Damage resistance curves have been calculated for typical whiskers-reinforced ceramic composites, and the results from the present spatially dependent models are compared with results from calculations with spatially independent models. The influence of the radius of the bridging element, the volume fraction of whiskers and the material properties are illustrated and the use of spatially independent models is discussed.

  • 11626.
    Östlund, Sören
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Large scale yielding for dynamic crack growth in a strip geometry1991Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 49, nr 3, s. 219-237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic crack growth in a strip geometry has been studied by a convective formulation of the finite element method. The strip is assumed to be made of a material described by an elastic-viscoplastic constitutive equation and the loading conditions are plane strain mode I. The plastic strain-rates are characterized by a power-law overstress model giving an asymptotic elastic singularity at the crack tip. Two different types of loading on the strip geometry have been investigated. In the first geometry the horizontal boundaries parallel to the crack plane were subjected to prescribed displacements perpendicular to the crack plane and the crack tip was loaded in essentially the same way as for a crack in a plate subjected to tensile loading perpendicular to the crack. The second type of loading consisted of a prescribed rotation of the trailing edge in the moving finite element mesh. This created primarily bending loading of the structure.The crack tip energy flow has been calculated for different levels of yielding around the crack tip. The results are compared to the true small scale yielding solution obtained from a boundary layer analysis.The results reported indicate that for the tensile loading there exists a rather wide range of load levels for which the boundary layer solution gives a good description of the fields around the crack tip. For the bending loading the results indicate that the boundary layer solution is a correct description only in cases of extremely small scale yielding. Comparisons between large scale yielding and the boundary layer solution are also made for the effective stress and the effective plastic strain.

  • 11627.
    Östlund, Sören
    KTH, Tidigare Institutioner, Hållfasthetslära.
    On numerical modeling and fracture criteria of dynamic elastic-viscoplastic crack growth1990Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 44, nr 4, s. 283-299Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic steady-state small-scale yielding crack propagation in an elastic-viscoplastic structure is studied by a convective formulation of the finite element method. The loading condition is mode I plane strain.The plastic strain-rates are characterized by a power-law overstress model based on a general theory by Perzyna. For values of the stress exponent less than 3, the elastic strain-rates are more singular than the plastic strain-rates and consequently the near tip fields will exhibit an asymptotic elastic behaviour. The size of the zone where this elastic singularity dominates is typically of the order 10–3–10–5 of the size of the active plastic zone. These relatively small dimensions severely complicate the finite element modeling. Although the energy flow is calculated with a path-independent integral of J-integral type, its value will be dependent on the size of the near-tip elements unless extremely small finite elements are used. This is an important difference compared with many other situations, for example the elastic case and a stationary crack in a power-law hardening material, where the use of a path-independent integral improves the numerical accuracy even if the crack tip region is modeled with a rather coarse mesh. This size effect is discussed in detail. An application of the results with numerical data for a realistic situation shows that the crack tip energy flow might be vanishingly small compared to the energy dissipation in the plastic region. This indicates that the energy flow to the crack tip is perhaps not an appropriate parameter for the description of small-scale yielding crack growth in the present type of material model.The paper also contains an investigation of the introduction of a variable order singular element at the element positions adjacent to the crack tip. It is shown that this type of element does not improve the numerical behaviour in the present formulation.

  • 11628.
    Östlund, Sören
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Three-Dimensional Deformation and Damage Mechanisms in Forming of Advanced Structures in Paper2017Ingår i: ADVANCES INPULP AND PAPERRESEARCH,OXFORD 2017: Transactions of the 16th Fundamental Research Symposium, Pembroke College, Oxford, England, September 2017 / [ed] Warren Batchelor and Daniel Söderberg, 2017, Vol. 2, s. 489-594Konferensbidrag (Refereegranskat)
    Abstract [en]

    There is a large potential for wood-fibre based materials such as paper and board to contribute to lightweight structures in several applications, particularly packaging.  Fibre-based packaging materials have important advantages in comparison to fossil-based plastics regarding biodegradability, recyclability and renewability.  Individualisation has become a crucial criterion for the use of packaging solutions and forming of advanced paperboard structures is a key technology for manufacturing of such packaging shapes.  New sustainable packaging concepts are creating a need for paper materials with considerably enhanced properties.

    Paper and board are in processes for manufacturing of geometrically advances structures in general subjected to complex and often little known multi-axial states of loading and deformation that are not necessarily quantified by conventional measures for paper performance.  Today, commercial paperboard is optimised for folding and printing, and not for applications involving forming of advanced structures. It is likewise important to design the manufacturing processes to meet the particular properties of paperboard.  Manufacturing methods that are suitable for metals and plastics are inevitably not suitable for paper and board since the deformation and damage mechanisms of fibre network materials are different from metals and plastics.

    In this paper recent findings in the literature on 3D forming of paper and paperboard structures are reviewed.  In particular, deformation and damage mechanisms involved in pertinent forming operations and how they are related to paper and board properties in order to enhance the development of new advanced paper materials and structures are analysed.

    In the last decade, there have been major advancements in the development of geometrically advanced 3D paperboard structures including technological advances of various forming processes, enriched understanding of the importance and influence of process parameters, and new paperboard materials with significantly improved forming properties.  However, there is still a lack of knowledge regarding the deformation mechanisms of these complex systems, and particularly regarding the influence of friction.  One remedy would be the enhancement of numerical simulation tools.  Optimisation of existing forming processes and development of new ones as well as tailored paper and board materials with properties customised to the demands of existing and new 3D forming processes will also play important roles.  This development is only in its beginning and major progress is expected in the near future.

  • 11629.
    Östlund, Sören
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Blom, Karin
    KTH, Skolan för teknikvetenskap (SCI).
    Hjorth, P.-O.
    SAM Samarbetande konsulter AB.
    Ahlstrand, Jonas
    SAM Samarbetande konsulter AB.
    Continuous improvement of a CDIO program using management by means2007Ingår i: Proceedings of the 3rd International CDIO Conference, 2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Vehicle Engineering program at KTH was one of the first programs that adopted the CDIO-model for engineering education. The implemented changes were during the first three years subjected to a number of internal and external evaluations, with very positive judgments. Perhaps, the most important task for the program management after such a major overhaul of a program is to motivate faculty for continuous improvement work. Faculty have put a lot of effort into the change process, and they are in general not easily susceptible to further demands from the program management. Thus, there was an appropriate opportunity to try a new management philosophy.

    This paper describes how the management by means concept is introduced in the continuous improvement work of the Vehicle Engineering program. This concept, which is in contrast with traditional management by results concepts, has been used successfully in industrial engineering development work. The main feature of the management by means concept is that the development work is driven not by explicit preconceived targets, but by common values and principles.

    The paper presents the development of common values and principles for the Vehicle engineering program, and the implementation of them in the practical work, carried out in a change group covering all first year courses. Benefits and difficulties are described and the experiences gained so far are discussed, particularly, the dual loyalties of faculty that arise in the educational system at KTH where a program, in general, is not owned by a department.

  • 11630.
    Östlund, Sören
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Asymptotic crack tip fields for dynamic fracture of linear strain-hardening solids1988Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 24, nr 11, s. 1141-1158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Asymptotic crack tip fields, for dynamic crack propagation in an elastic-plastic material, have been calculated. The material is characterized by J2flow theory with linear-strain hardening. The possibility of plastic reloading on the crack flank is taken into account. Numerical results for the strength of the crack tip singularity, the angular positions of elastic unloading and possible plastic reloading regions, and the angular variation of the stress and velocity fields, are presented as functions of the crack tip speed and the ratio between tangent modulus and elastic modulus. Calculations have been performed for crack tip speeds below a certain limit velocity which depends on the tangent modulus and the loading conditions. The different loading modes which have been studied are modes I and II (plane strain and plane stress) and mode III (antiplane strain).

  • 11631.
    Östlund, Sören
    et al.
    Swedish Institute of Composites.
    Gudmundson, Peter
    Swedish Institute of Composites.
    Numerical-Analysis Of Matrix-Crack-Induced Delaminations In [+/-55-Degrees] Gfrp Laminates.1992Ingår i: COMPOSITES ENGINEERING 2, ISSN 0961-9526, Vol. 2, nr 3, s. 161-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a three-dimensional glass epoxy angle-ply laminate of the type [+/- 55-degrees] containing matrix cracks and two types of matrix-crack-induced interlaminar local delaminations has been numerically analyzed by the finite element method. Due to periodicity and symmetry only a representative volume element in the form of a parallelepiped bounded by neighbouring matrix cracks needs to be modelled. The additional contributions to the reduction of stiffness coefficients due to local delaminations are compared to the stiffness of undamaged laminates and laminates containing only matrix cracks. Furthermore, the growth of delaminations and progressive matrix cracking are investigated by calculations of their respective total energy release rates as functions of the delamination size and matrix crack density. Implications of the influence of matrix-crack-induced delaminations on the mechanical behaviour of the composite laminate are discussed.

  • 11632.
    Östlund, Sören
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    The Application Of Moving Finite-Elements For The Study Of Crack-Propagation In Linear Elastic Solids.1987Ingår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 25, nr 5, s. 765-774Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mode I crack propagation in linear elastic solids is studied by a convecting finite element mesh. The finite element formulation is briefly described. Two different approaches for the determination of the stress intensity factor K1 have been investigated, one using the COD relation to K1 and one using the dynamic G-integral. Different test problems, including stationary cracks, steady-state crack propagation and transient crack propagation, have been thoroughly examined.

  • 11633.
    Östlund, Sören
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Linvill, Eric
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Wallmeier, M
    Continuum Modeling of Wrinkles and Explicit FEM Modeling of Paperboard Deep-Drawing2016Ingår i: 2016 Progress in Paper Physics Seminars / [ed] Samuel Schabel, 2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Deep drawing of paperboard requires the creation of wrinkles for successful forming of a paperboard cup. A phenomenological model for the mechanical response of wrinkles is proposed and based on the assumption that the wrinkles have a mechanical response equivalent to that of a plastic hinge (i.e. the internal moment in the hinge is held constant during deformation). This 1-D model has been verified with two experiments.

                Furthermore, this phenomenological model has been expanded into a 3-D continuum constitutive model, which considers the initiation and propagation of wrinkles, large deformations due to wrinkle formation and wrinkle compression, and permanent deformations. This 3-D continuum model has been compared to and verified against experimental deep-drawing results. Experiments and simulations have been compared in terms of springback, wrinkle propagation, and punch force. Additionally, the model provided insight into the deep-drawing process by establishing better understanding of the initiation of wrinkling.

  • 11634.
    Östlund, Sören
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Mäkelä, Petri
    Tetra Pak Packaging Solutions AB.
    Fracture properties2011Ingår i: Mechanics of Paper Products / [ed] Kaarlo Niskanen, Berlin: Walter de Gruyter GmbH & Co. KG , 2011, 1, s. 67-89Kapitel i bok, del av antologi (Refereegranskat)
  • 11635.
    Östlund, Sören
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Nilsson, Fred
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Cohesive modelling of process regions for cracks in linear elastic structures-fundamental aspects1993Ingår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 16, nr 2, s. 215-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The process region at the tip of a crack in a linear elastic structure has been modelled by a cohesive zone. Growth of the front end of the cohesive zone is governed by a critical stress intensity factor criterion, and advance of the original traction free crack is determined by a critical crack opening at the rear end of the cohesive zone.

    Damage resistance curves relating the applied stress intensity factor to the growth of the cohesive zone have been calculated for an idealized structure containing two characteristic dimensions. Instability resulting in failure of the structure is found to occur either by unstable growth of the front end of the cohesive zone, without a fully developed cohesive zone, or by unstable growth of the original flaw, when the crack opening displacement at the rear end of the cohesive zone reaches a critical value.

    The influence of the size of the structure compared to the length of the cohesive zone is investigated, and conditions for the limits of validity of the small scale yielding assumption are discussed. Comparisons are made between the maximum load and the length of the cohesive zone at instability resulting from the present analysis, and the values predicted by linear elastic fracture mechanics.

  • 11636.
    Östlund, Sören
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Nilsson, Fred
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Cohesive zone modelling of damage at the tip of cracks in slender beam structures1993Ingår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 16, nr 6, s. 663-676Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of simple beam theory for cohesive zone modelling of the damage response at the crack tip in linear elastic isotropic double cantilever beam (DCB) specimens has been investigated. Damage resistance curves (DR-curves) relating the applied stress intensity factor to the growth of the cohesive zones for beam theory modelling has been compared with two-dimensional elasticity calculations for different material parameters and specimen dimensions. A substantial difference is observed between DR-curves for the two types of models. As expected this difference vanishes for decreasing beam heights. For large beam heights the DR-curves calculated by two-dimensional elasticity are approaching small-scale yielding DR-curves, i.e. DR-curves for an edge crack in an infinite plate. The beam height for which beam theory is applicable could be up to 10-3 times the height for which small scale bridging DR-curves are applicable.

  • 11637.
    Östlund, Sören
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Niskanen, Kaarlo
    KCL.
    Kärenlampi, Petri
    University of Helsinki.
    On the prediction of the strength of paper structures with a flaw1999Ingår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 25, nr 10, s. 356-360Artikel i tidskrift (Refereegranskat)
  • 11638.
    Östlund, Sören
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Through-thickness mechanical testing and computational modelling of paper and board for efficient materials design2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The objective of most methods for mechanical testing of paper and paperboard is production control, i.e. to secure that the performance of the produced material fulfils certain minimum end‐use requirements. There is in the industry an ever increasing demand for improved efficiency in paper and board converting and end‐use, and this demand paves the way for the development of new test methods that enables a better understanding of the material design. There is a need for better control of changes in the pulping and papermaking processes at different structural levels, and for efficient characterization of these changes. To achieve such control, novel test methods and computational modelling are required.

    The objective of this paper is to discuss some newly proposed test methods and to illustrate how these in combination with simulations are a valuable tool for efficient materials design. The mechanical properties that are covered in the paper include in‐plane residual stresses and transverse shear properties of paper and paperboard. The methods will be shortly described and some important experimental results will be presented. Finally, some examples of computation modelling related to these properties will be discussed.

  • 11639.
    Öun, Martin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Ericson, Peter
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Larsson, Svante
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Modellering och analys av kuggrigg2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna rapport har skrivits som ett resultat av ett kandidatexamensarbete på uppdrag av Sveriges Transmissionskluster i samarbete med Institutionen för Maskinkonstruktion vid KTH. Rapporten beskriver modellering samt styvhets- och egensvängningsanalyser av en kuggrigg, FZG Standard Test Rig, som vid KTH skall användas vid tester av skvalpförluster i växellådor. Kuggriggen modellerades först mycket detaljerat i CAD-programmet Solid Edge. Därefter förenklades modellen i flera steg och överfördes till ANSYS. Där utfördes en styvhets- och egensvängningsanalys med hjälp av FEM. Kuggingreppen har beskrivits med glidande och rullande kontakt och de lager som har förenklats har uttryckts som solidkroppar med bestämd styvhet. Den maximala vriddeformationen i axlarna blev 4,5 grader då riggen var belastad med 1000Nm. Det visade sig att vridstyvheten i axlarna inte varierade linjärt och att deformationen i växellådorna inte ökade i proportion till belastningen. Den lägsta uppmätta frekvensen blev 136Hz, vilket motsvarar 8160rpm, detta då riggen är belastad med 50Nm. För frivibrationsanalysen som utfördes uppskattas frekvensen till 198Hz, 11885rpm. Egenfrekvenserna ligger båda långt utanför riggens arbetsområde men vad som inte undersökts är hur störningarna, som kuggingreppen ger upphov till, påverkar systemet. Vid maximal belastning uppgick den lägsta säkerheten mot plasticering till en faktor 4 och infaller då i den drivande växellådan.Modellen och analyserna baseras på en verklig kuggrigg som, då arbetet inleddes, mättes upp och fotograferades för att möjliggöra återskapandet av kuggriggen i Solid Edge. Analyserna baserar sig sedan på den återskapade modellen och inga verkliga försök har genomförts. Tillsammans med denna rapport är CAD-modellen, en demonstrationsfilm av riggens funktion och ANSYS-analysen resultatet av detta kandidatexamensarbete.

  • 11640.
    Čelik, Haris
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Phan, M. Q.
    Identification of input-output maps for bilinear discrete-time state-space models2012Ingår i: Adv Astronaut Sci, 2012, s. 393-412Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a formulation to identify the input-output maps of discrete- time bilinear state-space models. The new method uses input-output data from one experiment, and the input data need not be of special types such as extended pulses. The initial conditions can be non-zero and unknown. Recent methods, on the other hand, require data from multiple experiments, specialized input signals, and zero initial conditions. In the present method, a Nonlinear Auto-Regressive model with eXogenous input (NARX) is identified and used to predict the bilinear system response directly without returning to the bilinear state-space format. Numerical examples are provided to illustrate the identification method.

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