Change search
Refine search result
1234567 1 - 50 of 439
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Adlercreutz, Ludvig
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    A Study of Automotive Composites and Optimisation for Chassis Implementation2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the quest of reducing emissions of passenger cars a trend in the car industry has recently been tointroduce lightweight composite materials to replace steel which has been the otherwise main materialto use. In this report the weight-optimising of a structural underbody for a passenger car using twodifferent manufacturing methods is described. The two methods are Advanced Sheet MouldingCompound (A-SMC) and Resin Transfer Moulding (RTM). A-SMC is characterised by a low cycle time andfast layup of the material resulting in lower cost. RTM is slower and thus more expensive but has bettermaterial properties which results in lower weight. The novel approach is to use A-SMC to construct thecomplete underbody as one piece which has not been done before. The geometry is FEM -optimised forminimum material thickness under a standard load case for torsional stiffness.The simulations showed that the underbody was not possible to be manufactured using A-SMC in itsoriginal shape without being reinforced. When reinforcing the structure it met the design constraintsand the weight was optimised to 53.9 kg with the possibility for further improvements. The RTMmethod resulted in 25.83 kg without any reinforcements but showed potential for further weightreduction by changing the geometrical design. A final analysis of the underbody combined the twomanufacturing methods and the weight was here optimised to 25.27 kg without any reinforcements.

  • 2.
    Afshari, Davood
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Mechanical Properties of Resistance Spot Welds in Lightweight Applications2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This licentiate thesis is concerned with residual stresses in aluminum alloy 6061-T6 resistance spot welded joint. Several topics related to mechanical strength of welded structures are treated such as; nugget size and microhardness and microstructures of weld zone and their influence on mechanical strength of welded structure, failure load measurement using tensile-shear test, resistance spot welding simulation, residual stress measurement by X-ray diffraction method and analysis effect of welding parameters on the mechanical strength and the residual stresses.

    To investigate the effect of resistance spot weld parameters on mechanical strength of welded structures, various welding parameters e.g. welding current, welding time and electrode force are selected to produce welded joints with different quality. According to the failure mode, the empirical equation was used to prediction of failure load base on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. Microhardness tests are done to find hardness profiles due to microstructural changes and determine the minimum hardness.

    In addition, an electro-thermal-structural coupled finite element model and X-ray diffraction residual stress measurement have been utilized to analyze residual stresses distribution in weld zone. The electrical and thermal contact conductance, as mandatory factors are applied in contact area between electrode-workpiece and workpiece-workpiece to resolve the complexity of the finite element model. The physical and mechanical properties of the material are defined as thermal-dependent in order to improve the accuracy of the model. Furthermore, the electrodes are removed after holding cycle using the birth and death elements method. Moreover, the effect of welding parameters on maximum residual stress is investigated and a regression model is proposed to predict maximum tensile residual stresses in terms of welding parameters.

    The results obtained from the finite element analysis have been used to build up two back-propagation artificial neural network models for the residual stresses and the nugget size prediction. The results revealed that the neural network models created in this study can accurately predict the nugget size and the residual stresses produced in resistance spot weld. Using a combination of these two developed models, the nugget size and the residual stresses can be predicted in terms of spot weld parameters with high speed and accuracy.

  • 3.
    Afshari, Davood
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sedighi, Mohammd
    Iran Univ Sci & Technol, Tehran, Iran.
    Barsoum, Zuhier
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Peng, Ru Lin
    Linkoping Tech Univ, Linkoping, Sweden .
    An approach in prediction of failure in resistance spot welded aluminum 6061-T6 under quasi-static tensile test2012In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 226, no B6, p. 1026-1032Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to predict the failure load in resistance spot welded aluminum 6061-T6 sheets with 2mm thickness under quasi-static tensile test. Various welding parameters, e. g. welding current, welding time and electrode force are selected to produce welded joints with different quality. The results show that for all the samples in this study only interfacial failure mode was observed in tensile-shear test and no pull-out mode was observed. According to the failure mode, an empirical equation was used for the prediction of failure load based on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. For determination of the minimum hardness, microhardness tests have been carried out to find hardness profiles. The minimum hardness value was observed for a thin layer around the nugget with large and coarse grains. The results show that by using the presented empirical equation, the failure can be predicted with a good agreement only by measuring nugget size.

  • 4.
    Afshari, Davood
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Sedighi, Mohammd
    Iran Univ Sci & Technol, Tehran, Iran.
    Karimi, M. R.
    Barsoum, Zuhier
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    On Residual Stresses in Resistance Spot-Welded Aluminum Alloy 6061-T6: Experimental and Numerical Analysis2013In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 22, no 12, p. 3612-3619Article in journal (Refereed)
    Abstract [en]

    In this study, an electro-thermal-structural-coupled finite element (FE) model and x-ray diffraction residual stress measurements have been utilized to analyze distribution of residual stresses in an aluminum alloy 6061-T6 resistance spot-welded joint with 2-mm-thickness sheet. Increasing the aluminum sheet thickness to more than 1 mm leads to creating difficulty in spot-welding process and increases the complexity of the FE model. The electrical and thermal contact conductances, as mandatory factors are applied in contact areas of electrode-workpiece and workpiece-workpiece to resolve the complexity of the FE model. The physical and mechanical properties of the material are defined as thermal dependent to improve the accuracy of the model. Furthermore, the electrodes are removed after the holding cycle using the birth-and-death elements method. The results have a good agreement with experimental data obtained from x-ray diffraction residual stress measurements. However, the highest internal tensile residual stress occurs in the center of the nugget zone and decreases toward nugget edge; surface residual stress increases toward the edge of the welding zone and afterward, the area decreases slightly.

  • 5.
    Afshari, Davood
    et al.
    School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran .
    Sedighi, Mohammd
    Iran Univ Sci & Technol, Tehran, Iran.
    Karimi, M. R.
    Barsoum, Zuhier
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Prediction of the nugget size in resistance spot welding with a combination of a finite-element analysis and an artificial neural network2014In: Materiali in tehnologije, ISSN 1580-2949, E-ISSN 1580-3414, Vol. 48, no 1, p. 33-38Article in journal (Refereed)
    Abstract [en]

    The goal of this investigation is to predict the nugget size for a resistance spot weld of thick aluminum 6061-T6 sheets 2 mm. The quality and strength of spot welds determine the integrity of the structure, which depends thoroughly on the nugget size. In this study, the finite-element method and artificial neural network were used to predict the nugget size. Different spot welding parameters such as the welding current and the welding time were selected to be used for a coupled, thermal-electrical-structural finite-element model. In order to validate the numerical results a series of experiments were carried out and the nugget sizes were measured. The results obtained with the finite-element analysis were used to build up a back-propagation, artificial-neural-network model for the nugget-size prediction. The results revealed that a combination of these two developed models can accurately and rapidly predict the nugget size for a resistance spot weld.

  • 6. Alam, M M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsen, P
    Kaplan, A F H
    Haggblad, H A
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 10, p. 2246-2258Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations.

  • 7. Alam, M. M.
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsén, P.
    Kaplan, A. F. H.
    Häggblad, H. A.
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by 4-point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro-and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 8. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Häggblad, Hans Åke
    Jonsén, Pär
    Kaplan, Alexander
    The Effects of Surface Topography and Lack of Fusion on The Fatigue Strength of Laser Hybrid Welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics, 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welds (before, during and after the process) differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the micro-topography (i.e. the surface ripples) can be more important than the macrogeometry of the weld surface or lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the micro-topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface, the tendency to LOF can be explained. Stress analysis was carried out by Finite element analysis (FEA) for the complex joint geometry and a bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface micro-topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

  • 9. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsén, Pär
    Häggblad, Hans Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints – Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference / [ed] Erling Dam Mortensen, 2009Conference paper (Other academic)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

  • 10. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsén, Pär
    Häggblad, Hans Åke
    Kaplan, Alexander
    Geometrical Aspects of The Fatigue Behaviour of Laser Hybrid Fillet Welds2009In: Proceedings of the Fatigue Design Conference, 2009Conference paper (Refereed)
  • 11. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Josén, Per
    Häggblad, Hans Åke
    kaplan, Alexander
    Fatigue Behaviour Study of Laser Hybrid Welded Eccentric Fillet Joints - Part I2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference / [ed] Erling Dam Mortensen, 2009Conference paper (Other academic)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

  • 12. Alkhagen, M.
    et al.
    Toll, Staffan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    A triaxial rheometer for soft compressible solids2002In: Journal of Rheology, ISSN 01486055 (ISSN), Vol. 46, no 1, p. 31-47Article in journal (Refereed)
    Abstract [en]

    The compression and the shear of soft compressible solids were studied using the triaxial rheometer. The sample was fixed between two parallel plates and the deformation was controlled by an x, y, z displacement on one plate while the stress was measured on the other. The triaxial stress transducer eliminates the edge effects by only measuring the stress on an interior region of the plate. The edge effects and the associated measurement errors were analyzed by the simple isotropic elastic theory and were compared to the measurements done on the chloroprene rubber foam.

  • 13. Allaoui, Aissa
    et al.
    Toll, Staffan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Evesque, Pierre
    Bai, JinBo
    On the compressive response of carbon nanotube tangles2009In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, no 35, p. 3169-3173Article in journal (Refereed)
    Abstract [en]

    The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes. the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.

  • 14. Al-Zubaidy, M. N.
    et al.
    Chan, J. F. L.
    Gibson, A. G.
    Toll, Staffan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Properties of orthotropic glass-polypropylene composites manufactured by weaving of prepreg tapes and other routes2000In: Plastics, Rubber and Composites Processing and Applications, ISSN 09598111 (ISSN), Vol. 29, no 10, p. 520-526Article in journal (Refereed)
    Abstract [en]

    This paper reports a study of the melt impregnation and weaving of glass-polypropylene prepreg tapes into sheet for use as a precursor for pressed thermoplastic composite products and a comparison of the properties attainable with those achievable by other comparable routes. Melt impregnation has been used successfully to manufacture well impregnated tapes, with and without internal coupling agent. It appears that weaving could be an economically viable process for converting unidirectional tape into a conformable, press formable prepreg. The properties of glass-polypropylene laminates manufactured by pressing the tape woven product were compared with those of other glass-polypropylene composites, including crossply laminate made from Plytron and samples prepared by film stacking. Quasi-static mechanical properties were found to be comparable with those of Plytron and superior to those of the other materials. In the coupled samples, coupling was somewhat less effective than in Plytron. The impact behaviour of the pressed, tape woven products was impressive and superior to any of the other materials tested. © 2000 IoM Communications Ltd.

  • 15.
    Andersson, Rolf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Utvärdering av infästningar i sandwichkonstruktioner för fordonsapplikationer2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The automotive industry is increasingly studying lightweight solution in their designs, also rational production and low costs in materials and manufacturing methods are of great interest. This thesis consisted in the practical evaluation of anchors for sandwich panels. The object was to study loads of shearing and pull out of the plane. The experiments were carried out on panels made up of 1mm aluminium coatings and 50mm extruded polystyrene (XPS) at its core. As the fasteners used simple methods such as blind rivets, screw and glue. 44 tests were performed. Out of these 32 considered pullout of the plane and 12 considered shearing. The results show that it is possible to have good strength in shearing and pull with simple methods.

  • 16.
    Andersson, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Pipe-In-Pipe system for offshore applications: Post buckling analysis associated with thermal expansion2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The usage of Pipe-In-Pipe (PIP) solutions for offshore applications has increased during the lastyears. The solution gives high thermal insulation and protects the flow line from environmental impacts. One critical load case is buckling of the pipeline system due to thermal expansions of the inner pipe. This project intends to increase knowledge about PIP systems, investigate the impact of different parameters as well as update parameters in an existing SIMLA model. A FE-model of a PIP system was created in ANSYS with a refined section where pipes and centralizers are modelled with solid elements.The ANSYS-model was tested against a verified FE-model created in SIMLA. The global results obtained from ANSYS and SIMLA did not give a perfect match. The ANSYS model tended to buckle in another way, which is assumed to be related to different modelling of resistance between the pipeline and the seabed as well as unwished properties between the side section and the midsection.Local results obtained from ANSYS showed that there are discontinuities in bending moment and effective axial forces when passing a centralizer. The contact force between centralizer and pipes give rise to high friction forces that acts along the same line as the axial force in the pipes.Increased friction coefficient between centralizer and outer pipe resulted in increased discontinuity in axial force. Selection of a proper friction coefficient thus has significant influence on the results.Centralizer stiffness was evaluated by a local FE-model where a centralizer was compressed between the inner and the outer pipe. Displacement of inner pipe was evaluated as a function of applied force. The result showed that the force-displacement curve describing centralizer stiffness follows 

     Q (Δ)=( Δ) 

    where      is a constant depending on dimensions and material of the centralizer. Linearized indifferent sections and with a centralizer thickness of 0,1 meter the following expression gave stiffnesses in the range 100-1000 MN/m, which agrees with stiffnesses used in the SIMLA model.displacements up to 0.3 mm the radial stiffness used in SIMLA is still good to use.

  • 17. André, Alain
    et al.
    Norrby, Monica
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Nilsson, Sören
    Nyman, Tonny
    An Experimental And Numerical Study Of The Effect Of Some Manufacturing Defects2013In: Proceedings of the 19th International conference on composite materials, ICCM-19, 2013Conference paper (Refereed)
    Abstract [en]

    Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

  • 18.
    Arrou-Vignod, Pierre
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Simultaneous modal adjustment of multiple aircraft configurations using an optimization method2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When designing an airplane, it is necessary to know precisely the vibration modes of the structure. To do so, the Finite Element model of the airplane is adjusted to ground vibration tests results using optimization. Particularly, for airplanes able to carry several external payloads, this adjustment process must be performed for all payloads configurations. In this Master Thesis, the possibility of adjusting simultaneously different airplane configurations to their respective tests results is explored. Such a method ensures that the final Finite Element model is the same in all configurations. After implementation in the company’s software, this method is subsequently tested over two configurations. The results obtained are compared to those from separate adjustment of the models with the same variable parameters. Comparison shows that simultaneous model adjustment is promising. A better choice of variable parameters is required to improve results. 

  • 19.
    Asgher, Wasim
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Effect of material grade on fatigue strength and residual stresses in high strength steel welds2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis work is concerned with effect of material grade on fatigue strength of welded joints. Fatigue strength evaluation of welded joints in as welded and post weld treated condition was carried out with effective notch method. Results of peak stress method have also been compared with those of effective notch method for as welded joints. In addition, using the results of effective notch method, the effect of important weld and global geometry factors on notch stress concentration factor has been studied with 2-level design of experiment and a mathematical relation among stress concentration factor and the geometric factors has been proposed. Overall, thickness of the base plate and toe radius is found to be the most important factors determining fatigue strength of the joint.

    Welding induced residual stresses have also been predicted using 2D and 3D FEM analysis to see their effect on fatigue strength of the joints. Also, transversal residual stresses were measured using X-ray diffraction method to assess the accuracy of predicted results. Based on simulation results, effect of geometric factors on maximum value of transversal residual stress was also investigated.

  • 20.
    Augustis, Nerijus
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Load bearing Composite Beam in a Bus Structure2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 21. Aygül, M.
    et al.
    Al-Emrani, M.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Investigation of distortion-induced fatigue cracked welded details using 3D crack propagation analysis2014In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 64, p. 54-66Article in journal (Refereed)
    Abstract [en]

    The behaviour of distortion-induced fatigue cracks in welded details in an existing bridge was studied analytically by performing crack propagation analysis based on linear elastic fracture mechanics. The real load history of the bridge was obtained from strain measurements. These loads were utilised to examine the crack growth rate and the residual service life of the cracked detail. Moreover, the effectiveness, accuracy and applicability of the crack propagation analysis on bridge structures were investigated by simulating a complex case of fatigue cracking using several crack propagation analyses. The results of the analyses revealed that the fatigue crack in the studied details had significantly different crack growth characteristics in different directions. In the thickness direction, for instance, the crack was seen to propagate at a certain rate, which increased with the propagated crack from the beginning and, as expected, the crack propagation rate decreased when the crack grew longer. The crack was subsequently arrested half way through the thickness of the plate. In the longitudinal direction, the crack was not, however, arrested in the same way as in the thickness direction and it continued to propagate at a reduced yet constant crack growth rate. The results also revealed that, even though distortion-induced fatigue cracking was usually caused by a mixed-mode condition (i.e. a combination of modes I, II and III), the governing propagation mode is still mode I. Furthermore, it was also observed that the contribution of modes II and III to crack propagation was very little and dependent on the location of the propagated crack front, as well as the geometrical configuration of the cross-beam.

  • 22.
    Azizi Samir, M. A. S.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Alloin, F.
    Dufresne, A.
    High performance nanocomposite polymer electrolytes2006In: Composite interfaces (Print), ISSN 0927-6440, E-ISSN 1568-5543, Vol. 13, no 4-6, p. 545-559Article in journal (Refereed)
    Abstract [en]

    Solid lithium-conducting nanocomposite polymer electrolytes based on poly(oxyethylene) (POE) were prepared using high aspect ratio cellulosic whiskers and lithium imide salt, LiTFSI. The cellulosic whiskers were extracted from tunicate - a sea animal - and consisted of slender parallelepiped rods that have an average length around 1 μm and a width close to 15 nm. High performance nanocomposite electrolytes were obtained. The filler provided a high reinforcing effect, despite the favorable cellulose/POE interactions that were expected to decrease the possibility of interwhisker connection and formation of a percolating cellulosic network, while a high level of ionic conductivity was retained with respect to unfilled polymer electrolytes. Cross-linking and plasticizing of the matrix as well as preparation of the composites from an organic medium were also investigated.

  • 23.
    Azizi Samir, M. A. S.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Université Joseph Fourier, France.
    Alloin, F.
    Dufresne, A.
    Review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 2, p. 612-626Article in journal (Refereed)
    Abstract [en]

    There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers. Cellulose, the world's most abundant natural, renewable, biodegradable polymer, is a classical example of these reinforcing elements, which occur as whiskerlike microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, with the consequence of axial physical properties approaching those of perfect crystals. This quite "primitive" polymer can be used to create high performance nanocomposites presenting outstanding properties. This reinforcing capability results from the intrinsic chemical nature of cellulose and from its hierarchical structure. Aqueous suspensions of cellulose crystallites can be prepared by acid hydrolysis of cellulose. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspension by subsequent vigorous mechanical shearing action. During the past decade, many works have been devoted to mimic biocomposites by blending cellulose whiskers from different sources with polymer matrixes.

  • 24.
    Back, Robin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Optimeringsmetoder för ASMC-strukturer2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Thin metal sheets have for long been the dominant structural components in automotive bodies, but as environmental concerns mount new materials are needed to reduce mass. Advanced Sheet Moulding Compounds (ASMC) is a carbon fibre composite with short fibres and has been put forward as an alternative. It is both light and has good durability and can be formed in a mould similarly to steel sheets. A distinct advantage is that unlike for steel sheets the thickness in an ASMC component can be varied and stiffeners integrated. This creates great opportunities for optimisation, but as know-how in the industry is scarce a methodology is necessary. This master’s thesis describes a method developed for optimising structural components manufactured in ASMC by analysing a backplate mounted in a Body-In-White (BIW). The optimisation design process was first developed in a simplified model made to mimic a BIW without all the complexities therein. In this thesis free-size optimisation was done individually and coupled with adding uni-directional (UD) fibres and ribs to the backplate. This process was then verified in an accurate car body model and the process translated rather well to a more realistic model as favourable results were obtained. Optimisation resulted in more than 50% decrease in the component’s mass and body torsional stiffness could be increased by up to 7%. A step-by-step guide for this process is presented. Moving forward the design methodology needs to be verified and developed further for different structures and load cases. It is believed that the process detailed works well for many different structures as is, but improvements can be made and are ultimately necessary.

  • 25.
    Bardet, Valentine
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Automation of inserts-checking on an Aluminiumsandwich structure2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In space projects, checking inserts can be tedious, even more so for high density of inserts. This paper deals with the development of an automation tool for insert checking. All the principles used to perform inserts calculations are based on the ECSS-Design Handbook [1]. Those principles are summarised and adapted to the tool. The tool requires only a point cloud extracted from a CADmodel giving the position of inserts to be checked and the loads calculated thanks to an FEM-model at those same points to calculate safety margins. This paper details the process followed by the tool to calculate inserts strength and describes possible measures for improvements.

  • 26.
    Barmicho, Ilona
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue Life Assessment of Cut Edges in High Strength Steel2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The interests in more effective and lighter structures have increased the use of high strength steels for higher performances. Plate materials are optimized so thinner structures and higher material strengths are reached, this leads to the cut quality might be a new issue.

    In this investigation steel thickness of 6 and 16 mm with minimum yield strength from 355 to 960 MPa are fatigue tested with constant amplitude tensile loading. The specimens were cut using waterjet and also with thermally cut methods such as plasma and oxygen. Before fatigue testing the cut surfaces were measured and roughness Rz values were obtained.

    Empirical and analytical results of the surface roughness influencing the fatigue strength for different steel strengths are presented.

    Since thermal cutting methods have been developed over the years the FAT values are higher for those IIW are recommending.

    When the quality of the cut surface can be kept high the fatigue strength will also be higher than those recommended. This means having a cutting process that provides smooth surfaces such as waterjet and plasma cutting the fatigue life will be longer.

  • 27.
    Barmicho, Ilona
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Load bearing Composite Beam in a Bus Structure2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 28. Barsoum, I.
    et al.
    Khan, F.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Analysis of the torsional strength of hardened splined shafts2014In: Materials and Design, ISSN 0261-3069, Vol. 54, p. 130-136Article in journal (Refereed)
    Abstract [en]

    The current study presents a finite element modeling framework to determine the torsion strength of hardened splined shafts by taking into account the detailed geometry of the involute spline and the material gradation due to the hardness profile. The aim is to select a spline geometry and hardness depth that optimizes the static torsion strength. Six different spline geometries and seven different hardness profiles including non-hardened and through-hardened shafts have been considered. The results reveal that the torque causing yielding of induction hardened splined shafts is strongly dependent on the hardness depth and the geometry of the spline teeth. The results from the model agree well with experimental results found in the literature and reveal that an optimum hardness depth maximizing the torsional strength can be achieved if shafts are hardened to half their radius.

  • 29.
    Barsoum, IImad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Petr Inst, U Arab Emirates.
    Al Ali, K. F.
    A procedure to determine the tangential true stress-strain behavior of pipes2015In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, E-ISSN 1879-3541, Vol. 128, p. 59-68Article in journal (Refereed)
    Abstract [en]

    Determining the tangential mechanical properties of a tube is essential for simulation of various manufacturing processes that involve the use of a tubular geometry. The aim of this study is to develop a procedure to determine the tangential true stress-strain behavior of pipes. For this purpose a modified ring test setup is proposed consisting of a ring specimen loaded with two separate D-blocks. Using a finite element model, an optimized ring specimen geometry is obtained. The optimized ring specimen exhibits uniform tangential distribution in the gauge region of the specimen and necking occurs consistently at the center of the gauge length. It is found that friction has a substantial effect on the mechanical response of the ring test for which two different setups to reduce friction are proposed. One using lubricated D-blocks (DB) and one using lubricated D-blocks with needle roller bearing (RB). Assisted by the FE model, the friction during the experiment is account for and a data analysis procedure to determine the tangential stress-strain curve of the pipe is proposed. It is found that the results using this procedure show very good agreement with previously published results.

  • 30.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Avancerade metoder för noggrannare dimensionering av svetsade konstruktioner2009In: Svetsen, ISSN 0039-7091, Vol. 68, no 3Article in journal (Other (popular science, discussion, etc.))
  • 31.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue Assessment of Cruciform Joints Welded with Different Methods2005In: IIW Doc. No. XIII-2074-05, 2005Conference paper (Other academic)
  • 32.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue design of welded structures: effect of weld quality and residual stresses, XIII-2312-102010Conference paper (Other academic)
  • 33.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue Strength of cruciform joints fabricated with different welding processes2007In: International Symposium on Integrated Design and Manufacturing of Welded Structures, Eskilstuna, 2007Conference paper (Other academic)
  • 34.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    HENRY GRANJON PRIZE COMPETITION 2010 Winner Category C: "Design and Structural Integrity" FATIGUE DESIGN OF WELDED STRUCTURES - SOME ASPECTS OF WELD QUALITY AND RESIDUAL STRESSES2011In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 55, no 11-12, p. 2-11Article in journal (Refereed)
    Abstract [en]

    The research work reported in this paper aims to increase the accuracy of fatigue life prediction of welded steel structures using local analysis methods by i) establishing a link between weld quality and fatigue life ii) developing simplified engineering methods using finite element routines for prediction of welding residual stresses iii) incorporating the residual stresses into the fatigue life predictions. Acceptance criteria were developed for the weld quality by comprehensive FE-and fracture mechanical analysis and fatigue testing. The results are the foundation for the new weld class system within the Volvo group company. Simplified FE welding simulation routines and procedures for incorporating the predicted residual stresses into crack growth analysis were developed showing good agreement with residual stress measurements and fatigue testing.

  • 35.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Local weld geometry and the influence on fatigue strength2010In: Proceedings of the Swedish Conference on Lightweight Optimised Welded Structures: Borlänge, March 24-25, 2009 / [ed] Zubeir Barsoum, Jack Samuelsson, Borlänge, 2010, p. 26-38Conference paper (Other academic)
  • 36.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Numerical Analysis and Measurement of Residual Stresses in Multi Pass Welding - Influence on Fatigue Root Crack Propagation2006In: TRENDS IN WELDING RESEARCH, PROCEEDINGS / [ed] David SA; DebRoy T; Lippold JC; Smartt HB; Vitek JM, MATERIALS PARK: ASM INTERNATIONAL , 2006, p. 589-594Conference paper (Refereed)
    Abstract [en]

    The purpose of this study is to investigate the residual stresses near the weld root and the weld toe for multi-pass welded tube-to-plates, and the influence of residual stresses on multiaxial fatigue of tubular joints. Two different tubular joint configurations were studied; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. An axi-symmetric finite element model was developed to calculate the temperature distribution, HAZ, penetration depth and the residual stress distribution for the sequentially coupled thermo-mechanical analysis. The calculated geometry and the temperature distribution of the fusion zone showed good agreement with the micro samples of the welds. The calculated residual stresses was compared with experimental results and showed qualitatively good agreement. The "design root crack" is under compressive stresses in both configuration, -230 MPa for the single-U weld groove and -120 MPa for the fillet weld, respectively. Also the weld toe, transition between weld and tube, is under compressive stresses. Multi-axial fatigue tests were performed in order to study weld root crack propagation. The tube structures were loaded with a static internal pressure in order to separate the design root crack and initiate the crack growth. The fatigue tests show that, depending on the size of the static imposed internal pressure, different crack paths are received.

  • 37.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Ny doktorsavhandling: Restspännings- och utmattningsanalyser av svetsade stålkonstruktioner2008In: Svetsen, ISSN 0039-7091, Vol. 67, no 3Article in journal (Other (popular science, discussion, etc.))
  • 38.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Prediction of Welding Residual Stresses2007In: International Symposium on Integrated Design and Manufacturing of Welded Structures, Eskilstuna, 2007Conference paper (Other academic)
  • 39.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Prediction of welding residual stresses by simplified approaches2010In: Proceedings of the Swedish Conference onLightweight Optimised Welded Structures: Borlänge, March 24-25, 2009 / [ed] Zubeir Barsoum, Jack Samuelsson, Stockholm: KTH Royal Institute of Technology, 2010, p. 39-50Conference paper (Other academic)
  • 40.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Residual Stress Analysis and Fatigue Assessment of Welded Steel Structures2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This doctoral thesis is concerned with fatigue life of welded structures. Several topics related to fatigue of welded structures are treated such as; weld defects and their influence on fatigue performance of welded structures, fatigue life prediction using LEFM (Linear Elastic Fracture Mechanics), fatigue testing, welding simulation, residual stress prediction and measurement and their influence on fatigue life.

    The work that is reported in this doctoral thesis is part results of the Nordic R&D project QFAB (Quality and Cost of Fabricated Advanced Welded Structures) and the Swedish R&D project LOST (Light Optimized Welded Structures). One of the main objectives is to compare different welding processes for the fatigue performance, weld quality and gain understanding of the weld defects, their appearance in different welding processes and their effect on fatigue life. Another main objective is to study welding residual stresses and their effect on fatigue. The design rules are in some cases conservative and especially on the weld root sides the knowledge about the residual stress field may improve the life prediction. The aim is to develop simplified procedures for analysis of residual stresses, their relaxation and influence on fatigue life.

    Fatigue testing of Hybrid Nd: YAG laser/MAG and MAG welded (tandem arc solid wire, flux cored wire, tandem flux cored wire) non-load carrying cruciform joints was carried out. Four batches were produced, tested and the results were compared. The local weld geometry of the cruciform welded joints was measured and analyzed. Residual stress measurement was carried out close to the toe region using X-ray diffraction. Weld defects, in most cases cold laps, in the cracked specimens were measured.

    Further fatigue testing, weld defect assessment and residual stress and local weld geometry measurements were carried out on joints welded with flux cored and metal cored arc wires. Two-and three dimensional LEFM crack growth analysis were carried out in order to predict the influence of weld defects, local weld geometry and residual stresses.

    Residual stresses in multi-pass welded tube-to-plates were studied for two different tubular joint configurations; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. Torsion fatigue tests were performed in order to study crack propagation from the weld root. Mode III propagation from the lower and upper weld toe on the same tubular joints was also studied. Some tubes were stress relieved (PWHT) and some were fatigue tested with internal static pressure.

    A three dimensional finite element welding simulation of the multi-pass welded tubular joint was carried out. The calculated temperatures in the transient thermal analysis were compared with measured temperatures. The FE predicted residual stresses in the as-welded conditions were verified with hole drilling strain gage measurements. The residual stresses were used as internal stresses in the finite element model for the torsion fatigue simulation in order to study the cycle by cycle relaxation of the residual stresses in constant amplitude torsion loading.

    A two dimensional finite element welding simulation procedure was developed in order to predict welding residual stress. The predicted residual stresses were used together with a developed 2D LEFM subroutine to predict the fatigue life, crack path and the effect of residual stresses on weld root defects. The developed simulation subroutines were validated with results found in the literature.

    Residual stresses measurement, two-and three dimensional welding simulations were carried out in fillet welded joints in order to study the three dimensional effects of the welding process, boundary conditions and modelling technique on the formation of residual stresses.

  • 41.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Residual stress predictin and relaxation in welded tubular joints under constant cyclic loading2006In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 524-525, p. 323-330Article in journal (Refereed)
    Abstract [en]

    In this paper three-dimensional welding simulations were carried out in FE software ANSYS in order to predict transient temperatures and the residual stresses in a three pass welded tubular joints. The thermal analysis and the moving heat source were verified with temperature measurements and the computed residual stresses were verified with hole drilling measurements. Then residual stress relaxation analyses were carried out on the tubular structure, with similar load cases as in earlier fatigue testing on the same tubular joint structures.

  • 42.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Barsoum, Imad
    Residual stress effects on fatigue life of welded structures using LEFM2008Conference paper (Refereed)
  • 43.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Residual stress effects on fatigue life of welded structures using LEFM2009In: IIW International Institute of Welding: 62nd AnnualAssembly, 2009Conference paper (Other academic)
  • 44.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Residual stress effects on fatigue life of welded structures using LEFM2009In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 16, no 1, p. 449-467Article in journal (Refereed)
    Abstract [en]

    In this paper a welding simulation procedure is developed using the FE software ANSYS in order to predict residual stresses. The procedure was verified with temperature and residual stress measurements found in the literature on multi-pass butt welded plates and T-fillet welds. The predictions show qualitative good agreement with experiments. The welding simulation procedure was then employed on a welded ship engine frame box at MAN B&W. A subroutine for LEFM analysis was developed in 2D in order to predict the crack path of propagating fatigue cracks. The objective was to investigate fatigue test results from special designed test bars from the frame box where all test failed from the non-penetrated weld root. A subroutine was developed in order to incorporate the predicted residual stresses and their relaxation during crack propagation by isoparametric stress mapping between meshes without and with cracks, respectively. The LEFM fatigue life predictions shows good agreement with the fatigue test result when the residual stresses are taken into account in the crack growth analysis.

  • 45.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Gustafson, Mats
    Spectrum fatigue of high strength steel joints welded with low temperature transformation consumables2007In: 2nd International Conference on Fatigue Design, 2007Conference paper (Refereed)
    Abstract [en]

    In the present paper constant (CA) and variable amplitude (VA) fatigue testing have been carried out on out-ofplane gusset fillet welded high strength steel joints. The joints were welded with conventional weld fillermaterial and martensitic low transformation temperature weld filler, LTT, in order to study the influence of theresidual stress on the fatigue strength. Residual stress measurements were carried out close to the weld toe usingX-ray diffraction technique in order to study the relaxation due to VA fatigue. The residual stress showeddifferent level of relaxation depending on the VA spectrum loading used. The LTT joints shows ~40% increasein mean fatigue strength compared to the conventional joints in CA. The LTT joints shows ~12% increase inmean fatigue strength compared to the conventional joints. The LTT joints shows 33% increase in mean fatiguestrength in CA compared to VA testing. However, the improvement of the fatigue strength is less significant invariable amplitude testing mainly due to the relaxation of the compressive residual stresses.

  • 46.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Gustafsson, M.
    Fatigue of high strength steel joints welded with low temperature transformation consumables2009In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 16, no 7, p. 2186-2194Article in journal (Refereed)
    Abstract [en]

    In the present paper constant (CA) and variable amplitude (VA) fatigue testing have been carried out on out-of plane gusset fillet welded high strength steel joints. The joints were welded with conventional weld filler material and martensitic low transformation temperature weld filler, LTT, in order to study the influence of the residual stress on the fatigue strength. Residual stress measurements were carried out close to the weld toe using X-ray diffraction technique in order to study the relaxation due to VA fatigue. The residual stress showed different level of relaxation depending on the VA spectrum loading used. The LTT joints show similar to 40% increase in mean fatigue strength compared to the conventional joints in CA The LTT joints show similar to 12% increase in mean fatigue strength compared to the conventional joints. The LTT joints show 33% increase in mean fatigue strength in CA compared to VA testing. However, the improvement of the fatigue strength is less significant in variable amplitude testing mainly due to the relaxation of the compressive residual stresses.

  • 47.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsson, B.
    Influence of weld quality on the fatigue strength in seam welds2011In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 18, no 3, p. 971-979Article in journal (Refereed)
    Abstract [en]

    In this paper a research study has been carried out on the link between weld quality of production welds and the fatigue strength. It has been carried out as a part of a Swedish Technology Platform for lightweight optimised welded structures (LOST), where some of the work packages within the project intend to connect the design and analysis to production and weld quality. One of the results is a new weld quality system from Volvo Group, which has a scientific background, is open for public use and focus on features important for fatigue in welded joints. In this study the emphasis is on a couple of features within the new weld quality system: weld toe radius and the possible existence of weld defects such as cold laps. Large scatter of the local weld geometry was observed for different welding processes. Also the results show that the weld position has a significant effect on the quality and the fatigue resistance of fillet welds and that it may be the difference between normal quality and high quality welds.

  • 48.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Jonsson, Bertil
    Fatigue Assessment and LEFM Analysis of Cruciform Joints Fabricated with Different Welding Processes, XIII-2175-072007In: IIW International Institute of Welding: 60th Annual Assembly, 2007Conference paper (Other academic)
    Abstract [en]

    In this study fatigue testing and defect assessment were carried out on specimens welded with robotic and manualwelding using fl ux cored (FCAW) and metal cored (MCAW) fi ller materials in order to study the effect of the weldingmethod on the fatigue strength and weld quality. Thirteen different batches were investigated of which two wasshot peened before fatigue testing. The local weld geometry was measured for all the specimens before testing.The specimens welded with fl ux cored weld wire showed the best fatigue strength, small defects and low residualstresses. Large scatter in the fatigue data is observed, especially when manual welding is employed. The few largestdefects were removed by the shot peening process, although small defects survived. This led to a smaller scatterin fatigue live for the shot peened specimens. Linear elastic fracture mechanics, LEFM, was employed for analysisof the fatigue test results. The fatigue life predictions using a 2D LEFM FE-model for simulating a continuous coldlap defect along the weld toe showed a qualitative agreement with the fatigue test results. The 2D analysis showedthat a continuous cold lap defect should be no more than 0.5 mm deep in order to comply with the requirement offatigue lives for normal weld quality according to the IIW design rules. For larger defects (> 0.8 mm) an increased toeradius will have a small effect on the fatigue strength. A 3D LEFM analysis of crack growth from a spatter-inducedcold lap defect was also carried out. This showed similar trends in crack growth compared to the 2D analysis ofa continuous cold lap, although the spatter-induced cold lap defect (semi-elliptical) had a longer fatigue life (x2.7),and hence is less dangerous from a fatigue point of view.

  • 49.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Khurshid, Mansoor
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Cargotec Sweden AB.
    Ultimate Strength Capacity of Welded Joints in High Strength Steels2017In: 2nd International Conference on Structural Integrity, ICSI 2017 / [ed] Iacoviello, F Moreira, PMGP Tavares, PJS, Elsevier, 2017, Vol. 5, p. 1401-1408Conference paper (Refereed)
    Abstract [en]

    High strength steels are nowadays used in a wide range of weight lifting applications, e.g. spreaders and cranes, where there is a demand on lightweight design of these structures with increased structural performance where the welds become more sensitive to failure. This study focuses on investigating the influence of the mismatch in the yield strength of the weld filler material and the welds penetration depth on the ultimate strength capacity and failure modes of butt and fillet welded high strength steels of yield strength in the range of 350 960 MPa. The load carrying capacities of these mentioned joints are evaluated with experiments and compared with the estimations by finite element analysis (FEA), and design rules in Eurocode 3 and American Welding Society Code AWS D1.1. Fully penetrated joint with under-matched filler material is more ductile and the ultimate strength capacity of base plate can be achieved. It is observed that joints with under-matched filler material are more sensitive to penetration ratio. This influence is more pronounced in joints in S960 steel welded with under-matched filler material. It is also found that the design rules in Eurocode3 (valid for design of welded joints in steels of grade up to S700) can be extended to designing of welds in S960 steels using correlation factor of one.

  • 50.
    Barsoum, Zuheir
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Khurshid, Mansoor
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Barsoum, I.
    Fatigue strength evaluation of friction stir welded aluminium joints using the nominal and notch stress concepts2012In: Materials & Design, ISSN 0261-3069, Vol. 41, p. 231-238Article in journal (Refereed)
    Abstract [en]

    In this study the fatigue strength is investigated for Friction Stir Welded (FSW) overlap and butt welded joints in different thicknesses based on nominal and effective notch stress concepts. The fatigue test results are compared with fatigue strength recommendations according to EN 1999-1-3 and International Institute of Welding (IIW). The results are also compared with available published data and Finite Element Analysis (FEA) is carried out to investigate the effect of plate thickness and nugget size on the fatigue strength of overlap joints. 3-3 mm butt welded joints shows the highest fatigue strength in comparison with 3-5 mm butt welded and overlap joints. Slopes of the SN-curves for two different joint types differ from the slope recommended by IIW. A specific failure trend is observed in overlap FSW joints. However, the slopes of the SN-curves are in close agreement with slopes found in EN 1999-1-3. The slopes of various published results and test results presented in this study are in good agreement with each other. The suggested fatigue design curves for the nominal and effective notch stress concept have a higher slope than given for fusion welds by IIW.

1234567 1 - 50 of 439
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf