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Michael Vormwald - One of the best experts on this subject based on the ideXlab platform.
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fatigue crack growth in cruciform welded Joints influence of residual stresses and of the weld toe geometry
International Journal of Fatigue, 2017Co-Authors: Tchoffo D Ngoula, Th H Beier, Michael VormwaldAbstract:Abstract The aim of the present investigation is to calculate the fatigue life of cruciform welded Joints by taking into account both the effect of residual stresses and the influence of the weld toe geometry. Two and three dimensional finite element models, with cracks as initial defects, will be constructed for this purpose. Fatigue crack growth analyses are performed by using the node release technique, together with the finite element program ABAQUS. The welding residual stresses, as well as the plasticity induced crack closure effects, are considered. The effective Cyclic J-Integral (ΔJeff) is used as crack tip parameter in a relation similar to the Paris equation for the calculation of the fatigue life. For this purpose, a specific code was written for the determination of ΔJeff at each crack length configuration. The impact of residual stresses on ΔJeff as well as on the fatigue life during short crack growth is investigated. Results reveal that the influence of residual stresses can be neglected only for large load amplitudes. The calculated fatigue lives are compared with experimental data and a good accordance between both results is achieved. The influences of the weld toe radius and of the weld flank angle are also investigated.
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Cyclic J Integral numerical and analytical investigations for surface cracks in weldments
Engineering Fracture Mechanics, 2017Co-Authors: Tchoffo D Ngoula, Mauro Madia, Th H Beier, Michael Vormwald, Uwe ZerbstAbstract:Abstract The Cyclic J -Integral (Δ J -Integral) is a crack tip parameter of elastic-plastic fracture mechanics which can be used as governing parameter for the description of fatigue crack growth (FCG) in metallic structures. In this contribution, it is applied for modelling FCG in weldments. The Δ J -Integral is determined by means of analytical approximation formulas as well as numerical methods. An analytical solution, which takes into account effects of the local ligament plasticity, was derived. This solution is based on well established methods such as R6, BS7910 and SINTAP which were modified for Cyclic loading. It incorporates methods for the description of short crack closure behaviour as well as the well known analytical (long) crack closure function of Newman. A specific code was written to evaluate the Δ J -Integral numerically in the course of finite element based crack growth simulations. The code was first validated for an infinite plate with centre crack by applying elastic and elastic-plastic material behaviour. Next, the Δ J -Integral was calculated for cracks in various butt and cruciform welded Joints. The results were compared with the results of the derived analytical approximation formula. A good accordance was achieved between the results. Note that the work was part of the German research cluster IBESS the aim of which was the development of a method for fracture mechanics based determination of the fatigue strength of weldments. Since the question behind the present paper was restricted to the Cyclic elastic plastic crack driving force needed for the short fatigue crack propagation stage, only the geometrical aspects of weldments (i.e. the weld toe notch) are addressed here whilst other characteristics such as material inhomogeneity (HAZ) or residual stresses are discussed by other papers of this special issue.
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an experimental evaluation of three critical plane multiaxial fatigue criteria
International Journal of Fatigue, 2007Co-Authors: Yanyao Jiang, Olaf Hertel, Michael VormwaldAbstract:Abstract The Fatemi–Socie criterion, the Jiang criterion, and a short crack growth based criterion were evaluated using the combined axial-torsion fatigue testing results obtained from extensive experiments on thin-walled tubular specimens made from S460N. The Fatemi–Socie criterion combines the maximum shear strain amplitude with a consideration of the normal stress on the critical plane. The Jiang criterion makes use of the plastic strain energy on a material plane as the maJor contributor to the fatigue damage. By assuming an initial crack length, the short crack model attributes the fatigue life to the action of a crack driving force, namely the effective Cyclic J-Integral. The results show that all the three criteria correlated well with the experimental observations in terms of fatigue life predictions. A great discrepancy was found between the predicted cracking directions and the observed cracking orientations.
S Beretta - One of the best experts on this subject based on the ideXlab platform.
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short cracks growth in low cycle fatigue under multiaxial in phase loading
International Journal of Fatigue, 2018Co-Authors: S Foletti, F Corea, Silvio Rabbolini, S BerettaAbstract:Abstract Crack propagation in full plastic regions is one of the main aspects of fatigue life design for components subJected to high strain concentrations. Residual life assessment for those components, in which high stress concentrations cause Cyclic yielding of the material, can be considered as a crack propagation problem by assuming crack growth from the first load cycle. The aim of this paper is to study the crack growth behaviour of short cracks in low cycle fatigue under a multiaxial loading condition. In particular, a series of experiments in LCF regime at room temperature was performed to determine crack growth during axial, torsional and axial-torsional tests. Crack advancement was checked with the plastic replica technique, during test interruptions. Experimental results were compared, in terms of crack growth rates and fatigue life assessment, with those analytically calculated, considering different multiaxial fatigue parameters introduced in an exponential crack growth law and an approach based on the multiaxial Cyclic J-Integral concept.
Paulo J Tavares - One of the best experts on this subject based on the ideXlab platform.
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fatigue life prediction based on an equivalent initial flaw size approach and a new normalized fatigue crack growth model
Engineering Failure Analysis, 2016Co-Authors: Jose A F O Correia, P M G P Moreira, S Blason, A M P De Jesus, Alfonso Fernandez Canteli, Paulo J TavaresAbstract:Abstract A general procedure for fatigue life prediction of structural details based on Fracture Mechanics approach is presented in this paper, taking advantage of the new normalized fatigue crack growth model proposed by Castillo et al., here denoted as CCS model. An extension to the CCS model is proposed by adopting the Cyclic J-Integral range instead of the stress intensity factor range as reference parameter. This enables the generalized elastoplastic conditions resulting for the cracked geometry of the structural detail to be considered by means of the Cyclic J-Integral values obtained from a finite element analysis, for different loading levels and crack lengths. As a practical application, the proposed approach is applied to a notched plate made of P355NL1 steel, using the equivalent initial flaw size (EIFS) concept. Fatigue crack growth data for CT specimens from the literature is evaluated to estimate the modified CCS crack growth model parameters. The predicted fatigue propagation lifetime prediction is compared with the results and, finally, the goodness of the predictions is analysed and deviations discussed.
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fatigue life prediction based on crack growth analysis using an equivalent initial flaw size model application to a notched geometry
Procedia Engineering, 2015Co-Authors: Ana Sofia Figueiredo Alves, P M G P Moreira, Jose A F O Correia, A M P De Jesus, L M C M V Sampayo, Paulo J TavaresAbstract:Abstract Several methods for fatigue life prediction of structural components have been proposed in literature. The fatigue life prediction based on crack growth analysis has been proposed to assess the residual fatigue life of components, which requires the definition of an initial flaw. Alternatively, Fracture Mechanics crack growth-based fatigue predictions may be used to simulate the whole fatigue life of structural components assuming that there are always initial defects on materials, acting as equivalent initial cracks [1,2]. This latter approach is applied to a notched plate made of P355NL1 steel [3]. Fatigue crack growth data of the material is evaluated using CT specimens, covering several stress R-ratios. Also, S-N fatigue data is available for the double notched plate, for a stress R -ratio equal to 0 [3]. An estimate of the equivalent initial flaw size is proposed, using a back-extrapolation calculation [1,2]. The crack propagation model takes into account the elastic–plastic deformations in the crack-tip area within the calculation, based on the Cyclic J-Integral method. The performances of predictions are analyzed and deviations discussed.
Zhiliang Zhang - One of the best experts on this subject based on the ideXlab platform.
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a 3d numerical study of ductile tearing and fatigue crack growth under nominal Cyclic plasticity
International Journal of Solids and Structures, 1997Co-Authors: Bjorn Skallerud, Zhiliang ZhangAbstract:Abstract Structures subJected to severe Cyclic loading may fail due to low cycle fatigue. During the latter part of the fatigue life the crack growth rate may increase due to the occurence of crack growth from static failure modes, e.g. void growth. The present investigation attempts to predict the combined crack growth by means of nonlinear FE methods. The case studied is an axially loaded flat plate with embedded, nearly circular cracks growing under nominal Cyclic plasticity, as test data for this case has been obtained previously. The fatigue part of the crack growth is determined by using the computed Cyclic J-Integral and the static mode crack growth from ductile tearing is determined from computations accounting for void nucleation/growth/coalescence by means of a modified Gurson-Tvergaard model. Comparison with the test results shows acceptable correspondence.
S Foletti - One of the best experts on this subject based on the ideXlab platform.
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short cracks growth in low cycle fatigue under multiaxial in phase loading
International Journal of Fatigue, 2018Co-Authors: S Foletti, F Corea, Silvio Rabbolini, S BerettaAbstract:Abstract Crack propagation in full plastic regions is one of the main aspects of fatigue life design for components subJected to high strain concentrations. Residual life assessment for those components, in which high stress concentrations cause Cyclic yielding of the material, can be considered as a crack propagation problem by assuming crack growth from the first load cycle. The aim of this paper is to study the crack growth behaviour of short cracks in low cycle fatigue under a multiaxial loading condition. In particular, a series of experiments in LCF regime at room temperature was performed to determine crack growth during axial, torsional and axial-torsional tests. Crack advancement was checked with the plastic replica technique, during test interruptions. Experimental results were compared, in terms of crack growth rates and fatigue life assessment, with those analytically calculated, considering different multiaxial fatigue parameters introduced in an exponential crack growth law and an approach based on the multiaxial Cyclic J-Integral concept.
