Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in ...Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.展开更多
Inl this investigation the different tests were carried out on the butt joints of several kinds of steels to study the effects of weldmatching on the fracture initiation under statie and dynamic loading, on the fractu...Inl this investigation the different tests were carried out on the butt joints of several kinds of steels to study the effects of weldmatching on the fracture initiation under statie and dynamic loading, on the fracture propagating arresting properties, on the fatigue behavior and finally on the residual stress distribution, The testing results show that overmatching of metal increases the possibility of having a general yieleding and may help to enlarge the tolerate of weld defects for crack initiation under dynamic or static loading. In the propagating and arresting cases the beneficial effct of overmatching of weld metal was found .However non significant effect of the weldmatch mg on the propagation thresholds △Kth and da'dN was found.展开更多
In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical st...In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.展开更多
In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP...In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP treatment was performed on compact tension(CT) specimen from single side and double sides. The surface integrity was measured with Vickers hardness tester, X-ray diffractometer and confocal laser scanning microscope, respectively. FCG rate test and fracture toughness test under plane stress were carried out after LSP treatment. The microstructure features of cross-sections were observed with scanning electron microscope. The results showed that the micro-hardness and residual stress of CT specimens were increased dramatically after LSP treatment. Compared to the base metal(BM), the fatigue life was prolonged by 2.4 times and fracture toughness was increased by 22% after multiple LSP.展开更多
Due to the complex structure and dense weld of the orthotropic steel bridge deck(OSBD),fatigue cracks are prone to occur in the typical welding details.Welding residual stress(WRS)will cause a plastic zone at the crac...Due to the complex structure and dense weld of the orthotropic steel bridge deck(OSBD),fatigue cracks are prone to occur in the typical welding details.Welding residual stress(WRS)will cause a plastic zone at the crack tip.In this paper,an elastoplastic constitutive model based on the Chaboche kinematic hardening model was introduced,and the extended finite element method(XFEM)was used to study the influence of material elastoplasticity and crack tip plastic zone on the law of fatigue crack propagation.By judging the stress state of the residual stress field at the crack tip and selecting different crack propagation rate models to investigate the crack propagation law when plastic deformation was considered,the propagation path and propagation rate of fatigue crack of the OSBD were obtained.The results show that,whether the residual stress field is considered or not,the plastic deformation at the crack tip will not cause the obvious closure of the fatigue crack at the U-rib toe during the crack propagation process,but will significantly affect the crack propagation path.When material plasticity is considered,the propagation angle of fatigue crack at the U-rib toe basically remains unchanged along the short-axis direction of the initial crack,but is going up along the long-axis direction,and the crack tip plastic zone inhibits the propagation of the crack tip on one side.Compared with linear elastic materials,the crack propagation law considering material plasticity is more consistent with that in actual bridge engineering.In terms of the propagation rate,if the residual stress field is not considered,the fatigue crack propagation rate at U-rib toe with plasticity considered is slightly higher than that without plasticity considered,because plastic deformation will affect the amplitude of energy release rate.When considering the WRS field,the fatigue crack propagation rate at U-rib toe is increased due to the combined actions of plastic deformation and stress ratio R.展开更多
The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate...The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate their applicability for differentstress ratios and in the presence of residual stresses. Total fatigue life using the two-phase model consists of crack initiationphase, calculated by strain-life approach, and crack propagation phase, calculated by fracture mechanic’s approach. Calibrationof the fatigue parameters is performed for each phase by fitting numerical to the experimental results. Comparative analysisof calculated and measured fatigue lives is then conducted for different stress ratios, in both stress-relieved and as-weldedconditions. Given that calculation parameters are calibrated for the basic case, uncertainty of predictions is large, showingthat application of the method for real-life complex marine structures is challenging.展开更多
Cold expansion is an efficient way to improve the fatigue life of an open hole. In this paper, three finite element models have been established to crack growth from an expanded hole is simulated. Expansion and its de...Cold expansion is an efficient way to improve the fatigue life of an open hole. In this paper, three finite element models have been established to crack growth from an expanded hole is simulated. Expansion and its degree influence are studied using a numerical analysis. Stress intensity factors are determined and used to evaluate the fatigue life. The residual stress field is evaluated using a nonlinear analysis and superposed with the applied stress field in order to estimate fatigue crack growth. Experimental test is conducted under constant loading. The results of this investigation indicate expansion and its degree are a benefit of fatigue life and a good agreement was observed between FEM simulations and experimental results.展开更多
Results indicate that under cyclic tension the growth rate of short fatigue crack from notch root will be lowered greatly by tensile pre-loading,but only a little change by compressive pre-loading. The effect of tensi...Results indicate that under cyclic tension the growth rate of short fatigue crack from notch root will be lowered greatly by tensile pre-loading,but only a little change by compressive pre-loading. The effect of tensile pre-loading will decrease with the increase of stress ratio.The variation of short fatigue crack growth rate is related to the residual stress distribution around notch root.展开更多
基金supported by the National Natural Science Foundation of China(No.50609009)Natural Science Foundation of College of Jiangsu Province(No.07KJD580056)
文摘Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.
文摘Inl this investigation the different tests were carried out on the butt joints of several kinds of steels to study the effects of weldmatching on the fracture initiation under statie and dynamic loading, on the fracture propagating arresting properties, on the fatigue behavior and finally on the residual stress distribution, The testing results show that overmatching of metal increases the possibility of having a general yieleding and may help to enlarge the tolerate of weld defects for crack initiation under dynamic or static loading. In the propagating and arresting cases the beneficial effct of overmatching of weld metal was found .However non significant effect of the weldmatch mg on the propagation thresholds △Kth and da'dN was found.
基金the DAAD Faculty Development for Ph.D.Candidates(Balochistan)2016(57245990)-HRDI-UESTP’s/UET’s funding scheme in cooperation with the Higher Education Commission of Pakistan(HEC)for sponsoring the stay at IMF TU Freiberg,Germany.
文摘In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.
基金Project(52075552) supported by the National Natural Science Foundation of ChinaProject(kq2007085) supported by Changsha Municipal Natural Science Foundation,China。
文摘In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP treatment was performed on compact tension(CT) specimen from single side and double sides. The surface integrity was measured with Vickers hardness tester, X-ray diffractometer and confocal laser scanning microscope, respectively. FCG rate test and fracture toughness test under plane stress were carried out after LSP treatment. The microstructure features of cross-sections were observed with scanning electron microscope. The results showed that the micro-hardness and residual stress of CT specimens were increased dramatically after LSP treatment. Compared to the base metal(BM), the fatigue life was prolonged by 2.4 times and fracture toughness was increased by 22% after multiple LSP.
基金The works described in this paper are substantially supported by the grant from the National Natural Science Foundation of China(Grant No.51678135)the Natural Science Foundation of Jiangsu Province(No.BK20171350)Six Talent Peak Projects in Jiangsu Province(JNHB-007),which are gratefully acknowledged.
文摘Due to the complex structure and dense weld of the orthotropic steel bridge deck(OSBD),fatigue cracks are prone to occur in the typical welding details.Welding residual stress(WRS)will cause a plastic zone at the crack tip.In this paper,an elastoplastic constitutive model based on the Chaboche kinematic hardening model was introduced,and the extended finite element method(XFEM)was used to study the influence of material elastoplasticity and crack tip plastic zone on the law of fatigue crack propagation.By judging the stress state of the residual stress field at the crack tip and selecting different crack propagation rate models to investigate the crack propagation law when plastic deformation was considered,the propagation path and propagation rate of fatigue crack of the OSBD were obtained.The results show that,whether the residual stress field is considered or not,the plastic deformation at the crack tip will not cause the obvious closure of the fatigue crack at the U-rib toe during the crack propagation process,but will significantly affect the crack propagation path.When material plasticity is considered,the propagation angle of fatigue crack at the U-rib toe basically remains unchanged along the short-axis direction of the initial crack,but is going up along the long-axis direction,and the crack tip plastic zone inhibits the propagation of the crack tip on one side.Compared with linear elastic materials,the crack propagation law considering material plasticity is more consistent with that in actual bridge engineering.In terms of the propagation rate,if the residual stress field is not considered,the fatigue crack propagation rate at U-rib toe with plasticity considered is slightly higher than that without plasticity considered,because plastic deformation will affect the amplitude of energy release rate.When considering the WRS field,the fatigue crack propagation rate at U-rib toe is increased due to the combined actions of plastic deformation and stress ratio R.
文摘The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate their applicability for differentstress ratios and in the presence of residual stresses. Total fatigue life using the two-phase model consists of crack initiationphase, calculated by strain-life approach, and crack propagation phase, calculated by fracture mechanic’s approach. Calibrationof the fatigue parameters is performed for each phase by fitting numerical to the experimental results. Comparative analysisof calculated and measured fatigue lives is then conducted for different stress ratios, in both stress-relieved and as-weldedconditions. Given that calculation parameters are calibrated for the basic case, uncertainty of predictions is large, showingthat application of the method for real-life complex marine structures is challenging.
文摘Cold expansion is an efficient way to improve the fatigue life of an open hole. In this paper, three finite element models have been established to crack growth from an expanded hole is simulated. Expansion and its degree influence are studied using a numerical analysis. Stress intensity factors are determined and used to evaluate the fatigue life. The residual stress field is evaluated using a nonlinear analysis and superposed with the applied stress field in order to estimate fatigue crack growth. Experimental test is conducted under constant loading. The results of this investigation indicate expansion and its degree are a benefit of fatigue life and a good agreement was observed between FEM simulations and experimental results.
文摘Results indicate that under cyclic tension the growth rate of short fatigue crack from notch root will be lowered greatly by tensile pre-loading,but only a little change by compressive pre-loading. The effect of tensile pre-loading will decrease with the increase of stress ratio.The variation of short fatigue crack growth rate is related to the residual stress distribution around notch root.
