Papers by Keyword: Equivalent Plastic Strain

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Authors: Hui Kai Gao, Jian Meng Huang
Abstract: The contact between substrate and micro-cantilever simplified as an ideal flat substrate contact with a micro-cantilever rough surface. A three-dimensional adhesive contact model was established on isotropic rough surfaces exhibiting fractal behavior, and the equivalent plastic strain was discussed using the finite element analysis. The maximum equivalent plastic strain and its depth were presented with the different paths of rough solid when loading. The result show that the equivalent plastic strain versus different depth which at different locations showed different laws, in the top area of the asperities versus different depth, the maximum equivalent plastic strain occurs in the subsurface range about 0.5μm from the surface or on the surface. In addition, with different deformation characteristics, the degree of the equivalent plastic strain was different.. The contact model between micro-cantilever rough surface and flat substrate will lay a foundation to further research on the substance of the process of friction and wear.
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Authors: Lian Feng Lai, Cheng Hui Gao, Jian Meng Huang
Abstract: A three-dimensional contact model was established between two isotropic rough surfaces exhibiting fractal behavior,and the equivalent plastic strain was discussed using the finite element analysis. The maximum equivalent plastic strain and its depth are presented with the different paths of rough solid when loading. The result showed that the equivalent plastic strain versus different depth which at different locations showed different laws, in the top area of the asperities versus different depth, the maximum equivalent plastic strain occurs in the subsurface which range about 5 um from the surface. In addition, with different deformation characteristics, the degree of the equivalent plastic strain was different. The contact model between two rough solids will lay a foundation to further research on the substance of the process of friction and wear.
265
Authors: T. Yokota, H. Ohtsubo, S. Endo
Abstract: Effect of austenite as a harder second phase on ferrite substructure evolution by intercritical rolling has been investigated using 0.12C-0.3Si-1.35Mn steel. Slab was reheated at 780°C (ferrite; α + austenite; γ phase region) and rolled with 90% reduction down to 12mm in thickness using laboratory mill. 700°C (ferrite; α + cementite; θ phase region) rolled plate was also prepared to compare with 780°C rolled plate. Microstructure distribution along the plate thickness has been observed in detail by SEM and EBSD. Microstructure showed mixed structure of fine-grained ferrite and elongated ferrite for both of the plates. The ratio of fine-grained ferrite region was around 50% at the plate surface, however, fine-grained ferrite formation hardly occurred at mid thickness for 700°C rolled plate. FEM analysis revealed that fine-grained ferrite distribution along the thickness can be well explained by equivalent plastic strain distribution along the plate thickness for 700°C rolled plate. Equivalent plastic strain showed maximum value near the plate surface due to shear strain component, and it could help substructure evolution and fine grained ferrite formation. On the other hand, the ratio of fine-grained ferrite region reached to 50% all through the thickness for 780°C rolled plate. Austenite as a harder second phase seems to promote ferrite substructure evolution even at mid thickness of the plate.
607
Authors: Gyu Baek An, Mitsuru Ohata, Masahito Mochizuki, Han Sur Bang, Masao Toyoda
Abstract: It has been well known that ductile fractures of steels are accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. This study fundamentally clarifies the effect of strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining under static loading, on critical conditions for ductile cracking from the pre-notch root. In order to evaluate the stress/strain state in the pre-notch root of specimens, a thermal elastic-plastic finite element (FE) analysis has been carried out.
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Authors: Yusuke Shimada, Yoichi Kayamori, Takehiro Inoue, Tetsuya Tagawa
Abstract: Cleavage fracture in steel is usually evaluated by using the stress criterion. However, some researchers indicated the necessity of strain in the stress criterion according to the cleavage fracture test results of steel base metal. If so, the cleavage fracture criterion should be also applicable to steel welded joints. In this study, cleavage fracture tests, SEM fracture surface observations and FEA were conducted using the smooth and notched round bar tensile specimens of the simulated HAZ microstructure of JIS SM490A. Cleavage trigger types did not influence the cleavage fracture properties of the specimens obviously. FEA results suggested that the critical condition of cleavage fracture initiation was associated not only with stress but also with strain.
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Authors: Nuo Bao, Chun Jie Wang, Lin Zhu, Shun Guang Song
Abstract: Thermal cycling was applied to assess the effect of tin-lead solder 63Sn37Pb and lead-free solder 95.5Sn3.8Ag0.7Cu on the reliability of 3D PLUS solder joints. Nonlinear finite element method and viscoplastic Anand model were used to evaluate the stress and strain distribution and dangerous position of solders under the thermal cycling condition. The law of solder joints stress and plastic strain were finally obtained and showed significant cyclical changes. The stress and strain emerged the trend of accumulated enhancement with the process of time, then ultimately stabilized. Comparing two curves of equivalent stress and plastic strain obtained from lead-free and tin-lead solder, it was found that the reliability of 95.5Sn3.8Ag0.7Cu was better than that of 63Sn37Pb.
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Authors: Bo Rui Yan, G.Z. Wang, Fu Zhen Xuan, Shan Tung Tu
Abstract: In this paper, the finite element method (FEM) based on GTN damage model was used to obtain ductile fracture toughness and investigate the establishment method of unified correlation of in-plane and out-of-plane constraints with ductile fracture toughness of steels. The unified constraint parameter Ap at different equivalent plastic strain (εp) isolines has been calculated and analyzed for SEN(B) specimens with a wide range of in-plane and out-of-plane constraints. The results show that the average Ap along the specimen thickness (Apave) can well characterize a wide range of in-plane and out-of-plane constraints. The suitable εp isolines range for establishing the unified correlation between Apave and ductile fracture toughness of the steel has been obtained. For the specimens with lower constraint, the higher εp values should be used. The results also show that the correlation line of JC/Jref-Apave1/2 is independent of the selections of the suitable εp isolines and the reference specimen. This may bring convenience for the establishment and application of the JC/Jref -Apave1/2correlation lines. Using ductile fracture toughness data of a small number of specimens with different constraints (such as three specimens with different a/W) together with FEM calculations of the parameter Ap, the correlation line of JC/Jref-Apave1/2can be established. The correlation line may be used in structural integrity assessments incorporating both in-plane and out-of-plane constraints.
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Authors: Mohamad Shahrul Effendy Kosnan, Zaini Ahmad, Abdoulhdi Amhmad Borhana, Mohd Nasir Tamin
Abstract: Deformation response and failure process of a spot welded joint are investigated in this study. For this purpose, a cross-tension spot welded joint sample made of dual phase steel sheets (DP600) is prepared and tensile tested to failure. Complementary FE simulation of the test is performed. The FE model acknowledges the variation of properties across the spot welded region. Rice-Tracey ductile damage model is approximated and employed in the simulation. Close comparison of load-displacement curves and deformed shape with measured values serve as validation of the FE model. Results show that FE simulation with damage-based model adequately predicts tensile deformation and failure of the spot welded joint. Tensile failure of the joint is confined to the heat affected zone and heat affected/fusion zone interface of the joint. Localized through-thickness necking of the sheet metal is captured. In addition, the predicted fracture of the spot welded joint is accompanied by localized extensive plastic deformation.
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Authors: Xiao Ming Yuan, Li Jie Zhang, Xin Ying Chen, Bing Du, Bao Hua Li, Li Guo Fan, Yue Pan
Abstract: In order to predict the result of impact test in the design phase and reduce the experimental times, which can save cost and shorten development cycle, a finite element model of aluminum alloy wheel 13-degree impact test is established based on Abaqus. All mechanical parts such as the standard impact block, the assembly of the wheel and the tire, the support and bolts are included in the finite element model. The predicted result of finite element analysis and the experimental result agree very well shows the finite element model is correct. The equivalent plastic strain value was also put forward as fracture criterion for the wheel in the impact test which realizes the transition from the qualitative analysis to the quantitative analysis in the development process of aluminum alloy wheel.
1191
Authors: Dong Xiao Qiao, Xing Hua Yu, Wei Zhang, Paul Crooker Yu, Stan David, Zhi Li Feng
Abstract: Stainless steel has been widely used in challenging environments typical to nuclear power plant structures, due its excellent corrosion resistance. Nickel filler metals containing high chromium concentration, including Alloy 82/182, are used for joining stainless steel to carbon steel components to achieve similar high resistance to stress corrosion cracking. However, the joint usually experience weld metal stress corrosion cracking (SCC), which affects the safety and structural integrity of light water nuclear reactor systems. A primary driving force for SCC is the high tensile residual stress in these welds. Due to large dimension of pressure vessel and limitations in the field, non-destructive residual stress measurement is difficult. As a result, finite element modeling has been the de facto method to evaluate the weld residual stresses. Recent studies on this subject from researchers worldwide report different residual stress value in the weldments [5]. The discrepancy is due to the fact that most of investigations ignore or underestimate the thermal recovery in the heat-affect zone or reheated region in the weld. In the current study, the effect of heat treatment on thermal recovery and microhardness is investigated for materials used in dissimilar metal joint. It is found that high equivalent plastic strains are predominately accumulated in the buttering layer, the root pass, and the heat affected zone, which experience multiple welding thermal cycles. The final cap passes, experiencing only one or two welding thermal cycles, exhibit less plastic strain accumulation. Moreover, the experimental residual plastic strains are compared with those predicted using an existing weld thermo-mechanical model with two different strain hardening rules. The importance of considering the dynamic strain hardening recovery due to high temperature exposure in welding is discussed for the accurate simulation of weld residual stresses and plastic strains. Finally, the experimental result reveals that the typical post-buttering heat treatment for residual stress relief may not be adequate to completely eliminate the residual plastic strains in the buttering layer.
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