• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1250-1264
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• 2023

This paper presents approximate in-depth residual stress and plastic strain profiles for laser-peened alloy 600 surface via FE analysis. In approximations, effects of the initial welding residual stress and the number of shots are quantified. Based on FE analysis results, residual stress profiles are quantified by two variables; the maximum difference in stress before and after LSP, and the depth up to which the compressive residual stress exists. Plastic strain profiles are quantified by one variable, the maximum equivalent plastic strain at the surface. The proposed profiles are validated by comparing with published LSP experimental results for welded plates. Effects of the initial welding residual stress and the number of shots on these variables are discussed. The proposed profile can be directly applied to predict the mitigation effect of LSP on PWSCC and to efficiently perform structural integrity assessment of laser peened nuclear components.

• Journal of Ship and Ocean Technology
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• 제11권2호
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• pp.26-33
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• 2007

For the assessment of the retardation of fatigue crack propagation behavior due to overload, new FE analysis algorithms considering compressive residual stress redistribution near crack tip was proposed in this paper. The size of plastic zone near crack tip was obtained by elasto-plastic analysis and it was compared with Irwin's equation. The amount of residual stress redistribution was assessed by subsequent elasto-plastic analysis, and the difference of residual stress distributions between constant amplitude load and overload was obtained. In the analysis of fatigue crack propagation, the applied SIF range was evaluated by ASTM E647, and the effect of residual stresses on crack propagation was considered using the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

• Journal of Welding and Joining
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• 제21권7호
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• pp.71-77
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• 2003

In this study, an investigation based on the superposition principle to predict residual stress redistribution caused by crack propagation itself initially through residual tensile stress field was performed by finite element method. The tendency in residual stress redistribution caused by crack propagation recognized both from the analytical results and experimental result was the residual stress concentration consecutively occurred in the vicinity of crack tip even the situation that the crack propagated to the region initially residual compressive stress existed. The software for the analysis is ABAQUS, which is a general purpose finite element package. The analytical method that attempt to take the plastic deformation at the crack tip due to tensile residual stress into the consideration of residual stress redistribution caused by crack propagation was proposed. The plastic zone size at the tip of fatigue crack and redistributed residual stresses were calculated by finite element method on the bases of the concept of Dugdale model. Comparing these analytical results with experimental results, it is verified that the residual stress redistribution caused by crack propagation can be predicted by finite element method with the proposed analytical method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.183-188
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• 2007

In this paper, we propose a 2D-FE model in single impact with combined physical factors to obtain a unique residual stress by shot peening. Applied physical parameters include elastic-plastic deformation of shot ball, material damping coefficients, strain rate, dynamic friction coefficients. Single impact FE model consists of 2D axisymmetric elements. The FE model with combined factors showed converged and unique distributions of surface stress, maximum compressive residual stress and deformation depth. Further, in contrast to the FE models with rigid shot and elastic deformable shot, FE model with plastic deformable shot produces residual stresses very close to experimental solutions by X-ray diffraction. We therefore validated the 2D FE model with combined peeing factors and plastic deformable shot. This FE model will be a base of the 3D FE model for residual stresses by multi-impact shot peening.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1347-1356
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• 2024

Measuring the residual stress in the components in nuclear power plants is crucial to their safety evaluation. The instrumented indentation technique is a minimally invasive approach that can be conveniently used to determine the residual stress in structural materials in service. Because the indentation behavior of a structure with residual stresses is closely related to the elastic-plastic behavior of the indented material, an accurate understanding of the elastic-plastic behavior of the material is essential for evaluation of the residual stresses in the structures. However, due to the analytical problems associated with solving the elastic-plastic behavior, empirical equations with limited applicability have been used. In the present study, the impact of the non-equibiaxial residual stress state on indentation behavior was investigated using finite element analysis. In addition, a new nonequibiaxial residual-stress prediction methodology is proposed using a convolutional neural network, and the performance was validated. A more accurate residual-stress measurement will be possible by applying the proposed residual-stress prediction methodology in the future.

• Journal of Welding and Joining
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• 제10권4호
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• pp.250-258
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• 1992

In order to clarify the mechanical behavior of welding crack and to evaluate the mechanical characteristics of welded parts in thick plate, it is very important to accurately predict the welding deformation and residual stress including transient state before welding. In this paper, the theory of a three-dimensional elasto-plastic problem for the analysis of mechanical phenomenon of welding joint on the plate is developed into an efficient and accurate method based on the finite element method, and then several examples are considered by using the proposed model. The results of numerical analyses are discussed in the viewpoint of the mechanical characteristics of the distribution of three-dimensional welding residual stresses, plastic strains and their production mechanism on the thick plate.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.167-170
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• 2003

Thermal elastic-plastic analysis was performed to assess the initial residual stress distribution of welded joints considering temperature dependent material properties. The test model was the idealized boxing fillet specimen, frequently appeared in the joints of longitudinal and transverse members of ship structure. Residual stress relaxations due to external loads were analyzed by subsequent elastic-plastic analysis considering loading and unloading steps, and the characteristics of residual stress relaxations were discussed with the levels of external loads. Additionally, to define the fatigue life of crack initiation and propagation, the S-N data for each crack length were appraised.

• Structural Engineering and Mechanics
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• 제63권1호
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• pp.1-9
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• 2017

Shot peening is a cold surface treatment employed to induce residual stress field in a metallic component beneficial for increasing its fatigue strength. The experimental investigation of parameters involved in shot peening process is very complex as well as costly. The most attractive alternative is the explicit dynamics finite element (FE) analysis capable of determining the shot peening process parameters subject to the selection of a proper material's constitutive model and numerical technique. In this study, Ansys / LS-Dyna software was used to simulate the impact of steel shots of various sizes on an aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The influence of shot velocity and size on the plastic deformation, compressive residual stress and force-time response were investigated. The results exhibited that increasing the shot velocity and size resulted in an increase in plastic deformation of the aluminium target. However, a little effect of the shot velocity and size was observed on the magnitude of target's subsurface compressive residual stress. The obtained results were close to the published ones, and the numerical models demonstrated the capability of the method to capture the pattern of residual stress and plastic deformation observed experimentally in aluminium alloys. The study can be quite helpful in determining and selecting the optimal shot peening parameters to achieve specific level of plastic deformation and compressive residual stress in the aluminium alloy parts especially compressor blades.

• Tribology and Lubricants
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• 제24권2호
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• pp.90-95
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• 2008

An elastic-plastic contact analysis is developed using a semi-analytical method. The elastic contact is solved within a Hertz theorem. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact stress and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The distribution of contact stress, residual stress and plastic strain are obtained by the changed surface geometry.

• 대한조선학회논문집
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• 제41권6호
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• pp.84-90
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• 2004

For the precise assessment of the effect of welding residual stresses on structural strength and fatigue crack growth behavior, new FE analysis algorithms for the estimation of residual stress relaxation due to external load and redistribution due to fatigue crack propagation were proposed in this paper. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis In the analysis of fatigue crack propagation, the applied SIF(Stress Intensity Factor) range was evaluated by $\frac{1}{4}$-point displacement extrapolation method, and the effect of welding residual stresses on crack propagation was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.