• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1452-1460
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• 2001

A new method of parameter determination in the fatigue residual strength degradation model is proposed. The new method and minimization technique is compared experimentally to account for the effect of tension-compression fatigue loading of spheroidal graphite cast iron and graphite/epoxy laminate. It is shown that the correlation between the experimental results and the theoretical prediction on the fatigue life and residual strength distribution using the proposed method is very reasonable. Therefore, the proposed method is more adjustable in the determination of the parameter than minimization technique for the prediction of the fatigue characteristics.

• Advanced Composite Materials
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• v.17 no.3
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• pp.301-317
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• 2008

The energy release rate associated with crack growth in adhesive double cantilever beam (DCB) specimens, including the effect of residual stresses, was formulated using beam theory. Because of the rotation of the asymmetric arms in the adhesive DCB specimens due to temperature change, it is necessary to correct the evaluated fracture toughness of the DCB specimens, specifically in the case of a large temperature change. This study shows that the difference between the true toughness and an apparent toughness due to the consequence of ignoring residual stresses can be calculated for a given specimen geometry and thermo-mechanical properties (e.g. coefficient of thermal expansion). The calculated difference in the energy release rates based on the present correction method is compared with that from FEM in order to verify the present correction method. The residual stress effects on the evaluation of the adhesive fracture toughness are discussed.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.58-64
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• 2001

In this study, it is developed that the system for effective prediction of residual stresses by the back-propagation algorithm using the neural network. To achieve This goal, the series experiment were carried out and measured the residual stresses using the sectional method. Using the experimental results, the optional control algorithms using a neural network should be developed in order to reduce the effect of the external disturbances during GMA welding processes. Then the results obtained from this study were compared between the measured and calculated results, weld guality might be controlled by the neural network based on backpropagation algorithm. This system can no only help to understand the interaction between the process parameters and residual stress, but also improve the quantity control for welded structures.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.63-66
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• 2000

This research addresses study on thermal residual stress of a composite patch repair of the edge cracked aluminium panel of aging aircraft. Composite patch repair is an efficient and economical technique to improve the damage tolerance of cracked metallic structures. These are thermal residual stresses due to the mismatch of coefficient of thermal expansion, and these are affected by the curing cycle of patch specimen. In this study, three curing cycles were selected for F.E. analysis. This study features the effect on composite patch and aluminum by thermal residual stress during crack propagation in aluminum plate.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.73-78
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• 2003

The residual stresses and. distortions of structures by welding exert negative effect on the safety of railroad structures. This investigation performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in butted-welded joint. Considering this initial residual stresses, local stress and strain at the critical location (weld toe) during the loading were analyzed by elastic plastic finite element analysis. Fatigue crack initiation life and fatigue crack propagation life of butt-welded specimen were predicted by local strain approach and Neuber's role and Paris law. It is demonstrated that fatigue life estimates by local strain approach closely approximate the experimental results.

• Journal of the Korean Society of Safety
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• v.8 no.1
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• pp.71-79
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• 1993

The welding implementation used widely in the industrial field is gradually increasing due to weight reduction. unlimited material thickness. simplified structure design. and 1 manufacturing time and cost reduction. The most significant factor that influences the fatigue crack growth rate is the residual stress generated during the welding process. Many researchers have studied the effect of the residual stress on crack growth behavior. Through a fatigue test in a various-thickness welded specimen. redistributed residual stress is measured as the crack is developed. Then. by superposing the measured residual stress on the K value obtained by the finite element method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.09a
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• pp.17-22
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• 2005

The residual birefringence in molded plastic parts can be divided into two kinds of residual birefringence, i.e., the flow induced residual birefringence produced in flowing stages and the thermally induced residual birefringence produced in cooling stage. In this paper, the effect of new injection-press molding process with normal injection mold, i.e. I) injection-compression mode, ii) injection-press mode, on the distribution of birefringence was studied. It was found that the values of the birefringence was reduced at i) low clamping force and ii) longer mold opening length by injection-press molding.

• International Journal of Korean Welding Society
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• v.4 no.1
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• pp.10-14
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• 2004

In this paper, a study on the residual stress of plate with longitudinal stiffeners is explained in terms of the welding sequences. In order to verify the results of numerical analysis, the hole drilling method (HDM) is performed, to measuring the residual stresses of the test plates in $CO_2$ Flux Cored Arc Welding (FCAW) under various welding conditions. The non-linear transient analysis technique for the numerical analysis in a large and complicate structure is considered. The residual stress of plate in consideration of the welding sequences and directions is evaluated by some numerical simulations and also by experiments. Comparison of numerical analysis results with experimental data shows the accuracy and validity of the proposed method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.589-596
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• 2010

In this study, we calculate the welding residual stresses for a butt-welded thin-walled plate by carrying out three-dimensional finite-element analyses. To study the effect of mechanical boundary conditions on the welding residual stresses, various boundary conditions are considered. The welding residual stresses obtained in the measurements and finite-element analyses are validated by comparing them with the welding residual stress profiles in the R6 code. The results of this study are used to analyze the influence of residual stress on the crack formation in thin-section weldments.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.4
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• pp.79-86
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• 2010

Mechanical structures with power sources experience repeated force produced by motors. In result, the life of the pipes reduces and ultimately, the pipes collapse. Such pipes are formed into several shapes and particularly, the U-shape pipe is damaged frequently. In most cases, the U-shape pipe is made with a straight pipe by complicated bending work. During this work process, plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the fracture behavior of the pipe and induces the change of the stress ratio (min. stress/Max. stress = R). For this reason, residual stress has to be evaluated. In this paper, the residual stress of a U-shaped pipe was evaluated by FEM analysis. In addition, fatigue tests of the U-shaped pipe were performed by using a uniaxial fatigue testing machine. The results of the fatigue test were modified with the results of FEM (Finite Element Method) analysis for residual stress. The modified fatigue test results of the U-shaped pipe were compared with those of a straight pipe.