• Communications for Statistical Applications and Methods
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• 제7권3호
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• pp.789-798
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• 2000

The mean residual function is the expected remaining life of an item at age x. The problem of trend change in the mean residual life is great interest in the reliability and survival analysis. In this paper, we develop a family of test statistics for testing whether or not the mean residual life changes its trend. The asymptotic normality of the test statistics is established. Monte Carlo simulations are conducted to study the performance of our test statistics.

• Journal of the Korean Statistical Society
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• 제26권4호
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• pp.531-541
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• 1997

The asymptotic distribution of residual autocorrelation functions from a generalized p-order random coefficient autoregressive process (GRCA(p)) is derived. To this end, we first describe the GRCA(p) models and then consider the normalised residuals after fitting the model. This result can be applied to the residual analysis for the diagonostic purpose.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.163-168
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• 1994

Zinc coated steel sheets have been widely used in automotive industry. High power laser welding has been used as an excellent welding means for thin sheets. The welding residual stress, which was brought in laser welding, causes making weak the mechanical strength. The purpose of this study is to get the residual stress distribution in various laser welding condition by FEM and verify the results by X-Ray diffraction. Welding residual stresses have been calculated by thermal elasto-plastic analysis using finite element method. Form the results, it can be known that the laser welding condition affects to distribution of the residual stress.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2003년도 춘계학술발표대회 개요집
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• pp.266-268
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• 2003

Residual stresses, which can be produced during the manufacturing process, play an important role in an industrial field. Residual stresses of structures by welding process are exerting negative effect on the fatigue behavior and safety of structure. Results from the elasto-plastic finite element analysis of the welds for a nuclear component, the residual stress distribution after welding. In this study, a finite element technique is developed to simulate the relaxation of the residual stresses due to the mechanical loads of welds.

• 한국자동차공학회논문집
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• 제9권1호
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• pp.198-204
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• 2001

The shot peening is largely used for a surface treatment of metallic components where small spherical pellets called shots are blasted onto the surface with velocities up to 100 m/s. This treatment leads to improvement of fatigue behavior due to the developed compressive residual stresses, and so it has gained widespread acceptance I the automobile and aerospace industries. The residual stress profile on surface layer depends on the parameters of shot peening, which are, shot velocity, shot diameter, coverage, impact angle, material properties etc. and the method to confirm this profile is the measurement by X-ray diffractometer only. Despite the importance to automobile ad aerospace industries, little attention has been devoted to the accurate modelling of the process. In this paper, the simulation technique is applied to predict the magnitude ad distribution of the residual stress and plastic deformation caused by shot peening with the help of the finite element analysis.

• 대한조선학회논문집
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• 제48권3호
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• pp.238-245
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• 2011

Welding inevitably introduces the residual stresses which affect the fatigue strength of the joint structure. The mitigation of fatigue strength depends on the residual stress magnitude and distribution. Stress relief analyses are of practical interest for all cyclic loaded welded structures, such as ships and offshore structures. In order to estimate the effects of relaxation of residual stresses in the welded structure, this paper presents a finite element analysis procedure and experimental results for the welded structure. Cruciform specimens joint by MAG welding have been tested to measure the released stress. Relieved welding residual stresses obtained by finite element analysis are compared with those measured by experiment.

• Journal of Welding and Joining
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• 제28권1호
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• pp.86-91
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• 2010

In the present study, two-dimensional plane deformation thermo elasto-plastic analysis has been carried out, in order to investigate the thermal and mechanical behaviour (residual stress, plastic strain, magnitude of stress and their distribution and production mechanism) on multi-pass FCA butt weldment of high strength EH36-TMCP ultra thick plate. Moreover, this study can be considered as a basis for analysing the fracture toughness, KIC, and its effect on welding residual stress redistribution with notch on multi-pass FCA butt weldment, in future. The results of welding residual stress obtained from thermo elasto-plastic analysis has been compared and verified with the results measured by XRD.

• 한국정밀공학회지
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• 제27권4호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.237-242
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• 2001

Residual stress is a dominant obstacle to efficient production and safe usage of products by reducing the mechanical strength and failure properties. Especially, it causes interfacial failure and substrate deflection in the case of thin film. So, the exact evaluation and optimum control of thin film residual stress is indispensable. However, hole drilling or X-ray diffraction techniques have some limits in application to thin film. And, curvature technique for thin film materials cannot give the information about local stress variation. Therefore, we applied the nanoindentation technique in evaluating the thin film residual stress. In this study, we modeled the change of indentation loading curve for residually stressed and stress-free thin films during stress relaxation. The value of residual stress was directly related to the indentation depth change by relaxation. The residual stress from nanoindentation analysis was consistent with the result from curvature technique.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.834-837
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• 2005

This study presents a study on the influence of process parameters(semi-die angle, die reduction, friction condition, and bearing length) in drawn wire on residual stresses were investigated using FE-analysis. In this study, semi-die angle and die reduction have a significant effect on the residual stresses at the surface of drawn wire. In the previous study, in order to reduce the residual stresses, several methods were suggested: addition of axial tension, application of skin pass, straightening in multi-roll straightener etc. In this study, it can be known that the concurrent application of skin pass with low die reduction and low semi-die angle at the final stage of drawing operation reduces dramatically the both axial and hoop residual stresses after drawing.