• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.108-113
• /
• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Journal of the Korean Data and Information Science Society
• /
• v.8 no.2
• /
• pp.225-230
• /
• 1997

We, in this paper, propose an estimator of mean residual life function by using the residual survival function under random censoring and prove the uniform consistency and weak convergence result of this estimator. Also an example is illustrated by the real data.

• Journal of Korean Society for Quality Management
• /
• v.23 no.3
• /
• pp.93-101
• /
• 1995

We present a brief survey concerning the relations between mean residual life and failure rate. Change points of mean residual life and failure rate are known to be different in general and we explore such situations in this paper. A few parametric models which show bathtub-shaped failure rate are examined in details, including the shape of its corresponding mean residual life function. We give some graphical comparisons of trend changes of mean residual life and failure rate for various choices of parameters for each parametric model.

• Journal of the Korean Data and Information Science Society
• /
• v.15 no.4
• /
• pp.965-971
• /
• 2004

In this paper we consider several nonparametric estimators for the mean residual life by using the partial moment approximation under the proportional hazard model. Also we compare the magnitude of mean square error of the proposed nonparametric estimators for mean residual life under the proportional hazard model.

• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.2
• /
• pp.104-110
• /
• 2013

In this paper, the design procedure and results for 'Residual Life Prediction System Considering Corrosion and Coating' are explained, which is one module of 'Life-cycle Management System of Ship and Offshore Plant's' Operation. This 'Residual Life Prediction System' has two main functions; one is residual life prediction function based on probability processing using corrosion measurement data of ship's major structural members, and another is rust rate prediction function based on visual image processing of inspection photos. The analysis of system user requirements and functions are introduced, and the structure and environment of the developed system are explained.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1086-1091
• /
• 2003

The problem of residual stresses and fatigue behavior in welded structures is the main concern of welding research fields. The residual stresses and distortions of structures by welding exert negative effect on the safety of mechanical structures. Postweld heat treatment is usually carried out to relieve this residual stresses of welded joints. In this paper the influence of postweld heat treatment on fatigue life of butt-welded joint was investigated. To predict the effect of PWHT, an analytical model is developed by finite element and local strain approach and the result of fatigue life analysis is compared to experimental results. It is demonstrated that fatigue life estimates closely approximate the experimental results and PWHT provides some increase of fatigue lives in long-life fatigue region and no increase in short-life fatigue region because of the residual stress relaxation under tensile loads.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.8
• /
• pp.2053-2061
• /
• 1994

The static and fatigue tensile tests have been conduted to predict the fatigue life of 8-harness satin woven and plain woven carbon/epoxy composite plates containing a circular hole. A fatigue residual strength degradation model, based on the assumption that the residual strength for unnotched specimen decreases monotonically, has been applied to predict statistically the fatigue life of materials used in this study. To determine the parameters(c, b and K) of the residual strength degradation model, the minimization technique and the maximum likelihood method are used. Agreement of the converted ultimate strength by using the minimization technique with the static ultimate strength is reasonably good. Therefore, the minimization technique is more adjustable in the determination of the parameter and the prediction of the fatigue life than the maximum likelihood method.

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

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.348-352
• /
• 2004

Recently the steel parts used for automiles and trains are required to be used under higher stress than ever before in need of the weight down. However, threr are a lot of problems with developing such of fatigue strength and fatigue life are mainly focused on by adopting residual stress. And got the following characteristics from crack growth test carried out stress ratio. Fatigue life shows more improvement in the Un-peening material. And Compressive residual stress of surface on the Shot-peening processed operate resistance force of fatigue. So we cam obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is dependent of Paris equation. (2) Although the maximum compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maximum compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.

• Journal of Welding and Joining
• /
• v.18 no.5
• /
• pp.33-40
• /
• 2000

Fatigue crack propagation life of weld toe crack through residual stress field was estimated with Elber's crack concept. Propagation of weld toe crack is heavily influenced by residual stress caused by welding process, so it is essential to take into account the effect of residual stress on the propagation life of weld toe crack. Fatigue crack at transverse and longitudinal weld toe was studied respectively, which represent typical weld joint in ship structure. Numerical and experimental studies are performed for both cases. Residual stress near weldment was estimated through nonlinear thermo-elasto-plastic finite element method, and residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated with Newman-Forman-de Koning-Henriksen equation which is based on Dugdale strip yield model in estimating crack closure level U at different stress ratio. Calculated crack propagation life coincided well with experimental results.