• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.177-184
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• 2014

In this study, we investigated the variations in welding residual stresses in dissimilar metal butt weld due to width of repair welding and re-distribution behaviors resulting from similar metal welding (SMW) and mechanical loading. To this end, detailed two-dimensional axi-symmetric finite element (FE) analyses were performed considering five different repair welding widths. Based on the FE results, we first evaluated the welding residual stress distributions in repair welding. We then investigated the re-distribution behaviors of the residual stresses due to SMW and mechanical loads. It is revealed that large tensile welding residual stresses take place in the inner surface and that its distribution is affected, provided repair welding width is larger than certain value. The welding residual stresses resulting from repair welding are remarkably reduced due to SMW and mechanical loading, regardless of the width of the repair welding.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.832-842
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• 1996

Fatigue life prediction and fatigue behavior of circular notched carbon fiber reinforced plastic laminates are presented. Point and average stress criteria by Whitney and Nuismer are generalized to fatigue fracture criteria for notched laminates. Residual strength degradation model and the assumptions on the stress redistribution are introduced during the derivation of prediction equations. S-N curve, Basquin's relation, and H and H's FLPE1 are chosen for evaluation of residual strength of unnotched laminates and six prediction equations are derived. Experiments are performed using Graphite/Epoxy laminates whose fiber orientation is $[0$^\circ$/+45$^\circ$/-45$^\circ$/90$^\circ$]s. Presented prediction equations are reasonably close to experimental data and proposed appoach is found to be suitable to predict fatigue life of notched composite laminates.

• Journal of the Korean Society of Safety
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• v.13 no.2
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• pp.45-53
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• 1998

A method to predict the creep behavior of fiber-reinforced ceramic composites at high temperatures was suggested based on finite element modeling using constituent creep equations of fiber and matrix and showed good agreement with the experimental results. The effects of matrix creep behavior, fiber volume fraction, and residual stresses on the composite creep behavior were also investigated. The results showed that the primary behavior of composites was greatly affected by that of matrix but post-primary behavior was governed by fiber creep characteristics. The increase of fiber volume fraction from 15 vol% to 30 vol% caused the 50% and 40% decrease of steady-state creep rates and total creep strains at $1200^{\circ}C$, 180MPa, respectively. Feasible compressive residual stresses in the matrix caused by different thermal expansion coefficients between the fiber and the matrix could significantly reduce total creep strains of the composite. The creep deformation mechanism in the fiber-reinforced ceramic composites could be explained by the stress transfer and redistribution in the fiber and matrix due to different creep characteristics of its constituents.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.707-712
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• 2015

During the welding process, welding distortion is caused by the non-uniformity of the temperature distribution in the weldment. Welding distortion is redistributed because the residual stress and rigidity change according to the removal of the welded structure. In shipbuilding in particular, this phenomenon may be observed during the cutting process of lugs that are attached to blocks for transfer. The redistribution of welding distortion also causes problems, such as damage to the cutting tool. The aim of this study is to experimentally analyze the redistribution of welding distortion because of the partial removal of the welded structure. In the experiments conducted in this study, fillet welding and cutting were performed, and longitudinal bending and angular distortion in the welded structures were then investigated and analyzed.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.577-584
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• 1997

Evaluation of rolling contact fatigue damage as well as material development for roll of rolling mill is being studied until quite recently. In this paper, a focus has been imposed on evaluating the rolling contact fatigue damage. In order for this, the accumulating process of rolling contact damage using the ferritic, pearlitic and bainitic DCI has been analyzed by X-ray diffraction technique. The main finds are; 1) The graphite in DCI is considered to be a cause of interfering in the redistribution of stress. Eventually, it results in the branching of crack. 2) The evaluation of rolling contact fatigue damage can be estimated in terms of the change of residual stress and/or a half-value breadth on surface during rolling contact.

• Geomechanics and Engineering
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• v.10 no.3
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• pp.325-334
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• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

• Journal of the Korean institute of surface engineering
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• v.30 no.3
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• pp.191-201
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• 1997

Non-passivated electrolytic tinplates withour conventinal chemical treatment self-oxidize in ambient atmosphere to from yellow stain on the outermost surface during the long-term storage. The degree of yellowness of the stain increased linerly with the oxide thickness due to the interfeefence color of the $SnO_2$ Even though the thickness of the oxide layer was very thin, less than 100$\AA$ , it exerts an undesirable influence on the can-making processes, particularly the stripping behavior after ironing. Investigations were carried out on the morphologies of the coating layer, the changes in oxide thickness during successive can-making processes and the averge friction coefficients with the different oxide thinkness. These oxide layers were broken up and distributed within the bulk tin coating during the ironing process. This redistribution of the oxide layer prvented smooth pressing-aside of the tin coating layer, resulting in an increase in the ironing friction coefficient. As the friction was increased, the residual stress along the can wall thinkness(i.e., the hoop stress) was also increased. Due to both the oxibe layer accumulation, which increased the friction coefficient, and the hoop stress, can stripping efficiency without roll-back is reduced.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1411-1417
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• 2010

CFRP (Carbon Fiber Reinforced Plastic) has received considerable attention in various fields as a structural material, because of its high specific strength, high specific stiffness, excellent design flexibility, favorable chemical properties, etc. Most products consisting of several parts are generally assembled by mechanical joining methods (using rivets, bolts, pins, etc.). Holes must be drilled in the parts to be joined, and the strength of the components subjected to static and fatigue loads caused by stress concentration must be decreased. In this study, we experimentally evaluated the variation in the residual strength of a holenotched CFRP plate subjected to fatigue load. We repeatedly subjected the hole-notched specimen to fatigue load for a certain number of cycles, and then we investigated the residual strength of the hole-notched specimen by performing the fracture test. From the results of the test, we can observe the initiation of a directional crack caused by the applied fatigue load. Further, we observed that the residual strength increases with a decrease in the notch effect due to this crack. It was evaluated that the residual strength increases to a certain level and subsequently decreases. This variation in the residual strength was represented by a simple equation by using a model of the decrease in residual strength for plain plate, which was developed by Reifsnider and a stress redistribution model for hole-notched plate, which was developed by Yip.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.20-28
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• 1997

용접부에는 많은 취약조건들이 존재하며 파괴의 주 원인이 되고 있어 이들에 대한 많은 연구가 진행되고 있다. 따라서, 현재 용접재료, 용접 조건 및 용접방법 등 을 개선함으로써 여러 방면에서 좋은 결과를 얻고 있다. 그러나 아직도 용접시의 열소 성변형과 구속조건에 따라 분포하는 잔류응력에 의한 피로균열거동에 대한 연구는 정확한 잔류응력 측정의 어려움으로 미흡한 상태이다. 특히 잔류응력의 측정기술과 반복하중에 의한 피로균열 진전시 잔류응력의 이완 등은 이들을 해석하는데 많은 어 려움을 주고 있다. 용접시 높은 열에 의한 재료의 팽창과 냉각시의 수축변형은 용접 부재에 인장 및 압축 잔류응력을 유발시키고, 인장잔류응력은 균열 진전될 때 잔류 응력은 오히려 균열을 지연시키기도 한다. 또한 잔류응력장에서 피로 균열이 진전될 때 잔류응력은 일반적으로 작용하중의 크기와 반복 수 그리고 균열 진전 등으로 인하 여 이완되고 재분포된다. 본 해설에서는 용접재의 피로거동중에 발생하는 잔류응력의 재분포 현상을 하중의 범위, 하중 반복수, 균열 진전의 영향으로 구분하여 각각의 영향에 대해서 기술하고자 한다.

• Smart Structures and Systems
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• v.13 no.6
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• pp.943-957
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• 2014

When subjected to fatigue loading, the main failure mode of partially prestressed concrete (PPC) structure is the fatigue fracture of tensile reinforcement. Therefore, monitoring and evaluation of the steel stresses/strains in the structure are essential issues for structural design and healthy assessment. The current study experimentally investigates the possibility of using fiber Bragg grating (FBG) sensors to measure the steel strains in PPC beams in the process of fatigue loading. Six full-scale post-tensioned PPC beams were exposed to fatigue loading. Within the beams, the FBG and resistance strain gauge (RSG) sensors were independently bonded onto the surface of tensile reinforcements. A good agreement was found between the recorded results from the two different sensors. Moreover, FBG sensors show relatively good resistance to fatigue loading compared with RSG sensors, indicating that FBG sensors possess the capability for long-term health monitoring of the tensile reinforcement in PPC structures. Apart from the above findings, it can also be found that during the fatigue loading, there is stress redistribution between prestressed and non-prestressed reinforcements, and the residual strain emerges in the non-prestressed reinforcement. This phenomenon can bring about an increase of the steel stress in the non-prestressed reinforcement.