• 대한기계학회논문집A
• /
• 제30권9호
• /
• pp.1110-1115
• /
• 2006

Cold expansion of fastener holes has been successfully used for many years to impart beneficial compressive residual stresses. Beneficial compressive residual stress of fastener hole that has been cold expanded before is reduced by using of materials for a long time. As a result, fatigue life of material is reduced. So, compressive residual stresses of material have to regenerate by re-cold expansion method. In this paper, it was carried out a finite element analysis about variation of residual stress due to tensile stress and residual stress distribution that was regenerated by re-cold expansion method in the fastener hole. Here, a diversity tensile stress was used. Also, it was performed a finite element analysis according to cold expansion rate of re cold expansion in order to obtain a beneficial compressive residual stress.

• 반도체디스플레이기술학회지
• /
• 제3권2호
• /
• pp.35-40
• /
• 2004

The total relaxed stress in annealing and the thermal strain/stress were obtained from the identification of the residual stress-free state using electronic speckle pattern interferometry (ESPI). The residual stress fields in case of both single and film / substrate systems were modeled using the thermo-elastic theory and the relationship between relaxed stresses and displacements. We mapped the surface residual stress fields on the indented bulk Cu and the 0.5 $\mu\textrm{m}$ Au film by ESPI. In indented Cu, the normal and shear residual stress are distributed over -1.7 GPa to 700 MPa and -800 GPa to 600 MPa respectively around the indented point and in deposited Au film on Si wafer, the tensile residual stress is uniformly distributed on the Au film from 500 MPa to 800 MPa. Also we measured the residual stress by the x-ray diffractometer (XRD) for the verification of above residual stress results by ESPI...

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
• /
• pp.58-58
• /
• 2010

The purpose of this study is to evaluate the structural safety at the topside weldment of hull structure, which was welded after launching. For it, the variations of residual stress and distortion at the topside weldment with loading conditions such as hull girder hogging bending moment after launching and free initial loading state was evaluated by using FEA. And the maximum stress range at the weldment under design loads specified by classification society was evaluated by FEA. In this case, the residual stress and welding distortion at the topside weldment was assumed to be initial imperfection. In accordance with FEA results, regardless of initial loading condition, tensile residual stress was found. However, the residual stress and welding distortion at the topside weldment produced under hogging condition was less than those of topside weldment under free loading state. That is, the amount of residual stress at the topside weldment decreased with an increase in the amount of tension load caused by hogging condition. It was because the compressive thermal strain at the topside weldment produced during welding was reduced by tensile load. However, the maximum stress range at the topside weldment under maximum hull girder bending moment was almost similar regardless of initial loading condition. So, if the problem related to the soundness of weldment is not introduced by initial load, the effect of initial loading condition during welding on fatigue strength of topside weldment could be negligible.

• 대한기계학회논문집A
• /
• 제30권7호
• /
• pp.826-832
• /
• 2006

For the improvement of safety and endurance in welded steel structure, it is needed to consider welding residual stress distribution and rolling directional characteristics of materials. In this study, it was investigated experimentally about characteristics of fatigue crack propagation according to welding residual stress and rolling in FCAW(flux cored arc welding) butt-jointed steel plates. SS400 steel plates of 3mm thickness were selected and tested for this study. When the angles between tensile loading direction and rolling direction in welded materials are increased from $0^{\circ}\;to\;90^{\circ}$, their fatigue crack propagation rates are increased. These results are same as predicted increments of fatigue crack propagation rate when stress ratio is increased from 0 to 0.5. When the angles of rolling direction and welding direction to tensile loading direction are $0^{\circ}\;and\;90^{\circ}$ respectively, fatigue crack propagation rate in welded material is lowest.

• 한국표면공학회지
• /
• 제37권4호
• /
• pp.226-233
• /
• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

• 대한기계학회논문집A
• /
• 제24권2호
• /
• pp.279-289
• /
• 2000

Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of $\psi$ = $0^{\circ}$. Tensile residual stresses(+) of $\sigma_{zz}$ = 45 MPa and $\sigma_{\theta\theta}$ = 25 MPa were introduced in the intrados surface at the position of $\psi$ = $0^{\circ}$. Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of $\psi$ = $90^{\circ}$, i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.

• 터널과지하공간
• /
• 제5권4호
• /
• pp.363-375
• /
• 1995

Critical literature review in this study revealed that there can be a significant influence of the residual stress on the engineering properties of rock. The review also showed that few number of research works on the quantification of the influence was attributed to the limitation of the two classical measurement techniques, viz, X-ray diffraction and mechanical relaxation method. In this study, a new way of approach was sought based on the assumption that residual stress up to the failure. A series of hoop tests conducted onthe samples from the limb of Carboniferous Limestone in Clevedon, England, revealed that (i) there is no preferential orientations of microcracks and minerals which have been widely believed as the main source of the strength anisotropy of rock; (ii) the anisotropy of the tensile strength of the limestone results from the influence of the residual stress; (iii) since jointing commenced within the fold, residual stored strain energy has been released preferentially in the direction perpendicular to the major joints(o$^{\circ}$ and 90$^{\circ}$); (ⅳ) during the hoop test making it much easier to create tensile fracture in these directons, viz 45$^{\circ}$ and 135$^{\circ}$)was released during the hoop test making it much easier to create tensile fracture in these directions, viz 45$^{\circ}$and 135$^{\circ}$;(v) the direction in which the stored strain energy may be presumed to be the least, required the greatest work to cause failure.

• 소성∙가공
• /
• 제26권3호
• /
• pp.162-167
• /
• 2017

The tensile surface residual stress in the multi-pass drawn wire deteriorates the mechanical properties of the wire. Therefore, the evaluation of the residual stress is very important. Especially, the axial residual stress on the wire surface is the highest. Therefore, the objective of this study was to propose an axial surface residual stress prediction model of the multi-pass drawn steel wire. In order to achieve this objective, an elastoplastic finite element (FE) analysis was carried out to investigate the effect of semi-die angle and reduction ratio of the axial surface residual stress. By using the results of the FE analysis, a surface residual stress prediction model was proposed. In order to verify the effectiveness of the prediction model, the predicted residual stress was compared to that of a wire drawing experiment.

• Journal of Welding and Joining
• /
• 제26권6호
• /
• pp.92-96
• /
• 2008

An investigation was performed to predict residual stress redistribution for the crack propagation initially through tensile residual stress field. The analytical method, which is based on Dugdale model by finite element analysis using elastic analysis method considering the superposition principle, was proposed to estimate the redistribution of residual stress caused by crack propagation. The various aspect of distribution of residual stress caused by crack propagation was examined based on the configuration change of specimen. The analysis results show that the aspect of redistribution of residual stress caused by crack propagation depends on the width of the specimen provided that the initial distribution of residual stress is identical.

• Journal of Welding and Joining
• /
• 제14권4호
• /
• pp.43-52
• /
• 1996

The plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical properties of the plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings were examined in this study. The distribution of the residual stress with the coating thickness was also examined by X-ray diffraction method. The pore in the coatings could be classified into two types ; one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occurred at the interface of top coat and substrate or top coat and bond coat depending on the existence of bond coat. It was found that the compressive residual stress near the interface decreased with the increase of the top coat thickness. The tensile adhesion strength of the coating without bond coat was higher than that with bond coat, because the coating with bond coat has higher horizontal crack density near the interface between bond coat and top coat.