• Journal of Mechanical Science and Technology
• /
• 제18권11호
• /
• pp.1996-2008
• /
• 2004

A seamless analysis of material behavior incorporating complex geometry and crack- tip modeling is one of greatly interesting topics in engineering and computational fracture mechanics fields. However, there are still large gaps between the industrial applications and fundamental academic studies due to a time consuming detailed modeling. In order to resolve this problem, a numerical method to calculate an energy release rate by virtual crack closure technique was proposed in this paper. Both free mesh method and finite element method have been utilized and, thereafter, robust local and global elements for various geometries and boundary conditions were generated. A validity of the proposed method has been demonstrated through a series of fracture mechanics analyses without tedious crack-tip meshing.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.356-361
• /
• 2008

In characteristics of fatigue crack propagation, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. The purpose of this paper is to analyze the characteristics of fatigue crack propagation in constant loading condition for sheet Al 2024-T3 alloy of two sort of thickness and identify the difference of fatigue life in thin sheet specimen comparing experimental results of thin sheet specimen and relatively thick sheet specimen under same fatigue loading condition. In applying fatigue related material constants from fatigue crack propagation analysis, we attempt to operate the fatigue life estimating process of thin sheet specimen by modified Paris‘ law considering crack closure phenomenon and analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.

• Journal of Welding and Joining
• /
• 제18권5호
• /
• 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.

• 대한조선학회논문집
• /
• 제38권3호
• /
• pp.74-83
• /
• 2001

Paris가 피로균열전파에 파괴역학의 개념을 도입한 이후, Paris 법칙에 의하여 피로균열성장문제를 다루어 왔으나, Elber가 제안한 유효응력강도계수가 균열 전파 실험과 잘 일치하는 것이 밝혀진 이후 많은 연구자들이 유효응력비인 개구비를 정확히 추정하기 위한 연구를 계속하여 왔다. 본 연구는 변동하중 하의 피로균열전파 거동을 해석함에 있어서 균열의 개폐구 거동을 고려한 해석적 수치 모델을 개발하여, 선체구조 설계나 선박검사 시에 활용 가능한 정밀한 균열전파 추정방법을 제안하고자 한다.

• Journal of Mechanical Science and Technology
• /
• 제16권10호
• /
• pp.1246-1252
• /
• 2002

Ultrafine grained (UFG) low carbon (0.15 wt.% C) steel produced by equal channel angula. pressing (ECAP) was tested for investigating the effect of load ratio on the fatigue crack growth rate. Fatigue crack growth resistance and threshold of UFG steel were lower than that of asreceived coarse grained steel. It was attributed to the less tortuous crack path. The UFG steel exhibited slightly higher crack growth rates and a lower △Kth with an increase of R ratio. The R ratio effect on crack growth rates and △Kth was basically indistinguishable at lower load ratio (R >0.3), compared to other alloys, which indicates that contribution of the crack closure vanishes. The crack growth rate curve for UFG steel exhibited a longer linear extension to the lower growth rate regime than that for the coarse grained as-received steel.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1999년도 춘계학술대회 논문집
• /
• pp.32-38
• /
• 1999

Fatigue crack propagation behavior for block load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum alloy 5052-H32. Initial crack was made by applying cyclic load to a through crack with chevron notch. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was applied to check the crack closure and cracked area. The present study results can be usefully applied to predicting the change of crack propagation rate, the crack closure, and the delay of crack propagation.

• 대한기계학회논문집A
• /
• 제20권7호
• /
• pp.2234-2245
• /
• 1996

In this study residual stress in weldment was considered about the effect on the fatigue propagation and about the effect of redistribution of residual stress. Then, fatigue tests were conducted by the center notched specimens machined with welded plate. The residual stress and its redistribution after the crack growth were measured by the magnetizing stress indicator and hole-drilling method. Fatigue crack propagation was estimated by the specimens having residual stress redistributed after the cracks growth and having the effects of crack closure. Crack growth rates were predicted and compared with experimental results. It had been found that the predicted crack propagation rates have a good agreement with experimental results when the redistribution of residual stress was considerd.

• 대한기계학회논문집
• /
• 제12권4호
• /
• pp.781-789
• /
• 1988

본 연구에서는 용접성이 좋고 강도도 적당하며 부식에 대한 저항성이 좋아 해 양구조물 및 용접구조용재로서 널리 사용되고 있는 5083-H113 Al 합금을 준비하고 이 재료의 균열형태에 따른 피로균열진전거동을 밝히기 위하여 관통균열과 포면균열의 진 전거동에 미치는 응력비의 영향을 균열닫힘과 함께 검토하였다.

• 한국해양공학회지
• /
• 제16권6호
• /
• pp.55-59
• /
• 2002

Delamination means that cracking occurs on the interface layer between composite laminates. In this paper, to predict the delamination growth in composite laminates subjected to low-velocity impact, the unit load method was introduced, and an eighteen-node 3-D finite element analysis, based on assumed strain mixed formulation, was conducted. Strain energy release rate, necessary to determine the delamination growth, was calculated by using the virtual crack closure technique. The unit load method saves the computation time more than the re-meshing method. The virtual crack closure technique enables the strain energy release rate to be easily calculated, because information of the singular stress field near the crack tip is not required. Hence, the delamination growth in composite laminates that are subjected to low-velocity impact can be efficiently predicted using the above-mentioned methods.

• 대한기계학회논문집
• /
• 제14권3호
• /
• pp.603-609
• /
• 1990

본 연구에서는 미소균열의 정의로서 균열의 크기가 재료의 조직의 크기와 order적으로 같은 균열의 특성이라는 것과 균열의 크기가 소성역 크기와 order적으로 같은 균열의 특성에 착안해서 탄소강 평활재와 예균열재(pre-cracked specimen)에 대 해서 응력비 R=-1 및 R=0의 피로한도 특성과 평활재의 미소균열의 검출 및 정류균열의 생성기구를 균열 열림 닫힘에 주목해서 검토하였다.