• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.256-259
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• 2005

Mixed-mode interlaminar fracture toughness of carbon fabric/epoxy composites, which are applicable to tilting train carbody, was evaluated through the MMB (Mixed-mode bending) test. Specimens were made of CF3327 plain woven fabric with epoxy and a starter delamination at one end was made by inserting Teflon film with the thickness of 12.5 μ m. Mixed-mode interlaminar fracture test was conducted for 6 types of specimens with the mode II ratio of 20 ,35, 50, 65, 80, 90%. Also crack propagating behaviors and fractured surfaces were examined through an optical travelling scope and a scanning electron microscope, respectively.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2001년도 추계공동학술발표회 논문집
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• pp.121-126
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• 2001

• 대한기계학회논문집A
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• 제25권4호
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• pp.703-713
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• 2001

Mechanical joints such as bolted or riveted joints are widely used in structural components and the reliable determination of the stress intensity factors for corner cracks in mechanical joints is needed to evaluate the safety and fatigue life. This paper analyzes the mixed-mode stress intensity factors of surface and deepest points for quarter elliptical corner cracks in mechanical joints by weight function method and the coefficients included in weight function are determined by finite element analyses for reference loadings. The extended form of the weight function method for two-dimensional mixed-mode to three-dimensional is presented and the number of terms in weight function is determined by comparing the results for the different number of terms. The amount of clearance is an important factor in evaluating the severity of elliptical corner cracks in mechanical joints and even horizontal crack normal to the applied load is under mixed-mode in the case that clearance exists.

• 한국항공우주학회지
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• 제33권10호
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• pp.35-41
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• 2005

재료주축과 경사진 중앙균열을 내포하는 직방성 복합재료 내 균열문제를 해석하였다. 이 균열체에는 외부경계에서 2축방향으로 작용하는 하중을 받고 있다. 복합재료 내 초기균열의 진전각을 예측하기 위하여 수직응력비 이론을 적용하였으며, 균열진전각에 미치는 2축하중과 섬유재료주축의 영향을 분석하였다. 본 해석을 통하여 균열진전각은 수평하중에 많은 영향을 받고 있으며, 또한 균열경사각과 섬유배향각에도 큰 영향을 받음을 확인하였다.

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.371-379
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• 2017

Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, two crack growth criteria and the respective crack paths prediction in functionally graded materials (FGM) are compared. The maximum tangential stress criterion (${\sigma}_{\theta}-criterion$) and the minimum strain energy density criterion (S-criterion) are investigated using advanced finite element technique. Using Ansys Parametric Design Language (APDL), the variation continues in the material properties are incorporated into the model by specifying the material parameters at the centroid of each finite element. In this paper, the displacement extrapolation technique (DET) proposed for homogeneous materials is modified and investigated, to obtain the stress intensity factors (SIFs) at crack-tip in FGMs. Several examples are modeled to evaluate the accuracy and effectiveness of the combined procedure. The effect of the defects on the crack propagation in FGMs was highlighted.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.292-297
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• 2001

Composite patch repair of cracked aircraft structures has been accepted as one of improving fatigue life and attaining better structural integrity. Analysis for the stress intensity factor at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels are developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior. In order to investigate the crack growth direction, maximum tangential stress(MTS) criteria is used. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stress intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. The research on cracked structure subjected to mixed mode loading is accomplished and it is evident that more work using different approaches is necessary.

• Geomechanics and Engineering
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• 제29권5호
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.298-303
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• 2001

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for a compact tension specimen in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives very much. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• 한국지반공학회논문집
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• 제36권3호
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• pp.25-36
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• 2020

동토의 세립분 함유량에 따른 파괴특성을 파악하기 위해 -10℃의 온도에서 다양한 세립분 함유량과 초기 노치(notch)의 위치를 조정한 직사각형 공시체를 제작하여 Three-point bending 시험을 수행하였다. 시험결과를 바탕으로 동토의 mode I 파괴인성(fracture toughness)을 산정하였으며, 하중-변형 곡선의 최대점까지의 fracture energy를 산정하여 동토의 mixed-mode(mode I + II) 파괴특성을 파악하였다. 시험결과, 최대하중 및 mode I 파괴인성은 세립분 함유량 10%까지 증가하다가 15%에서 다시 감소하는 경향을 나타내었다. 또한, 노치의 위치가 공시체 중심에서 멀어질수록 mode II 하중의 증가로 인해 균열이 진행하는데 필요한 fracture enenrgy가 증가하는 것으로 나타났으며, 세립분 함유량이 증가할수록 mode II 하중의 증가비율 또한 증가하는 것으로 나타났다.

• 대한토목학회논문집
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• 제14권4호
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• pp.761-769
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• 1994

열차 바퀴의 접촉하중에 의해 레일이 받는 하중형식은 모드 I과 모드 II가 조합된 혼합모드 하중 상태로서 본 연구에서는 레일강의 피로파괴거동을 규명하기 위해 Richard가 개발한 혼합모드 파괴시험편 및 시험 지-그(Jig)를 이용하여 파괴시험을 실시하였으며 그 결과로부터 혼합모드에 대한 용력강도계수의 상관관계를 이용하여 균열성장경로를 평가하고 기제안된 다양한 파괴기준을 비교하였다. 그 결과, 레일강의 균열성장경로는 최대원주응력설과 변형에너지밀도설을 파괴기준은 주변형률설을 따름을 알 수 있었다.