• 한국세라믹학회지
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• 제35권12호
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• pp.1257-1265
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• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• Structural Engineering and Mechanics
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• 제25권5호
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• pp.501-518
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• 2007

In this work, a new approach is developed for dynamic analysis of a composite beam with an interply crack, based on finite element solution of partial differential equations with the use of the COMSOL Multiphysics package, allowing for fast and simple change of geometric characteristics of the delaminated area. The use of COMSOL Multiphysics package facilitates automatic mesh generation, which is needed if the problem has to be solved many times with different crack lengths. In the model, a physically impossible interpenetration of the crack faces is prevented by imposing a special constraint, leading to taking account of a force of contact interaction of the crack faces and to nonlinearity of the formulated boundary value problem. The model is based on the first order shear deformation theory, i.e., the longitudinal displacement is assumed to vary linearly through the beam's thickness. The shear deformation and rotary inertia terms are included into the formulation, to achieve better accuracy. Nonlinear partial differential equations of motion with boundary conditions are developed and written in the format acceptable by the COMSOL Multiphysics package. An example problem of a clamped-free beam with a piezoelectric actuator is considered, and its finite element solution is obtained. A noticeable difference of forced vibrations of the delaminated and undelaminated beams due to the contact interaction of the crack's faces is predicted by the developed model.

• 대한기계학회논문집A
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• 제21권3호
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• pp.511-518
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• 1997

The technique of fretting fatigue test was developed and fretting fatigue tests of A12024-T4 were conducted under several conditions. The newly developed calibration methods for measuring surface contact tractions showed good linearity and repeatability. The plate type specimen to which tow bridge type pads were attached and vision system was used to observe the crack behaviour. The oblieque cracks appeared in the early stage of crack growth and they became mode I cracks as they grow about 1 mm. The mode I transition points were found to be longer when surface tractions are higher or bulk stress is lower. Before the crack becomes mode I crack, 'well point' where crack grow about rate is minimum, was detected under every experimental condition. The crack behaviour was found to be affected by surface tractions, contact area, bulk stress. It was also found that partial slip and stick condition is most detrimental and the crack starts from the boundary of stick and slip. For gross slip crack started at the outside edge of pad. After crack mode transition, fretting fatigue cracks showed almost same behaviour of plain mode I fatigue cracks. Equivalent stress intensity factor was used to analyze the behaviour of fretting fatigue cracks and it was found that stress intensity factors can be applied to fretting fatigue cracks.

• 비파괴검사학회지
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• 제33권2호
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• pp.187-192
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• 2013

크랙 계면에서의 접촉 열저항에 의해 만들어지는 온도 강하 특성을 적외선을 이용하여 측정함으로써 피로균열을 검사하였다. 크랙과 같은 불연속면을 지나는 열 유동은 연속체에서와는 달리 접촉경계면에서 급격한 온도구배를 나타내는데 이 변화를 표면에서의 적외선 방사량으로 측정하여 피로균열의 위치를 탐지하였다. 표준 피로균열 시편의 중앙부에 노치를 생성한 후 저주기 피로균열을 노치 끝단으로부터 발생시킨 다음, 이 시편의 한쪽 끝단에 할로겐램프를 이용하여 일정한 열을 가함으로서 시편의 길이 방향으로 열 유동이 일어나도록 하면서 시편의 표면온도 분포를 적외선 실험장치로 계측하였다. 열 유동이 크랙을 지나면서 온도구배가 크게 변화하는 것을 적외선 열화상 이미지로부터 알 수 있었으며 균열 면에서의 적외선 온도 데이터로부터 크랙의 위치와 크기를 평가할 수 있음을 실험적으로 확인하였다.

• 대한기계학회논문집
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• 제18권3호
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• pp.540-547
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• 1994

Contact and frictional locking conditions and the effect of shielding due to contact at the facet, which could be represented by the difference in energy release rate, as a function of phase angle of loading are analyzed in this study for the case of interfacial cracks by assuming single crack-kink model. The analysis of contact effects on interfacial fracture resistance shows that relative shielding increases as the shear component was increased, which indicates a qualitative agreement with the previous experimental results.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1078-1084
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• 2005

The relationship between fatigue crack opening behavior and the reversed plastic zone sizes is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the track tip area. The smaller element size than reversed plastic zone size is used fer evaluating the distribution of reversed plastic zone. In the author's previous results the FEA could predict the crack opening level, which crack tip elements were in proportion to the theoretical reversed plastic zone size. It is found that the calculated reversed plastic zone size is related to the theoretical reversed plastic zone size and crack opening level. The calculated reversed plastic zone sizes are almost equal to the reversed plastic zone considering crack opening level obtained by experimental results. It can be possible to predict the crack opening level from the reversed plastic zone size calculated by finite element method. We find that the experimental crack opening levels correspond with the opening values of contact nodes on the calculated reversed plastic zone of finite element simulation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 창립기념 춘계학술대회 논문집
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• pp.315-322
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• 1998

A two dimensional elasto-plastic finite element program taking into account contact between crack surfaces if developed in order to analyze subsurface cracking in rolling contact. But the friction between upper and lower surface of the crack is not considered. Under the assumptions of small deformation and small displacement, the incremental theory of plasticity is used to describe plastic deformation. J-integral is computed as the applied Hertzian load slides over the surface with friction. J-integral is correlated with wear rate of the rail. The propagation rate of the right tip of the surface crack is fast by 45% than that of the left side.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.172-178
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• 2001

Using dislocation pileup theory, the near surface crack initiation life was calculated. The crack initiation life calculted in the previous study is not a real life strictly and just for the cracking in substrate. In this study, two life equations which can be applied for each near-surface and substrate were used for a comparative study. The downward tendency of life at near surface and substrate was similar and the crack initiation life at near-surface was much shorter than the life in substrate. The improvement of the crack initiation life equations which were proposed by W. Cheng was discussed.

• 비파괴검사학회지
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• 제28권3호
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• pp.292-301
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• 2008

A linearized model for hysteretic acoustic nonlinearity of imperfectly joined interface is proposed and analyzed by using Coulomb damping to investigate the characteristics of the reflection and transmission coefficients for harmonic waves at the contact interface. Closed crack is modeled as non welded interface that has nonlinear discontinuity condition in displacement across its boundary. Based on the hysteretic contact stiffness of the contact interface, the reflected and transmitted waves are determined by deriving the tractions on both sides of the interface in terms of the discontinuous displacements across the interface. It is found that the amplitudes of the reflected and transmitted waves are dependent on the frequency and the hysteretic stiffness. As the frequency of the incident wave increases, the higher reflection and lower transmission are obtained. It also shows that the hysteresis of the interface increases the reflection coefficient, but reduces the transmission coefficient. A fatigue crack is also made in aluminum specimen to demonstrate these characteristics of the reflection and transmission of contact interfaces.

• Steel and Composite Structures
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• 제45권4호
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• pp.501-511
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• 2022

In this study, a two-dimensional model of the contact problem has been examined using the finite element method (FEM) based software ANSYS and based on the multilayer perceptron (MLP), an artificial neural network (ANN). For this purpose, a functionally graded (FG) half-infinite layer (HIL) with a crack pressed by means of two rigid blocks has been solved using FEM. Mass forces and friction are neglected in the solution. Since the problem is analyzed for the plane state, the thickness along the z-axis direction is taken as a unit. To check the accuracy of the contact problem model the results are compared with a study in the literature. In addition, ANSYS and MLP results are compared using Root Mean Square Error (RMSE) and coefficient of determination (R2), and good agreement is found. Numerical solutions are made by considering different values of external load, the width of blocks, crack depth, and material properties. The stresses on the contact surfaces between the blocks and the FG HIL are examined for these values, and the results are presented. Consequently, it is concluded that the considered non-dimensional quantities have a noteworthy influence on the contact stress distributions, and also, FEM and ANN can be efficient alternative methods to time-consuming analytical solutions if used correctly.