• 한국전기전자재료학회논문지
• /
• 제22권1호
• /
• pp.67-73
• /
• 2009

The stress-strain behavior and its effects on the crack initiation and growth of ITO film on PET substrate with a sheet resistance of 45 ohms/sq were investigated. Electrical resistance increased gradually at the strain of 0.7% in the elastic to plastic transition region of the stress strain curves. Numerous cracks were observed after 1% strain and the increase of the resistance can be linked to the cracking of ITO thin films. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. The spacing between horizontal cracks (perpendicular to the stress axis) increased with decreasing strain rate, The increase of crack density with decreasing strain rate can be attributed to the higher fraction of the plastic strain to the total strain at a given total strain. As the strain increased over 5% strain, cracks parallel to the stress axis were developed and increased in number with strain, accompanied by drastic increases of resistance.

• 대한기계학회논문집A
• /
• 제24권2호
• /
• pp.378-385
• /
• 2000

Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.

• 한국해양공학회지
• /
• 제1권2호
• /
• pp.93-100
• /
• 1987

Corrosion fatigue cracking of the austenitic stainless steel(bese metal & heat affected zone by TIG weld) was studied experimentally under the environments of various specific resistance and air. The characteristics of corrosion fatigue crack growth rate and the environmental constants of paris' rule were investigated for SUS 304 weldments in the various specific resistance. The influences of stress intensity factor range and corrosion on the crack growth rate were compared. The characteristics of corrosion fatigue cracking for the weldments were inspected from mechanical, electrochemical and microstructural point of view. Main results obtained are as follows: 1) As the specific resistance decreases, the environmental constant C of paris'rule increases(hence the corrosion fatigue crack growth rate is rapid), but the environmental constant m decreases, so the effect of corrosion to the crack growth rate is more susceptible than thet of stress intensity factor range. 2) As the stress intensity factor range decreases, the corrosion fatigue crack growth rate of heat affected zone is more susceptible than that of the base metal. 3) The corrosion fatigue crack growth rate of the heat affected zone is more rapid than that of the base metal, because of the phenomenon of softening and the less noble potential coused by wedlding heat cycle. 4) The corrosion fatigue cracking of SUS 304 weldment appears transgranular fracture.

• 한국재료학회지
• /
• 제3권2호
• /
• pp.166-174
• /
• 1993

반도체 소자의 표면 보호용으로 사용되는 상압 CVD 방법에 의한 PSG(Phosposilicate glass)막 및 플라즈마 CVD방법에 의한 PE-SiN(Plasma enhanced CVD S${i_2}{N_4}$)막의 항균열 특성을 알루미늄박막이 증착되어 있는 실리콘 기판위에서 조사했다. 45$0^{\circ}C$에서 30분간으 열처리를 반복하면서 균열 발생 유무 및 그 형태를 조사하여 이러한 균열의 생성을 각 막의 막응력과 관련하여 검토하였다. 이들 박막에서의 균열 발생은 하부 조직인 알루미튬배선과의 열팽창계수차에 의한 것임을 알 수 있었다. PSG막 두께가 증가할수록 인장응력이 증가하여 항균열성이 저하되었다. PSG막의 P농도가 증가할수록 막응력은 압축응력쪽으로 이동하였고 균열 발생은 억제되었다. PE-SiN 막도 높은 압축응력을 갖게 함으로써 항균열성을 향상시킬 수 있었다. 본 실험의 결과로부터 반복 열처리시 균열 발생여부에 대한 실험식을 제시하였다.

• 대한기계학회논문집A
• /
• 제29권9호
• /
• pp.1225-1234
• /
• 2005

Mode I stress intensity factor $(K_I)$ of Notched Ring Test(NRT) specimen for measuring slow crack growth resistance was found using finite-element method. The theoretical $K_I$ value of NRT was not available in any references and could not be solved analytically. At first, in order to verify the accuracy of the finite-element approach, published $K_I$ values of several cracks were calculated and compared with finite-element results. The results were in good agreement within inherent errors of theoretical $K_I$. Finally the mode I stress intensity factor of NRT was found using 2- and 3-dimensional finite-element methods and expressed as a function of the applied load. This enabled direct comparison of resistance to slow crack growth between NRT and Notched Pipe Test(NPT), which employ different loading regime.

• 대한기계학회논문집
• /
• 제18권12호
• /
• pp.3227-3235
• /
• 1994

This paper deals with an evaluation of the residual stress due to shot peening induced in a carburized gear tooth and its application to the fatigue crack propagation problem. A practical method is proposed on the basis of the assumption that the residual stress is caused by the difference of volume expansion in the case and the core, and the influence of both the reduction of retained austenite and the strain due to shot peening are considered. The evaluated residual stress is close to the measured stress, though the surface stress is rather overestimated. The stress intensity factor is computed by the influence function method, and it is shown that the factor is decreased by the residual stress in shot peened gear tooth. The shot peening is fairly effective to the reduction of fatigue crack growth rate. The crack propagation is simulated and the resistance due to shot peening is quantitatively demonstrated and discussed.

• 신재생에너지
• /
• 제6권1호
• /
• pp.38-45
• /
• 2010

Abstract Under the physical stress on photovoltaic (PV) module, it will be warped according to elongation of the front glass and then micro-crack will be occurred in the thermally sealed solar cell. This micro-crack leads to drop of short circuit current of the PV module. This is because of increase of resistance component by micro-crack. Micro-crack at specific solar cell in the module lessens the durability of PV module with reduced output, hot-spot caused by solar cell output mismatch and increased resistance component. This study shows the relation between electrical characteristics and micro- cracks due to mechanical stress on PV module.

• Journal of Advanced Marine Engineering and Technology
• /
• 제25권5호
• /
• pp.1108-1114
• /
• 2001

The fatigue crack propagation behavior of the SA516-Grade 70 steel which is used for pressure vessels was experimentally examined under the condition of at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ration of R=0.1 and 0.3. The fatigue crack propagation rate , da/dN, related with the stress intensity factor range, $\vartriangle$N, was influenced by the stress ration within the stable growth of fatigue crack(Region II) with an increase in $\vartriangle$N. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations revels that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack and oxide-induced by high temperature.

• 한국해양공학회지
• /
• 제13권2호통권32호
• /
• pp.58-65
• /
• 1999

The effect of specimen thickness on fatigue crack growth rate was studied. The objective of the present study is to investigate the effect of specimen thickness on the fatigue crack growth behavior at various stress intensity factor ranges and also the variation of material restance to fatigue crack growth. The fatigue crack growth resistance was treated as a spatial stochastic process, which varies randomly on the crack path, Compact tension specimens with a LT orientation for structural steel were used. All testing was done at a constant stress intensity level. The experimental data were analyzed for the size effect to determine the Weibull distributions of the material resistance.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2000년도 추계학술대회 논문집
• /
• pp.147-153
• /
• 2000

The fatigue crack propagation behavior of the SA516/70 steel which is used for pressure vessels was examined experimentally at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ratio of R=0.1 and 0.3. The fatigue crack propagation rate da/dN related with the stress intensity factor range $\Omega\textrm{K}$ was influenced by the stress ratio within the stable growth of fatigue crack(Region II) with an increase in $\Omega\textrm{K}$. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack closure and oxide-induced by high temperature.