• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.9
• /
• pp.1109-1116
• /
• 2013

This study aims to investigate the spatial randomness of fatigue crack growth rate for the friction stir welded (FSWed) 7075-T651 aluminum alloy joints. Our previous fatigue crack growth test data are adopted in this investigation. To clearly understand the spatial randomness of fatigue crack growth rate, fatigue crack growth tests were conducted under constant stress intensity factor range (SIFR) control testing. The experimental data were analyzed for two different materials-base metal (BM) and weld metal (WM)-to investigate the effects of spatial randomness of fatigue crack growth rate and material properties, the friction stir welded (FSWed) 7075-T651 aluminum alloy joints, namely weld metal (WM) and base metal (BM). The results showed that the variability, as evaluated by Weibull statistical analysis, of the WM is higher than that of the BM.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.9
• /
• pp.999-1004
• /
• 2014

In the present paper, the effects of initial crack location on spatial randomness of fatigue crack growth resistance (FCGR) in friction stir welded (FSWed) AA7075-T651 plates were studied. The objective of this study is to characterize the statistical properties of FCGR for three different types of initial crack location (ICL) specimens. In this work, the FCGR coefficients were treated as a spatial random process. It was found that the FCGR coefficients for all initial crack location specimens closely followed a two parameter Weibull distribution. The shape parameter of the Weibull distribution for BM-ICL specimens showed the largest value of 7.50, and that for the WM-ICL specimens showed the smallest value of 2.61. In addition, the autocorrelation functions for all the ICL specimens followed the exponential function.

• Proceedings of the Korean Institute of Industrial Safety Conference
• /
• 2002.05a
• /
• pp.177-183
• /
• 2002

인명이나 물적 재산에 많은 손실을 가져주는 기계설비 및 구조물의 파괴현상에 대한 연구는 재해 원인을 분석하고 안전대책을 수립하기 위한 측면에서 대단히 중요하며, 지금까지 많은 연구가 행하여져 오호 있다 프랙탈기하학에 대한 연구는 Mandelbrot/sup l)/에 의하여 제안되어 20년 정도의 짧은 기간임에도 불구하고 여러 분야의 자연현상을 모델화하기 위하여 다양하게 발표가 되고 있다. 프랙탈 특성은 자연현상의 불규칙한 변화를 정량적으로 나타내기 위한 프랙탈차원으로 평가된다 프랙탈차원은 파면 및 균열의 불규칙성을 정량화함으로써 균열수명을 보다 더 정확히 예측하는데 적용될 수 있다.(중략)

• Journal of the Korea Concrete Institute
• /
• v.18 no.3 s.93
• /
• pp.355-360
• /
• 2006

The Alkali-Silica Reaction(ASR) may cause a serious failure in the concrete pavements and structures. Several researches in some nations have conducted the continuous studies to prevent failure of the concrete structures by the ASR distress as well as the studies to manifest the mechanism. The researches on the ASR have not been performed affluently in Korea because the distress due to ASR has seldom been reported literarily. In this study, we tried to set up the systematic scheme practically for verifying the cause of distress due to ASR by using the visual inspections in field, the chemical method, petrographic analysis, and Electron Dispersive X-ray Spectrometer(EDX) method of Scanning Electron Microscopy(SEM) in laboratory. The chemical method, petrographic method using SEM, and X-ray method were used to verify the cause of pattern crack on the surface and internal crack in the plain concrete pavement. It can be concluded that the distress of a specific site in plain concrete pavement was mainly due to ASR. The chemical method, the petrographic method and EDX method using SEM may be the effective tools for verifying the cause of AAR distresses.

• Journal of the Korean Society for Precision Engineering
• /
• v.11 no.1
• /
• pp.192-200
• /
• 1994

The methodology of a simple probabilistic fatigue crack under random loading is proposed. Using the crack closure concept, the crack opening stress is assumed to be constant during random loading. The loading history was analyzed to determine the probability density functions, probability distribution functions and other related parameters for the probabilistic fatigue crack growth analysis. Fatigue crack growth using the exisiting available data was predicted by the proposed probabilistic analysis and compared with experimental data.

• Korean Journal of Food Science and Technology
• /
• v.31 no.1
• /
• pp.164-170
• /
• 1999

Cracking of rice caused by moisture migration during storage under different relative humidity conditions was investigated for the establishment of safe storage condition of rice. Rice was cracked when a large difference in equilibrium relative humidity $({\Delta}ERH)$ between the rice and the environment was present. External and internal cracks were generated as the results of moisture desorption and adsorption, respectively. The external cracks by moisture desorption generated in all directions and shaped irregularly, while the internal cracks by moisture adsorption did in radial direction and showed a typical shape. The cracking trend could be analyzed by the Weibull function, and the cracking constant increased with ${\Delta}ERH$. The frequency of cracked rice increased linearly with In $({\Delta}ERH)$. The critical crack-inducing ${\Delta}ERH$ was $11.3{\sim}16.4%$ during desorption and $10.8{\sim}17.1%$ during adsorption. A diagram for the safe storage of rice was developed with respect to the initial moisture content and the water activity of rice.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.5 s.176
• /
• pp.1288-1296
• /
• 2000

In this study, fatigue crack behavior between arbitrarily located defects was investigated by experiment. Especially, stress interaction between micro hole defects and fatigue cracking, and fatigue crack initiation life following the variation of location of micro hole defects were considered. In addition, crack initiation position by micro hole stress interaction and the relationship between stress concentration factor and fatigue initiation life are studied in detail.

• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.2
• /
• pp.228-240
• /
• 1991

Many experimental data of fatigue crack propagation show that the fatigue crack propagation process is stochastic. Therefore, the study on the crack propagation must be based on the probabilistic approach. In the present paper, fatigue crack propagation process is assumed to be a discrete Markov process and the method is developed, which can evaluate the reliability of the structural component by using Markov chain model(Unit step B-model) suggested by Bogdanoff. In this method, leak failure, plastic collapse and brittle fracture of the critical component are taken as failure modes, and the effects of initial crack distribution, periodic and non-periodic inspection on the probability of failure are considered. In this method, an equivalent load value for random loading such as wave load is used to facilitate the analysis. Finally some calculations are carried out in order to show the usefulness and the applicability of this method. And then some remarks on this method are mentioned.

• Polymer(Korea)
• /
• v.32 no.3
• /
• pp.270-275
• /
• 2008

Crack growth characteristics of elastomeric materials are an important factor determining the strength and durability. In this study, the fatigue crack growth characteristic of filled EPDM compounds with different reinforcing fillers, such as silica and carbon black, was investigated using a newly designed tester. Frequency and test temperature had significant effects on the fatigue crack growth. The crack growth rate decreased with increasing frequency and the rate increased with increasing temperature. A power law relationship between the tearing energy and crack growth was observed for filled EPDM compounds. The crack growth rate reduced with increasing filler contents. Silica filled EPDM showed a better fatigue resistance than carbon black filled EPDM. The crack growth rate of silica filled EPDM decreased up to 30 phr and increased again at 50 phr. The formation of microductile type pits was observed on the fatigue-failure surface of unfilled EPDM, and relatively coarse surface with randomly distributed tear lines was observed on the failure surface of silica filled EPDM.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.18 no.4
• /
• pp.278-291
• /
• 1998

Fracture process of continuous fiber reinforced composites is very complex because various fracture mechanisms such as matrix cracking, debonding, delamination and fiber breaking occur simultaneously during crack growth. If fibers cause crack bridging during crack growth, the stable crack growth and unstable crack growth appear repeatedly. Therefore, it is very difficult to exactly determine tile starting point of crack growth and the fracture toughness at the critical crack length in composites. In this research, fracture toughness test for CFRP was accomplished by using acoustic emission(AE) and recording of tile fracture process in real time by video-microscope. The starting point of crack growth, pop-in point and the point of unstable crack growth can be exactly determined. Each fracture mechanism can be classified by analyzing the fracture process through AE and video-microscope. The more reliable method ior the fracture toughness measurement of composite materials was proposed by using the combination of R-curve method, AE and video microscope.