• Composites Research
• /
• v.12 no.4
• /
• pp.8-16
• /
• 1999

In this study, when the applied directions of tensile loading is changed fatigue damage of quasi-isotropic composite laminates was discussed. Low cycle fatigue tests of $[0/-60/+60]_s$ laminates and $[+30/-30/90]_s$ laminates were carried out. Material systems used were AS4/Epoxy and AS4/PEEK. The fatigue damage of $[+30/-30/90]_s$ laminates differed from that of $[0/-60/+60]_s$ laminates. The position of delamination generated at AS4/Epoxy and AS4/PEEK $[+30/-30/90]_s$ laminates appeared differently according to the kind of matrix. Critical values of strain energy release rate were obtained by using the strain measured at the initiation of delamination. The experimental results agreed well with the results obtained by the proposed method for determining strain energy release rate.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.10 no.3
• /
• pp.39-43
• /
• 2010

The main objective of this research is to develop a mechanistic performance predictive model for fatigue cracking of asphalt-aggregate mixtures. Controlled-stress diametral fatigue tests were performed to characterize fatigue cracking of asphalt-aggregate mixtures. Performance prediction model for fatigue cracking was developed using the internal damage ratio (IDR) growth method. In the IDR growth method, the general concepts of the dissipated energy, the reference tensile strain, the threshold tensile strain, and the strain shift factor were introduced. The source of the dissipated energy in the fatigue test is from the intrinsic viscoelastic material property of an asphalt concrete mixture and the damage growth within the asphalt concrete specimen. In controlled-stress mode test, the dissipated energy is gradually increased with an increasing number of load applications.

• Journal of the Korean Institute of Gas
• /
• v.19 no.5
• /
• pp.41-46
• /
• 2015

It is known that in aluminum 6061-T6, which is composed of $Mg_2Si$ and ${\beta}-Al_5FeSi$, void nucleation grows around ${\beta}-Al_5FeSi$ of Al606-T6. In this work, growth of voids was checked by scanning a 6061-T6 specimen with SEM observation. The effects of dislocation damping, coherency strain and voids on ultrasonic attenuation and nonlinearity parameters were experimentally measured. It was observed that a nonlinearity parameter increases until 75 percent of fatigue life and decreases after that. From the results, the authors inferred that dislocation damping and coherency damping increase nonlinearity parameters and void nucleation decreases them as ultrasonic scattering increases with void. The application of nonlinearity parameters in estimating degradation of materials with complex microstructures through fatigue process, therefore, should be carefully considered.

• Journal of Ocean Engineering and Technology
• /
• v.5 no.2
• /
• pp.225-225
• /
• 1991

• Journal of Korean Society of Steel Construction
• /
• v.12 no.2 s.45
• /
• pp.151-165
• /
• 2000

Since vehicles become large and heavy and traffic volume is increased rapidly, many fatigue damages have been reported in bridge members. In order to prevent fatigue damages of bridge members and maintain safety it is essential to perform rational fatigue check. Only one vehicle is loaded on a bridge deck for the fatigue design. But in reality it is seldom that only one vehicle passes on a bridge deck. Usually more than two vehicles are passing on a bridge deck simultaneously. Therefore, it is necessary to consider the influence of simultaneous loading for a rational fatigue design. In this study, the influence of simultaneous loading is investigated by performing stress variation analysis due to vehicle load on the basis of linear superposition method and Monte-Carlo simulation of traffic flow, and then calculating the measure of fatigue damages.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2000.04a
• /
• pp.35-35
• /
• 2000

터빈의 핵심구동부품은 손상이 누적되어 파괴에 이를 경우 치명적인 결과를 야기할 수 있기 때문에, 부품사용조건에서의 소성변형과 이에 따른 손상 누적을 정확히 예측하고 평가함으로써 균열생성 시점을 정확히 파악하여야 할 필요가 있다. 현재 터빈디스크와 같이 고온 고응력에서 사용되고 있는 소재부품의 수명은 궁극적으로 크리프변형과 피로시험의 공동작용으로 결정되며, 재료특성모델링 시험에 있어서도 dwell time 피로시험을 통해 dwell time 효과를 점검하고 점소성 재료변형에 근거하여 피로에 의한 변형 현상을 설명할 수 있다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.9
• /
• pp.903-910
• /
• 2015

The purpose of this research is to develop a full-spectral fatigue analysis program, based on rigid-body ship motion analysis, in order to perform a full-spectral fatigue analysis that considers hydroelasticity effects. To gain credibility, fatigue analysis results of two ship types, performed by the developed program, were compared with those of a classification society, and it was found that both are identical. Full-spectral fatigue analysis considering hydroelasticity effects would be developed in further studies by including flexible-body ship motion analysis results and by supplementing the developed program with a wide-band fatigue damage model.

• Journal of Life Science
• /
• v.20 no.6
• /
• pp.870-876
• /
• 2010

The purpose of this study was to examine the effect of kinesio taping on muscle strength and changes of muscle fatigue and damage. 10 male subjects participated in 1-RM and isometric cybex muscle strength tests with and without taping application. Muscle strength (bench press, leg press) and extension (knee, shoulder) strength were significantly increased after taping, but there was no significant difference in flexion (knee, shoulder) strength. The concentration of fatigue factors (ammonia, phosphorous), muscle damage index substances (CK, LDH), IGF-I and creatinine were reduced after taping, but there were no significant differences.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.4
• /
• pp.306-313
• /
• 2011

The damage tolerance analysis is required to guarantee the structural safety and the reliability for aircraft components. The damage tolerance method, which evaluate the life considering the initial crack, considers a fatigue design model of the aircraft main structure. The fatigue crack growth life should be calculated in damage tolerance analysis and the inspection time to define the replacement cycle. In this paper, the damage tolerance analysis is performed for a turbine wheel which has complex geometry. The equation of the stress intensity factor for complex geometry is hard to know, so that they are usually processed by finite element analysis which takes long time. To solve this problem, the stress intensity factors at specified crack are obtained by the FEA and the crack growth life is evaluated using the surrogate model which is generated by the regression analysis of the FEA data. From the results, the efficiency of the crack growth life calculation and the damage tolerance analysis could be increased by taking the surrogate model.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.2 no.1
• /
• pp.81-88
• /
• 1998

과적차량의 통행에 의한 교량구조물의 손상도를 평가하는 방법의 개발이 매우 활발하다. 본 연구에서는 과거 15년동안 통행한 교통데이타를 분석하고, 이 데이타를 근거로 교량의 손상도를 분석한다. 차량의 분류는 4종으로 대표하여 차량하중을 분석하였으며 해석시에는 이를 대표하는 2종을 사용하였다. 3차원해석을 통하여 구한 영향면을 이용하여 부재력을 계산하고 이를 이용하여 등가응력범위를 구한다. 이 결과는 모형실험을 통하여 구한 피로결과와 비교하였다. 분석결과 설계하중을 초과하는 과적차량이 교량에 미치는 손상정도는 적은 통행빈도에도 불구하고 매우 큼을 알 수 있고, 이러한 실제교통량의 분석을 통한 교량의 손상평가방법은 과적차량에 의한 교량손상정도를 유용하게 평가할 수 있다.