• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.3
• /
• pp.259-267
• /
• 2014

Fatigue tests were performed in various simulated body environments reflecting various factors (such as body fluids, artificial saliva) relevant within a living body. First, the fatigue limit under a simulated body environment (artificial saliva) was evaluated and the governing factors of implant fatigue strength were looked into by observing the fracture mode. The fatigue life of an implant decreased in the artificial saliva environment compared with that in the ringer environment. Furthermore, in the artificial saliva environment, the implant fracture mode was fatigue failure of fixture as opposed to the abutment screw mode in the ringer environment. In the fatigue test, corrosion products were observed on the implant in the simulated body environment. A larger amount of corrosion products were generated on the artificial saliva specimen than on the ringer specimen. It is thought that the stronger corrosion activity on the artificial saliva specimen as compared with that on the ringer specimen led to an overall decrease of fatigue life of the former specimen. In the case of the implant with a nitrided abutment screw eliminated hardened layer (TixN), a several times increase in fatigue life is achieved in comparison with tungsten carbide-coated implants.

• Journal of the Korean Society for Railway
• /
• v.13 no.6
• /
• pp.577-582
• /
• 2010

The importance of maintenance of rail surface defects is increasing according to the KTX operation. That is because during high speed operation of rolling stocks, rail surface defects shorten fatigue life of rail, accelerate track degradation and deteriorate ride comfort. Rail grinding has been applied for effective rail maintenance in Kyeong-Bu HS line. This paper evaluates the effectiveness of rail grinding in term of rail fatigue life. To this end, the stresses of the rail are measured under KTX running and the equivalent stress range is calculated by RMC after the frequency analysis done with rainflow counting method. Also, The Modified Miner's rule is applied to predict the fatigue life of ground rail. The result of the analysis shows that the fatigue life of ground rail is increased by 15%.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.3
• /
• pp.907-915
• /
• 1991

본 연구에서는 피로 크랙 발생 및 파단수명의 통계학적 분포특성을 명확히 하 기 위해서 단축인장을 받고, 크랙 선단 곡율반경이 일정한 중앙 크랙을 가진 81개의 시험편을 사용하여 4개의 응력 레벨하에서 피로 시험을 행한후 많은 데이터들로 부터 피로크랙의 발생, 파단특성에 대한 신뢰성 있는 통계학적 확률특성을 제시하고, 이들 데이터를 활용하여 수명예측을 행해보고저 한다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.5
• /
• pp.1191-1198
• /
• 2015

In this study, vehicle/track interaction analysis by the Saemaul powered vehicle was carried out. The prediction equation for the bending stress of rail was estimated using the rail bending stress by the rail surface irregularities at welds. Also, the fatigue analysis using a S-N curve of welds in the conventional railway was carried out. We estimated the fatigue life of CWR by the fracture probability. By the rail grinding, the fatigue life of CWR was evaluated in consideration to reduce the rail bending stress through removing the rail surface irregularities. Therefore, it presented the fatigue life of CWR according to the rail grinding execution plan in the conventional railway.

• Composites Research
• /
• v.16 no.1
• /
• pp.13-18
• /
• 2003

Prediction of composite fatigue life is not a straightforward matter, depending on various failure modes and their interactions. In this paper, a methodology is presented to predict fatigue life and residual strength of composite materials based on Phenomenological Model(non-linear fatigue damage model). It is assumed that the residual strength is a monotonically decreasing function of the number of loading cycles and applied fatigue stress ratio and the model parameters(strength degradation parameter and fatigue shape parameter) are assumed as function of fatigue life. Then S-N curve is used to extract model parameters that are required to characterize the stress levels comprising a randomly-ordered load spectrum. Different stress ratios (${\sigma}_{min}/{\;}{\sigma}_{max}$) are handled with Goodman correction approach(fatigue envelope) and the residual strength after an arbitrary load cycles is represented by two parameter weibull functions.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.26 no.5
• /
• pp.1-10
• /
• 2022

For Cu-Cr alloy developed for rocket engines, estimated fatigue lives were calculated using various fatigue life prediction methods and compared with fatigue life acquired from low-cycle fatigue tests. The utilized methods for fatigue life prediction are as follows: Coffin-Manson relation, plastic/total strain energy density relations, Smith-Watson-Topper relation, Tomkins relation, and Jahed-Varvani relation. As results of estimation of fatigue lives, it satisfied within scatter band two compared to the test fatigue lives in all methods. The quantitative calculation of the deviation of predicted fatigue lives gives that the total strain energy density relation presents the best result.

• Journal of the Korean Society of Safety
• /
• v.15 no.4
• /
• pp.163-169
• /
• 2000

This paper mainly deals with fatigue lift estimation and prediction in notched structures. The fatigue crack initiation life and the fatigue crack growth behavior in the DEN specimens were predicted using S.I.F. K solution derived in this study and the Paris' crack growth equation. Predicted results showed good agreement with experimental crack growth behaviors under constant-load-amplitude.

• Journal of Navigation and Port Research
• /
• v.29 no.10 s.106
• /
• pp.871-876
• /
• 2005

Application of semiconductor sensors has been widely spreaded into various industries because those have several merits like easy miniaturization and batch production comparison with previous mechanical sensors. But external conditions such as thermal and repetitive load have a bad effect on sensors's lifetime. Especially, this paper was focused on fatigue life of a interconnect made by various materials. Firstly we implemented the stress analysis for interconnect under thermal load and wording pressure. And the fatigue lifetime of each material was induced by Manson & Coffin Equation using the plastic stress-strain curve obtained by the plastic-elastic Finite Element Analysis. The Fatigue lifetime in its bottom is smaller than others and bending load have not an effect on the fatigue lifetime of the interconnect but the stress distribution.

• Composites Research
• /
• v.16 no.6
• /
• pp.48-55
• /
• 2003

This research makes comparisons of empirical fatigue-lives between AC8A A1 alloy and the metal matrix composites(A1/A12O3, A1/A12O3/A12O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, AE method to predict fatigue-crack initiation before visible in sight and SEM(scanning electron microscope) photographs of each material. According to the test results of the notched specimen. the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

• Journal of Aerospace System Engineering
• /
• v.14 no.spc
• /
• pp.22-30
• /
• 2020

Composite rotor blades for rotorcraft have an intrinsic vulnerability to foreign object impact from its inherent structural characteristics of insufficient strength in the thickness direction, which may easily lead to internal structure damage. Therefore, defects and strength reducing effects caused by foreign object impact should be considered in fatigue evaluation of composite blades. For this purpose, the flaw tolerant safe-life and fail-safe concepts were adopted in fatigue evaluation since 1980s, and recently those concepts have been replaced by the damage tolerance concept. In this paper, the relevant standards for fatigue evaluation are analyzed focusing on fiber reinforced composite rotor blades used in rotorcraft. In addition, fatigue evaluation procedure of composite blades considering impact damages is proposed by reviewing the practices implemented through domestic development projects.