| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 99 === This thesis aims to investigate the effects of two-stage fatigue loading adjustment on the dynamical reliability of composite laminates. The major achievements can be divided into four parts. First, the proposed reliability-dependent hazard rate function h(R)=eo+c(1-R)^p named the (eocp) model is verified to be useful for describing the dynamical reliability of composites under constant-amplitude cyclic stress. A large amount of simulated fatigue data are generated to study the characteristics of the (eocp) model for composites subjected to fatigue loading adjustment. Secondly, based on the strength-life equal rank assumption, two parameters, the transition period and reliability drop, are defined to depict the effects of high-low and low-high adjustment, respectively, on the reliability degradation of composites. Thirdly, the application of the (eocp) model for single-stage fatigue loading is extended to two-stage cases, using a piecewise combination with transition period or reliability drop to show the whole picture of dynamical reliability. The linear damage sum is examined and found to be larger than unity for high-low loading, and on the contrary for low-high cases. Bigger the difference between the high and low level stresses results in the larger deviation from unity. Finally, another reliability-dependent hazard rate function h(R)=eg+u(-lnR)^q named generalized Gompertz model is proposed. The proposed model, with the intrinsic weakness parameter eg denoting the initial hazard rate of material under loading, has greater physical meaning than does the Weibull-type hazard rate function. Furthermore, the proposed model could be more flexible in describing the dynamical reliability than the Weibull function.
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