| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 92 === Many scholars analyzed the complicated cumulative fatigue composite behaviors by different angles, such as simply in terms of fatigue cycles, or in terms of the change of material natures (stiffness, strength…). Clark, et al. modified the power-law shear modulus degradation model and suggested the exponential function can be effectively used instead of power function, and succeed in predicting the fatigue behaviors of sandwich composite. We extend this concept to modify Yang’s residual stiffness degradation model, then prove the validity of predict the residual stiffness and fatigue life of composite.
Composite laminates subject dual-step loading and how to predict the fatigue behaviors accurately, it has been an important subject all the time. However, as long as the effects of loading sequence of composite subjected to fatigue loadings is accounted, the aforementioned fatigue models can predict the fatigue behavior of composite under two-step loading definitely and completely. In this research, a mathematical model of composite laminates under dual stress levels established based on residual stiffness degradation. It is, then, used to investigate the loading sequence effect of Graphite/Epoxy composite laminates under fatigue loadings. Though the equivalent damage model, we can derived the loading sequence theory of residual stiffness degradation model, then co-operate with failure strain criterion, established the fatigue life damage model, and comparing experimental test results in three cumulative damage models.
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