| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 101 === The two-stage cumulative bending fatigue behavior of the sandwich beams with glass/polypropylene laminate faces and aluminum foam cores was experimentally studied in this thesis to elucidate the loading sequence effect of the innovative material. The experimental results show that the sums of the cycle ratios of the two stages are larger than unity no matter in the high-to-low or low-to-high loading cases. Furthermore, the sums of the cycle ratios of the two stages in the low-to-high loading cases are higher than those in the high-to-low cases, indicating that the loading sequence effect is significant for this sandwich material. Mine’s rule was found to fail to predict the remaining fatigue lives of the second stages for the linear damage rule cannot explain the loading sequence effect. The damage defined as the decreasing of the specimen stiffness with the cycle ratio was employed in the non-linear damage rule to predict the cumulative fatigue lives. Although the employed stiffness-based non-linear damage rule can describe the loading sequence effect, the difference between the predicted results and the experimental data is still apparent. The residual strengths at two loading levels employed in the two-stage cumulative fatigue tests were also studied in this thesis. Experimental results show that the residual strengths almost remain constant until the cycle ratio reached 0.9, implying that the residual strength is not an appropriate parameter to evaluate the cumulative fatigue lives.
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