关键词: 聚合物基复合材料, 纤维增强, 应变率强化, 剩余强度, 变频加载, 统计建模, 疲劳损伤

Abstract:

To address the strain-rate dependence of the mechanical properties in polymer matrix composites， the strain-rate strengthening effect on the static and fatigue properties of such composites is investigated， quantified， and a method for assessing residual strength and fatigue damage of these composites under variable-frequency loading is proposed. Firstly， power-law S-N curve fitting was performed on the fatigue life data with and without static strength respectively， and the loading frequency sensitivity of static strength and fatigue life was analyzed. Besides， the strengthening magnitude of strain rate on material strength was quantified by integrating strain rate strengthening coefficient， which ensured the strain rate consistency of the data for characterizing the mechanical properties of the composite materials. Secondly， a probabilistic residual strength model independent of stress level was derived using the concept of strength reserve， which can predict the strength degradation process at any stress level with only one set of model parameters. Finally， based on the developed model and published data， the residual strength prediction under variable frequency loading was carried out. The results show that the cumulative damage caused by the ascending-frequency and descending-frequency loading are 0.323 and 0.493 respectively， which are less than 5% different from the experimental data， and the prediction results are reliable.

Key words: polymer matrix composites, fiber reinforcement, strain-rate strengthening, residual strength, variable frequency loading, statistical modelling, fatigue damage