Micro Mechanical Study on Fatigue Damage Mechanism of Composite Materials

开发了复合材料层合板在循环荷载作用下损伤累积的计算机辅助测试系统。应力-应变图中的刚度降低和能量假设作为循环数的函数进行监测。得到了玻璃、碳、芳纶及其混杂纤维增强塑料疲劳损伤刚度退化的主曲线。讨论了混合效应和设计准则。对单向、交叉层合和准各向同性碳环氧复合材料层合板进行了静态和疲劳试验，讨论了层合板的S-N图和刚度退化曲线，并特别考虑了分层和基体裂纹的扩展行为。基于断裂力学方法的循环荷载下的分层生长模型。用能量释放率测量分层时的应力和应变浓度。基于能量释放率的模型很好地解释了弹性模量对疲劳强度的影响。为了准确测量疲劳分层扩展行为，在恒裂纹剪切位移速率下进行了端缺口弯曲（ENF）试验。得到了II型能量释放速率与分层生长速率之间的幂原始关系。

Computer aided testing system was developed for measuring damage accumulation of composite laminates under cyclic load. Stiffness reduction and energy assumption in the stress versus strain diagram are monitored as a function of cycle numbers. A master curve of stiffness degradation of fatigue damage is obtained for glass, carbon, aramid and their hybrid fibers reinforced plastic. Hybrid effect and design criteria were discussed.Static and fatigue tests were carried out for unidirectional, cross plied and quasi-isotropic carbonepoxy composite laminates, and their S-N diagrams and stiffness degradation curves were discussed with special consideration on propagation behavior of delamination and matrix cracks.A model of delamination growth model under cyclic load based on the fracture mechanics approach. Stress and strain concentration at delamination was measured by energy release rate. Effect of elastic moduli on fatigue strength was well explained by the model based on the energy release rate. In order to measure the accurate behavior of fatigue delamination growth, end notched flexur (ENF) test was carried out under constant crack shear displacement rate. A power raw relation between mode II energy release rate and delamination growth rate was obtained.