Probabilistic Assessment of Fatigue Delamination Growth in Fibre Reinforced Composite Laminates

这个第一个Grant研究项目旨在扩大目前对聚合物纤维增强复合材料在疲劳载荷下的不确定行为的理解。其主要目标是表征和预测分层传播数据中的散射效应，这是复合材料的固有特性。复合材料被用于航空航天、汽车和海军结构的主要承载元件。复合材料具有优异的比刚度和强度，与基于合金的设计解决方案相比，可以减轻结构重量，从而最大限度地提高车辆的有效载荷并减少燃料消耗。复合材料结构单元表现出特殊的破坏模式，具有良好的面内强度，但穿透厚度非常弱，即容易出现分层，即相邻层间断裂。在影响航天结构中复合材料构件的结构失效中，约有60%是由后者造成的。疲劳在承受高振动和循环载荷的旋转部件中尤其重要，例如航空发动机；此外，几乎看不见的损伤导致的分层增长对复合材料机身和翼板来说是一个重大危险。因此，预测疲劳脱层的发生和发展对于评估复合材料结构的使用性能和可靠性至关重要。疲劳状态下的分层扩展模型是复合材料结构损伤容限设计的基石。分层扩展表现出显著的统计离散性，因此损伤容限设计需要估计层间裂纹在两次检查之间达到临界可检测长度的概率，然后最终可以修复或替换有缺陷的结构元件。大多数主要的复合材料结构元件仍然是根据安全寿命标准设计的，即限制允许应变，以便初始缺陷不会增长。因此，设计者采用了很大的安全系数，并有可能通过这里提出的工作大幅减轻重量，其主要目的是更好地了解疲劳行为的可变性。

This First Grant research project aims to expand the current understanding of the uncertain behaviour of polymeric fibre reinforced composites subjected to fatigue loading. The primary goals are characterising and predicting the effect of scatter in delamination propagation data, which is intrinsic to compositesComposite materials are employed in primary load bearing elements of aerospace, automotive and naval structures. The excellent specific stiffness and strength of composites allow reducing the structural weight with respect to alloy based design solutions, thus maximising vehicle payloads and reducing fuel burn. Composite structural elements exhibit peculiar failure modes, having excellent in-plane strength but being extremely weak through-the-thickness, i.e. prone to delaminations, i.e. fracture between contiguous plies. The latter are held responsible for about 60% of structural failures affecting composite elements in aerospace structures. Fatigue is particularly important in rotating components subject to high vibration and cyclic loading, e.g. aero engines; moreover delamination growth from barely visible damages represents a significant hazard for composite fuselage and wing panels. Therefore the prediction of the onset and growth of delaminations due to fatigue is crucial for assessing the operating performance and reliability of composite structures. Modelling the delamination propagation under fatigue represents the corner-stone of a damage tolerance approach to the design of composite structures. Delamination growth exhibits a significant statistical dispersion, so damage tolerance design requires estimating the probability of having interlaminar cracks reaching critical detectable lengths between inspections, following which the defective structural elements can be eventually repaired or substituted. The majority of primary composite structural elements are still designed according to safe-life criteria, i.e. limiting the allowable strains so that initial defects do not grow. Thus designers employ large safety factors, and there is potential for substantial weight savings as a result of the work proposed here, which essentially aims to better understand the variability in fatigue behaviour.