Environmental effects on the durability of advanced composite materials

先进的复合材料部件是通过将树脂浸渍纤维层层堆叠并在高温高压下固化而制成的。由于层的数量和方向是设计变量，零件和材料是同时设计的。复合材料为制造商制造高性能、耐腐蚀、轻质结构提供了新的可能性，但由于其降解和失效机制的不确定性，复合材料尚未充分发挥其在结构中的潜力。研究是至关重要的，以支持数十亿美元的复合材料工业的发展。拟议研究计划的总体目标是全面了解复合材料的水分降解，并预测其在现实世界应用中对结构完整性的长期影响。了解复合材料的劣化对于确保对目前使用的老化结构进行适当的检查和维护以及在未来的设计中采用最好的方法是很重要的。我们在之前的工作中研究了湿降解的一些方面，如吸湿机理、湿对环氧树脂性能的影响以及湿对复合材料分层生长的影响。必须探索更多的途径，以充分了解复合材料暴露于潮湿环境中的渐进损伤。在使用中，钝器（如掉落的工具）的低速撞击会对层压复合材料造成内部损伤，从表面上看不出来。随后的加载可能导致损伤增长，导致分层，这可能会在不被发现的情况下进行，直到结构完全失效。已经提出了一些模型来预测低速冲击引起的损伤，但是冲击和水分暴露的综合影响，以及它们对复合材料结构的剩余强度和寿命的影响仍未得到充分的研究。在这个项目中，将开发一种方法来理解和预测湿复合材料的冲击损伤形成和增长。冲击损伤可能包括纤维断裂、基体开裂和/或纤维基体脱粘。水分通过改变基体和纤维-基体界面，可以改变断裂过程，并对复合材料的损伤容限产生不利影响。冲击损坏将通过彻底检查实验室生产的损坏样品来检查。将对失效标准进行评估，以确定哪一种更能预测损伤的发生和发展。它旨在将损伤力学、破坏准则和断裂力学结合在数值模型中，模拟从冲击到最终断裂的完整复合破坏过程，并包含水分效应。这项研究的结果将有利于航空航天工业，为复合材料的损伤容忍哲学的实施铺平道路。

Advanced composite parts are fabricated by stacking plies of resin-impregnated fibres and curing under high temperature and pressure. Since the number and orientation of the plies are design variables, the part and the material are being designed simultaneously. Composites offer new possibilities to manufacturers to fabricate high performance, corrosion resistant, lightweight structures, but they have not yet reached their full potential in structures due to lingering uncertainty about their degradation and failure mechanisms. Research is paramount to support the development of the multi-billion dollar composite industry. The overall objective of the proposed research program is to develop a comprehensive understanding of the moisture degradation of composites and to predict its long-term effects on the integrity of structures in real world applications. Understanding the deterioration of composites is important to ensure proper inspection and maintenance of aging structures currently in service and to adopt the best possible methodologies in future design. Some aspects of moisture degradation have been investigated in our previous work such as the mechanics of moisture absorption, moisture effects on the properties of epoxy, and moisture effects on delamination growth in composites. More avenues must be explored to fully understand progressive damage in composites exposed to wet environments. In service, low-velocity impacts from blunt objects, like a dropped tool, can create internal damage to a laminated composite that is invisible from the surface. Subsequent loading can cause damage growth leading to delamination, which may progress undetected until complete failure of a structure. Models have been proposed to predict damage induced by low-velocity impact but the combined effects of impact and moisture exposure, and their consequences on the residual strength and life of a composite structure remain vastly unexplored. In this program, a methodology will be developed to understand and predict impact damage formation and growth in wet composites. Impact damage may involve fibre breakage, matrix cracking and/or fibre-matrix debonding. Moisture, by altering the matrix and the fiber-matrix interface, may change the fracture process and adversely affect the damage tolerance of a composite. Impact damage will be examined by thorough inspection of laboratory produced damaged samples. Failure criteria will be evaluated to determine which ones better predict damage initiation and progression. It is intended to combine damage mechanics, failure criteria and fracture mechanics in numerical models that will simulate the complete composite failure process from impact to final fracture with the inclusion of moisture effects. The results of this research will benefit the aerospace industry by paving the way to the implementation of a damage tolerance philosophy to composites.