Damage growth and failure in composites

复合材料在商用飞机结构中越来越大规模的应用意味着我们正在进入一个新的时代。因此，解决与复合材料有关的基本问题的需要比以往任何时候都更加重要。然而，我们仍有许多不了解的地方。如何以一贯准确而又保守的方式预测实际结构的失效，而又不显着和不可接受的保守，目前学术界尚未达成共识。然而，工业界正在设计、制造和认证比铝制飞机更轻的飞机。理想情况下，学术方面的基本发展将使我们能够提供与断裂力学和塑性理论为金属设计和分析提供的共识和开放知识支持相同水平的工业设计和分析。我们无法制定适当的失效标准的一个主要原因是很难用小样本复制大型结构的失效。因此，在这个项目中，我们将开发和使用一系列测试几何形状，涵盖一系列特征和尺寸，以表征纤维增强聚合物基复合材料层压板在拉伸、压缩和横向冲击下的失效。使用两种或两种以上的材料类型和一系列的铺层来触发不同的失效事件和序列，我们将跟踪损伤的演变和随之而来的机械响应。利用这些信息，我们将创建一个框架，根据损伤增长的驱动力和损伤对材料刚度的影响来解释损伤历史的演变。我们将确保描述在广泛的几何和材料条件下是一致的。这种结构材料表征的结果将用于在其他程序下开发的数值损伤模型，最终目的是为设计师提供有效和有效的设计工具，以及有效和准确表征材料的标准方法。

The increasingly large scale use of composite materials in commercial aircraft structures means that we are now entering a new era. Therefore, the need to solve fundamental problems relating to composite materials is now even more important than ever before. However, there is much that we still do not understand. There is currently no consensus agreement in the academic world on how to predict failure in realistic structures in a consistently accurate yet conservative manner, without being significantly and unacceptably conservative. And yet industry is designing, building and certifying aircraft that are lighter than their aluminum predecessors. Ideally, fundamental developments on the academic side would allow us to provide such industrial design and analysis with the same level of consensus and open knowledge support as provided for metals design and analysis with fracture mechanics and plasticity theory. One major reason that we have been unable to develop proper failure criteria is that it has been very difficult to replicate failure in large structures using small specimens. Therefore, in this program we will be developing and using a family of test geometries spanning a range of features and sizes needed to characterize the failure of fibre reinforced polymer matrix composite laminates in tension, compression and tranverse impact. Using two or more material types and a range of lay-ups to trigger different failure events and sequences, we will be tracking the evolution of damage and the consequent mechanical response. Using this information, we will create a framework to explain the evolution of the damage history in terms of the driving force for damage growth and the effect of that damage on the stiffness of the material. We will ensure that the description is consistent across a wide range of geometrical and material conditions. The results from this structured materials characterization will be used to exercise numerical damage models developed under other programs, with the final intention being to provide designers with efficient and valid design tools, as well as standard methods to characterize materials efficiently and accurately.