Effect of High Strain Rates on Notch Sensitivity in Composite Materials

1.通过拉伸试验确定带缺口的纤维增强复合材料的应变率敏感性2.发展有限元模拟技术以预测高应变率下的亚临界损伤。观察玻璃纤维增强缺口试件亚临界损伤发展过程。模拟损伤过程，并与准静态试验结果进行比较。为了比较数值计算和实验结果，并研究不同损伤模式的相互作用，几乎所有的飞机结构都需要缺口或孔来进行紧固，进入和减轻重量。这种缺口的存在显著降低了材料的承载能力。这种减少影响所有类型的材料，但在复合材料（如碳纤维增强塑料）中，损伤过程比其他工程材料复杂得多。这是因为复合材料有许多不同的失效方式，因为它是由嵌入基质材料中的纤维层组成的。不同失效机制的相互作用会影响材料的整体强度，特别是当材料中有孔时。在飞机设计中，为了飞机的安全性，有必要确保始终考虑最坏的情况。例如，如果材料在快速加载时较弱，则在设计中必须考虑到这一点，如果可能发生这种加载的话。高速加载确实可以通过与跑道碎片、鸟类或弹道的撞击而发生。虽然高速加载对复合材料的影响已被广泛研究，但当材料中有孔时，对这种加载的影响知之甚少。这项工作的目的是解决知识的不足，以确保设计的安全性。这是通过测试不同的复合材料，有孔和无孔，在各种加载速率，直到非常高的速度，使用专门设计的设备来完成。这将生成有关孔周围发生的情况的有用数据，并更好地了解发生的复杂损坏模式。由于这种测试的成本很高，因此可以预测损坏的计算机模型非常有用。将开发一个模型，该模型将考虑高速加载下的损伤及其相互作用的复杂性。

1. To experimentally determine the strain rate sensitivity of notched, fibre reinforced composites through tensile tests 2. To develop finite element modelling techniques to predict the sub-critical damage at high strain rate 3. To observe the sub-critical damage development in notched glass fibre reinforced specimens 4. To characterise the damage process and compare results to quasi-static tests5. To compare numerical and experimental results and investigate the interaction of different damage modesNotches or holes are required in nearly all aircraft structures for fasteners, access and weight saving. The presence of such notches significantly reduce the load carrying capability of the material. This reduction affects all types of materials but in composites (e.g. carbon fibre reinforced plastic) the damage process is considerably more complex than in other engineering materials. This is because there are many different ways that a composite can fail since it is made up from layers of fibres embedded in a matrix material. The interaction of the different failure mechanisms affects the overall strength of the material, especially when there is a hole in it.In aircraft design it is necessary for the safety of the aircraft to ensure that the worst case is always considered. If for example the material was weaker when it was loaded very quickly then this would have to be taken into account in the design if it was possible that such loading could occur. High speed loading can indeed occur through impact with runway debris, birds or ballistics. Whilst the effect of high speed loading on composite materials has been extensively researched, very little is known about the effect of such loading when there is a hole in the material. This work aims to address that shortfall in knowledge to ensure safety in design.This is to be accomplished by testing different composite materials with and without holes at a variety of loading rates up to very high speed using specially designed equipment. This will generate useful data about what is happening around the hole and a better understanding of the complex damage modes which occur. Because such testing is expensive to carry out, computer models which can predict the damage are very useful. A model will be developed which will take account of the complexities of the damage and their interaction under high speed loading.