Effect of High Strain Rates on Notch Sensitivity in Composite Materials

1. 通过拉伸试验，实验确定缺口纤维增强复合材料的应变率敏感性。发展有限元建模技术，预测高应变率下的亚临界损伤。观察缺口玻璃纤维增强试样的亚临界损伤发展。表征损伤过程，并将结果与准静态试验进行比较。为了比较数值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用于紧固件、通道和减重。这种缺口的存在大大降低了材料的承载能力。这种减少影响到所有类型的材料，但复合材料（如碳纤维增强塑料）的损伤过程比其他工程材料要复杂得多。这是因为复合材料是由嵌入在基体材料中的纤维层组成的，因此有许多不同的方式可能会失效。不同破坏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，确保总是考虑到最坏的情况对飞机的安全是必要的。例如，如果材料在快速加载时较弱，那么如果这种加载可能发生，则必须在设计中考虑这一点。高速载荷确实可以通过跑道碎片、鸟类或弹道的撞击发生。虽然高速加载对复合材料的影响已经得到了广泛的研究，但对材料中有孔时高速加载的影响知之甚少。这项工作旨在解决知识的不足，以确保设计的安全性。这是通过使用专门设计的设备在各种加载速率下测试不同的复合材料，包括带孔和不带孔，以达到非常高的速度。这将产生有关孔洞周围发生的情况的有用数据，并更好地了解发生的复杂损伤模式。由于进行这种测试的成本很高，因此能够预测损伤的计算机模型非常有用。将建立一个模型，该模型将考虑损伤的复杂性及其在高速载荷下的相互作用。

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.