Effect of High Strain Rates on Notch Sensitivity in Composite Materials

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.