J. Barton - EPSRC- EP/G042403/1 -Composite material performance and damage tolerance

The underlying motivation for this research is the scientifically driven need to fully understand the structural performance of polymer composite materials and structures in high-strain rate events. Composite materials are used in land, sea and air vehicles in high performance applications, particularly where speed and manoeuvrability are primary considerations. High strain rate events occur during collision with other objects and in the case of military vehicles when subject to or close to a blast. After experiencing the event the structure may fail completely or it may suffer damage that will reduce its service life, which is sometimes accompanied by sudden unexpected failure. The loss in integrity of the material will therefore increase the risk of serious injury to passengers or third-parties. Furthermore in defence applications the risk of damage to systems and instrumentation is an important key concern that will have a knock-on effect in terms of threat to life. To reduce and mitigate the risk it is essential that the behaviour of the material subject to high velocity deformation is known and the effect on the structural performance is established. This proposal addresses both of these challenges. The material behaviour is a function of the time the event takes and the applied deformation or strain. High velocity deformations are accompanied by a temperature change in the material. The proposal takes all three of these factors (time, strain and temperature) into account and combines two full-field measurement techniques into simultaneous high speed data capture methodology to provide a new means of materials characterisation. The techniques are: Digital Image Correlation (DIC) based on an optical measurement of deformation and Infra-Red Thermography (IRT). Significant innovation will be required to make these techniques suitable for high speed measurement, in terms of illumination, surface preparation and optical access/magnification. A further facet to the work is investigating behaviour after the high velocity deformation event and the subsequent evolution of damage in components that have experienced an event that has not caused failure. In summary the proposed methodology brings together material evaluations at small scale using high resolution techniques that covers the material performance during a high velocity deformation and its performance after the event. The outcome of the work will be a new approach to material and component assessment. The work will provide materials models that can be combined with existing analytical models and therefore establish a underpin residual strength predictions. The methodology will provide a basis for design that enhances damage tolerance, and which links the material properties with the experimentally derived material performance limits. This is of paramount importance, as the purpose of the proposed work is to establish a methodology that can be applied generally and establish a fundamental 'bench-mark' for high velocity material characterisation. The methodology will provide a complete thermomechanical model of the material behaviour and will provide a safer environment in both civil and military applications.