Energy absorption evaluation and design at the ballistic level in composites

Abstract

The research presented in this thesis is directed towards the evaluation and understanding of a range of composite materials impacted at a ballistic level under both normal and oblique orientations, and the development of a novel recycled composite material with enhanced ballistic performance. It compares the ballistic performance of normal and oblique impacts of metallic and composite materials, describes the development, production and testing of a novel recycled composite material, and the performance of a Kolsky experiment on this novel material.

For the Certification Authorities within the Aerospace Industry, the effects of angled impacts onto composites have not been addressed to the same extent as normal impacts, primarily because perpendicular impacts are largely considered to be the worst case scenarios. However, this research highlights certain aspects within the behaviour of composite materials in which that assumption may be too simplistic.

Composites offer many advantages in ballistic protection but they are still relatively expensive and once damaged the ‘used’ material is usually discarded in secure landfill or burnt, and new pristine protective panels are required in their place. The development of a new recycled composite material could potentially therefore reduce costs, for example, if employed in partly replacing current battle-damaged polymeric armour panels used in the protection of air/land/sea vehicles, equipment and buildings.

Further insight has been gained through the implementation of a Kolsky bar impact test based on a Hopkinson bar methodology, which has been modified to encompass a Taylor impact type concept. In this test, a polymeric specimen is fired against an instrumented steel bar, which measures the strain generated during the impact event, and the process of material deformation and disintegration is captured on video for subsequent analysis. Tests have been carried out on Aluminium, pristine cylindrical and cuboid Dyneema® specimens and also recycled cylindrical Dyneema® specimens.