Investigating geometrical and manufacturing effects on the impact performance of UHMWPE composites

Abstract

The need to continually enhance the ballistic performance of UHMWPE composite body armour has prompted numerous investigations into the failure mechanisms of these material systems, and the effects of dimensional and manufacturing parameters on their ballistic performance. Past studies have identified the contribution of the fibres to the laminate impact performance, while relatively little attention has been paid to the role of the matrix and its contribution to the overall energy dissipation. Likewise, while flat laminate panels have been studied extensively, in reality, panels used in impact protection are not necessarily flat, with many possessing single or double curvature. Furthermore, modern processing methods such as drape-forming, used in the fabrication of UHMWPE composite shells such as ballistic-grade helmets, induce the geometrical and manufacturing deformations of curvature and in-plane shear. The effects of these deformations on the ballistic impact performance of UHMWPE composites have, however, not previously been investigated. The two features must therefore be
studied in isolation, in order to gain an understanding of their effects on impact performance.
In this thesis, cohesive elements are implemented into existing numerical tools to model interlaminar contact in flat laminates. The cohesive elements are used to investigate the in-plane and through-thickness dissipation of energy at sub-laminate interfaces under ballistic impact loading, as well as highlighting the contribution of the matrix to overall energy absorption by the laminate. Curved panels are tested under ballistic impact, demonstrating the geometrical effects of curvature on laminate response. In addition, existing numerical tools are shown to require modifications not previously necessary for flat configurations, to capture the impact response of curved laminates. A process is then developed for manufacturing sheared plates that are tested under ballistic impact, demonstrating the effects of in-plane shear deformation on the ballistic performance of UHMWPE composite plates. Finally, it is shown that current manufacturing standards are unsuitable for promoting uniform impact
performance across the surface of doubly-curved components.

Date of Award	23 Jun 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Stephen R Hallett (Supervisor) & Luiz F Kawashita (Supervisor)