AbstractThe 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|
|Supervisor||Stephen R Hallett (Supervisor) & Luiz F Kawashita (Supervisor)|