Ultra-high molecular weight polyethylene (UHMWPE) fibre reinforced composite materials are widely used in ballistic impact and collision scenarios due to their extremely high specific strength and stiffness. Exceptional levels of protection are provided by controlling the damage and deformation mechanisms over several length scales. In this study, the role of UHMWPE fibre architecture (cross-ply, quasi-isotropic and rotational “helicoidal” layups) is considered on the damage and deformation mechanisms arising from low velocity impacts with 150 J impact energy and clamped boundary conditions. Dyneema® panels approximately 2.2 mm thick were impacted with a fully instrumented hemi-spherical impactor at velocities of 3.38 m/s. Full field deformation of the panels was captured through digital image correlation (DIC). The results indicate that the cross-ply laminate [0°/90°] had the largest back face deflection, whilst quasi-isotropic architectures restricted and reduced the central deflection by an average of 43%. In the case of the [0°/90°] panel, the deformation mechanisms were dominated by large amounts of in-plane shear with limited load transfer from primary fibres. Conversely, the failure of the quasi-isotropic panels were dominated by large amounts of panel buckling over various length scales. The observed mechanisms of deformation with increasing length scale were; through thickness fibre compression, fibre micro-buckling, fibre re-orientation with large matrix deformation, lamina kink band formation, and laminate buckling. The helicoidal panels showed that bend-twist and extension-twist coupling were important factors in controlling clamped boundary conditions and the laminate buckling/wrinkling shape. Further examination of the impact zone indicated that the damage mechanisms appear to be fibre orientation dependent, with quasi-isotropic laminates having up to 37.5% smaller impact damage zones compared with [0°/90°]. The experimental observations highlight the importance of fibre orientation in controlling the deformation mechanisms under dynamic impact, in particular limiting the shear deformation of Dyneema® panels.
- Digital image Correlation
- Drop weight