Low-velocity impact response of injection-moulded polypropylene plates - Part 1: Effects of plate thickness, impact velocity and temperature

The low-velocity, low-energy impact response of a mineral and elastomer modified polypropylene was characterised by instrumented falling-weight impact testing of plates with annular clamping. Different loading conditions were assessed by varying plate thickness (2-4 mm), incident impact velocity/energy (up to 4.4 ms−1/34 J) and temperature (−60 to 20 °C). Force-deflection curves and fracture patterns were categorised and analysed. The main trends can be explained in terms of 1) deformations spanning from small-strain bending to large-strain stretching, 2) fracture responses spanning from linear-elastic brittle to highly ductile, 3) process-induced anisotropy, and 4) friction effects. With the highest impact velocity used in this study, plates thinner than ∼2.5 mm fractured at both −30 and 20 °C, although with different mechanisms. A remarkable finding was that the central radial crack under the striker ran parallel to the (injection moulding) flow direction for the most brittle fractures (at low temperatures), while it ran perpendicular to the flow direction in other cases.