Simulation of the drop impact test for moulded thermoplastic containers

An analysis is made of the drop impact test for moulded plastics containers, as a first step towards the simulation of the impact event for design and development purposes. Experimental data are analysed from instrumented base drop impact testing of water-filled blow-moulded bottles, 20 and 210 l drums. Each type of container is found to exhibit a characteristic pulse time for the internal pressure during impact. Analysis shows that the observed behaviour of the flexible container/water-filled system is normally best described in terms of solid body dynamics, rather than an approach based on water hammer concepts. A simple equivalent mass–spring model is developed which predicts the characteristic pulse time and pressure distribution on the walls of the vessel throughout the impact test. It is shown that this model should be applied when the length of the vessel does not exceed a critical length. An expression for determining this critical length is given. Loads and loading rates predicted by the mass–spring model can be used as input to a simplified FEM simulation of the drop impact test on any vessel.