Puay Joo Tan

Inertia effects in uniaxial dynamic compression of a closed cell aluminium alloy foam

Abstract The dynamic compressive characteristics of a closed cell aluminium alloy foam (manufactured by Hydro Aluminium AS, Norway) have been studied experimentally by using a direct impact technique for a range of velocities up to 210 m s–1. Experimental data on the dynamic initial crushing and plateau stresses are compared for two average cell sizes of approximately 4 and 14 mm. The data reveal significant dynamic enhancements of the initial crushing strengths throughout the range of velocities used. The dynamic plateau stresses are insensitive to impact velocity below the values of 50 and 100 m s–1 for the large and small cell foams respectively. Beyond a critical velocity value of ~ 100 m s–1, the crushing wave front propagates through the foam with shock like characteristics. The inertia effects associated with the dynamic localisation of crushing and the microinertia of the cell wall/edge material on the dynamic strength enhancement are discussed. A one-dimensional shock model based on a rate independent, rigid, perfectly plastic locking idealisation of the nominal stress–strain curve for foams is employed to provide a first order understanding of the various parameters involved in the crushing process. The results of the analyses are seen to predict well the dynamic strength enhancements that are measured experimentally. The sources of discrepancies are highlighted and discussed, as are the limitations and shortcomings of the shock model.

High‐Rate Compaction of Aluminium Alloy Foams

The response of aluminium foams to impact can be categorised according to the impact velocity. Tests have been carried out at a range of impact velocities from quasi‐static to velocities approaching the speed of sound in the foam. Various experimental arrangements have been employed including pneumatic launcher tests and plate impact experimants at velocities greater than 1000 m s−1. The quasi‐static compression behaviour was approximately elastic, perfectly‐plastic, locking. For static and dynamic compression at low impact velocities the deformation pattern was through the cumulative multiplication of discrete, non‐contiguous crush bands. Selected impact tests are presented here for which the impact velocity is less than the velocity of sound, but above a certain critical impact velocity so that the plastic compression occurs in a shock‐like manner and the specimens deform by progressive cell crushing. Laboratory X‐ray microtomography has been employed to acquire tomographic datasets of aluminium foams b...