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This paper details an investigation of the high strain rate compression testing of GFPP with the Split Hopkinson Pressure Bar (SHPB) in the through-thickness and in-plane directions. GFPP posed challenges to SHPB testing as it fails at relatively high stresses, while having relatively low moduli and hence mechanical impedance. The modifications to specimen geometry and incident pulse shaping in order to gather valid test results, where specimen equilibrium was achieved for SHPB tests on GFPP are presented. In addition to conventional SHPB tests to failure, SHPB experiments were designed to achieve specimen equilibration at small strains, which permitted the capture of high strain rate elastic modulus data. The strain rate dependency of GFPP’s failure strengths in the in-plane and through-thickness direction is modelled using a logarithmic law.

Abstract: One-dimensional models for compaction of cellular materials exhibiting strain hardening are proposed for two different impact scenarios. The models reveal the characteristic features of deformation under the condition of decreasing velocity during the impact event. It was established that an unloading plastic wave of strong discontinuity propagates in the foam and it has a significant dynamic effect on the foam compaction and energy absorption. The proposed models are based on the actual experimentally derived stress strain curves. The compaction mechanism in three aluminium based foam materials, two of them with relatively low density – Alporas and Cymat with 9% and 9.3% relative density, respectively and a higher density Cymat foam with 21% relative density, is analysed. Numerical simulations were carried out to verify the proposed models. The predictions of the proposed models are compared with published analytical models of compaction of cellular materials which assume a predefined densification strain. It is shown that the approximation of a cellular material with significant strain hardening by the Rigid Perfectly-Plastic-Locking (RPPL) model can lead to an overestimation of the energy absorption capacity for the observed stroke due to the non-uniform strains along the compacted zone of the actual material in contrast to the predefined constant densification strain in the RPPL model. The assumption of a constant densification strain leads also to an overestimation of the maximum stress, which occurs under impact. [Copyright &y& Elsevier]

Abstract: The response of composite sandwich structures to blast loading has received little attention from researchers when compared to the research performed on their metallic counterparts, despite the fact that composite sandwich panels are becoming more generally used in practice. This paper reports on a preliminary experimental investigation into the response of sandwich panels comprising E-glass fibre reinforced vinyl ester facesheets and closed cell PVC foam cores to localised blast loading. The loading is generated by detonating discs of plastic explosive in close proximity to the panel. Multiple failure modes were exhibited by the panels. A failure progression pattern was identified, with increasing impulse: front facesheet delamination, core compression, back facesheet delamination, fibre fracture, core fragmentation, plastic deformation and debonding of the back facesheet following by complete core penetration. No back facesheet rupture was observed, but this was anticipated as the next failure mode to occur at higher impulse levels. The panels with denser cores exhibited lower levels of damage. Theoretical estimates of midpoint displacement were calculated using an analytical beam model. Simple estimates of the delamination, core compression and fibre fracture energies were also made. The energy partition showed that delamination, core compression and fibre fracture were significant energy absorption modes, and that fibre fracture energies exceeded the core compression and delamination energies at higher impulses. This was particularly evident for the lower density core which provided lower resistance to front facesheet deflection. [Copyright &y& Elsevier]