Impact characterisation of low fibre-volume glass reinforced polyester circular laminated plates

Drop-weight impact tests have been carried out for low fibre-volume glass-polyester laminates for a range of diameter to thickness ratios. Three damage stages were defined, ‘un-delaminated’, ‘delaminated’ and ‘fibre damage’. Analysis of the impact response using a mainly graphical methodology allowed further characterisation of the behaviour. Impact damage occurs in two stages: hidden internal delamination damage at low incident energy, and then finally perforation failure. Bending and membrane effects are significant for thin laminates. For thick laminates shear deflection, delamination and indentation damage are more important. Some form of strain-rate stiffening effects appear to be significant for bending, but not for shear-controlled deflections or when damage is present. Indentation follows the Hertzian contact law at low contact forces, but a linear contact stiffness is seen at higher forces. A fracture mechanics model describes well the onset of delamination, and gives good scaling between specimen sizes. An energy balance approach gives good correlation between impact force and incident energy. Fibre failure leading to penetration is back-face tension controlled. The complex behaviour observed shows that the impact response must be characterised before mathematical modelling might be attempted. Modelling of the un-delaminated behaviour should consider bending, shear, indentation and membrane effects.