Effect of laminate thickness and of matrix resin on the impact of low fibre-volume, woven roving E-glass composites

Instrumented falling weight tests led to the definition of three behaviour `regimesʹ; `undamagedʹ, `internal delaminationʹ and `severeʹ (at low, medium and high incident energies, respectively). The reduction in stiffness due to the internal delamination gave a bi-linear force–deflection relationship. A shear-dominated theory and an energy balance approach gave the relationship between incident energy and maximum force. By considering deviations from this model the complex impact behaviour seen was related to the damage modes observed. At low incident energies bending was significant for all except for the thickest polyester laminates. Delaminated behaviour was shear-dominated for all except the thinnest laminates. At higher incident energies back-face fibre damage controlled behaviour before membrane effects became significant for thinner laminates, and indentation damage of thicker laminates became influential. Subtle differences between the damage modes of the epoxy and polyester laminates were seen; the epoxy laminates suffered more back-face fibre damage, but less internal delamination.