THE DAMAGE TOLERANCE OF GRP LAMINATES UNDER BIAXIAL PRESTRESS

The damage tolerance of E-Glass reinforced/polyester laminated plates subjected to a low velocity impact while under an in-plane prestress i s investigated. Prior to test, the plates are subjected to either unia xial or biaxial loading by means of a specially designed test rig whic h enables independent tension/tension, tension/compression or compress ion/compression testing in all stress/strain quadrants. Impact tests a re carried out for a single strike energy for a comprehensive range of pre-strains. Absorbed energy, damage area, peak impact loads and the maximum permanent indentation depth are assessed in characterising the resulting damage. It is shown that the shape, orientation and size of the damage zone is strongly influenced by the nature and magnitude of the pre-strain. Impact specimens subject to shear loading give rise t o the largest increase in damage area when compared to unstressed plat es.