The fracture toughness of a glass chopped-strand-mat/polyester-resin laminate

Abstract

Measurements of the critical strain energy release rate G_c and the critical crack tip stress intensity factor K_c have been made on chopped-strand-mat/polyester-resin laminates using centre-notched specimens of constant width and varying initial crack length. In the determination of G_c allowance was made for irrecoverable energy due to progressive damage. The G_c values were converted to K_c values using the relationship K_c²=EG_c, where E is the initial modulus of the material. The direct determination of K_c gave lower values. However, when Irwin's plastic-zone correction factor for metals was applied, using the resin cracking stress as an equivalent yield stress, the corrected values compared well with those obtained from the G_c values. All the results showed a variation of K_c with initial crack length.