Study of fracture toughness evaluation of FRP

Abstract

Using the fibre reinforced plastics (FRP) laminates consisting of glass chopped strand mat and unsaturated polyester resin, experiments were conducted under various conditions in order to determine the fracture toughness for crack instability. Crack growth was judged not by cracking of the resin matrix but by break of the glass fibres. The crack front was considered to be located in the section which was cracked through the 90% of the specimen thickness. Crack extension resistance (R-curves) thus obtained did not significantly vary with specimen thickness and initial crack length, but depended greatly on specimen configurations, compact tension (CT) and centre-cracked tension (CCT) specimens. The R-curve for a CT specimen was steeper than the one for a CCT specimen, which is quite contrary to the tendency for metals. It was deduced that the instability fracture toughness calculated from the maximum load on a load-deflection diagram, Kmax, was scarcely affected by specimen thickness, initial crack length and specimen geometry (i.e. loading configuration), and therefore could be regarded as a material constant of the FRP used.