Estimation of Mode I Interlaminar Fracture Toughness of CFRP Laminates by Using Wedge Insert Fracture Test

摘要

A new estimating method for mode I interlaminar fracture toughness of CFRP laminates was proposed with the aim of applying to dynamic fracture test. In this method, a wedge indentor was used to cause mode I interlaminar fracture in a precracked coupon specimen. That is, compressive load, which is convenient to dynamic test, can be used in this method, while tensile load, which is not appropriate to dynamic is necessary for the conventional double cantilever beam test. Finite element analyses and quasi-static experiments were carried out to validate an estimating formula for the mode I energy release rate, which is based on the beam theory and the compliance method. As the result, this method is found to be able to estimate the mode I interlaminar fracture toughness of CFRP laminates and to obtain the same stress field as the one formed in the double cantilever beam specimen. But in this method one has to measure accurately thecrack length at the fracture initiation, which is difficult under high rate loading. Three types of CFRP laminates were tested in order to investigate the effect of the toughness of matrix resin. They are: T300/2500 (Toray) which has standard epoxy matrix resin, IM600/133 (Q-C133, Toho rayon) which has toughened epoxy matrix resin, and HTA/PEEK (Toho rayon) which has thermoplastic matrix resin of high fracture toughness. The experimental results show that the toughness of the matrix resin scarcely affects the estimation of the mode I interlaminar fracture toughness and that the fracture toughness estimated by the present method is comparable to that estimated by the double cantilever beam test.