On the Method of Determination of Strain Energy Release Rate During Fatigue Delamination in Composite Materials

Abstract

In this paper, the problem of calculation of the energy release rate for a fatigue test on composite material has been investigated. The application of the Linear Elastic Failure Mechanics (LEFM) leads to the use of varation of the energy release rate (Δ G). As the energy release rate is a function of the load squared, the variation of G becomes either a function of variation of the load squared (Δ G = f(Δ(P2))) or a function of the square of the load variation (Δ G = f((Δ P)2)). In this paper, we determine, by different fatigue tests, which of the two theoretical results is the best to describe the experiments. These fatigue tests have been made on DCB test-specimen in mode I with different R ratios (R = Pmax / Pmin) and different maximum loads. The material was a unidirectionnal glass-epoxy. The results show that considering Δ G as a function of (Δ P)2 $$(\Delta G = \frac{1}{2}(P_{\max } - P_{\min } )^2 \frac{{\partial C}}{{\partial A}} = \frac{1}{2}(P_{\max }^2 (1 - R)^2 \frac{{\partial C}}{{\partial A}}$$ seems more appropriated to describe a cracking test in fatigue.