Mode I delamination propagation and R-ratio effects in woven composite DCB specimens for a multi-directional layup

In this paper, a method is proposed for evaluating the delamination growth rate da/dN for any given R-ratio (load or displacement ratio) using data from a relatively small number of tests. To this end, double cantilever beam (DCB) specimens fabricated from a plain woven prepreg (G0814/913) arranged in a multi-directional (MD) layup were tested. First, quasi-static tests were carried out to obtain the resistance G(IR)-curve. Then, constant amplitude fatigue tests were preformed to determine the delamination growth rate da/dN. In both tests, displacement control was imposed. Four different cyclic displacement ratios R-d, namely 0.1, 0.33, 0.5 and 0.75, were used for the fatigue tests. When the delamination growth rate da/dN, calculated from the experimental data, was plotted with respect to gm,,c and Delta G(Ieff) = (root GImax - root GImin)(2), different behavior of the da/dN curves was observed. In addition, modification of the Hartman-Schijve representation was made. When the da/dN data was plotted with respect to the new modified representation which was denoted here as Delta K-1 all of the data obtained for different displacement ratios collapsed into one master curve. From this master curve, da/dN values may be calculated for any given R-ratio. (C) 2016 Elsevier Ltd. All rights reserved.