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

Abstract 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 G Imax and Δ G Ieff = ( G Imax - G Imin ) 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 Δ K ‾ I , 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.