Influence of curved delamination front on toughness of multidirectional DCB specimens

Mode I delamination toughness (GIc) of a laminated composite depends not only on the stacking sequence or indirectly coupling parameter of Dc=D122D11D22, but also on specimen geometrical ratios a0/b and a0/h. In this study, a non-uniformity ratio, β = (GImax − GIavg)/GIavg%, is introduced to take into account the influence of above factors on the energy release rate distribution along the width of double cantilever beam (DCB) specimens simultaneously. Results show that the GIc of multidirectional DCB specimens with 0°//0° crack interface and β < 20% can be predicted by measuring the GIc of the unidirectional plies with an error less than 10%. Moreover, a methodology is proposed to predict the maximum delamination toughness (GImax) of multidirectional DCB specimens from β parameter without performing any experiments. With the present method, the effect of curved thumbnail shape of energy release rate along the delamination front is considered on the available closed-form relations for GI.