Prediction of compression-after-impact (CAI) strength of CFRP laminated composites

In order to predict CAI strength of IM7/8552 composite laminate ([45/-45/0/90]3s), the SoutisFleck model, that mathematically replaces microbuckling/kinking of the 0°-plies with a through-thickness line crack, was used. The model requires a damage area, reduced properties in the damage site and in-plane stress distribution near the damage site. The damage site was modelled as an equivalent hole and a soft inclusion. For the in-plane stress distribution near an open hole or a soft inclusion, a complex variable method was used. The damage area and reduced properties in the damage site predicted from the damage model developed using a simple non-linear approximation method (Rayleigh-Ritz method) in the current study were applied to the Soutis-Fleck model. From the comparison of the theoretical predictions and experimental measurements for CAI strength, it was found that when fibre breakage occurs at certain plies, the equivalent hole model was more suitable for the prediction. The difference between the theoretical and experimental strength results was less than 10%. However the soft inclusion model over-predicted the residual strength by between 37% and 40%.