The effect of thickness on the fracture behavior of graphite/bismaleimede laminates with central circular holes

The influence of thickness and hole radius on the fracture strengths of Narmco V 5245C-G40-600 graphite/bismaleimide laminates was studied. Tests were run on 8 ply, 40 ply, and 80 ply quasi-isotropic laminates of stacking sequence [0/ ± 45/90]. Both unnotched and notched laminates were tested. Unnotched strength was found to be inversely proportional to thickness. Notched strengths were compared to three different failure models based on the stress distribution around the hole.

Damage development around the holes was studied using x-ray radiography. In general, the small holes created more damage than the large holes and the thin laminates were more susceptible to damage than the thick laminates. All notched specimens exhibited matrix cracking in the 90° plies around the hole and vertical splitting in the 0° plies at the edge of the hole.