The influence of porosity on the interlaminar shear strength of carbon/epoxy and carbon/bismaleimide fabric laminates

The resin system affects the shape and size of voids in composite laminates and the associated fracture parameters. Most work on the effects of voids in the literature deals with carbon/epoxy laminates; little experimental data are available on other resin systems of practical importance. This work aims at comparing the effect of voids on carbon/epoxy and carbon/bismaleimide fabric laminates. Specimens with void contents in the range 0 to 6% were produced from both materials. The void content is correlated to ultrasonic attenuation and microscopic inspection was carried out to analyze the sizes and shapes of the voids. The interlaminar shear strength was measured by the short-beam method described in ASTM D2344 and the adequacy of a fracture criterion to represent the experimental data for both materials is assessed. The influence of voids on the interlaminar shear strength of both materials is compared in terms of the corresponding fracture parameters and the shape and the location of the voids.