Damage tolerance of a stitched carbon/epoxy laminate

Polymer composite laminates are prone to delamination when impacted. This behaviour generally results in a low damage tolerance, which is of great concern for load carrying applications. The possibility of improving the low velocity and ballistic impact damage tolerances of a carbon fibre brittle epoxy laminate by stitching has been investigated by determination of damage width, compression strength and other properties after falling weight and ballistic impact. The damage tolerance of the stitched laminate was found to be much better than that of a prepreg laminate with a brittle epoxy matrix (914C), better than that of a laminate with a toughened epoxy matrix (6376C) and about equal to that of a laminate with a very tough thermoplastic matrix (APC-2). The compression strength after a 45 J low velocity impact of a quasi-isotropic laminate 3 mm thick was 150 MPa for the 914C laminate and 270 MPa for the stitched laminate. In the ballistic case compression strength was increased by about 50% for near quasi-isotropic laminates of thickness 5 mm. (C) 1997 Elsevier Science Limited.