Flexural properties of stitched GRP laminates

The flexural properties (elastic moduli, yield strength and maximum strength) and flexural failure processes of GRP laminates reinforced through-the-thickness with Kevlar(R)-49 stitches were studied under four-point bending at strain rates between about 10(-6) and 3 x 10(-2) s(-1). The flexural properties of the non-stitched laminate were larger than the stitched laminates over the range of strain rates studied. Scanning electron microscopy revealed that some of the failure processes in the non-stitched laminate differed from those of the stitched laminates, which occurred at lower flexural stresses. It appears that the lower flexural properties of the stitched laminates result from damage caused by stitching as well as by the stitches being stress concentration sites during bending. (C) 1996 Elsevier Science Limited