Experimental study on the effect of stitch arrangement on mechanical performance of GFRP laminates manufactured on a basis of stitched preforms

Abstract

This article presents the results of interlaminar shear and flexural tests of stitched polyester glass fiber laminates in dependence on stitch density and main geometric stitching parameters: stitch length and stitch spacing. Purpose of the study is to work out guidelines and indications for manufacturers of composite laminates who use or who plan to use stitching technique. It was found that stitching significantly improves interlaminar shear strength which increases with stitch density. However, stitching causes deterioration of in-plane flexural properties – the deterioration progresses when stitch density increases. Obtained results indicate that it is better to achieve increase in stitch density (resulting in improvement of interlaminar shear strength) by reduction of stitch length than by reduction of stitch spacing. Stitched laminate shows higher flexural strength and flexural modulus when bent into direction parallel to the stitch lines than when bent into the transverse direction. The results obtained within the study and their approximation constants may be a base for a new theoretical model simulating behavior of stitched laminate during static bending and enabling prediction of its mechanical performance.