Creep response of woven-fibre composites and the effect of stitching

This paper presents an investigation of the tensile creep behaviour of woven;fibre composites stitched with cotton and carbon threads along or perpendicular to the lending direction. Creep tests were conducted at ambient temperature with low to medium stress levels. It has been found that through-thickness stitching can significantly improve the creep resistance of composites, provided the stitches are aligned in the direction of loading. At a given time, the stress level required to induce the same amount creep strain in stitched composites was about twice that for unstitched composites. The creep data were analysed by using the Findley equation and the time-hardening exponent was found to remain approximately constant, while the amplitude of transient creep strain varied with both stress levels and stitching methods. (C) 1997 Elsevier Science Limited.