Abstract
The effect of stitch density (SD) on fatigue life, stiffness degradation and fatigue damage mechanisms in carbon/epoxy (T800SC/XNRH6813) stitched using Vectran thread is presented in this paper. Moderately stitched composite (SD = 0.028/mm(2); 'stitched 6 x 6') and densely stitched composite (SD = 0.111/mm(2); 'stitched 3 x 3') are tested and compared with composite without stitch thread (SD = 0.0; 'unstitched'). The experiments show that the fatigue life of stitched 3 x 3 is moderately better than that of unstitched and stitched 6 x 6. Stitched 3 x 3 pattern is also able to postpone the stiffness degradation onset. The improvement of fatigue properties and postponement of stiffness degradation onset in stitched 3 x 3 is primarily due to an effective impediment of edge-delamination. Quantification of damage at various cycles and stress levels shows that stitch density primarily affects the growth rate of delamination. (C) 2014 Elsevier Ltd. All rights reserved.