Activation theory for creep of woven composites

Plain woven composites have been found to exhibit significant creep at ambi ent and various elevated temperatures with low to medium stress levels. One effective means to improve the creep resistance of woven composites is to introduce through-thickness stitching. Experiments were conducted using spe cimens stitched with different threads at various densities. The results sh owed that stitching can significantly reduce delamination and hence enhance creep resistance, provided the stitches are aligned in the direction of lo ading. The effectiveness of stitching was found to increase with stitch den sity and thread modulus. To provide an engineering method for correlating t he experimental results, the Findley equation was employed for stage I cree p, Norton's law and the Four Element Model were employed for stage II creep ; good agreement between the experimental data and the models have been obs erved. (C) 1999 Elsevier Science Ltd. All rights reserved.