Validity of the SWT Parameter for Woven-roving GFRP Subjected to Torsional or Bending Moments

Abstract

The Smith-Watson-Topper (SWT) parameter, when proved to be valid, has allowed a great reduction in the number of tests required to estimate the effect of mean stress on the fatigue life of metals and some composites. If the SWT parameter is found to be valid, then plotting it, instead of the maximum or the amplitude stress component, against the number of cycles to failure tends to plot a single curve regardless of the value of the mean stress. Torsional fatigue tests were performed on thin-walled tubular specimens, made from woven-roving glass fiber-reinforced polyester (GFRP) with two fiber orientations, [45]2s and [0,90]2s, at different negative stress ratios, R 1/4 1, 0.75, 0.5, 0.25, and 0. The validity of the SWT parameter was also checked for similar specimens subjected to bending moments with the same stress ratios. It has been found that the SWT parameter is valid for torsional and bending fatigue loadings for GFRP with [45] and [0,90] fiber orientations, by plotting a single curve versus the number of cycles to failure for all tested stress ratios. This results in a great reduction in time and effort when studying a similar case in future.