A New Failure Criterion for Woven-Roving Fibrous Composites Subjected to Tension-Compression Local Plane Stresses With Different Stress Ratios

Thin-walled tubular specimens, made from woven-roving glass fiber-reinforced polyester (GFRP) with two fiber orientations, $[±45°]2s$ and $[0,90°]2s,$ were tested under torsional fatigue tests at negative stress ratios $R,$$R=−1,$$−0.75,$$−0.5,$$−0.25,$ 0. The mean-amplitude diagram of the $[0,90°]2s$ specimens was found to be divided into two regions; region (1) in which the mean stress is ineffective and region (2) in which the mean stress has a detrimental effect on the amplitude component. All examined failure criteria were found to be valid for the $[0,90°]2s$ specimens, without any modifications; using the amplitude component and the corresponding fatigue strength in region (1), and the equivalent static stress with the corresponding static strength in region (2). For the $[±45]2s$ specimens, having the mean stress being effective in the whole mean-amplitude diagram, the equivalent static stress was used with the corresponding static strength in different failure criteria. None of the available criteria succeeded in predicting failure for the studied case; consequently, was introduced, which a new modifying term $SWT2/F1sF1f$ was introduced, which made Norris-Distortional, Tsai-Hahn, and Tsai-Hill criteria suitable for this case.