| description abstract | 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. | |
