A failure envelope for ±60° filament wound glass fibre reinforced epoxy tubulars

Multiaxial stress tests were performed on filament wound glass fibre reinforced epoxy tubulars and the first failure modes observed and the stress and strain failure envelopes recorded. The tubes were produced by filament winding technique. Specimens were tested under various ratios of axial stress and circumferential stress in a MTS testing system modified to apply the internal pressure. Fourteen stress ratios were tested (hoop stress: axial stress) ranging from 0:1 (pure axial tension), 1:1, 2:1, constrained ends (εA = 0, ≈3.5:1), 4:1, 4.5:1, 5:1, 7:1, 12:1, 1:0 (pure internal pressure), 7:−1, 2:−1, 1:−1 (pure shear) and 0:−1 (pure axial compression). Five specific failure modes were observed: (1) axial failure along a dominant helical crack under axial tension dominated stress ratios. (2) Weepage at the stress ratio of 2:1 and constrained end condition. (3) Local leakage via fluid jets in the range of 4:1 to 5:1. (4) Burst under stress ratios dominated by hoop stress. (5) Axial collapse under compressive axial loads. The resulting failure strain failure envelope was fit using the maximum strain criteria with necessary modifications in the regions of leakage and axial compression. Both of these ranges were found to be fit by linear segments.