A New Failure Criterion for Woven-roving GFRE Thick Tube Subjected to Combined Fatigue Bending Moments and Internal hydrostatic Pressure

摘要

Choosing the suitable failure criterion represents the main target for many researchers working with materials, and it represents the first step for new materials before being used in the field. Considering composite materials, specifically, makes it more challenging, because of their very special behavior and characteristics. Besides, it must be noted that, the suitability of a certain criterion differs greatly according to the tested material, and its stress state. Thick-walled tubular specimens, made from woven-roving Glass Fiber-Reinforced Epoxy (GFRE) with two fiber orientations, [0°,90°]_(3s) and [±45°]_(3s), and two manufacture methods M_1 and M_2 to prepare the test specimens, were tested under combined fatigue bending and Internal hydrostatic Pressure at different pressure ratios (P_r), P_r = 0, 0.25, 0.5, 0.75 (i.e. pressures amounting to 0%, 25%, 50% and 75% of the burst pressure). The [0°,90°]_(3s) specimens were found to have higher bending strength than the [±45°]_(3s) specimens, at all pressure ratios; This is due to the fiber orientation [0,90°]_(3s) has a minimum value of stress component σ_6 which equal to zero. For both fiber orientations [0°,90°]_(3s) and [±45°]_(3s) and both manufacture methods M_1 and M_2, were found none of the available criteria succeeded in predicting failure for the studied case, this due to the effect of hoop stress on values of amplitude component and the corresponding fatigue strength; consequently. A new modifying term was introduced that made Norris-Distortional, Tsai-Hahn, and Tsai-Hill criteria suitable for this studied case, resulting in a new criterion.