Study on the Non-Liner Stress-Strain Relation and Progressive Damage of Plain Woven GFRP under Tension/Tension Biaxial Loading

摘要

Combined normal stresses (σ_1 and σ_2) were applied to tubular specimens normal and parallel to the material axes. In all cases, acoustic emissions (AE) were measured in details for distinguishing damage accumulation. The S-S relationships in both directions were not strongly affected by a biaxial stress ratio, α (= σ_1/σ_2) in comparison with the S-S relationships under tension/shear biaxial loading since the load was primarily sustained by fibers under tension/tension biaxial loading in the material axes. The S-S curves in both direction are represented by two straight lines intersecting with each other at their knee points while the secondary knee does not appear as soon as the first knee has been observed except at α= 1/1. Consequently, the initial yield stress condition is represented by two lines parallel to either σ_1 or σ_2 axes. They are drawn based on the knee stresses at α=1/0 and 0/1. The maximum stress theory fits the experimental failure envelope better than the Tsai-Wu failure criterion.