Effect of Loading Path on Mechanical Response of a Glass Fabric Composite at Low Cyclic Fatigue under Tension/Torsion Biaxial Loading

Abstract

The present paper shows how loading path affects the low cyclic fatigue failure of a glass fabric/vinylester resin composite. The focus is placed on the stress-strain response both in tension and shear as well as on the fatigue life under tension/torsion biaxial loading at low cycle fatigue up to 10,000 cycles. Three types of loading paths were applied: Type I-Biaxial loads were applied proportionally to the specimens. Namely the resultant stresses, tensile and shear stresses increased simultaneously. Type II-A tensile load was first applied. Then, a torsion moment was applied to attain a (biaxial stress ratio) = 3/1 while the tensile load was kept constant. The applied loads were removed in the reverse order. Type Il I-Contrary to Type II loading, first a torsion moment was applied. Then, a tensile load was applied to attain a L = 3/1 while the torsional moment was kept constant. The maximum stress states in the laminate during each loading period are the same for all loading cases. The experimental results revealed that: (1) No significant effect of loading path on the fatigue life exists. (2) The modulus decay in shear with respect to the number of loading cycles is affected by loading path while the modulus decay in tension was not significantly affected. (3) There exist peculiar responses in stress-strain relations both in tension and shear when loading path is changed although the final strain state is almost the same in all loading cases as long as the internal damage is not much accumulated. A model for explaining the peculiar stress-strain behaviors was proposed based on the Continuum Damage Mechanics (CDM) in conjunction with the lamination theory. The calculated stress-strain responses reasonably agree with the experimental stress-strain behaviors under biaxial loadings having different loading paths.