Damage Accumulation during Fatigue in Plain-Woven Glass Fabric Reinforced Plastic under Tension/Torsion Biaxial Loading.

Abstract

Damage accumulation In GFRP during tension/torsion biaxial fatigue was studied. Under uniaxial tension and biaxial loadings, longitudinal fibers continuously break from the first cycle to the final failure of the material at low cyclic fatigue. In the case of high cyclic fatigue, a few longitudinal fibers break during a first few cycles. Few longitudinal fibers fail after the first stage of fatigue. Primary types of internal damage at the second stage are debonding and cracking in the matrix. After such damage grows to some extent, longitudinal fibers resume to fail. This fiber breakage leads to the final fracture of the material. In the case that a combined load is applied, longitudinal fibers are not aligned parallel to normal stress due to shear deformation. These misalignment and shear deformation cause a peeling stress at the interface between fibers and matrix. As a result of this peeling stress, debonds propagate more rapidly under biaxial loading than under uniaxial tension or pure shear loading. This mechanism could be a reason for shorter fatigue life under combined loading than that under uniaxial tension and pure shear loadings.