Effect of cyclic fatigue conditions on nonlinear dynamic viscoelasticity and fatigue behaviors for short glass-fiber reinforced nylon6

Fatigue behaviors of short glass-fiber reinforced nylon6 (GF/Ny6) under three cyclic fatigue conditions, tension-tension (T-T), tension-compression (T-C) and compression-compression (C-C), were investigated on the basis of nonlinear dynamic viscoelastic analysis. A nonlinear viscoelastic parameter (NVP) was used for quantitative evaluation of nonlinear dynamic viscoelasticity for the (GF/Ny6) during the fatigue process. The magnitude of NVP increased with a decrease in the fatigue under three cyclic fatigue conditions. Under the T-T type cyclic deformation, glass-fibers that lay parallel to the cyclic deformation direction were broken during the fatigue process. After NVP attained a constant magnitude, cracks propagated perpendicularly to the cyclic deformation direction from the glass-fiber ends and ultimately, the (GF/Ny6) was fractured. The stress distribution in the matrix nylon6 became more inhomogeneous due to both glass-fiber breakage and crack propagation, resulting in an increase in NVP. In the case of the C-C type cyclic deformation, debonding at the (glass-fiber/matrix nylon6) interface occurred during the fatigue process, and the magnitude of NVP was strongly related to the progress of interfacial debonding between glass-fibers and the matrix nylon6. Under the T-C type cyclic deformation, the magnitude of NVP increased accompanying crack growth during the tensile deformation process and also, interfacial debonding during the compressive deformation process.