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Effect of Cyclic Fatigue Conditions on Nonlinear Dynamic Viscoelasticity and Fatigue Behaviors for Short Glass-Fiber Reinforced Nylon 6

Fatigue behaviors of short glass-fiber reinforced nylon 6 (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 lifetime 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 nylon 6. 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.