Influence of matrix ductility on the high-temperature fatigue behavior of off-axis woven-ply thermoplastic and thermoset laminates

Abstract

This work was aimed at comparing the influence of ductility on the off-axis tension–tension fatigue behavior of woven-ply TP- and TS-based laminates at a test temperature T such as: TgC/PPS<T<TgEpoxy. Depending on the matrix nature and test frequency, the results confirm that the polymer matrix ductility is instrumental in ruling the fatigue response of woven-ply PMCs thanks to the presence of matrix-rich regions which proved to play a significant role. The fatigue behavior of TP-based laminates at T>Tg is primarily due to fiber reorientation coming along with matrix plasticization during loading phase, as well as the disorientation of fibers and the matrix viscoelastic response during unloading phase, rather than to fatigue damage accumulation. On the contrary, the fatigue behavior of Epoxy-based laminates at T<Tg is primarily due to fatigue damage which is more extensive at high frequency. The reduction of stress intensities in the matrix due to more or less plasticization may delay the initiation–propagation of matrix cracks, the debonding at the fiber/matrix interface, ultimately resulting in an extension of the fatigue life. Thus, a frequency increase virtually does not influence the fatigue life of C/PPS laminates, whereas it dramatically decreases the fatigue life of Epoxy-based laminates (−100%), because of a more extensive damage and a faster damage growth.