Thermomechanical fatigue behavior of CF/PEKK composite under low and ultrasonic frequencies

Abstract

This study aimed to extract the thermomechanical fatigue behavior of a CF/PEKK composite under low and ultrasonic frequency fatigue tests (LFFTs and UFFTs) in the presence of the self-heating effect. Preliminary increasing amplitude tests (IATs) were performed to obtain the minimum load level at which the self-heating is observable. Extracting the fatigue strength from T-σ curves for three mean stress levels resulted in constructing S-N curves for the LFFT regime at different load levels using a shift procedure. However, combining LFFT and UFFT results via S-N curve was impractical, while joining such results through the heat dissipation rate (q̇) was feasible for various constant amplitude tests and IATs. The derived σ-q̇ curves from combining LFFT and UFFT results and comparing the fracture mechanisms of CF/PEKK composite using fractography would make a step for bridging the transition zone between LFFTs and UFFTs and making the results transferable. The microscopy images obtained from fractography also confirmed the similarities of fatigue fracture mechanisms between LFFTs and UFFTs.