Influence of fiber orientation on self-heating during fatigue of polymer matrix composites under low and ultrasonic cyclic frequencies

Abstract

This work compares self-heating and its influence on fatigue strength and life of a quasi-isotropic CF-PAEK laminate with that of an orthotropic CF-PEKK laminate using thermographic approaches at low ( ≤ 40 Hz) and ultrasonic frequencies ( ≈ 20 kHz). The fatigue strengths were found to be approximately 47.9 MPa for CF-PAEK and 50.0 MPa for CF-PEKK at a low frequency of 40 Hz. At a cyclic frequency of 20 kHz, fatigue strength decreased by approximately 12% and 16%, respectively, reaching a value of 42 MPa for the CF-PAEK and CF-PEKK laminates. The total heat dissipation rates escalated from an order of magnitude of 10 5 J m − 3 s −1 at low to about 1 0 6 J m − 3 s − 1 at ultrasonic frequencies. A critical aspect of this work is the separation of damage-related heat dissipation rate from reversible internal friction in order to use it as a reliable physical indicator to characterize self-heating in polymer matrix composites (PMCs). The damage-related heat dissipation rate was higher for the CF-PAEK laminate under low frequency cyclic loading, leading to shorter fatigue lives in the high-cycle fatigue regime. In the very high-cycle fatigue regime, comparable damage-related heat dissipation rates between CF-PAEK and CF-PEKK laminates lead to comparable fatigue lives. These results, alongside literature data on the self-heating of PMCs with different fiber orientations, show that a major portion of the self-heating temperature rise associated with high heat-dissipation rates for off-axis fiber orientations under shear-dominated loading can be primarily attributed to contributions from internal friction.

The authors' abstract, as published at the source. Composites Science and Technology, 2026 · DOI ↗