Fatigue characteristics of a glass-fiber-reinforced polyamide

Abstract

This paper deals with prediction of the temperature rise in the stress-controlled fatigue process of a glass-fiber-reinforced polyamide and the application of a temperature and frequency superposition procedure to the S-N curve. An experimental equation was derived to predict the temperature rise from calculations based on the fatigue test conditions and viscoelastic properties of the material. The temperature rise (ΔT) can be expressed as a product of a coefficient term Φ(L, κ) concerning heat radiation and the test-specimen shape and a function term Pfat concerning the viscoelastic properties and fatigue test conditions. Φ(L, κ) was found experimentally to derive the equation for predicting the temperature rise blow or above the glass transition temperature (Tg) of the material. The equation σR = −STf A log NfR + STf B was obtained as a procedure for applying temperature and frequency superposition to S-N curves in consideration of ΔT. This procedure was obtained by combining both temperature- and frequency-superposition techniques. Here, σR and log NfR represents the stress and the fatigue lifetime calculated at a given temperature and frequency, A and B denote the slope and intercept of any arbitrarily chosen S-N curve, and STf is a shift factor for temperature and frequency superposition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1783–1793, 1999