R. W. Lang

Mechanisms of fatigue fracture in short glass fibre-reinforced polymers

Fatigue-crack profiles and fracture surfaces of several short glass fibre-reinforced polymers were examined to gain insight into the mechanisms of cyclic damage and fatigue-crack propagation in these materials. Several distinctly different features were noted between fracture surfaces generated by stable fatigue crack growth and those produced by monotonic or unstable fracture. Among the most significant differences were the higher degree of single and multiple fibre fracture generally observed on stable fatigue-crack growth fracture surfaces, and the variations in the interfacial failure site in well-bonded systems. While the former effect is attributed to the occurrence of crack closure and the build-up of compressive stresses in the crack-tip damage zone during unloading, the differences in the interfacial failure mode are related to the adverse effect of fatigue loading on the interfacial bond strength. No features could be identified that would allow a quantitative correlation between the applied stress intensity factor level or the crack growth rates and characteristic fracture surface details.

Fatigue Crack Propagation in Short-Glass-Fiber-Reinforced Nylon 66: Effect of Frequency

The fatigue crack propagation (FCP) response of nylon 66 and composites containing 16 and 31 vol. % short glass fibers was determined at frequencies of 1, 10, 50, and 100 Hz. The sensitivity to frequency was found to depend on glass content and, in the case of the pure matrix, on the value of the stress intensity factor range, ΔK.