Static mode fatigue crack propagation and generalized stress intensity correlation for fatigue–brittle polymers

Stable fatigue crack propagation is predominantly described by the Paris power law correlation of the crack growth rate with the amplitude cyclic stress intensity. The Paris relationship works well for most ductile materials but does not capture the response for fatigue–brittle materials lacking a cyclic damage mechanism, including ceramics and many polymers. Instead, crack growth rate of fatigue–brittle materials correlates to the peak cyclic stress intensity factor, $$\hbox {K}_{\mathrm{max}}$$ . This work shows that $$\hbox {K}_{\mathrm{max}}$$ correlation of fatigue crack growth is derived directly from static mode crack tip behavior with constant correlation coefficients, and that $$\Delta \hbox {K}$$ correlations are not generally applicable for static mode crack propagation in fatigue–brittle polymers. This derivation predicts load ratio, frequency, and waveform effects, which are included in a general static mode fatigue crack propagation law. Fatigue crack propagation data of a known fatigue–brittle polymer are presented to demonstrate static mode crack propagation behavior correlation with $$\hbox {K}_{\mathrm{max}}$$ with constant parameters.