Fatigue crack growth analysis in polymeric materials

Fatigue crack growth in polymers is analyzed using the two-parametric approach. Polymers deform by crazing, viscoelastic deformation, or brittle fracture, contributing to crack growth. The analysis shows that irrespective of the nature of the deformation of the material ahead of the crack tip, the crack growth rate data can still be represented by the L-shaped curves in the delta K-K-max plane defining two limiting variables delta K* and K-max*. Thus, as in metals and alloys, the L-shaped curves depict the intrinsic fatigue behavior. The analysis further confirms that the load ratio effects in all materials are intrinsic to fatigue. A simple method for the prediction of these L-shaped fatigue curves is proposed.