The influence of porosity on short fatigue crack growth at large strain amplitudes

Abstract

The influence of pore microstructure (0% to 6% rounded porosity, isolated vs. interconnected) on short crack growth during low cycle fatigue has been evaluated using powder-processed titanium as a model. The presence of porosity enhances short crack propagation adjacent to the pores as a result of localized, pore-induced plasticity. Observations of short cracks using surface replicas indicate that once a crack extends beyond a plastic zone of an isolated pore it decelerates to propagation rates similar to those observed for fully dense materials of similar grain sizes. For low levels of porosity in which the pores are isolated, the vast majority of short crack growth occurs outside the pore-induced plastic zones, and thus the overall short crack growth rates are not significantly affected. However, when the pores are interconnected, short cracks propagate at higher rates of growth than cracks of comparable size in the dully dense material. The enhanced growth rates appear to be a result of the continuous nature of the plastic zones which provide a high strain amplitude propagation path.