Back to basics for the fatigue crack growth rate in metallic alloys

icaf2023 Tracking Number 32

The field of fracture mechanics started with Griffith’s energy concept for brittle fracture in 1920. In 1963, Paris et al. used a fracture mechanics’ parameter to introduce an equation for the fatigue crack growth rate in ductile materials and this equation is now commonly known as the ‘Paris law’. However, the Paris law and the semi-empirical models that followed ever since do not fully account for the main intrinsic and extrinsic properties involved with fatigue crack growth in metallic alloys. In contrast, here we introduce a dimensionally correct fatigue crack growth rate equation that is based on the original crack driving force as introduced by Griffith and the presence of plasticity in a metal to withstand crack propagation. In particular we found that the fatigue crack growth rate shows a power law relationship with the cyclic strain energy release rate over the maximum stress intensity factor. The new description corrects for the ratio between the minimum and maximum stress during a loading cycle at constant amplitude and for crack growth retardation under variable amplitude loading. It is shown that the outcome of this study allows for reliable predictions of variable amplitude fatigue crack growth life in civil and aerospace structures that currently still heavily rely on testing to ensure safety against catastrophic failure. It is argued that the novel concept presented is an essential step in describing ab initio the fatigue crack growth rate phenomenon in metallic systems