The energy dissipation during fatigue crack growth in metallic materials

An energy equation for fatigue crack growth was proposed. It equates the total external work per cycle (dW/dN) to the sum of plastic dissipation (dUpl/dN), change in strain energy stored (dUe/dN) and the energy dissipated in new crack surface formation (dUa/dN). Fatigue crack growth experiment of 7075-T6 was used to derive the relation between fatigue crack growth rate (da/dN) and variables in this equation. The result shows dUpl/dN and dUe/dN are not straightforwardly related to da/dN. The dUa/dN, whose value cannot be obtained sufficiently precise experimentally, can be the variable straightforwardly related to da/dN within the range of test.