Fatigue Crack Propagation Beyond General Yield

Tests are carried out on compact tension specimens of AISI 1020 hot-rolled steel at nominal stress levels beyond yield. The results show that crack propagation rates can be correlated successfully using an operational definition of the range ΔJ of the J-integral. The rate of crack growth per cycle da/dN is shown to be related to ΔJ by da/dN=A (ΔJ)^α for conditions ranging from linear elastic to limit load. The exponent α agrees well with other published data on low strength steels and the quantity A is found to have a weak dependence on frequency. Examination of the fracture surface reveals that static failure modes are operating at the high crack propagation rates.