Effects of Stress Intensity Factor Range for Fabricating Fatigue Pre-cracks on Fracture Toughness of Ultra-High Strength Steel

The quasi-static fracture toughness (K_ⅠC) test of D406A ultra-high strength steel was carried out by using multi-sample method, the effects of stress intensity factor range for prefabricating fatigue crack on the fatigue pre-crack propagation cycle, fatigue pre-crack propagation rate, fracture surface morphology and ultimate fracture toughness were investigated. The results show that the fatigue pre-crack propagation cycle and rate were both of an exponential relationship with the stress intensity factor range, and the fatigue crack spacing on the fracture samples and the final fracture toughness increased with the increase of stress intensity factor ranges. If the maximum stress intensity factor was selected in the range of (20%-30%)K_ⅠC of the material, the K_ⅠC test results would be relatively stable.