采用多试样法对D406A超高强度钢进行了准静态断裂韧度K_ⅠC试验，分析了不同应力强度因子幅预制疲劳裂纹对疲劳预裂纹扩展周期、疲劳预裂纹扩展速率、试样断口形貌以及最终断裂韧度试验结果的影响。结果表明：疲劳预裂纹扩展周期和扩展速率均与应力强度因子幅呈指数变化规律，断口上的疲劳裂纹间距及最终断裂韧度试验结果均随应力强度因子幅的增大而增大，在材料断裂韧度K_ⅠC的20%~30%选择最大应力强度因子进行K_ⅠC试验结果较为稳定。

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.