| Dynamic stress intensity factor(DSIF)is an important index of fracture characteristics for the material subjected to the impact loading.In general,the dynamic fracture toughness of the material is determined by instantaneous dynamic stress intensity factor at crack initiation.However,it is difficult to accurately determine initiation time,which heavily influence the determination of initiation toughness of materials.Considering the merit of the numerical method to find crack initiation moment,the hybrid method of experimental and numerical method will be provided to determine the dynamic crack initiation toughness and to study crack propagation in this paper.For this purpose,a three-point bending specimen for mode I fracture-initiation toughness of metals was researched in detail.An approximate algorithm was proposed to calculate the fracture-initiation toughness under impact load.The ultimate strength ?_b is the fracture criterion,which means the crack begin to propagate when the stress is greater than thes_b.To calculate the DSIF,the impact loading is divided into several sub-step and the crack size can be modified in calculating every DSIF at every sub-step loading moment.By this way,both the DSIF curve and the crack propagation curve can be obtained.The inflection point on the crack size propagation curve is the crack initiation point.The moment of the inflection point is the crack initiation moment,which can be used to determine the fracture-initiation toughness.In order to verify the availability of the proposed method,both numerical and experimental studies are performed.The numerical simulation results are in good agreement with the theoretical results,which indicates the availability of the approximate method.In addition,the DSIF of the DZ417G high-temperature nickel-base alloy is researched by experimental method.The results show that the three methods have good consistency under the two experimental conditions. |
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