Research on Dynamic Fracture Toughness for High Toughness Material ----Measuring Method and Property------

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Although many attempts have been made to determine the accurate value of dynamic fracture toughness, no standard method such as KIC or JIC test method has been found and there are many uncertain properties about dynamic fracture toughness.In this reseach, a simple system of measuring dynamic fracture toughness was developed using a drop weight striker and 3-point bend specimens. In the system, the impact force is determined by analyzing the output of the strain gage near the tip of the striker using the Fast Fourie Transformer, and the dynamic stress intensity factor is calculated by a simple formula proposed previously.A dynamic fracture toughness test was conducted on an aluminum alloy 2124-T6, a fiber reinforced metal SiC 25%/2124-T6 and a nuclear pressure vessel steel A508S. The dynamic fracture toughness for the two formers which were relatively brittle was easily determined using the developed measuring system, while for the latter which was rather ductile it was found neccessary to introduce a simple method for estimating the dynamic elastic-plastic fracture toughness parameter J-integral.By applying the idea of plastic region correction, a simple method was developed for estimating the J-integral. It was found that the value of J-integral obtained by the simple method agreed well with the one by the finite element method (FEM) and the CPU time of the simple method was about 1/100 times shorter than that of the FEM.A finite element technique to calculate the stress intensity factor for a fast crack was developed using a commonly used triangular constant strain element and the J-integral. This technique may be conveniently used to measure the dynamic fracture toughness for a rapidly propagating crack.