シャルピー試験機を用いた簡便なJ_<IC>試験法について

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Since elastic-plastic fracture toughness J_<IC> was proposed by Landes and Begley, considerable work on it has been carried out and systematization of the J_<IC> test method has been accomplished actively. ASTM E 813-81 in USA and JSME S 001-1981 in Japan, which are concerned with standard test methods for fracture toughness J_<IC> have been published. From the industrial and practical point of view, it is as a matter of course that a more economical and convenient test method is desired. In the present study, a significantly simple test method for evaluating J_<IC> by using a Charpy impact testing machine without instrumentation has been investigated. The materials used in the present study were SM50B steel. A 533 B Class I steel, HT80 Steel, AISI 4340 steel, Type 304 stainless steel and 7075 Aluminum alloy. It was found that the maximum load point coincides with the ductile crack initiation point in the 25% side-grooved Charpy-size specimen with the crack length to width ratio a/W of 0.6. The ratio of the absorbed energy up to maximum load E_m to the total absorbed energy E_t was found to correlate with the material constant: E_m/E_t=58.2 (_<flow>/E_f). From the foregoing results, a quite simple and convenient test method for estimating J_<IC> has been proposed as follows: (1) Prepare a 25% side-grooved Charpy-size specimen with the crack length to width ratio a/W of 0. 6. (2) Carry out a Charpy impact test and measure the total absorbed energy E_t. (3) Determine the J_<IC>-value by substituting the E_t-value into the following equation: J_<IC>=58.2(_<flow>/E_f)(2E_t/B_<eff>b). Since the scatter of J_<IC> estimated by using the present test method was considered to remain in the narrow range of 20%, in practical use it is not a serious problem.
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シャルピー試験機を用いた簡便なJ_<IC>試験法について

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