Abstract
Since elastic-plastic fracture toughness JIC was proposed by Landes and Begley, considerable work on it has been carried out and systematization of the JIC 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 JIC, 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 JIC by using a Charpy impact testing machine without instrumentation has been investigated. The materials used in the present study were SM 50 B steel, A 533 B Class 1 steel, HT 80 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 Em to the total absorbed energy Et was found to correlate with the material constant : Em/Et= 58.2 (σflow/Eεƒ). From the foregoing results, a quite simple and convenient test method for estimating JIC 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 Et. (3) Determine the JIC-value by substituting the Et-value into the following equation : JIC=58.2 (σflow/Eε ƒ) × (2Et/Beffb). Since the scatter of JIC 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.
