1984 年 33 巻 369 号 p. 742-748
Instead of the conventional Charpy test using a 10mm square bar specimen with U-notch of 1mm radius and 2mm depth[(a)-specimen], the Izod test using a round bar specimen has been sometimes used by the present authors, for convenience of machining and heat treatment of its specimen. The standard specimen being used by them is a round bar of 14mm diameter with a circumferential U-notch of 1mm radius and 2mm depth[(b)-specimen]. But it is frequently required to use slenderer specimens. In the present experiment, two kinds of selenderer round bar specimens of heat treated 0.55% carbon steel were investigated for their impact properties by the instrumented impact test. One was a round bar of 11.5mm diameter with a geometrically similar notch to the standard specimen[(c)-specimen]. The other was a round bar of 11.5mm diameter with a different shape notch, but the minimum diameter and the stress concentration factor of the notch were equal to those of the standard[(d)-specimen].
The results obtained are as follows:
(1) The individual impact values (Total, crack initiation and propagation) Ir1 of (c)-specimen were approximately related to those Ic of (a)-specimen by the equation Ir1=0.8Ic. This relationship has been well established between (b)-specimen and (a)-specimen.
(2) In the case of impact value Ir2 of (d)-specimen, the crack initiation impact value was relatively large. The relation, Ir2=2Ic, was found to exist between the crack initiation impact values of (d)-specimen and (a)-specimen. However, the crack propagation impact value was related to that of (a)-specimen by the equation, Ir2=0.8Ic, as similar to the case of other round bar specimens.