Abstract
Although many attempts have been made to determine the accurate value of Impact fracture toughness KId, no standard method such as the KIc test method has been found. It is desired that a simple method will be established. In the present research, a KId test using a drop weight and 3-point bend specimens was conducted on three metals, i.e., 2124-T6 aluminum alloy, 2124-T6 aluminum alloy with 25%SiC whisker (SiC 25%/2124-T6), and nuclear pressure vessel steel A508S.
For the SiC 25%/2124-T6 specimen, which fractured in a brittle manner, the electric potential method was usefully employed to detect crack initiation, and the value of KId was easily determined. The 2124-T6 specimen fractured with a little plastic deformation (but in a “small scale yielding” condition). It was found possible to detect crack initiation by the electric potential method, though it was not so easy as in the SiC 25%/2124-T6 specimen. The value of KId was determined by a similar procedure to that for the SiC 25%/2124-T6 specimen. For the A508S specimen, which fractured after a considerable plastic deformation, it was impossible to detect crack initiation by the electric potential method. By dropping the weight from various heights on several specimens and then observing the fracture surfaces with an electronmicroscope, the critical height for which a crack just initiated was determined. The value of KId was obtained from the maximum value of the J-integral calculated for the critical height.
