The effect of side-grooves on elastic-plastic fracture-toughness (JIc) determination of high- and medium-strength structural steels, HT80 and SM50A, was investigated by using CT-type specimens of three different thicknesses; the ratio of net thickness to gross thickness was kept at 0.75 and the net thickness was ranged from 6 to 18mm. The JIc tests were conducted in accordance with the standard JIc test method proposed by the Japan Society of Mechanical Engineers (JSME).
The use of side-grooved specimens generally made it much easier to determine the onset of ductile tearing by the R-curve method and the electric potential method, and improved accuracy and scatter of the toughness values thus determined, provided all the size-requirements for the specimen prescribed in the JSME method were satisfied.
The critical stretched zone width (SZWc) of the side-grooved specimens was found to be smaller than that previously determined for the standard CT specimens without side-grooves. This was attributed to higher triaxiality produced by the side-grooves. The SZWc values of the side-grooved specimens were rather insensitive to the specimen thickness in the range of thickness investigated.
Good agreement was observed between the JIc values at physical onset of ductile tearing and the JIc values determined by the R-curve method and the electric potential method. The stretched zone width method gave slightly larger JIc values than those by the R-curve method for SM50A, as has been observed for the standard specimens without side-grooves.