A resistance curve based on J integral is experimentally obtained for center cracked tension specimen of SCM 4 steel. Displacements are measured at two separate points; at one point, the displacement is obtained from clip gauge, while at the other point, it is obtained from extensometer. Specimens are prepared in two different shapes, i.e, one with side groove and the other without side groove. The crack initiation point, as well as $J_Ic$, is determined in accordance with A.S.T.M. standard method for compact tension and three point bend specimens.
The result shows that the value of $J_Ic$ for side-grooved specimens is lower than for non side-grooved specimens and the slope of the J resistance curve is less steep for side-grooved specimens than for non side-grooved specimens. The slope of J resistance curve is steeper for center cracked tension specimens studied here than for compact tension and three point bend specimens tested by other researchers.
