Evaluation of tearing instability behaviour of carbon steel for nuclear primary system.

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Elastic-plastic fracture toughness and tearing instability tests under monotonic and cyclic loading have been made by using lTCT specimens. The material used in these tests is a carbon steel pipe made for a nuclear primary system. lTCT specimens with side groove of 2.5mm in depth is extracted from the pipe in L-C direction. The main conclusions are as follows.(1) This material shows very high fracture toughness of about <J_(lc)> =0.96Mj/ <m^2> . (2) <J_(lc)> , <delta_(ic)> , J-R curve, <T_J^(mat)> and <T_(delta)^(mat)> decrease with increasing temperature. However, deformation rate has a little effect on them. (3) Critical value at instability <J_(inst)> shows on dependence on the compliance of testing system, however it decreases with increasing temperature. (4) Stress ratio R has a little effect on <J_(inst)> under cyclic load. <J_(inst)> under R=0.1 shows a little higher value than that of R=-0.1. (5) <J_(inst)> under R=0.1 is almost equal to the <J_(inst)> under monotonic load. (6) <J_(inst)> under monotonic load shows a very little scatter, and the scatter can be expressed by the weibull distribution function.