CRACKS IN THE RESOLIDIFICATION LAYER OF STAINLESS-STEEL FORMED BY SIMULATED PLASMA DISRUPTION

An experimental study was made of the cracks in the resolidification layer ot stainless steel formed by a simulated plasma disruption. A neutral beam injector was employed as heat source, by which a heat flux of about 77 MW/m2 was applied on the test pieces for durations of 40 to 110 ms. The crack density and the crack depth increased with increasing duration until the heat load reached around 5 MJ/m2. At higher energy depositions the crack density decreased with increasing duration, while the crack depth changed little. After repetitive pulsed irradiation, the crack depth increased while the crack density was scarcely affected. A calculation was made using a one-dimensional stress analysis code to determine the stress and strain distribution during the heating up and cooling down processes. The increasing rate of strain in the resolidification layer decreased with increasing duration, which is one reason for the low crack density under the heavy-load condition. The residual stress in the resolidification layer increased under load repetition, which is considered to be one of the reasons for the deep cracks after repetitive irradiation.