Crack channelling and spalling in a plate due to thermal shock loading

The propagation of a pre-existing edge crack across a finite plate subjecte d to cold shock has been studied. The plate, initially at uniform temperatu re, is exposed to a cold shock on one surface whilst three different types of heat transfer boundary condition are separately considered for the oppos ing face: cold shock, thermal insulation and fixed temperature. For all thr ee boundary conditions, the plate experiences tensile stress near the cold- shocked surface and compressive stressing near the mid-plane. Consequently, a Mode I edge crack extending into the compressive region may grow in one of three different modes: continued extension in plane strain, channelling and spalling. The thermal shock conditions governing each failure mode are quantified, with a focus on crack channelling and spalling. The dislocation method is employed to calculate the energy release rates for plane strain cracking and steady-state channelling. For steady-state spalling, the energ y release rate is obtained by an energy analysis of elastic beams far ahead and far behind the crack tip. Analytical solutions are also obtained in th e short crack limit in which the problem is reduced to an edge crack extend ing in a half space; and the parameter range over which the short crack sol ution is valid for a finite plate is determined. Failure maps for the vario us cracking patterns are constructed in terms of the critical temperature j ump and Blot number, and merit indices are identified for materials selecti on against failure by thermal shock. (C) 2000 Elsevier Science Ltd. All rig hts reserved.