Theoretical and Experimental Analysis of Semi-Elliptical Surface Cracks Subject to Thermal Shock

This paper illustrates a procedure for estimating the stress intensity factors of a semi-elliptical surface crack in a thermally shocked thick plate.

The first step in this procedure is to calculate the time-dependent thermal stresses induced by sudden cooling of an uncracked plate by using the three-dimensional finite element codes for heat transfer and thermal stress analyses with the consideration of the space as well as time change of elastic constants. The stresses at the location of the crack surface in the uncracked plate are eliminated by the method of superposition in order to obtain a stress free crack surface.

The time-dependent distributions of the stress intensity factors along the crack front line are then determined by using the three-dimensional finite element method of crack analysis based on discretization error proposed by the present authors recently.

In order to study the effectiveness of the linear elastic fracture mechanics employed in this paper, a series of tests of brittle fracture using cracked polymethyl methacrylate (PMMA) plates is carried out by suddenly cooling the surface of plate. The measured and estimated times of fracture elapsed from the sudden cooling are found to coincide very well.