A contribution to fracture criteria for graphite

The calculation of stresses and strains in graphite core components of the high temperature reactor is generally performed using the rules of linear elasticity. In this paper two alternative methods to solve the problem of failure of graphite components are proposed: (1) The most reliabe test of fracture strength of a component is clearly the mechanical loading of a true replica of the component under conditions simulating the service conditions. However, such experiments are prohibitively expensive and, therefore, the strengths of the components are generally compared with those of classical specimen types viz. tensile, bend, torsion or compact (CT) specimen. It is proposed to use test specimens whose shapes and stress distributions are nearly the same as those of the components in regions where peak stresses are found. The two similar stress distributions are fitted to each other by means of a linear least squares fit. (2) The second procedure to evaluate fracture strengths is a new fracture criterion based on a linear elastic calculation of the energy density proportional constant k2, averaged over an element of volume ΔV. The quantities Ksub(i)2 related to different parts of the component are then weighted according to the Weibull statistics and summed over the total volume of the component V to yield a risk value. (Auth.)