Experimental verification of the effect of biaxial state of stress on the fracture-mechanical characteristics of WWER pressure vessel materials - a research programme

Previous experiments have shown that biaxial stress has an adverse effect on fracture toughness - under biaxial strain, fracture toughness may be some 40 % less than under uniaxial strain (ie., that found in standard tests using compact tension or three point bending). Under operating conditions, in the cylindrical part of a pressure vessel the stress is always biaxial; therefore, an experimental programme to check the effect of biaxial stress on reactor pressure vessel materials is proposed. The goal of the programme is defined, the current knowledge is summed up, and requirements on test specimens and test apparatus are set. The actual apparatus is described in some detail, and the method of test results evaluation is suggested. (A.K.) 2 figs., 1 ref