Elastic-plastic analysis of local and integral straining behaviour in a cracked plate

Abstract

For components of the primary coolant system of the German LMFBR prototype reactor SNR-300, integrity against anticipated accidents (Bethe-Tait) has to be shown for a cracked structure. Within this programme a number of tests with cracked wide plate specimens yielding overall limit strains of approximately 15% have been run; finite element calculations have been initiated for the wide plate geometry. The paper discusses the straining behaviour of a cracked plate by considering the numerical simulation of structures strained up to such high levels. The stress-strain diagram of the weldment of the austenitic stainless steel X6 CrNi 18 11 at 450°C has been used. Plane strain and stress conditions have been prescribed. The original plate dimensions ( t=thickness=40 mm; h=height=400 mm) have been used as well as a similar, but smaller plate of t=8.8 mm width. The crack length is defined as 0.1 t. The results show that for a cracked plate under high plastic strain the near-crack-tip-field values still govern the structural mechanical behaviour. Concerning the absolute dimensions the effects known for elasticity retain their influence in the plastic regime; however, the crack location becomes more unimportant with increasing strain, i.e. the appropriate pure geometry factor tends to unity in the plastic regime. The center-crack, defined as 2 a=0.1 t, corresponds to an equivalent edge crack of depth a=0.05 t in the elastic case. It can be shown that for high plastic strains this correspondence remains fully valid.