The effect of constraint on fracture properties of Z3CN20.09M after accelerated thermal aging

The main coolant piping material Z3CN20.09 M was heat treated at 400 °C for 18,000 h and then the fracture behavior has been studied. To understand the effect of in-plane constraint on fracture behavior, J-R curves were determined by the pre-cracked specimens with a wide range of crack depth ratios. And the stretch zone width (SZW) values were measured by experimental method and finite element method (FEM) based on fracture energy density. The comparisons of SZW value show that good agreements have been achieved among experimental tests and FEM. Moreover, to reveal and quantify the constraint effect (a/W), three-dimensional FEM was used to obtain the second terms in the Williams’ series expansion. The J-R curves, JIC and JSZW and SZW are higher at lower crack depth ratios a/W, and gradually decrease with increasing crack depth. Then, the constraint dependent fracture properties of Z3CN20.09 M were determined and could be used to predict fracture properties under other constraint conditions. •An accelerated thermal aging experiment was performed on Z3CN20.09 M at 400°C up to 18,000 h.•The influence of crack depth on fracture toughness was studied by stretch zone width (SZW) methods.•The JSZW could be used to evaluate the fracture toughness irrespective of the initial crack length.•T-stress was used to describe constraint levels and develops the constraint-dependent fracture properties.