Experimental evaluation of orientation and temperature dependent material stress-strain curves of Zr2.5%Nb Indian pressure tube material and development of a suitable anisotropic material model

Abstract Because of their hexagonal close-packed (HCP) structure and easy prismatic slip, the tensile properties of Zirconium based alloys show strong texture dependence and hence, anisotropy. The type of texture, microstructure and hence, the mechanical properties depend upon the sequence of manufacturing process followed in fabrication of components, such as pressure tubes (PT) in pressurized heavy water type reactors. Due to small wall thickness (i.e., 3.75 mm) of the pressure tubes, designing and machining of specimens in all the three directions, especially in the radial direction, is a challenge and this explains the reason for scarcity of work in this area in research literature. In this work, different types of specimens have been machined from transverse, longitudinal and radial orientations of the Zr2.5%Nb Indian PT following a novel design in order to study the anisotropy in the plastic deformation and hardening properties. In addition, shear specimens have been extracted from longitudinal-transverse plane to study the plastic deformation in shear. Tests on tensile and shear specimens have been carried out at room temperature (25), 100, 200 and 300 °C respectively. Using the experimental data, the parameters of Hill’s anisotropic yield function have been evaluated. In addition to evaluating the parameters at initial yield point, the nature of variation of these parameters with equivalent plastic strain, has also been established. This new material model where the anisotropic parameters evolve with plastic strain, shall be useful for design (by analysis) and integrity assessment of the pressure tubes for different types of postulated loading conditions.