Determination of correlation parameters for evaluation of mechanical properties by Small Punch Test and Automated Ball Indentation Test for Zr–2.5% Nb pressure tube material

Abstract

Empirical correlation parameters for evaluation of key mechanical properties of anisotropic Zr–2.5% Nb pressure tube (PT) material have been determined for Small Punch Test (SPT) and Automated Ball Indentation (ABI) Test. Parameters have been developed as a function of loading direction due to highly anisotropic nature of the material. Slopes of the linear fit correlations established for the SPT and ABI tests, showed good sensitivity of these techniques to wide range of microstructures in the alloy that resulted due to different heat treatment conditions. In the case of ABI, the difference in yield strength offset constant between the two directions of loading studied, represented the effect of texture. Similarly in the case of SPT the difference in intercept values of the, linear fit correlations established for evaluation of yield strength (YS) and the ultimate tensile strength (UTS) with respect to two directions of loading studied, clearly indicated the effect of anisotropy in the material. Comparison of tensile strength data, the ABI and SPT derived σy and σUTS data obtained for heat treated specimens used in the study, through currently established correlation parameters showed good agreement with each other for both the directions of loading, indicating proper standardisation of ABI and SPT techniques and proper values of empirical parameters have been arrived at for evaluation of key mechanical properties of Zr–2.5% Nb material. The overall study established that, the direction of loading bears significance while dealing with anisotropic material like Zr–2.5% Nb alloy and hence, direction specific correlations need to be used for evaluation of true mechanical properties for a given miniature test.