Mechanical behavior of the Zr-1%Nb alloy at high strain rates and stress triaxiality from 0.33 to 0.5

Abstract

It is important to know the patterns of a damage nucleation and fracture of the Zr-1% Nb zirconium alloy at high strain rates and in the presence of stress concentrators for the design of new critical structures of nuclear reactors, fuel claddings and pressure pipes. In this research the influence of the strain rate in the range from 0.1 to 10 3 s −1 on the plastic deformation resistance and the fracture character of the Zr-1% Nb alloy under tension at room temperature and the stress triaxiality parameter 0.33 < η < 0.5 was studied. The tests were carried out using an Instron VHS 40/50-20 servo-hydraulic testing machine on flat specimens with a smooth and notched gage parts. Video recording of the process of sample tension was carried out by the Phantom V711 camera at speed of recording of 100 000 frames per second. Strain fields in gage zone of specimens at 10 2 and 10 3 s −1 obtained by the Digital Images Correlation method. It was shown that the dynamic fracture of the Zr-1% Nb alloy is the result of nucleation and growth of damage in localized shear bands. Using numerical modeling, the evolution of damage and fracture of samples under high-speed tension is analyzed. It is shown that strain localization bands begin to develop in the incision zone at lower macroscopic strains. The location of the plastic strain localization bands and their intersection in the separation zone determines the orientation of the cracks near the stress concentrator zone.