The role of stress-state on the deformation and fracture mechanism of hydrided and non-hydrided Zircaloy-4

Abstract Zircaloy-4 was tested at room-temperature over a range of hydrogen content between 10 and 200 ppm, and stress-states between a triaxiality of −0.23 and 0.9. Triaxiality ( η ) is defined as the ratio of hydrostatic stress to von Mises stress and was controlled through use of select mechanical test specimen designs. Testing of smooth and notched tensile specimens ( η = 0.33 to 0.9) results in an increase in the stress to initiate plastic deformation and a decrease in strain to failure at higher values of η . Increases in triaxiality are shown to have a more significant effect on reducing the strain to failure when the material is hydrided. Increases in strain to failure are observed at lower values of triaxiality for dual keyhole specimens ( η = 0.1) and compression specimens ( η = −0.17 to −0.23), with hydrided material showing much less decrement in strain to failure at these lower triaxialities. Examinations of microstructure are used to show that a change in mechanism for deformation and fracture with triaxiality can explain these differences in mechanical behavior and a model is developed to describe the observed changes in strain to failure with stress-state.