DEPENDENCE OF THE THRESHOLD STRESS INTENSITY FACTOR ON HYDROGEN CONCENTRATION DURING DELAYED HYDRIDE CRACKING IN ZIRCONIUM ALLOYS

The theoretical work on the criterion for fracture initiation at hydrides at sharp crack tips in zirconium alloys is extended to include the effect of hydrogen concentration in solid solution on the threshold stress intensity factor, K(IH). The analysis shows that the crack-tip hydride can only grow to a certain maximum length which depends on hydrogen concentration in solution and the stress intensity factor. Analytical and numerical solutions of the critical hydride length for fracture show that it increases as temperature increases and as the stress intensity factor decreases. These results are used to develop the relationship between the hydrogen concentration in solution and K(IH). This shows that K(IH) increases as the hydrogen concentration in solution decreases. The variation of the crack-tip critical hydride length with temperature, yield strength and applied K(I) is also derived and the results compared with striation spacing data obtained from fracture surfaces.