PEAK AMPLITUDE DISTRIBUTION OF ACOUSTIC EMISSION EVENTS DURING DELAYED HYDRIDE CRACKING OF Zr-2.5% Nb ALLOY

Delayed Hydride Cracking: Theory and Experiment

“…As discussed in the foregoing paragraphs, for these ice-water quenched specimens T A is calculated assuming that the hydrogen concentration in the bulk is determined by the solvus for hydride dissolution, but with a magnitude equal to that given by TSSP2. [3] It is seen that the calculated values of L c increase much more steeply with K I than do the measured ones, which could be because, in actuality, there is a decrease in thickness of the hydrided region at the crack tip with increase in K I ; which has not been included in this model because of the lack of input data. Moreover, the calculated L c values increase slightly with K I above *15 MPaHm.…”

“…Figure 10.36 shows the results of the calculated K I versus L c dependence compared to the measured variation of striation spacing versus K I using values for the crack tip hydrided region's thickness and transformation strain that brings the calculated, lowest bound L c value given by Eq. 10.24 close to the experimentally determined one [3]. Also plotted on this graph are the dependences of L PZ and L max versus K I (given by Eqs.…”

“…In addition, their tests show a strong K I dependence for the ice-water quenched specimens suggesting that Stage II may not have been reached even up to K I values of 20 MPaHm. This K I dependence of the DHC growth rate of the ice-water quenched specimens may also be associated with a strong K I dependence of the striation spacing obtained in another set of experiments on ice-water quenched specimens at a slightly higher temperature of 225°C, approached from below [3]. Unfortunately, the total hydrogen content for the specimens of these latter tests was not explicitly stated and could have been either 50 or 100 wppm.…”

“…Simpson and Puls [83] and Ambler [1] had made initial attempts to explain these results theoretically based on early versions of the Dutton-Puls DHC growth rate model, while Amouzouvi and Clegg [2] attempted an explanation based on a dislocation sweeping model in their first attempt to explain their results and a critical hydride fracture criterion model derived from an energy balancing criterion in their second attempt [3]. Neither modeling attempts, however, resulted in good agreement between the predictions of the models and the experimental results.…”