Effect of Specimen Thickness on Threshold Stress Intensity Factor (K-IH) Associated with DHC in Zr-2.5 Nb Alloy Pressure Tube Material

Delayed hydride cracking (DHC) behavior for zirconium alloys is characterized in terms of DHC velocity, V-DHC, and Threshold Stress Intensity factor, K-IH. The effect of specimen thickness on Kw associated with DHC of unirradiated Zr-2.5 Nb pressure tube material was investigated. For this purpose, K-I at crack arrest for 1 mm-, 2 mm-, and 4.5 mm-thick specimens was determined using the load drop technique. Significant tunneling of the crack was observed for 1 mm- and 2 mm-thick specimens in the load drop test at 250 degrees C. The K-I at crack arrest was found to be increasing with the decrease in specimen thickness. However, extended finite element model (FEM) simulation revealed that K-I at crack arrest in the center of the 1-mm specimen and 2-mm specimen is comparable to the values 9.2 +/- 0.5 MPa.m(1/2)obtained for the 4.5 mm-thick specimen. Hence, if tunneling is not present in the specimen, the K-IH was found to be independent of specimen thickness.