Unloading-Compliance and Load-Drop Analysis of J_Ic Tests of Irradiated 348 Stainless Steel

Procedures for determining J-integral fracture toughness were applied to load versus load-line displacement data from a series of three-point bend specimens of irradiated 348 stainless steel tested at 23 and 427°C. The ASTM Test Method for J_Ic, a Measure of Fracture Toughness (E 813-81) was emphasized, using both unloading-compliance and load-drop measures of crack growth.

An effective modulus procedure was included in the unloading—compliance method using recently published load-line displacement results. Two procedures were used for calculating J_Ic from the J versus unloading-compliance crack growth plots: the linear fit procedure from ASTM Method E 813 and a power-law fit with a 0.2-mm offset value of J_Ic.

Based on the results of these various procedures, conclusions were reached regarding the most consistent measures of fracture toughness from these data. Suggestions were given regarding the use of effective modulus with unloading-compliance measurement of crack growth and the limitations of the load-drop method for measuring crack growth.