EFFECT OF LOADING MODE ON THE FRACTURE-TOUGHNESS OF A REDUCED-ACTIVATION FERRITIC MARTENSITIC STAINLESS-STEEL

The critical J integrals of mode I (J(IC)), mixed-mode I/III (J(MC)), and mode III (J(IIIC)) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J(MC) was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. The results showed that J(MC)s and tearing moduli (T-M) varied with the crack angles and were lower than their made I and mode III counterparts. Both the minimum J(MC) and T-M occurred at a crack angle between 40 and 50 degrees, where the load ratio sigma(i)/sigma(iii) was 1.2 to 0.84. The J(min) was 240 kJ/m(2), and ratios of J(IC)/J(min) and J(MC)/J(min) were about 2.1 and 1.9, respectively. The morphology of fracture surfaces was consistent with the change of J(MC) and T-M values. While the upper-shelf fracture toughness of F-82H depends on loading mode, the J(min) remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J(min).