Determination of the initation of stable crack growth (J-integral) in terms of the theorem of equivalent states

Elasto-plastic fracture mechanics presently suffers under the dilemma that experiments to determine crack initiation using different methods on ferritic, and more pronounced, on austenitic materials deliver results dependent on the method. Consequently, it seems hopeless that the relationship between J-integral, stress intensity K1 and Young's modulus E can be fullfilled. This work presents a procedure to determine the very beginning of stable crack growth and its assessment for three point bend type specimens and CT-samples according to ASTM-E 399 for the ferritic steel A 533 B 1 and the austenitic iron/nickel base alloy Incoloy 800H. A comparison between the procedure and the dc-potential drop technique is made. (orig./HP)