I'm not getting something, I'm looking for some hints.Component classified as in infinite plate. Maximum working stress is 50% of yield strength. Has crack 10.5mm long. Cyclic loading - mode 1. Is the crack acceptable? At what length the growing crack exceeds the safety factor? I just want hints as to how to answer the questions. I can calculate the crack length at which the working load leads to a sigma critical point. That's greater than 10.5mm. Okay, so there no imminent danger of cleavage fracture. But, that is not to say the crack is acceptable. There must some point where the crack length puts it within a margin of safety. But, I'm lost to understand this. I'm guessing that 10.5mm is beyond some safety factor. That there is a length smaller than 10.5mm which is acceptable. Just don't know how to get to it. Need some key words or something to help me. Thanks. P.S. Possibly talking about residual strength - not sure. Might be something else.