The Question I'm Trying to Solve Is: Aluminum alloy (7075-T651) is used for aircraft wing. The largest flaw size monitored in the wing was 9mm. What is the maximum allowable loading so that any catastrophic failure can be avoided? The fracture toughness of aluminum is 26MPa*m^0.5. Assume the geometrical parameter, Y = 1.1. So far this is what I've tried to do. K = psi(pi.a.B)^0.5 26 = psi(pi.0.009.1.1)^.05 rearrange to find psi. psi = 21735 I assume that's wrong, I don't think I'm even using the correct equation. If someone could point me in the right direction or even give me the correct equation, it would be greatly appreciated.