AlanStevens wrote:
Werner Exinger wrote:
There are some errors:
4) Unit problems: N.f^(2b) should yield pressure^2 and N.f1(b+c) should yield dimension pressure for the equation to be unit consistent. This would mean that c=0 which does not correspond to the value you provide.
I agree that Nf^2b would have to be pressure squared, but Nf^(b+c) would have to be dimensionless (because sigmaf*epsilonf has dimension pressure). That (and the fact that sigmaf^2/E is - rather neatly! - 1/Pa) is why I assumed Nf would be dimensionless.
However, I think we agree that, one way or another, the equation as it stands is either incomplete or in error.
Alan
You are right - I overlooked the unit of epsilon.f and I guess its wrong - it should be dimensionless.
I guess you that N.f should be unitless as probably N.f is the number of cycles needed for a crack to grow a specific length. It looks to me now that epsilon.f and sigma.f got mixed up. epsilon.f should be a unitless coefficient and sigma.f is stress and should have dimension pressure. This would straighten all out.
