Re: stress vs. strain determines crack limit

seferiad wrote:
> Hello,
> With respect to classic power-law crack growth in brittle materials,  the
> critical limit is given by
>
> K = Y*S*a^1/2,  where Y is a constant, S is the applied stress, and a is the
> crack length (which is taken as a square root).
>
> My question is : What is the true independent variable (i.e., stress or
> strain) that determines when the material fractures?  This equation suggests
> that it is the stress, since the strain is not given, but that might be more
> for convenience since we tend to measure stress, not strain.

How is stress MEASURED directly?

> Assuming the stress-strain relationship were perfectly linear it wouldn't
> matter, but since materials fracture in a regime in which the stress-strain
> is not linear, it changes the interpretation of fracture data.
>
> Thanks,
> Jay