Re: stress vs. strain determines crack limit

"jbuch" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> seferiad wrote:
> > Thanks for the detailed responses.  I'll pose a more specific question.
> > Let's say I have a bunch of fibers that perfectly obey Weibull
statistics
> > when  I do dynamic pull testing to destruction for the fibers. The
> > distribution when plotted on Weibull gives a slope = m (it doesn't
matter
> > what m is), but the fiber population is sufficiently strong so that a
> > significant fraction of the fiber will break at sufficiently high pull
force
> > so that the non-linear stress-strain relationship of glass will be
apparent.

> In general,  you should think very carefully about what you think is
> happening in a specimen and what is actually happening.
>
> Imagine three fibers having identical strengths. Imagine first that each
> fiber is exactly the same length as the others and is perfectly
> gripped... repeat, perfectly gripped .... in an Instron.
>
> As the specimen is loaded, all three fibers load in exactly the same way
> and will fail at the exact same time.... because of the exact identical
> strength assumption.

Don't ignore the effects of stress corrosion. Fibres loaded to less than
their normal breaking stress can eventually fail because of this.

It is arguable that rate of loading could also affect the results.

The same results can be observed in laminates or other composites.
-- 
Terry Harper
http://www.terry.harper.btinternet.co.uk/