## Material fatigue and stress

Could you please explain what each of the following symbols stand for:
da/dN=A(^K)m

I have worked out that da is the crack length
i have worked out that dN is the number of cycles
Are both of these correct?

Thanks

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 Recognitions: Gold Member Science Advisor What you have is a simplified model of the rate of crack propagation: $$\frac{da}{dN} = A\Delta K^m$$ 2*a is the crack length (not da), N is the number of cycles (not dN). ΔK is the stress intensity factor range: $$\Delta K = Y\sqrt{\pi a}(\sigma_{\rm max} - \sigma_{\rm min})$$ (Y is a crack geometry factor). A and m are empirical constants (found by plotting log(da/dN) versus log(ΔK)).
 Thanx for the help.

## Material fatigue and stress

you said that Y is a crack geometry factor, how do you find the crack geometry factor??

 Recognitions: Gold Member Science Advisor It depends on the shape/aspect ratio of the crack. Hopefully, there is a table or explanation in your textbook. Here's a page I found with a bunch of them that might help: http://www.ems.psu.edu/~green/436-8C.pdf