What do the symbols in da/dN=A(^K)m represent in material fatigue and stress?

AI Thread Summary
In the equation da/dN = A(ΔK)^m, da represents the change in crack length, and dN denotes the change in the number of cycles, confirming the user's understanding. ΔK is the stress intensity factor range, calculated using ΔK = Y√(πa)(σ_max - σ_min), where Y is a crack geometry factor. A and m are empirical constants derived from plotting log(da/dN) against log(ΔK). The crack geometry factor Y varies based on the crack's shape and aspect ratio, and resources such as textbooks or specific tables can provide guidance on determining it. Understanding these symbols is crucial for analyzing material fatigue and stress.
Ashley
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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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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.
 
One more thing

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