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Fracture mechanism in notched metal

Jabar's picture

G'day all

Having a metal element with a notch like crack (assume sharp one, exhibits plasticity),  what are the actual fracture mechanism (the phases the crack goes through) in the total fatigue-life. 

please comment on these scenarios:

1- crack initiation life calculated from the (S-N, e-N), then using LEFM/EPFM to determine the cycles for the crack propagation to failure...

Q/ how to find the crack length between the two phases, I mean from which stresses and at which crack length we start the crack propagation life estimation.

2- crack initiation life to be calculated form (SN, eN) curves for crack less than 1 mm, or even micro-mm)-then crack propagates through two phases: the short crack and length crack phases..the cycles from the initiation (micro-mm) to short crack (maybe till 2.5mm) to be determined from specific model for short crack, then we apply the fracture mechanics of the long crack.

 

If you can guide me to reference or have a comment will be appreciated 

 

Thanks

 

Mike Ciavarella's picture

I am not sure anybody ever provided a real answer.   Probably Keith Miller in metals would say 1mm.  Other would say the Topper critical distance.

You may search for my papers on Paris fatigue crack growth.

A generalized Parislaw for fatigue crack growthOne, no one, and one hundred thousand crack propagation laws: a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack … 

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