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Difference between 'Crack Propagation' and 'Fracture initiation'

Zartasha Mustansar's picture

Can anyone please tell how do we differentiate between "Crack propogation" and "Fracture initiation". A simple example will be much appreciated!

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You have two different stages: Damage initiation and propagation, which you may call crack initiation or propagation or fracture initiation and propagation. The first is the condition upon which a crack initiates. And the second upon which it propagates.

Zartasha Mustansar's picture

Zartasha Mustansar
PhD Student
SEAES
University of Manchester
UK

Zartasha Mustansar's picture

Hello Panos. Do you mean crack and fracture are interchangeable terms? I doubt it.

Zartasha Mustansar
PhD Student
SEAES
University of Manchester
UK

AS's picture

Perhaps considering an easy case of linear elastic mode 1 straight fracture can help. A fracture "propagates" if it exists and its tips have a well defined velocity. In such a case the energy released during propagation is well known since Irwin. If a fracture does not exist one talks of fracture initiation. I.e. you start with an undamaged elastic body and end up with a body that contains a displacement discontinuity after a finite time. In such a case, you cannot neither define a propagation velocity nor write an incremental formulation for the problem. The energy release rate is always unbounded.

In real materials, you may argue that initiation and propagation are less distinguishable phenomena. Existing cracks always localize deformations around the tip though, in locations that may be completely different than in uncracked materials. 

Hope this helps.

Alberto

Zartasha Mustansar's picture

Zartasha Mustansar
PhD Student
SEAES
University of Manchester
UK

Zartasha Mustansar's picture

Thanks Alberto. It was very helpful indeed.

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