I would agree with Dr. Arun that it is hard to see how crack closure concepts are particularly controversial. One might argue about the specific application of a crack closure model to a particular circumstance but there would seem to be a variety of applications where crack closure makes both phenomenological sense and clearly addresses the existing data (e.g., short versus long crack behavior in ceramics and composites).
Just to add a bit of spice to the discussion.
Is any one capable of generating crck length vs number of cycles data for a constant amplitude test,using a closure model ?
To expand the discussion I suggest that the researchers look at the Energy based approach to Fatigue.
Author self . Fatigue 2014, Melbourne , 3 The Energy based approach to Fatigue"
“The Energy based approach to Fatigue”, Advanced Materials Research, © (2014) Trans Tech Publications, Switzerland, Vols. 891-892 (2014) pp 821-826
I forgot that I started this topic. For all the closure afficandos, how do you choose between plasticity, ModeII, Oxide induced closure or non closure for a given circumstance ?
Please don't confound between closure and contact.
For me closure is a phenomenon that annuls the crack tip singularity !
- Dr Wu's answaer is very pertinant. Colsure is an aberration invented by academic researchers. It may not have any relevance in real time service aplications
- And one more aberration - How can you talk of Mode II induced crack closure ?- The definition of Mode II itself is based on crack surface contact. . In Mode II the effctive DeltaK is zero ?!::
Dear Mohan,
Your sentence (TOURS, 2001 ?) : "Closure killed imagination" is still written on my whiteboard.
It became a generic sentence for us @work when people focus on a concept that is a suitable workaround of the problem, without answering actually the question.
More scientists are thinking in terms of science ! Fors instance in composites one doesn't talk of even K, fracture phenomenon are described in terms of Strain Energy Release rates !
Dear RG colleagues,
Thank you so much for sharing this topic, I think that, all aspects of our mechanical or structural life (If applicable term!) are completely depends on this concept, so it is may good to describe this decade as a DECADE OF FRACTURE MECHANICS or of CRACK INITIATION AND PROPAGATION! Right?
Regards, Emad
The main diificulties are that different modes of closure are proposed :
- Plasticity induced closure
- Roughness induced closure
- Mode II type of closure
- You even have crcak tip wedge opening due to debris ..
None of these can be predicted !!
One of the biggest aberration is Mode II closure - mode II is sliding mode and you have contact between the surfaces all the time - In this case the crack should not grow as the effective DK is Zero !
You hve now new ideas based on Strain energy relese rate - you can explain quite afew of the crack problemes based on this "more physical concept"
In fact "Closure" killed the imagination of scientists !!
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