Topic is not controversial, the discussions made on this by the researchers are controversial. The crack closure concepts are very good and helpful in fatigue crack growth analysis

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 !

Crack closure may be observed under certain conditions, but it depends on the crack growth history (loading history). What observed from a particular testing procedure may not be relevant to crack growth problems in service..

• 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 !

I am one of them.

Let me know the controversy in this method, Actually its a good method to predict..I use it very often

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 !!