can we stop cracks due to elastic modulus changes ahead of crack tips?

Dear Colleague

   It is known that ahead of a crack subject to static or fatigue loading microcracking and damage makes the material soften (of smaller elastic modulus) but also its strength degrades (in composite materials, there are so called “wearout models” which associate strength reduction exactly to the reduction of modulus).

 
   Now, based on a paper under review on V-notch and cracks with radially graded materials, which you can find at https://www.researchgate.net/publication/381316809, I have obtained that the grading makes stress singularity possibly disappear which would seem to be beneficial for the crack. Hence, the concentration largely reduces.   But I certainly can imagine that this effect is mild in most (at least man-made) materials, because we all know that cracks propagate and that microcracks are certainly not likely to make the crack arrest!   Of course, there are techniques which in maintenance of some structures, do drill “holes” near the apex of the crack to make them arrest, and this is loosely also like elastic grading the material.

  Materials which may be intelligent may be bone, see paper below, but I am not particularly expert in the field, and I don’t know if its mechanisms are able to stop cracks during fatigue, and if this is due to some mechanism similar to what I am describing.  But of course the solution in Nature is interesting, and could be an inspiration for new man-made materials!

   I was talking with some colleagues about intelligent materials which release some gels to stop cracks --- this is not exactly my idea, but instead we need to invent something that reverses the process, namely if the damage is in a form which reduces modulus as I describe in the paper and yet the material degradation effect is minor with respect to this singularity reduction, then this is a potentially very big innovation! 

Are you interested to discuss further, and perhaps we can talk sometimes online on TEAMS or ZOOM?

Regards,

Prof. Michele Ciavarella

Professor of Mechanical Design. 

MC lab @ Dept "of excellence" of Mechanics, Mathematics and Management.  Email: mciava@poliba.it  Phone: +39-080-5963670, mob.+39 3342204656

Humboldt Fellow, Technical University Hamburg

RG, imechanica, Linkedin , CV

Bone and its adaptation to mechanical loading: a review

S J Mellon stephen.mellon@ndorms.ox.ac.uk and K E TannerView all authors and affiliations

Volume 57, Issue 5

https://doi.org/10.1179/1743280412Y.0000000008

Abstract

Bone is a remarkable living material that comes in two forms with different porosities and different macrostructure, but with the same highly organised microstructure and nanostructure. As bone accumulates damage, it is removed and replaced. When the mechanical demands on bone increase the bone mass increases, while reductions in the loading leads to the removal of bone, thus bone can be considered a ‘smart material’. The ongoing replacement of old bone tissue by new bone tissue is called remodelling. Bone formation, repair and remodelling is controlled and produced by four types of cell, namely osteoblasts, osteoclasts, osteocytes and bone lining cells. Bone remodelling is regulated by signals to these cells generated by mechanical loading. Exactly how loads are transferred into bone, how the bone cells sense these loads and how the signals are translated into bone formation or removal is unknown. In this review, the structure of bone and the cells responsible for maintaining bone are described. The mechanisms that cause bone to adapt to mechanical loading have been investigated. The methods that have been employed in attempts to determine this mechanism are considered.