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Mike Ciavarella's blog

optimal temperature and optimal temperature gradient in tyres?

Submitted by Mike Ciavarella on

Dear Colleagues

I have been playing with a very good student from Berlin with the idea that a temperature gradient along the depth of the tire could help reduce wear significantly. We all know that there is an optimal range of temperature for friction and wear --- much less known is an optimal "temperature gradient". I hope you find this study a good starting point on this idea. Maybe somebody wants to explore how to patent it!

https://lnkd.in/d5nibSYN

Mike

friction and persson's theory for fractal roughness

Submitted by Mike Ciavarella on
dear colleagues
 
  I recommend reading this recent paper
 
Chadha, V., Randolph, A. B., Reifler, K., Jacobs, T. D., & Beschorner, K. E. (2025). Validation of a Multiscale Hysteresis Mechanics Model in Predicting Oily Shoe-Floor Friction Across Surfaces With Varying Finishes. Journal of Tribology, 147(9).

Leonardo's universal friction coefficient is found to be universal after all!

Submitted by Mike Ciavarella on
research
friction
tribology granular materials
It turns out that friction coefficient 0.25 suggested as universal by Leonardo da Vinci more than 500 years ago has some universaility, as minimum friction coefficient for any granular material: it makes me proud as italian ;) 
I guess it would be interesting to show this experimental result also theoretically or numerically, any interest?
 

A new analytical model for fibrillar viscoelastic adhesion using the Schapery or the Shrimali-Lopez-Pamies nucleation models

Submitted by Mike Ciavarella on
research
fibrillar adhesion
adhesion
JKR
schapery
Persson-Brener
Shrimali - Lopez Pamies
Hello:  I would be interested in any comment about this preprint on fibrillar viscoelastic adhesion, originally devised by Schargott Popov and Gorb, where we use for the first time not only the Schapery model for nucleation of cracks, but also the Shrimali and Lopez Pamies, which leads to quite stronger enhancement of adhesion (the limit is the square of the Schapery one), and pull-off with no real prior propagation phase.  Propagation with Schapery nucleation criterion is found to be qualitatively similar to the Schapery and Persson-Brener propagation theories, except that

A new interesting theory by Persson on wear commented

Submitted by Mike Ciavarella on
wear

A very interesting wear theory by Persson and coworkers has been recently proposed (in fact, it is still under review!). 

I make some comments and simplifications here to show general trends

https://www.researchgate.net/publication/387143610_Some_comments_on_a_r…

Wear is a complex problem, and I don't think this theory will give easily quantatitative predictions, but it certainly deserves attention. 

My abstract follows

Finite strains explain the non-monotonic change of contact area in soft rubber contacts loaded in torsion?

Submitted by Mike Ciavarella on
contact area
rubber contact
tresca friction
adhesion
finite strain

In unidirectional sliding of rubber contacts on smooth hard surface it has been found that contact shrinks largely in longitudinal directions, and generally much less in the transverse direction, and two explanations have been suggested to explain this: one is the effect of mixed mode fracture mechanics in the presence of adhesion (with mode II reducing adhesion and mode III less clear), and another uniquely based on finite strain effects even for a simple material model as neo-Hookean hyperelastic material.

On friction effects and the conditions of failure of adhesion in punch shaped pillars and mushrooms

Submitted by Mike Ciavarella on
research
adhesion
mushrooms
kendall formula
friction

Considerable research has been conducted on shape of pillar ends for optimal adhesion. In experiments with elastomers it has been found that mushrooms-ended ones are superior to flat-ended ones, but early experiments have suggested an extremely strong scaling in strength with pillar radius (del Campo et al Langmuir;23 :10235-43, 2007). We discuss various theories and experimental results on scaling of strength, and in particular we elaborate recent experiments on single pillars with mushroom ends finding that the scaling on strength is much less surprising.

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