Mike Ciavarella's blog

Carbone and Pierro (Meccanica 48, 1819--1833 (2013)) discuss that punch shaped ends give less strong adhesion than mushrooms-ended ones because of the stress singularity at the corner. In particular, they assume large friction at the interface, which leads close to the classical Linear Elastic Fracture Mechanics singularity, corresponding to the classical scaling with the flat punch shaped pillar radius for what they call mode I of failure, ruled by the so-called Kendall formula. Their calculations are valid assuming perfect bonding for both punch or mushroom shaped ends.

dear Friends

We are hiring 2 post-docs soon in Italy at the Department of Mechanics DMMM of the Politecnico di BARI.  The subject is here described.

It is 50 years that people use models of viscoelastic fracture which assume the fracture energy in the process zone is independent on the crack speed. This has been assumed in the cohesive models by Knauss and Schapery and then by the dissipation theory of de gennes and Persson-Brener.  Researchers like to use this model because it is simple.   Unfortunately, it does not work, as we show in adhesion experiments in the recent JMPS paper attached.   We obtain nice results for a broad band power law material, but these results only work at very low speeds.

An index has been proposed by Fiorillo (document attached).   

Dear friend

We are in the time where big multi-centre projects with an ever-increasing number of scientists involved seem to multiply, and single scientist projects seem to die, apart from the happy island of ERC funding in Europe (probably NSF career funding in US?). I believe that with ERC funding and the direct call of ERC winners some European universities have taken a path of excellence to follow, while on multicentre big money projects they are less effective.

Dear colleague

   I wonder if you could be interested in this idea of "Cancelling the effect of sharp notches or cracks with graded elastic modulus materials", particularly if you know who could help doing some experiments. Thanks for any comment, since this is a preprint it would be useful to discuss to make improvements.    RegardsMike    Cancelling the effect of sharp notches or cracks with graded elastic modulus materials

Prediction of friction is one of the nigthmares of tribologists!   For elastomers, friction may be due to shear stresses or to dissipation and adhesion hysteresis.  Here we consider the two effects in rolling/ sliding a viscoelastic cylinder. We find that at low speeds the numerical bem results confirm Persson/Brener theory for crack propagation at large Tabor parameter.

dear collegues

   I have been attracted recently by a theory from Shrimali and Lopez-Pamies which is based on experimental evidence obtained from Suo's group in Harvard in 2012 in a (limited, but significant) set of experiments on rubber.   The theory assumes that the stretch to nucleating a crack is constant and independent on stretch rate.  The theory is then built on that, to predict the increase of fracture energy with rate.

Eighty outstanding researchers, innovators and communicators from around the world have been elected as the newest Fellows of the Royal Society, the UK’s national academy of sciences and the oldest science academy in continuous existence.

Call for PhD student grants and applications

Location: Polytechnic University of Bari, Department of Mechanics Mathematics and Management (DMMM), Via Orabona 4 - 70125 Bari – Italy

dear Colleagues

In writing a review of models on fretting fatigue, I am looking at the effect of friction coefficient.   Obviously, if friction is zero there is no fretting fatigue!   This goes without saying.

dear collegues, I may be interested to share your views on an "asperity theory" modified Persson's rubber friction contact mechanics theory which I find not clearly motivated and seems to lead to erroneous conclusions ---- but I am also unable to reproduce the results claimed by the authors. The preprint is here, and the original paper attached: https://www.researchgate.net/publication/359392510

M. Ciavarella (2021) Improved Muller approximate solution of the pull-off of a sphere from a viscoelastic substrate, Journal of Adhesion Science and Technology, DOI: 10.1080/01694243.2021.1882766

See also in attach the PDF.

dear collegues 

Crack propagation at the interface between viscoelastic and elastic materials

M.Ciavarella, R.McMeeking