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carpick's picture

Two Postdoc Positions: DFT/MD and AFM of Oxide Interfaces

The School of Engineering and Applied Science at the University of Pennsylvania invites applications for two full-time Postdoctoral Researcher positions in the laboratories of Prof. D.S. Srolovitz (https://www.seas.upenn.edu/directory/profile.php?ID=180) and Prof. Robert W. Carpick (http://carpick.seas.upenn.edu).

 

Mike Ciavarella's picture

On the application of fracture mechanics mixed-mode models of sliding with friction and adhesion --- the Menga, Carbone & Dini paradox

I attach a PREPRINT of a paper on the Menga, Carbone & Dini paradox (published in JMPS last year, available at https://arxiv.org/pdf/1710.06506.pdf), that is on the application of thermodynamics to mixed mode fracture mechanics models of contacts with friction and adhesion, and an apparent paradox which emerges from this treatment.  Comments welcome.   

Mike Ciavarella's picture

A comment on "A dimensionless measure for adhesion and effects of the range of adhesion in contacts of nominally flat surfaces" by M. H. Muser

I attach a Letter I sent to the Editor of a tribology journal, concerning adhesion of rough surfaces. 

I contend that some "criteria" that have been proposed based on extrapolation of numerical results are due to the limitations in present numerical sophisticated rough contact simulations, which only span at most 3 orders of magnitude of wavelengths, so typically people simulate from nanometer to micrometer scale.

Mike Ciavarella's picture

review paper: The role of adhesion in contact mechanics

Journal of The Royal Society Interface 16(151), February 2019.    DOI: 10.1098/rsif.2018.0738

Michele Ciavarella Junki Joe Junki Joe Antonio Papangelo James Richard Barber

Zhaohe Dai's picture

Interface-Governed Deformation of Nanobubbles and Nanotents Formed by Two-Dimensional Materials

In this paper, we experimentally characterize a simple and unified power law for the profiles of a variety of nanobubbles and nanotents formed by 2D materials such as graphene and MoS2 layers. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.266101

Key image

ABSTRACT

hyunwoo's picture

Multifunctional “Hydrogel Skins” on Diverse Polymers with Arbitrary Shapes

In this paper, we introduce a new simple yet effective strategy to form "hydrogel skins" on polymer-based medical devices with arbitrary shapes. Hydrogel skins can convert any surface of polymer devices into robust, wet, soft, slippery, antifouling, and ionically conductive without affecting the original properties and geometries.

Abstract

Mike Ciavarella's picture

Is Tribology Approaching Its Golden Age? Grand Challenges in Engineering Education and Tribological Research

An interesting paper by VL Popov which suggests many problems of tribology are still very far from being remotely solved.  Despite the very detailed theories for example on rough contact using fractal surfaces on which we have debated mainly academically , there is not a single theory for any quantitative prediction of friction coefficient which can vary by 1 order of magnitude and its dependence on many variables, let alone wear coefficient which can vary up to 7 orders of magnitude.  What is left to do, other than measure?   Is tribology bound to be in practice just an experimental area? 

Mike Ciavarella's picture

On stickiness criteria for multiscale random rough contacts

We have just submitted a paper which solves a problem that I have been struggling to solve for many years.

Any comments are welcome to improve, while the paper goes the standard review process in the journal we submitted it.

 

Mike Ciavarella's picture

are fractal surfaces adhesive? a new attempt on JMPS

In 2007 I wrote a question in Imechanica, IS THERE NO PULL-OFF FOR ADHESIVE FRACTAL SURFACES?

Clearly, in 2007 this question was too hard to answer.  I pointed there that Fuller and Tabor 1975 asperity theory predicted a weird limit for a true fractal surface, that of no stickiness for any fractal dimension or amplitude, in the limit.

ahmedettaf's picture

Mechanics and Mussel adhesion: How bulk porosity may help things stick better

On the Role of the Plaque Porous Structure in Mussel Adhesion: Implications for Adhesion Control Using Bulk Patterning

Ahmed Ghareeb and Ahmed Elbanna -- Journal of Applied Mechanics (2018)

 

Mike Ciavarella's picture

A recent PNAS paper explained! FRACTURE MECHANICS SIMPLE CALCULATIONS TO EXPLAIN SMALL REDUCTION OF THE REAL CONTACT AREA UNDER SHEAR

If you have seen the very nice PNAS paper which just appeared

Sahli, R., Pallares, G., Ducottet, C., Ben Ali, I.E., Al Akhrass, S., Guibert, M., Scheibert, J., 2018, Evolution of real contact area under shear, Proceedings of the National Academy of Sciences, 115(3), pp. 471-476.

Here we provide a simple explanation.

FACTA UNIVERSITATIS

Series: Mechanical Engineering

DOI: 10.22190/FUME180108007C

Short Communication

FRACTURE MECHANICS SIMPLE CALCULATIONS TO EXPLAIN SMALL REDUCTION OF THE REAL CONTACT AREA UNDER SHEAR

UDC 539.6

Partial constraint singularities in elastic rods

We present a unified classical treatment of partially constrained elastic rods. Partial constraints often entail singularities in both shapes and reactions. Our approach encompasses both sleeve and adhesion problems, and provides simple and unambiguous derivations of counterintuitive results in the literature. Relationships between reaction forces and moments, geometry, and adhesion energies follow from the balance of energy during quasistatic motion. We also relate our approach to the configurational balance of material momentum and the concept of a driving traction.

Mike Ciavarella's picture

An inspiring seminar by Prof. Huajian Gao -- Mechanics as an Enabling tool in bioinspired materials and biological interactions of nanomaterials

Professor Huajian Gao of Brown University speaks at MIT Distinguished Seminar Series (March 2016).

It is a unique opportunity to enjoy the many important recent achievements of Huajian's group.

Mechanics as an Enabling tool in bioinspired materials and biological interactions of nanomaterials

Here.

Not to be missed!

Mike Ciavarella's picture

Some Closed-Form Results for Adhesive Rough Contacts Near Complete Contact on Loading and Unloading in the Johnson, Kendall, and Roberts Regime

Michele Ciavarella  Yang Xu Robert L. Jackson

Some Closed-Form Results for Adhesive Rough Contacts Near Complete Contact on Loading and Unloading in the Johnson, Kendall, and Roberts Regime

Journal of Tribology Copyright VC 2018 by ASME JANUARY 2018, Vol. 140 / 011402-1

 

Recently, generalizing the solution of the adhesiveless random rough contact proposed

by Xu, Jackson, and Marghitu (XJM model), the first author has obtained a model for

adhesive contact near full contact, under the Johnson, Kendall, and Roberts (JKR)

Mike Ciavarella's picture

A very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model

"A very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model" is in press in Meccanica, can be viewed at http://rdcu.be/s0lV Abstract In the present note, we suggest a single-line equation estimate for adhesion between elastic(hard) rough solids with Gaussian multiple scales of roughness.

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