arXiv subjects

M. O. Robbins

Publications and source records attributed to M. O. Robbins.

3 recordsLinked to original sources

arXiv2009

Scaling of the Strain Hardening Modulus of Glassy Polymers with the Flow Stress

In a recent letter, Govaert et al. examined the relationship between strain hardening modulus $G_r$ and flow stress $σ_{flow}$ for five different glassy polymers. In each case, results for $G_r$ at different strain rates or different temperatures were linearly related to the flow stress. They suggested that this linear relation was inconsistent with simulations. Data from previous publications and new results are presented to show that simulations also yield a linear relation between modulus and flow stress. Possible explanations for the change in the ratio of modulus to flow stress with temperature and strain rate are discussed.

cond-mat.soft↗

arXiv2004

Finite-element analysis of contact between elastic self-affine surfaces

Finite element methods are used to study non-adhesive, frictionless contact between elastic solids with self-affine surfaces. We find that the total contact area rises linearly with load at small loads. The mean pressure in the contact regions is independent of load and proportional to the rms slope of the surface. The constant of proportionality is nearly independent of Poisson ratio and roughness exponent and lies between previous analytic predictions. The contact morphology is also analyzed. Connected contact regions have a fractal area and perimeter. The probability of finding a cluster of area $a_c$ drops as $a_c^{-τ}$ where $τ$ increases with decreasing roughness exponent. The distribution of pressures shows an exponential tail that is also found in many jammed systems. These results are contrasted to simpler models and experiment.

cond-mat.mtrl-sci↗

arXiv2000

Simple Microscopic Theory of Amontons' Laws for Static Friction

A microscopic theory for the ubiquitous phenomenon of static friction is presented. Interactions between two surfaces are modeled by an energy penalty that increases exponentially with the degree of surface overlap. The resulting static friction is proportional to load, in accordance with Amontons' laws. However the friction coefficient between bare surfaces vanishes as the area of individual contacts grows, except in the rare case of commensurate surfaces. An area independent friction coefficient is obtained for any surface geometry when an adsorbed layer of mobile atoms is introduced between the surfaces. The predictions from our simple analytic model are confirmed by atomistically detailed molecular dynamics simulations.

cond-mat.mtrl-sci↗