12,969 research outputs found
Asynchronous Variational Contact Mechanics
An asynchronous, variational method for simulating elastica in complex
contact and impact scenarios is developed. Asynchronous Variational Integrators
(AVIs) are extended to handle contact forces by associating different time
steps to forces instead of to spatial elements. By discretizing a barrier
potential by an infinite sum of nested quadratic potentials, these extended
AVIs are used to resolve contact while obeying momentum- and
energy-conservation laws. A series of two- and three-dimensional examples
illustrate the robustness and good energy behavior of the method
Contact mechanics in fretting fatigue
This paper studies the contact mechanics in a line contact during fretting fatigue conditions. In literature one can find numerical and analytical solutions of normal and tangential stresses for a variety of loading cases. However, a unified solution valid for all loading cases during fretting fatigue conditions is not available. We present in this paper a strategy to combine existing contact mechanics theories into a unified calculation procedure. Therefore, the relevant contact mechanics theories for an idealized cylinder-on-flat contact are selected and bundled. Two clear flowcharts group the existing theories, which results in a unified strategy that can easily be implemented in a programming language. A Matlab script was programmed and calculates the normal and tangential stress distribution based on the applied forces, the geometry of the contact, the coefficient of friction and the material properties. The present theory can be used to automate the calculation of the stress distributions, or as validation of new numerical techniques. The script is modular and can be extended to calculate the lifetime of a component, by adding lifetime criteria
Contact tribology also affects the slow flow behavior of granular emulsions
Recent work on suspension flows has shown that contact mechanics plays a role
in suspension flow dynamics. The contact mechanics between particulate matter
in dispersions should depend sensitively on the composition of the dispersed
phase: evidently emulsion droplets interact differently with each other than
angular sand particles. We therefore ask: what is the role of contact mechanics
in dispersed media flow? We focus on slow flows, where contacts are
long-lasting and hence contact mechanics effects should be most visible. To
answer our question, we synthesize soft hydrogel particles with different
friction coefficients. By making the particles soft, we can drive them at
finite confining pressure at all driving rates. For particles with a low
friction coefficient, we obtain a rheology similar to that of an emulsion, yet
with an effective friction much larger than expected from their microscopic
contact mechanics. Increasing the friction coefficient of the particles, we
find a flow instability in the suspension. Particle level flow and fluctuations
are also greatly affected by the microscopic friction coefficient of the
suspended particles. The specific rheology of our "granular emulsions" provides
further evidence that a better understanding of microscopic particle
interactions is of broad relevance for dispersed media flows
Contact mechanics for randomly rough surfaces
When two solids are squeezed together they will in general not make atomic
contact everywhere within the nominal (or apparent) contact area. This fact has
huge practical implications and must be considered in many technological
applications. In this paper I briefly review basic theories of contact
mechanics. I consider in detail a recently developed contact mechanics theory.
I derive boundary conditions for the stress probability distribution function
for elastic, elastoplastic and adhesive contact between solids and present
numerical results illustrating some aspects of the theory. I analyze contact
problems for very smooth polymer (PMMA) and Pyrex glass surfaces prepared by
cooling liquids of glassy materials from above the glass transition
temperature. I show that the surface roughness which results from the frozen
capillary waves can have a large influence on the contact between the solids.
The analysis suggest a new explanation for puzzling experimental results [L.
Bureau, T. Baumberger and C. Caroli, arXiv:cond-mat/0510232] about the
dependence of the frictional shear stress on the load for contact between a
glassy polymer lens and flat substrates. I discuss the possibility of testing
the theory using numerical methods, e.g., finite element calculations.Comment: Review paper, 29 pages, 31 picture
Influence of frozen capillary waves on contact mechanics
Free surfaces of liquids exhibit thermally excited (capillary) surface waves.
We show that the surface roughness which results from capillary waves when a
glassy material is cooled below the glass transition temperature can have a
large influence on the contact mechanics between the solids. The theory suggest
a new explanation for puzzling experimental results [L. Bureau, T. Baumberger
and C. Caroli, arXiv:cond-mat/0510232] about the dependence of the frictional
shear stress on the load for contact between a glassy polymer lens and flat
substrates. It also lend support for a recently developed contact mechanics
theory.Comment: 4 pages, 2 figure
Contact mechanics: relation between interfacial separation and load
I study the contact between a rigid solid with a randomly rough surface and
an elastic block with a flat surface. I derive a relation between the (average)
interfacial separation and the applied normal squeezing pressure . I
show that for non-adhesive inte raction and small applied pressure, p is
proportional to exp (-u/u_0), in good agreement with recent experimental
observation.Comment: 4 pages, 3 figure
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