The influence of temperature on viscoelastic friction properties

Viscoelastic friction strongly depends on temperature, which determines the material stiffness and, therefore, given a constant load, the volume that is deformed and dissipates energy. We compare the results obtained by a numerical approach introduced by Carbone and Putignano (2013) [1] with measurements that separate viscoelastic losses from Coulomb contribution. This is done for a range of temperatures. We show that viscoelastic friction curves for different temperatures can be arranged into a single master curve using a frequency shift coefficient, which can be found from the characterization of the viscoelastic material response. This shows that it is possible to accurately (a) use dynamic material analysis data to extrapolate viscoelastic friction measurements to values outside the tested range, and (b) use a tribometer to obtain fundamental viscoelastic material properties

Theory of Reciprocating Contact for Viscoelastic Solids

A theory of reciprocating contacts for linear viscoelastic materials is presented. Results are discussed for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. Depending on the size of the contact, the frequency and amplitude of the reciprocating motion, and on the relaxation time of the viscoelastic body, we establish that the contact behavior may range from the steady-state viscoelastic solution, in which traction forces always oppose the direction of the sliding rigid punch, to a more elaborate trend, never observed before, which is due to the strong interaction between different regions of the path covered during the reciprocating motion. Practical implications span a number of applications, ranging from seismic engineering to biotechnology.Comment: 8 pages, 5 figures, accepted for publication on Physical Review E, March 22, 201

Trends of Road Accidents in Italy 1996-2005

This paper presents an analysis of road accident trends in Italy from 1996-2005. Figures are given for the number of accidents, fatalities, injuries, registered vehicles, and rates. Road safety measures that have implemented since 2003 are briefly discussed. Analysis of the data yields trends, such as the number of fatalities per 100 accidents is fewer in urban areas and highways than on other roads. The paper concludes that there has been a significant decrease in the number of accidents, injuries, and fatalities during the 1996-2005 time period. Road safety rules and stronger enforcement are seen as contributing to the improvement of road users? behavior

Decomposition numbers for weight 3 blocks of Iwahori--Hecke algebras of type B

Let B be a weight-$3$ block of an Iwahori--Hecke algebra of type B over any field. We develop the combinatorics of B to prove that the decomposition numbers for B are all 0 or 1

A parametrically time-dependent methodology for reciprocating contact mechanics between viscoelastic solids

We implement an original Boundary Element methodology to study the reciprocating contact mechanics between linear viscoelastic materials. Results are shown for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. We observe the presence of multi-peaked pressure and displacement distributions; the hysteric friction curve is finally shown for different values of the frequency

A Green’s Function Molecular Dynamics Approach to the Mechanical Contact between Thin Elastic Sheets and Randomly Rough Surfaces

Adhesion of biological systems is often made possible through thin elastic layers, such as human skin. To address the question of when a layer is sufficiently thin to become adhesive, we extended Green’s function molecular dynamics (GFMD) to account for the finite thickness of an elastic body that is supported by a fluid foundation. We observed that thin layers can much better accommodate rough counterfaces than thick structures. As a result, the contact area is enlarged, in particular, when the width of the layer w approaches or even falls below the short-wavelength cutoff λs of the surface spectra. In the latter case, the proportionality coefficient between area and load scales is (w/λs)3, which is consistent with Persson’s contact mechanics theory

A parametrically time-dependent methodology for reciprocating contact mechanics between viscoelastic solids

We implement an original Boundary Element methodology to study the reciprocating contact mechanics between linear viscoelastic materials. Results are shown for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. We observe the presence of multi-peaked pressure and displacement distributions; the hysteric friction curve is finally shown for different values of the frequency