8 results
Filters
Settings
Now showing1 - 8 of 8
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wear due to fatigue initiationPersson and coauthors have recently proposed an extension of the Rabinowicz idea for fatigue wear at different scales of roughness, where Paris’ crack growth law is applied to ”potential” wear particles. However, Persson's theory suffers from the fact that initial size of defects is unknown and fatigue life is not entirely due to propagation, so we investigate a different formulation, where a law for initiation of cracks is used for a specimen with initial roughness of engineering interest. We find that results (in particular dependence on amplitude of roughness, and on friction coefficient) are qualitatively similar to the original Persson and coworkers’ theory, but may differ substantially quantitatively. As the assumption of a constant fatigue threshold may be incorrect for short cracks, both fatigue limit and fatigue threshold are made dependent of crack size, using the Murakami formulation as one of the possible alternatives. This makes wear rate be sensitive to the fine scale details of the roughness spectrum, which has an effect on increasing wear rate and small particles emission. The model seems to have qualitative trends in agreement with experiments, but obviously wear is a very complex phenomenon and many factors may be not captured.Publicationtype: Journal Article15 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Stickiness of randomly rough surfaces with high fractal dimension: is there a fractal limit?(2021-07); ; Two surfaces are “sticky” if breaking their mutual contact requires a finite tensile force. At low fractal dimensions D, there is consensus stickiness does not depend on the upper truncation frequency of roughness spectrum (or “magnification”). As debate is still open for the case at high D, we exploit BAM theory of Ciavarella and Persson-Tosatti theory, to derive criteria for all fractal dimensions. For high D, we show that stickiness is more influenced by short wavelength roughness with respect to the low D case. BAM converges at high magnifications to a simple criterion which depends only on D, in agreement with theories that includes Lennard-Jones traction-gap law, while Persson-Tosatti disagrees because of its simplifying approximations.Publicationtype: Journal Article71 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental observation of thermally-driven frictional instabilities on C/C materialsThe outstanding thermo-mechanical and tribological properties of C/C materials make them suitable in a wide range of industrial applications, where high performance at harsh temperature conditions are required. The great interest for their frictional properties points out the need to comprehend and characterize the dynamical phenomena occurring during frictional contact. Within this framework, this work offers an overview of their prevailing frictional and dynamic contact response taking place under different temperatures. The tests reveal a strong relationship between the C/C frictional response, the material propensity to destabilize the system dynamics and the working temperature, providing a glimpse into the occurrence of thermally-driven instabilities for C/C materials and offering information in terms of dynamical response in a broad range of temperature.Publicationtype: Journal Article36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electroadhesive sphere-flat contact problem: A comparison between DMT and full iterative finite element solutions(2020-12); ; The electroadhesive contact between a conductive sphere with a rigid substrate, both coated with an electrically insulating layer is studied, by adopting two solution strategies: (i) a DMT approximation and (ii) an iterative finite element model which accounts for the effect of the electroadhesive tractions on the deformation of the elastic solids. The contact problem is solved by varying the applied voltage and the elastic modulus of the coating layer. The two approaches (i) and (ii) give comparable results only in the limit of very low applied voltage, while they differ quantitatively and qualitatively at high voltage, as the DMT approach largely fails in predicting the repulsive contact force, which leads to greatly overestimate the macroscopic adhesive force.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The effect of wear on ThermoElastic Instabilities (TEI) in bimaterial interfaces(2020-02); There is ample evidence of ThermoElastic Instabilities (TEI) occurring in sliding contacts. The very first experiments of JR Barber in 1969 suggested wear interacts in the process of localization of contact into “hot spots”. However, studies on the interaction of TEI with wear are scarce. We consider the case of two sliding halfspaces and make a perturbation analysis permitting the formation of waves migrating over the two bodies, in presence of wear. We find that for exactly identical bodies wear does not affect the stability boundary. In the other limit case of bad conductor against a good conductor, wear tends to suppress TEI completely. Intermediate cases show a complex range of possible effects: for certain thermomechanical properties wear may even reduce the critical speed.Publicationtype: Journal Article97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Extensions and comparisons of BAM (Bearing Area Model) for stickiness of hard multiscale randomly rough surfaces(2019-05); In the present paper, we consider a recent very simple model for the estimate of adhesion between elastic (hard) rough solids with Gaussian multiple scales of roughness (BAM, Bearing Area Model), and compare it in particular with very recent extensive results from the numerical method of Joe, Thouless and Barber (JTB theory), in the range of non-hysteretic behaviour. BAM shows no sensitiveness to rms slopes and curvatures for the pull-off load or the apparent surface energy, in agreement with the JTB theory, but in contrast with the criterion proposed by Pastewka and Robbins for stickiness, especially in the fractal limit. Results show also reasonable accuracy with the JTB theory, and BAM theory is simpler than that of Persson and Scaraggi which involves convolution of adhesion tractions in the regions of separation.Publicationtype: Journal Article231 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modeling and simulation in tribology across scales: An overview(2018-09); ; ; ; This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and microscales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.Publicationtype: Journal Article174 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adhesion between self-affine rough surfaces: possible large effects in small deviations from the nominally Gaussian caseIt is shown that even small deviations from the ideal Gaussian random roughness case seem to lead to dramatic increase in adhesion of rough surfaces: this could be due to a finite number of asperities, or to a finite tail in the height distribution, particularly realistic at low fractal dimensions D, which is the case of most practical interest. It is emphasized that the assumption of a perfect Gaussian heigth distribution, including infinite tails, may be a strong one when studying adhesion in rough surfaces.Publicationtype: Journal Article86