Home Research


Dry contact mechanics of rough surfaces in presence of adhesion and friction

compress minimal               compress medium

compress maximum

The research activity in this field is mainly concerned with the investigation of the influence of roughness and surface energies on the contact behaviour of elastic bodies and on the frictional behaviour of soft viscoelastic materials. The activity has been carried out both at theoretical and experimental levels. Cutting edge models based on the most recent research findings as well as fully numerical calculations of the contact behavior between adhering rough elastic solids have been developed and partially tested experimentally.


Bio-mimetic micro-structured adhesive with superior performance


The superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics, engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers because experiments have proved their superiority compared to other micro- and nano-structures. Our research aims at elucitading the physical mechanism behind the enhanced adhesion of such microstructures, in order to provide useful tools to predict and optimize the adhesive performance of such devices depending on the geometry, mechanical properties of the material, and energy of adhesion. Our achievements can streamline optimisation of adhesive microstructures for industrial applications.


       Seals         The research has been focused also on the estimation of leakages in seals. A novel approach has been presented which is based on the analogy between the seal-substrate interface and a porous medium. It is assumed that the interface is constituted of a random distribution of non-contact patches (the pores) and small but numerous contact spots (islands). Leakage may occur only through the pores, of which the lateral size and height are distributed according to a probability density function, that is calculated on the basis of a recent theory of contact mechanics. The theoretical approach is based on a percolation scheme that has never been proposed before and it could be useful to stimulate further theoretical or experimental investigations.


EHL and mixed lubrication


The focus of this research has been to investigate the influence of roughness on lubricated contacts. A novel (homogeneization) model to describe the interfacial fluid-asperity and asperity-asperity contribution to total pressure has been developed to study the highly non-stationary squeeze of two approaching rough elastic bodies. The model has been shown to be in good agreement with some existing experimental literature and has been applied to the engineering case of CVT transmissions where wear and durability problems are strongly determined by the interfacial lubrication conditions between the contacting bodies.


 Roughness-induced hydrophobicity


Roughness-induced hydrophobicity has attracted much interest from both fundamental research, because of its potential applications to the high-tech field of microfluidics, and industry for the "self-cleaning" ability of such surfaces (e.g. superhydrophobic paints, car windscreens). In case of windshields the super-hydrophobic surfaces should be able to suspend rain drops despite the very large impact forces. We have developed a theoretical model to calculate the critical droplet pressure which lead to a strong deterioration of the water-repellent properties of such surfaces and proposed a criterion to design the surface roughness in such a way that the transition from the Cassie to the Wenzel state is avoided and the super-hydrophobic properties of the surface are preserved.


Crack propagation in viscoelastic soft materials

      crack1   crack2


Because of internal losses of viscoelastic materials propagating cracks have values of the energy release rates which depends on the crack speed. The research aims at determining the amount of energy required to propagate the crack as a function of crack advancing speed. The influence of viscoelasticity and non-uniform temperature distribution is taken into account. Our investigations shows that the energy per unit time required to move the crack may increase up to three or even more order of magnitude at high velocities, and that, because of the very high increase of temperature in a region very close to the crack tip an instable behaviour may take place at certain crack velocities.


 Mechanical Transmission
              cvt  The research activity is focused mainly on the dynamics of Continuously Variable Transmission (CVT): Pushing Belt CVTs, Chain Belt CVTS, Toroidal CVTs, and Infinitely Variable Transmissions (IVT). Tribological problems as elastohydrodynamics lubrication as well as mixed lubrication conditions are investigated.


cantilever afm This research aim at modelling the dAFM (dynamic atomic force microscopes) microcantilever dynamics in liquid environments. For such intruments a clear signal is one of the highest requirements in order to extract correct information from the measurement at so small length scales. However this is not a so straightforward task to be achieved because of the forces which act on the cantilever in operational conditions, expecially when a liquid enviroiment is required. Because of the micro-scale size of the cantilever, thermal noise due to Brownian forcing of liquid particles cannot be neglected and therefore proper insights about this effect are required. A novel analytical model has been developed to describe the influence of the surrounding liquid on a AFM cantilever dynamics, e.g. when biological liquids wraps the surfaces to be investigated. It has been shown that the liquid response consists of three terms: a viscous term, a velocity-diffusive term, and an inertial term. The analysis shows that neglecting the velocity-diffusive term may lead to large errors in the estimation of the cantilever response and, hence, of its thermal response which is often used to calibrate the instrument.


Copyright © 2010 --- TriboLAB
DIMEG - Politecnico di Bari,  Viale Japigia, 182 - 70126 BARI (Italy)

Tel. +39 080 596 2746, Fax +39 080 596 2746/2777

Contact us at tribolab.poliba@gmail.com