51 research outputs found
General contact mechanics theory for randomly rough surfaces with application to rubber friction
We generalize the Persson contact mechanics and rubber friction theory to the
case where both surfaces have surface roughness. The solids can be rigid,
elastic or viscoelastic, and can be homogeneous or layered. We calculate the
contact area, the viscoelastic contribution to the friction force, and the
average interfacial separation as a function of the sliding speed and the
nominal contact pressure. We illustrate the theory with numerical results for a
rubber block sliding on a road surface. We find that with increasing sliding
speed, the influence of the roughness on the rubber block decreases, and for
typical sliding speeds involved in tire dynamics it can be neglected
Quantifying Wetting Dynamics with Triboelectrification
Wetting is often perceived as an intrinsic surface property of materials, but
determining its evolution is complicated by its complex dependence on roughness
across the scales. The Wenzel state, where liquids have intimate contact with
the rough substrate, and the Cassie-Baxter state, where liquids sit onto air
pockets formed between asperities, are only two states among the plethora of
wetting behaviors. Furthermore, transitions from the Cassie-Baxter to the
Wenzel state dictate completely different surface performance, such as
anti-contamination, anti-icing, drag reduction etc.; however, little is known
about how transition occurs during time between the several wetting modes. In
this paper, we show that wetting dynamics can be accurately quantified and
tracked using solid-liquid triboelectrification. Theoretical underpinning
reveals how surface micro-/nano-geometries regulate stability/infiltration,
also demonstrating the generality of our theoretical approach in understanding
wetting transitions.Comment: Both Main and SI uploaded in a single fil
Scaling behaviour of braided active channels: a Taylor’s power law approach
none9At a channel (reach) scale, braided channels are fluvial, geomorphological, complex systems that are characterized by a
shift of bars during flood events. In such events water flows are channeled in multiple and mobile channels across a gravel floodplain
that remain in unmodified conditions. From a geometrical point of view, braided patterns of the active hydraulic channels are
characterized by multicursal nature with structures that are spatially developed by either simple- and multi-scaling behavior. Since
current studies do not take into account a general procedure concerning scale measurements, the latter behavior is still not well
understood. The aim of our investigation is to analyze directly, through a general procedure, the scaling behavior of hydraulically
active channels per transect and per reach analyzed. Our generalized stochastic approach is based on Taylor’s law, and the theory
of exponential dispersion distributions. In particular, we make use of a power law, based on the variance and mean of the active
channel fluctuations. In this way we demonstrate that the number of such fluctuations with respect to the unicursal behavior of the
braided rivers, follows a jump-process of Poisson and compound Poisson–Gamma distributions. Furthermore, a correlation is also
provided between the scaling fractal exponents obtained by Taylor’s law and the Hurst exponents.Samuele De Bartolo, Stefano Rizzello, Ennio Ferrari, Ferdinando Frega, Gaetano Napoli, Raffaele Vitolo,
Michele Scaraggi, Carmine Fallico, Gerardo SeverinoDE BARTOLO, Samuele; Rizzello, Stefano; Ferrari, Ennio; Frega, Ferdinando; Napoli, Gaetano; Vitolo, Raffaele; Scaraggi, Michele; Fallico, Carmine; Severino, Gerard
High lubricity meets load capacity: cartilage mimicking bilayer structure by brushing up stiff hydrogels from subsurface
Natural articular cartilage has ultralow friction even at high squeezing pressure. Biomimicking cartilage with soft materials has been and remains a grand challenge in the fields of materials science and engineering. Inspired by the unique structural features of the articular cartilage, as well as by its remarkable lubrication mechanisms dictated by the properties of the superficial layers, a novel archetype of cartilage‐mimicking bilayer material by robustly entangling thick hydrophilic polyelectrolyte brushes into the subsurface of a stiff hydrogel substrate is developed. The topmost soft polymer layer provides effective aqueous lubrication, whereas the stiffer hydrogel layer used as a substrate delivers the load‐bearing capacity. Their synergy is capable of attaining low friction coefficients (order 0.010) under heavily loaded conditions (order 10 MPa contact pressure) in water environment, a performance incredibly close to that of natural articular cartilage. The bioinspired material can maintain low friction even when subjected to 50k reciprocating cycles under high contact pressure, with almost no wear observed on the sliding track. These findings are theoretically explained and compounded by multiscale simulations used to shed light on the mechanisms responsible for this remarkable performance. This work opens innovative technology routes for developing cartilage‐mimicking ultralow friction soft materials
Lubrication of textured surfaces: A general theory for flow and shear stress factors
We report on a mean field theory of textured surface lubrication. We study the fluid flow dynamics occurring at the interface as a function of the texture characteristics, e.g. texture area density, shape and distribution of microstructures, and local slip lengths. The present results may be very important for the investigation of tailored microtextured surfaces for low-friction hydrodynamic applications
The friction of sliding wet textured surfaces: The Bruggeman effective medium approach revisited
The mean field fluid dynamics and the friction occurring in the wet sliding contact between inhomogeneous surfaces, characterized by a deterministically repeated pattern of microdefects, are modelled within the Bruggeman effective medium theory. By comparing with the results of an accurate numerical homogenization of the flow equations, and with asymptotic solutions, we discuss the validity of the mean field model and its limitations in relation to the occurrence of clustering and interference effects. Finally, an analytical upgrade to the Bruggeman approach, allowing for inclusion of the clustering effect, is presented and discussed
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