arXiv subjects

B. N. J. Persson

Publications and source records attributed to B. N. J. Persson.

At least 19 recordsLinked to original sources

arXiv2026

Why ice is so slippery

We simulate nanoscale ice--glass friction from first principles and upscale it by modelling frictional heating. Nanoscale simulations alone overestimate friction and miss its velocity dependence. Frictional heating warms the contact toward the melting point, thickening the premelting film tenfold and cutting its viscosity a hundredfold; friction drops with velocity, matching experiment. Premelting forms the film without sliding or heating, but its slipperiness hinges on frictional heating, as Bowden and Hughes proposed in 1939, without melting. Snow, other materials and coatings remain open.

cond-mat.mtrl-sci↗

arXiv2026

Sliding contact creates universal self-affine fractal surfaces

Surface roughness evolves during sliding, a process known as run-in, and the resulting topography controls friction, leakage, and failure from machines to geological faults. Yet the physical rule selecting this state remains unclear. We show that metals, rocks, and glasses develop universal self-similar roughness at short wavelengths, while retaining a material-dependent roll-off. A two-process model explains this behavior: junction formation and rupture drive universal roughening, whereas larger-scale deformation and/or fracture limit its growth.

cond-mat.soft↗

arXiv2026

Transient fluid removal at soft interfaces: Contact-time-controlled squeeze-out in a cylinder-on-flat contact

We study transient fluid removal in cylinder-on-flat contacts between stiff PMMA cylinders and a soft PDMS substrate. The cylinder geometry eliminates the edge-scraping mechanism that can occur for deformable rubber blocks, allowing the influence of sliding on fluid squeeze-out to be examined more directly. Experiments were performed mainly in glycerol at the low sliding speed $v=3 \ {\rm μm/s}$ using cylinders with different surface roughness. After the initial elastic-loading stage, we find that the friction during sliding depends primarily on the total time elapsed since application of the normal load rather than on the preceding sliding distance. The subsequent friction evolution follows approximately the same dependence on total contact time. Stationary squeeze-out calculations predict the evolution of the mean surface separation and real contact area, in reasonable agreement with that inferred from the measured friction. These results show that essentially the same squeeze-out process governs fluid removal during stationary contact and low-speed sliding, and that sliding-induced elastohydrodynamic effects have only a minor influence under these conditions.

cond-mat.soft↗

arXiv2026

Transient fluid removal at soft interfaces: Stationary squeeze-out and dynamic scraping in a block-on-flat contact

Fluid removal from rubber-substrate interfaces is crucial for maintaining friction during walking and vehicle braking on contaminated surfaces. We study the transient friction of rectangular rubber blocks sliding against tile and glass surfaces lubricated with water, glycerol, mud, or silicone grease. Two block configurations with different lengths in the sliding direction were tested after different stationary waiting times. For water, stationary squeeze-out is nearly complete before sliding begins. For glycerol, both stationary squeeze-out and sliding-induced fluid removal are important. For mud and grease, the steady-sliding state is reached after a sliding distance of the order of the block length, with little dependence on the preceding waiting time, showing that sliding-induced scraping dominates fluid removal for highly viscous substances. Dividing the contact into shorter blocks accelerates fluid removal by reducing the drainage distance and increasing the number of leading edges. Stationary squeeze-out calculations based on the measured surface roughness are in reasonably good agreement with the glycerol experiments. The results provide design guidelines for rubber tread blocks with multiscale drainage channels and sufficient compliance to promote transient fluid removal.

cond-mat.soft↗

arXiv2026

On the flash temperature in sliding rubber contacts

We present an analytical theory for the flash temperature for viscoelastic solids sliding on rigid and randomly rough surfaces. The theory takes into account the surface roughness on all relevant length scales.

cond-mat.soft↗

arXiv2026

Plastic smoothing of rough surfaces

When two metal blocks are squeezed together the stresses in the asperity contact regions are usually so large that the asperities deform plastically, at least at short length scales. Many tribology properties of contacts, such as the contact stiffness and the electric and thermal contact resistance, and the fluid flow at interfaces, depend on the surface topography and are hence modified by the plastic flow. Here I present a new way to obtain an effective power spectra of plastically deformed surfaces to be used in the Persson contact mechanics theory. I also present results for the surface height topography obtained using the plastically modified power spectra, and compare to the experimental results of Yusof and Ripin, who studied the influence of plastic flow on the topography for a smooth steel surface squeezed against a rough steel surface. Finally, I discuss why some surfaces after plastic deformation have similar Gaussian roughness as before plastic deformation, only with smaller roughness amplitude, while other surfaces shows very skewed roughness after plastic deformation.

cond-mat.soft↗

arXiv2026

On the flash temperature in accelerated sliding contacts

The temperature increase in the contact regions between solids in sliding contact can easily reach several hundred Kelvin and thereby dramatically affect friction and wear. Here I extend an earlier multiscale theory for the flash temperature (Ref. \cite{MP}) to the case of accelerated motion, and present numerical results illustrating the theory.

cond-mat.soft↗

arXiv2026

Adhesion-controlled sliding and the Stribeck curve in hydrophobic soft contacts

We present an experimental and theoretical study of dry and glycerol-lubricated sliding for polymethyl methacrylate (PMMA) cylinders with different surface roughness sliding on polydimethylsiloxane (PDMS) rubber. This system represents a hydrophobic soft contact, where adhesion may persist even in the presence of the lubricant and thereby modify both the real contact area and the sliding response. Dry-friction measurements, combined with contact-area calculations that include adhesion, provide a baseline for the lubricated study. For the two sandblasted surfaces, the measured Stribeck curves are described reasonably well by a mean-field mixed-lubrication theory with a fitted velocity-independent effective interfacial shear stress. In contrast, the smooth surface exhibits qualitatively different behavior. We attribute this to an adhesion-controlled sliding mode involving macroscopic Schallamach-wave-like instabilities at low sliding speeds, which are progressively suppressed as the sliding speed increases and forced wetting reduces direct solid-solid contact. The results show that, for soft hydrophobic contacts, the Stribeck curve cannot always be understood from classical fluid flow and load sharing alone. For sufficiently smooth and adhesive surfaces, adhesion changes not only the real contact area but also the sliding mode itself.

cond-mat.soft↗

arXiv2026

Flash temperature in sliding contacts: comparing theory with experiments

The temperature increase in the contact regions between solids in sliding contact has a huge influence on friction and wear. Here we test an analytical theory for the flash temperature, valid for randomly rough surface with multiscale roughness, by comparing the theory predictions with the experimental results of Sutter et al \cite{Sutter} for steel sliding on steel. The theory, which is based on the study of stress and temperature correlation functions, is valid for randomly rough surfaces with roughness on arbitrary many decades in length scale. Within the uncertainty of the experimental data (mainly the surface roughness power spectrum and the steel penetration hardness), there is good agreements between the theory and the experimental results.

cond-mat.soft↗

arXiv2026

On the flash temperature in sliding contacts

The temperature increase in the contact regions between solids in sliding contact can easily reach several hundred Kelvin and thereby dramatically affect friction and wear. The classical theories by Jaeger, Archard, and Greenwood, commonly used to estimate flash temperature, ignore the multiscale nature of real surfaces and instead approximate the frictional heat sources with circular or square shapes. Here, we present an analytical theory for the flash temperature valid for randomly rough surfaces with roughness across arbitrarily many decades in length scale. The theory extends established methods for stress correlation functions and peak stresses to temperature. Numerical results for rubber sliding on concrete, and granite on granite, are presented as illustrations. We show that classical theories for flash temperature fail severely for surfaces with multiscale roughness.

cond-mat.mtrl-sci↗

arXiv2026

Tire tread block dynamics

Temperature has a crucial influence on rubber friction and tire dynamics. The temperature field in a rubber tread block is the sum of the background temperature $T_0({\bf x},t)$, which varies slowly in time and space, and the flash temperature $ΔT({\bf x},t)$, which in nonzero only close to the macroasperity contact regions, and which varies rapidly in time often on the millisecond time scale. Here we study the motion of a single tire tread block and how it is influenced by the flash temperature. We also present a theory and experimental results for the size of the macroasperity contact regions. In particular, we show that for a large enough nominal contact area, in most cases the diameter $D$ of the macroasperity contact regions are nearly independent of the elastic modulus and the nominal contact pressure.

cond-mat.soft↗

arXiv2026

Granite sliding on granite: friction, wear rates, surface topography, and the scale-dependence of rate-state effects

We study tribological granite-granite contacts as a model for tectonic faulting, combining experiments, theory, and molecular dynamics simulations. The high friction in this system is not dominated by particulate wear or plowing, as frequently assumed, but by cold welding within plastically deformed asperity junctions. We base this conclusion on the observation that wear is repeatedly high after cleaning contacts but decreases as gouge accumulates, while friction shows the opposite trend. Moreover, adding water reduces wear by a factor of ten but barely decreases friction. Thermal and rate-dependent effects-central to most earthquake models-are negligible: friction remains unchanged between -40°C and 20°C, across abrupt velocity steps, and after hours of stationary contact. The absence of rate-state effects in our macroscopic samples is rationalized by the scale-dependence of pre-slip. The evolution of surface topography shows that quartz grains become locally smooth, with height spectra isotropic for wavelength below 10 microns but anisotropic at longer wavelengths, similar to natural faults. The resulting gouge particles have the usual characteristic sizes near 100 nm. Molecular dynamics simulations of a rigid, amorphous silica tip sliding on α-quartz reproduce not only similar friction coefficients near unity but also other experimentally observed features, including stress-introduced transitions to phases observed in post-mortem faults, as well as theoretical estimates of local flash temperatures. Additionally, they reveal a marked decrease of interfacial shear strength above 600°C.

physics.geo-ph↗

arXiv2026

Role of transfer films and interfacial cracking in metallic sliding wear

The origin of wear particles in metallic sliding contacts remains debated. Classical views based on cold-welded junctions suggest that plastic yielding of the real contact area should lead to large wear coefficients, in apparent contradiction with the small values typically measured for metals. Here we argue that this discrepancy can be resolved if most junctions do not directly produce wear particles, but instead cause metal transfer and the formation of a weakly bound transfer film. Wear then occurs intermittently when fragments of this film detach due to crack propagation at the interface between the transfer film and the underlying bulk metal. We perform unlubricated reciprocating sliding experiments on nominally smooth stainless steel, brass, and aluminum. For steel on steel, the wear mass loss shows an initial stage with negligible mass change up to a sliding distance of $\sim 2.4 \ {\rm m}$, followed by a linear regime. Transfer-film formation in dissimilar-metal contacts is evidenced by optical imaging, net mass gain of the steel slider, and energy-dispersive X-ray spectroscopy, and the collected debris is flake-like. These observations support a transfer-film-controlled wear mechanism associated with cold-welded junctions.

cond-mat.soft↗

arXiv2025

Rubber Friction: Theory, Mechanisms, and Challenges

Rubber friction is of major practical importance in applications such as tires, rubber seals, and footwear. This review article focuses on the theory and experimental studies of rubber friction on substrates with random roughness. We examine both steady sliding and accelerated motion, with particular attention to the origins of the breakloose friction force and the influence of pre-slip, elasticity, and flash temperature on friction dynamics. We further discuss rolling friction for cylinders and spheres, as well as sliding friction for triangular sliders on dry and lubricated rubber surfaces. Theoretical predictions are compared with experimental results obtained using different materials, geometries, and environmental conditions, highlighting the importance of accounting for multiscale roughness. Open challenges, such as the role of adhesion enhancement, energy dissipation due to crack opening, and the physical origin of the short-distance roughness cut-off, are discussed.

cond-mat.soft↗

arXiv2025

Leakage at interfaces: a comprehensive study based on Persson contact mechanics theory

We present a comprehensive study of gas leakage at interfaces based on Persson contact mechanics theory. A prototype syringe system consisting of a rubber stopper and a glass barrel is selected, where surface roughness is characterized using measurements from stylus profilometry and atomic force microscopy, and contact pressure distributions are obtained from Finite Element Method (FEM) calculations. Leakage prediction is performed using Multiscale Contact Mechanics (MCM) software. The predicted results show good agreement with experimental measurements under controlled dry conditions. Sensitivity analyses indicate that small variations in elastic modulus and contact pressure can significantly influence leakage, particularly near the percolation threshold. This work provides a generalized and validated framework for leakage prediction and offers practical guidance for the design of sealing systems in pharmaceutical and engineering applications.

cond-mat.soft↗

arXiv2025

Sliding wear: role of plasticity

We present experimental wear data for polymethyl methacrylate (PMMA) sliding on tile, sandpaper, and polished steel surfaces, as well as for soda-lime, borosilicate, and quartz glass sliding on sandpaper. The results are compared with a recently developed theory \cite{ToBe} of sliding wear based on crack propagation (fatigue), originally formulated for elastic contact and here extended to include plasticity. The elastoplastic wear model predicts wear rates that agree reasonably well with the experimental results for PMMA and soda-lime glass. However, deviations observed for quartz suggest that material-specific deformation mechanisms, particularly the differences between crystalline and amorphous structures, may need to be considered for accurate wear predictions across different materials. In addition, the model reveals a non-monotonic dependence of the wear rate on the penetration hardness $σ_{\rm P}$. Thus, for plastically soft material, the wear rate increases with increasing $σ_{\rm P}$, while for hard materials, it decreases. This contrasts with Archard's wear law, where the wear rate decreases monotonically with increasing $σ_{\rm P}$.

cond-mat.soft↗

arXiv2025

Sliding Friction of Hard Sliders on Rubber: Theory and Experiment

We present a study of sliding friction for rigid triangular steel sliders on soft rubber substrates under both lubricated and dry conditions. For rubber surfaces lubricated with a thin film of silicone oil, the measured sliding friction at room temperature agrees well with theoretical predictions obtained from a viscoelastic model originally developed for rolling friction. On the lubricated surface, the sliding friction is primarily due to bulk viscoelastic energy dissipation in the rubber. The model, which includes strain-dependent softening of the rubber modulus, accurately predicts the experimental friction curves. At lower temperatures ($T = -20^\circ {\rm C}$ and $-40^\circ {\rm C}$), the measured friction exceeds the theoretical prediction. We attribute this increase to penetration of the lubricant film by surface asperities, leading to a larger adhesive contribution. For dry surfaces, the adhesive contribution becomes dominant. By subtracting the viscoelastic component inferred from the lubricated case, we estimate the interfacial frictional shear stress. This shear stress increases approximately linearly with the logarithm of the sliding speed, consistent with stress-augmented thermal activation mechanisms.

cond-mat.soft↗

arXiv2025

Rubber wear on concrete: dry and in-water conditions

Rubber wear results from the removal of small (micrometer-sized) rubber particles through crack propagation. In this study, we investigate the wear behavior of Styrene-Butadiene Rubber (SBR) and Natural Rubber (NR) sliding on two different concrete surfaces under dry and wet (in water) conditions. Experiments are conducted at low sliding speeds ($\approx 3 \ {\rm mm/s}$) to minimize frictional heating and hydrodynamic effects. For two SBR compounds, we observe significantly higher wear rates in water compared to the dry state, with enhancement factors of $1.5-2.5$ for a low-glass-transition-temperature SBR compound ($T_{\rm g} = -50^\circ {\rm C}$) and approximately $4$ for a higher-glass-transition compound ($T_{\rm g} = -7^\circ {\rm C}$). In contrast, the NR compound showed no wear in water at low nominal contact pressures ($σ_0 \approx 0.12$, $0.16$, and $0.25 \ {\rm MPa}$), while at higher pressures ($σ_0 \approx 0.36$ and $0.49 \ {\rm MPa}$), the wear rates in dry and in-water states are similar. The findings provide insights into the mechanisms of rubber wear under varying environmental and mechanical conditions, highlighting the influence of material properties, interfacial effects, and applied pressures on wear behavior.

cond-mat.soft↗