Dynamic Friction Coefficient Research Articles

Natural Macromolecule-Based Lubricative Catheter Coatings with Sustained Adaptive Antibacterial Property for Encrustation and Infection Prevention.

Catheter-associated urinary tract infection (CAUTI) are a global health burden. Moreover, the friction during urinary catheter placement also induces pain in patients. Therefore, there is a pressing need to develop effective antibacterial and lubricative coatings on the surface of urinary catheter. In this work, a facile volatilization film-forming method is used to construct coatings on catheter surfaces. Xanthan gum (SR), which has good lubricative and antifouling properties, is oxidized to cross-link with multi-amino compounds, gentamicin (GS), and gelatin, to fabricate uniform coatings on silicone catheters (SR-GXGs). The structures of SR-GXGs are regulated by the components of the film formation solutions. The bacterial metabolism can produce an acidic micro-environment that can regulate GS release to achieve on-demand administration. SR-GXG2 can eliminate 99.99% of common pathogenic bacteria and reduce the dynamic friction coefficient by 98.73%, and showed high stability in a 7-day flowing experiment. In addition, the universality of this method is demonstrated on various kinds of matrices with different shapes, including commercial urethral catheters. In vivo, SR-GXG2can effectively avoid urinary tract injury and encrustation phenomenon because of its good anti-infection, antifouling, and lubricative properties. This work provides a promising strategy for developing multifunctional antibacterial coatings on medical catheters.

Calibration and experiments of discrete element flexible model parameters for kiwifruit stalk

A method combining experimental and simulation optimization was used to calibrate parameters to enhance the accuracy of discrete element model parameters during kiwifruit stem separation. First, physical experiments were conducted to determine the intrinsic and contact parameters of kiwifruit stalk. Second, the mechanical parameters of the kiwifruit stalks were determined using three-point bending and shear tests. On this basis, simulation tests were conducted on kiwifruit stalks by combining the Hertz-Mindlin model with a bonding model, and the optimal combination of bonding parameters was confirmed using the bending strength and maximum shear force. Finally, a discrete element model of the kiwifruit was built with the determined bonding parameters and simulated, and the reliability of the model was verified through mechanical tests. The results showed that the density was 867.5 kg/m3, Poisson's ratio was 0.26, the modulus of elasticity was 3.25 × 108 Pa, the recovery coefficient between the fruit stalks and steel parts was 0.365, and the average values of the static and dynamic friction coefficients between the kiwifruit stalks and steel parts were 0.268 and 0.152, respectively. The kiwifruit stem bonding parameters were normal stiffness per unit area kn=7.201×1011 N/m3, shear stiffness per unit area kt=2.379×1011 N/m3, critical normal stress σmax=5.937×108 Pa, critical shear stress tmax = 2.354×109 Pa, and bonded disc radius Rj=0.164 mm. Compared with the results of the mechanical tests, the relative errors of the bending strength and maximum shear of the discrete element model were 2.13% and 2.84%, respectively. The results showed that the discrete element model improves the simulation of the bending and shearing processes of kiwifruit stalks and is capable of characterizing the physical properties of kiwifruit stalks. The results of this study provide a theoretical foundation for the optimal design of end effectors.

Dynamic hysteresis of an oscillatory contact line

During oscillatory wetting, a phase retardation emerges between contact angle variation and contact line velocity, presenting as a hysteresis loop in their correlation – an effect we term dynamic hysteresis. This phenomenon is found to be tunable by modifying the surface with different molecular layers. A comparative analysis of dynamic hysteresis, static hysteresis and contact line friction coefficients across diverse substrates reveals that dynamic hysteresis is not a result of dissipative effects but is instead proportionally linked to the static hysteresis of the surface. In the quest for appropriate conditions to model oscillatory contact line motion, we identify the generalized Hocking's linear law and modified generalized Navier boundary condition as alternative options for predicting realistic dynamic hysteresis.

Tensile fracture behavior and friction and wear properties of TiB2 particle reinforced Al-Si matrix composites

In this study, TiB2/Al-Si composite material was fabricated by addition of Al-TiB2 master alloy, and the influence of varying micro-sized TiB2 particle content on the mechanical and tribological properties of the composite material was investigated. The results revealed that the introduction of TiB2 particles effectively refined the Al-Si matrix alloy microstructure, thereby enhancing the mechanical properties and wear resistance of the Al-Si matrix alloy. When the TiB2 particle content reached 0.8 wt%, the composite material exhibited optimal mechanical properties with a tensile strength of 318 MPa and elongation of 7.2 %, improving of 8.9 % and 69.1 %, respectively, compared to the matrix alloy. Moreover, wear rates of the composite material demonstrated significantly lower than the matrix alloy under different loading conditions in this paper. The improved mechanical properties of the composite material were attributed to grain refinement strengthening, second phase strengthening and the coefficient of thermal expansion strengthening. Under low loads, abrasive wear was the dominant wear mechanism; while under high loads, a combination of abrasive and adhesive wear occurred. The addition of TiB2 particles effectively enhanced the hardness of the matrix alloy, reduced the dynamic friction coefficient, suppressed adhesive wear, and improved the wear resistance of the composite material.

Friction in soft biological systems and surface self-organization: the role of viscoelasticity

AbstractFriction is a critical factor in the proper functioning of human organs as well as in the potential development of disease. It is also important for the design of diagnostic and interventional medical devices. Nanoscale surface roughness, viscoelastic or plastic deformations, wear, and lubrication all influence the functions of individual cells. The effects of friction in soft matter systems are quantified using different types of frictional coefficients, including the dynamic friction coefficient, friction-skin drag, and pressure drag. These coefficients are determined by the viscoelastic properties of the two systems in contact and their relative velocity. In this review, several biological systems are considered, including (i) epithelial tissues in contact with soft hydrogel-like implants, (ii) the collective migration of epithelial monolayers on substrate matrices, (iii) blood flow through blood vessels, and (iv) the movement of cancer cells past epithelial clusters along with the migration of epithelial cells within the cluster.

Evaluation Indexes of Skid Resistance of Epoxy Chip Seal Based on Texture Features at Different Scales

Epoxy chip seals are widely used to improve the skid resistance of cement concrete pavements, which is significantly affected by surface texture. However, current methods for characterizing the surface texture structure are not precise, and the standard is not uniform. Therefore, a high-toughness modified epoxy resin chip seal structure was developed to conduct an indoor accelerated abrasion test. The elevation data of the epoxy chip seal under different abrasion times and different abrasion loads were obtained using laser scanning, and the density/sharpness combination parameters were obtained using the Hilbert–Huang transform and spectral analysis. The correlation between the texture parameters and the dynamic friction coefficient was analyzed using a stepwise multivariate quadratic polynomial method. The results showed that the texture structure of the epoxy chip seal surface is positively distributed, and the macroscopic texture occupies 49.45%, while the probability of the microscopic texture is only 4.55%. Meanwhile, the correlation coefficient between the texture parameters and the dynamic friction coefficient is 0.9307, which demonstrates that the selected texture parameters discard the texture components unrelated to skid resistance performance and reflect the distribution of the pavement texture and the skid resistance performance well.

Viscosity Characteristics of Ideal Lubricants to Reduce Stress on Intestinal Mucosa During Balloon-Assisted Enteroscopy.

Balloon-assisted enteroscopy (BAE) is highly invasive and carries a higher risk of complications such as pain and perforation during enteroscope insertion. Applying lubricants to the small intestinal mucosa and reducing the dynamic friction coefficient (DFC) between the small intestinal mucosa and endoscopic shaft (ES) (or overtube (OT)) can minimize the invasiveness of BAE. However, the ideal viscosity characteristics of these lubricants remain unknown. In this study, a model is developed to measure the DFC using human small intestines from forensic autopsies and determine the ideal viscosity of low-friction lubricants that exhibit a minimal DFC, thus reducing the pressure on the intestinal lining during the procedure. The results reveal that the DFC is strongly correlated to the lubricant's viscosity rather than its chemical composition. Low-friction lubricants with viscosities within 0.20-0.32 and 0.35-0.58 Pa·s (at shear rates of 10 s-1) for the OT and ES, respectively, can significantly reduce the DFC, yielding optimal results. These findings highlight the role of viscosity in minimizing the friction between the equipment and small intestinal mucosa. The ideal low-friction lubricants satisfying the aforementioned viscosity ranges can minimize the invasiveness of BAE by decreasing the friction between the equipment and intestinal lining.

Finite Element Simulations and Statistical Analysis for the Tribological Design of Mutually Textured Surfaces and Related Experimental Validation

Abstract In the last few decades, micro-texturing has become a widely studied technique to modify the frictional behavior between surfaces in both dry and lubricated regimes. Among all the available techniques, the laser surface texturing appears to be fast, clean, and flexible, and thus a good candidate in realizing surface micro-patterns, also for the improvement of the tribological performance of automotive components when subjected to dry friction. For this reason, in the present work, the tribological response of four different patterns of micro-holes on two contrasting materials, specifically silicon carbide and carbon black have been investigated with a coupled experimental–numerical approach. The static and the dynamic friction coefficients have been extracted from the 25 different combinations of these surface textures including the flat counterparts. Then, the influence of the holes diameter, their density, and the material has been studied thanks to a multivariate linear regression. Specifically, it emerged that, in a dry regime, the most emerging parameter is the micro-holes diameter, for both static and dynamic frictions. Moreover, for both static and dynamic frictions, the material which more influences the effects of patterns to the overall frictional behavior is here the stiffest one. These insights for the design of micro-patterned surfaces with controlled frictional properties could be useful for those applications in which a dry friction regime is present.

Dynamical friction in dark matter spikes: Corrections to Chandrasekhar’s formula

We consider the intermediate mass-ratio inspiral of a stellar-mass compact object with an intermediate-mass black hole that is surrounded by a dark matter density spike. The interaction of the inspiraling black hole with the dark matter particles in the spike leads to dynamical friction. This can alter the dynamics of the black hole binary, leaving an imprint on the gravitational wave signal. Previous calculations did not include in the evaluation of the dynamical friction coefficient the contribution from particles that move faster than the inspiraling black hole. This term is neglected in the standard Chandrasekhar treatment where only slower moving particles contribute to the decelerating drag. Here, we demonstrate that dynamical friction produced by the fast moving particles can have a significant effect on the evolution of a massive binary within a dark matter spike. For a density profile ρ∝r−γ with γ≲1, the dephasing of the gravitational waveform can be several orders of magnitude larger than estimated using the standard treatment. As γ approaches 0.5 the error becomes arbitrarily large. Finally, we show that dynamical friction tends to make the orbit more eccentric for any γ<1.8. However, energy loss by gravitational wave radiation is expected to dominate the inspiral, leading to orbital circularization in most cases. Published by the American Physical Society 2024

EXPERIMENTAL DETERMINATION OF DYNAMIC COEFFICIENT OF AMONTON-COULOMB DRY FRICTION

The purpose of the study is to experimentally determine the dynamic coefficient of dry friction between different materials under vibrations due to the initial deflection. The principle of dry friction between the grillage and the foundation is used for the seismic isolation of buildings and structures. A measuring complex with corresponding strain-gauge measuring channels was prepared on the laboratory one-component shaking stand to record the relative and absolute displacements of two-mass systems. A theoretical solution to this nonlinear problem was obtained with the additional use of a special logical algorithm to determine the direction of the dry friction force between two masses. The value of the dynamic coefficient of dry friction was determined by comparing the numerical solution to the problem with experimental records by selecting the value of the dry friction coefficient. The values of the mass of rubbing elements with the surface treatment of the steel-on-steel contact and a separate option with lubrication of the contact surface with fluoroplastic 4-on-fluoroplastic 4 gaskets were changed in the experiment. The maximum velocity of the platform in experiments corresponds to a 9-point earthquake on the MSK-64 scale.

Vibration Control of Corrugated Steel Web Box Girder Bridge with Friction Pendulum Isolation

In order to investigate the feasibility and applicability of friction pendulum bearings for vibration control of large-span space beam-arch bridges with corrugated steel web box girders, taking the Huian Yellow River Bridge in Guide County, Qinghai Province, China, as an example. A three-dimensional calculation model of the friction pendulum isolation space beam-arch composite bridge with a corrugated steel web was established by MIDAS, the modal analysis was carried out, and the damping effect of the friction pendulum isolation bridge was investigated using the response spectrum and the time history analysis methods; the influence of the design parameters of the friction pendulum isolation on the reduction effect was further analyzed. The results show that the friction pendulum isolation improves the stress conditions of both the girder and the pier and reduces the displacement and acceleration of the pier top, as well as reduces the acceleration of the girder, and the damping ratio is more than 50%. The optimal dynamic coefficient of friction and the radius of curvature for the corrugated steel web composite bridge are 0.04 and 3.0 m, respectively. Friction pendulum isolation has a good seismic absorption effect and provides an effective way for the seismic control of the corrugated steel web composite bridge. Doi: 10.28991/CEJ-2024-010-10-01 Full Text: PDF

RESISTANCE OF HEAT-RESISTANT YTTRIUM-CONTAINING SEALING COATINGS TO MECHANICAL FRACTURE WHEN FORMING CUTTING PATHS

According to the results of tribotechnical tests of coatings made of KNA-82 alloy ligatures with the addition of yttrium of 0.1%, 0.3%, 0.5%, data were obtained that allowed us to establish the nature of changes in the dynamic coefficient of friction over the test period and numerous values of the energy intensity of material wear. The evaluation of coatings formed by the gas-flame and ion-plasma method was based on the following premise. The maximum resistance to mechanical fracture is determined by the manifestation of a constant minimum value of the dynamic coefficient of friction. This serves as an indicator of reduced friction force before reaching the fatigue limit. Another key factor is the number of separated particles produced per unit of integral work during the friction process. These evaluation parameters are lined up in a row by the number of points from 1 to 4. The maximum score corresponds to the maximum resistance, i.e., a lower value of the energy intensity of material wear and the minimum value of the stable friction coefficient. It has been determined that the same coincidence of these parameters according to the scores is almost at all stages of testing (I-III) was the coating formed by the gas-flame method with a yttrium concentration of 0.3%-0.5%. The exception was the coating formed by the ion-plasma method with a yttrium concentration of 0.1% at the fourth stage of testing.

A Euler-lagrange Model of dynamic internal friction

A Euler-Lagrange model of dynamic internal friction is proposed and is shown to match the frequency and decay of oscillations in both simple extension (pull) and cantilever beam experiments. The proposed dynamic internal frictional stress, τij, is proportional to the rate of change of the engineering stress, σ˙ij. i.e.τij=μmσ˙ij,with μm the dynamic internal friction coefficient. A single value of the dynamic internal friction coefficient is shown to match the results of the experiments for a number of different geometries of the silicon rubber, Dragon SkinTM. Dragon SkinTM is used in skin effects for movies and in prosthetics and cushioning applications. It is chosen here because of its ease of preparation and relatively simple non-linear stress-strain response. Because of these characteristics, it provides a simple starting place for simulating more complicated synthetic rubber and biological materials, which are used in a myriad of commercial applications.

Sticky feet: a tribological study of climbing shoe rubber

This study examines the tribological properties of climbing shoe rubbers, challenging the common belief in the climbing community that softer rubbers are inherently grippier. This study investigates the mechanical and wear characteristics of climbing shoe rubbers by employing a high-precision modular mechanical testing environment (Bruker UMT TriboLab) and representative granite counter-surfaces. Key parameters, including surface roughness, Shore A hardness, interfacial adhesion, static and dynamic friction coefficients, and material wear patterns, were analyzed. The mechanical properties of each rubber compound were characterized through Shore A hardness testing and ball indentation–retraction tests, measuring indentation force, energy, and adhesive properties. Sliding friction tests, simulating real climbing conditions, were conducted to understand the tribological behavior of each rubber compound under different loads, further analyzing static and dynamic friction coefficients and wear characteristics. The findings of this study indicate that rubber performance is a convolution of several factors, including material hardness, surface roughness, and interfacial adhesion. Contrary to popular belief, softer rubbers did not consistently exhibit superior tribological characteristics. The findings of this study suggest that climbing shoe selection and design should consider a broader range of material characteristics beyond hardness, emphasizing the role of surface roughness and adhesion in determining overall frictional performance. This research offers valuable insights for the climbing community, providing methodologies to benchmark climbing rubber material characteristics.

基于 EDEM 离散元方法的盐碱土壤参数标定与测试

In this study, saline soil parameters were calibrated based on EDEM discrete element method, soil density, soil elastic modulus, soil shear modulus, soil particle size distribution and Poisson's ratio were determined. The Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) model was used to simulate the characteristics of soil stress and strain of particles under external forces. The JKR contact parameter between saline soil particles was used as a test factor, and the soil accumulation angle was used as a test index to carry out the saline soil contact parameter calibration test. It was finally determined that an elastic recovery coefficient of 0.262, a static friction coefficient of 0.263, a dynamic friction coefficient of 0.234, and a JRK surface energy of 10.084 were the optimal combinations of contact parameters for saline soils.

An elementary approach based on variational inequalities for modeling a friction-based locomotion problem

We propose an elementary proof based on a penalization technique to show the existence and uniqueness of the solution to a system of variational inequalities modeling the friction-based motion of a two-body crawling system. Here for each body, the static and dynamic friction coefficients are equal.

Frictional Properties of Biomimetic Micro-Hexagonal-Textured Surfaces Interacting with Soft Counterfaces under Dry and Wet Conditions.

Biomimetic micro-hexagonal-textured surfaces have sparked interest for their application in fields that demand high friction and adhesion, such as micro-robotics and biomedicine. Despite extensive research conducted on this specific microstructure, its friction behavior against soft counterfaces remains a topic that has not been fully investigated yet. This study examines how micro-hexagon textures behave when they come into contact with engineered and biological materials like gelatin and chicken skin in dry and wet conditions. The results show clearly that under dry contact conditions, flat surfaces generate higher friction compared to hexagon micropattern surfaces. Under wet conditions, hexagon micropattern surfaces generate higher friction compared to flat surfaces. In wet conditions specifically, the static coefficient of friction is up to 13 times greater than that of a flat specimen against glass, up to 11 times greater against gelatin, and up to 6 times greater against chicken skin. For the dynamic coefficient of friction, the patterned surface demonstrates a maximum increase by a factor of 28 against glass, 11 against gelatin, and 5 against chicken skin. These results further develop our knowledge of these hexagon micropattern surfaces and pave the way for their utilization in future technological advancements in which soft and wet counterfaces are to be considered, such as in biomedical applications that can benefit from increased friction in wet conditions for better control and stability.

Some Aspects of the Effects of Dry Friction Discontinuities on the Behaviour of Dynamic Systems

Most studies in the literature consider the value of the coefficient of dynamic friction to be constant. We studied the evolution of a dynamic system when the coefficient of friction results in different values depending on the contact surfaces. A system with four balls fixed on an aluminium plate was driven with constant velocity into motion on the coaxial races of two identical outer bearing rings. The assembly presents a motion with periodic variable amplitude between two extremes, a fact that suggests the presence of a periodical excitation. The test was repeated, but this time, new bodies were used, which were two identical bodies made of two balls rigidised via a short cylindrical rod. When the rings were driven into rotational motion, the two bodies performed different motions; if the bodies were inter-changed, the differences between the motions remained. The rings were analysed, and a small region on the race of one ring was observed, where the roughness was considerably greater than the rest of the surface. Then, a mathematical model for the dynamic system with different friction coefficients was proposed and solved. This model is capable of simulating different situations, such as oscillatory motion and circular motion, with or without separation of the contacting bodies. Here, we present a dynamic model with Hertzian contact points in the presence of dry friction, with the coefficient of friction changing suddenly on the contacting surfaces.

Characterization of friction between metal-polymer material pairs with different speeds and surface pressures

Abstract Engineering design requires accurate knowledge of the friction conditions of material pairs. The friction coefficient (static or dynamic) depends on many parameters in addition to the pairs of materials used (e.g. surface roughness, temperature, humidity, surface pressure, etc.). In this study, based on our own measurements, we present the friction conditions of an aluminum (Al 6082-T6) – polypropylene homopolymer surface pair under different surface loads (5-15 MPa) and different relative speed differences (4-8–48-96 mm/min). The results of the experiments show that the static and dynamic friction coefficients decrease with the increase of surface load. As relative speed increases, the dynamic coefficient of friction increases, while the static coefficient of friction can be considered constant.

Static and dynamic friction and wear of cobalt-based coatings at elevated temperatures

Advanced ultra-supercritical power plants, in which steam temperatures exceed 700 °C, demand the development of protective coatings, particularly for valves governing the steam flow where sealing surfaces are subjected to high static tribological solicitations. In this context, we systematically investigated the friction (static and dynamic) and wear of two cobalt-based coatings and one nickel-based substrate. Results indicate that oxidation kinetics exhibits a double-edged sword effect in terms of tribological properties at elevated temperatures. Fast oxidation kinetics promotes the sintering of oxides, generating a smoother oxide tribofilm and lowering the dynamic coefficient of friction (COF). However, this can also significantly increase the static COF over loading time due to welding/sintering of oxidized asperities, leading to increased torque requirements for valve operation.