Friction Coefficient Research Articles

Analysis of bolt bonding surfaces by the finite element method based on the equivalent Iwan model

This study establishes a finite element model based on the Iwan model to accurately characterize the force–displacement relationship and energy dissipation in bolted joints under small-amplitude tangential displacement. The force–displacement behavior of the Iwan model is transformed into a stress–strain relationship using a hybrid hardened intrinsic model. A subroutine developed with UMAT and UHARD is used to simulate the elastic–plastic behavior of the Iwan model during surface contact in the finite element model. Three-dimensional modeling and joint simulation are conducted using ABAQUS software. Experimental data verify the model's validity, and the effects of multiple factors on the bolted bonding surface are analyzed. The influence of friction coefficient, cyclic displacement amplitude, and preload on the force–displacement relationship of the bolted bonding surface is explored. Polynomial interpolation of the loading and unloading curves is applied to investigate the energy dissipation phenomenon. Results show that the finite element method can effectively reflect the hysteresis and energy dissipation behavior of the bonding surface. Increased friction coefficient and preload improve residual stiffness and energy dissipation capacity, while larger cyclic displacement amplitudes increase energy dissipation but have a minimal effect on residual stiffness.

Microstructural, mechanical, and wear properties of ultrasonic assisted stir casted A356 Alloy/AlN composite

The ultrasonic-assisted stir-casting method has effectively prepared A356 alloy/AlN composites. The ultrasonic treatment and integration of AlN particles are shown to greatly enhance the mechanical and wear characteristics of the matrix via grain refinement. By incorporating 9 vol.% of AlN reinforced particles, the average grain size of A356 alloy was decreased from 36 μm to 10 μm. Additionally, the hardness and tensile strength experienced a respective rise of 60.6% and 32%. With an increase in the volume percentage of AlN particles, it is found that both the wear rate and the friction coefficient decreased. It is also observed that the A356 alloy displayed severe wear, whereas the composites exhibited moderate wear.

Influence of Detonation Spraying Parameters on the Microstructure and Mechanical Properties of Hydroxyapatite Coatings.

The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation of bioactive ceramic coatings. Calcium-phosphate materials based on hydroxyapatite have been proposed as bioactive ceramic coatings on titanium implants for the effective acceleration of bone tissue healing. To obtain bioactive ceramic coatings, pulse power sources are best suited, namely detonation spraying, in which the energy of the explosion of gas mixtures is used as a source of pulse action. The pulse mode of operation in the detonation spraying method is preferable for the formation of bioactive ceramic coatings. It provides a high velocity of hydroxyapatite particles, which promotes their effective fixation on the titanium substrate, while minimizing the heating of the material. This approach preserves the substrate structure and improves the coating adhesion. Four different types of coatings with varying O2/C2H2 molar ratios, ranging from 2.6 to 3.7, were obtained using detonation spraying. Powders and obtained coatings of hydroxyapatite were studied by Raman spectroscopy and XRD structural analysis. The results of XRD phase analysis showed the partial conversion of the hydroxyapatite phase to the α-tricalcium phosphate (α-TCP) phase during the detonation spraying process. The results obtained by Raman spectroscopy indicate that hydroxyapatite is the main phase in coatings. All hydroxyapatite-based coatings exhibited hydrophobic properties, which was confirmed by contact-angle values above 90° in wettability tests, characteristic of hydrophobic surfaces. The adhesive strength of the coatings was measured by the scratch test method. Tribological tests were conducted using the ball-on-disk method under both dry conditions and in Ringer's solution. This approach enabled the evaluation of wear resistance and friction coefficient of the coatings in different environments, simulating both lubrication-free conditions and those resembling physiological environments.

Constraint on the background stress in the source region of the 2016 Kumamoto earthquake sequence based on temporal changes in elastic strain energies and coseismic stress rotation

Summary We investigated the deviatoric stress magnitude of the background stress fields before the 2016 Kumamoto earthquake sequence in Japan based on temporal changes in elastic strain energies caused by the mainshock and coseismic stress rotation. We modelled the six components of background stress fields from stress orientations together with the parameter of effective friction coefficients (μ’ = 0.3, 0.15, 0.1, 0.05, and 0.03) using the 3-D Mohr diagram. We computed the absolute stress fields immediately following the primary events (the largest foreshock and mainshock) of the earthquake sequence by combining coseismic stress change fields with background stress fields. The total amount of elastic strain energy released by the mainshock increased with the effective friction coefficient. Considering the energy balance in which some part of the released energy must be consumed as radiated energy, we understood that the model with μ’ = 0.03 was unrealistic. We also examined the dependence of coseismic stress rotation on the effective friction coefficient. Furthermore, we applied a stress inversion method to moment tensor data of earthquakes to directly estimate coseismic stress rotation. Comparing the theoretical and estimated coseismic stress rotations, we concluded that the models with μ’ = 0.3 and 0.15 were more consistent with the observations than those with μ’ < 0.1. In the reasonable models, the deviatoric stress magnitudes were 37–65 and 39−70 MPa at a depth of 10 km on the northern and southern source faults, respectively.

APPLICATION OF ELECTROLYTE BASED ON SODIUM CARBONATE FOR ELECTROLYTEPLASMA SURFACE HARDENING OF STEEL 45

This article evaluates the electrolyte-plasma hardening (EPH) of steel 45 using an electrolyte based on sodium carbonate (Na₂CO₃). Theoretical foundations of the electrolysis process of a sodium carbonate aqueous solution were studied during the course of the work. The mechanical and tribological properties of 45 steel samples after EPH were studied. It was found that with an electrolyte composition of 20% Na₂CO₃ and 80% distilled water, a hardened zone with a thickness of up to 5 mm is formed after EPH. The increase in microhardness reached up to 690 HV, which corresponds to a 3–3.5 times increase compared to the initial state. The results of tribological tests showed that the friction coefficient of steel 45 decreased after EPH, indicating a significant improvement in tribological characteristics compared to the initial value before hardening. Electrochemical tests on the corrosion resistance of steel 45 were also carried out. After EPH, the corrosion rate significantly decreased for steel 45 samples, indicating its highest corrosion resistance.

The Exposure Height of Silicon Particle with Round Edges Effect on the Tribological Property of Al-Si Alloy Cylinder Liner

In order to improve the wear resistance of Al-Si alloy cylinder liners, surface treatment is usually used. The Al-Si alloy cylinder liner samples were prepared by mechanical grinding and laser finishing. The mechanical grinding samples were carried out by the independent design and development of a grinding machine. The laser finishing samples were laser-heated by a CO2 continuous transverse-flow laser. Both of the two surface treatments could provide the surfaces of protruding silicon particles with round edges to improve the wear resistance. However, in the exposure height of silicon particles with round edges, the study was lacking. The exposure height of silicon particles is important to the tribological properties of the Al-Si alloy cylinder liner, and should be analyzed in detail. The wear tests were completed by a contraposition reciprocating wear test rig under lubrication. It was found that when the silicon particles were exposed on the surface of the Al-Si alloy cylinder liner sample by 1.2 μm, the mechanical grinding samples and laser finishing samples all exhibited minimum friction coefficients and weight losses. This paper confirms that a suitable exposure height of silicon particles would reduce the probability of adhesion wear and abrasive wear of Al-Si alloy cylinder liners and increase the lubrication. It presents an excellent tribological property. However, when the exposure height of silicon particles is too high, the silicon particle is easily prone to plastic deformation or even falls off during the friction process due to the high stress and larger plastic contact index.

Mechanical and Tribological Properties of Carbon Fiber Reinforced POM Composite Filled With Maleamidic Acid Treated Carbon Nanotube

ABSTRACTIn order to attain improved mechanical properties of the carbon fiber (CF) reinforced polyoxymethylene (POM) composite, maleamidic acid treated carbon nanotube (CNT) was deposited on carbon fiber. The mechanical properties of composites have been investigated. The tensile strength values of the treated CF/POM composites at all CNT mixing ratios are found to be higher than that of untreated one. The surface morphologies of the fractured surfaces of the composites were recorded using scanning electron microscopy (SEM) to gain information about the fiber–matrix interfacial adhesion in the composites. The friction coefficient of all the CF/POM/CNT composites decrease as the load increases from 10 to 20 N under the same sliding speed of 1000 r/min. XPS results showed that the formation of C–O, C=O, and O–C=O based species give rise to chemical bonds of the CF and the POM.

A comprehensive investigation into the effect of vertical component of ground motion on response of sliding unanchored blocks

This study aims to quantify the effect of the vertical component of ground motion on the seismic response of sliding rigid blocks, in terms of maximum and residual displacements. A multi-stripe analysis approach is employed to examine the response with and without the vertical component under various levels of ground motion intensity. First, a parametric study is conducted using a Coulomb friction model with a constant coefficient of friction that does not account for any dependence of the friction coefficient on velocity or pressure. It is shown that the effect of the vertical component on maximum and residual displacement is more pronounced for ground motions that can barely initiate sliding. Moreover, the influence of the vertical component on the residual sliding displacement is higher than that on the maximum displacement. Subsequently, to account for the friction coefficient dependence on pressure and sliding velocity, two interface cases (steel-steel, and concrete-concrete) are analyzed. It is found that even when a variable coefficient of friction is used, the overall trends observed for a constant coefficient of friction do not change.

Experimental Investigations of Friction Properties of Carbon Particles Derived from Sargassum Algae

In Caribbean islands, the washing ashore of tons of pelagic Sargassum spp., consisting of two species Sargassum fluitans and Sargassum natans, has been regularly occurring since 2011. As green lubrication is a growing trend in the tribology industry, biochar is a promising alternative. Sargassum biochars, produced from Sargassum pelagic algae, are therefore being studied as solid lubricants. This study aims to explore their potential applications. Biochars from brown algae were pyrolyzed at 400 °C and then annealed at different temperatures (from 600 °C to 1500 °C). The Raman spectra collected on the different biochars showed that there was a structural organization of the biochars as the temperature increased. The tribologic properties of the biochars were studied and compared to a solid lubricant reference (exfoliated graphite). Raman spectroscopy analysis revealed a progressive structural reorganization with increasing temperature, leading to a 58% reduction in the coefficient of friction. The morphology and the structure of the tribofilm are investigated by profilometry, scanning electron microscopy, and Raman microspectrometry. Overall, these results can be considered as a first step for utilizing the biochar derived from brown algae Sargassum sp. as an additive in the lubricant industry, for the purpose of emission reduction.

Cold‐Sprayed Boron‐Nitride‐Nanotube‐Reinforced Aluminum Matrix Composites with Improved Wear Resistance and Radiation Shielding

In this study, the influence of cold‐spray processing on the integration of 1D boron nitride nanotubes (BNNTs) into aluminum (Al) matrix composite deposits is delved into. Successful deposition of Al‐BNNT composite is achieved by pre‐spray dispersion of BNNTs in Al powder via wet mixing aided by ultrasonication. Pure Al powder deposition at 380 °C is limited by nozzle clogging, restricting the deposit thickness to 0.2 mm, while the presence of BNNTs enables longer spraying due to nozzle cleaning and damping by hard BNNTs, allowing thicker Al‐BNNT deposits of about 2 mm. Microstructural analysis reveals severely deformed Al splats decorated with a uniformly distributed network of BNNTs at the intersplat boundaries, reducing the porosity from 8% to 4% and increasing the splat flattening by 40%. Tribological testing demonstrates resistance of BNNTs to normal force, resulting in a 21% improvement in coefficient of friction and a 65% reduction in wear volume in the Al‐BNNT composite. Additionally, incorporating 3 vol.% BNNTs enhances the neutron radiation shielding by 35%. These improvements in the composites are attributed to reduced porosity and the inherent properties of BNNTs, such as high strength, the ability to produce tribofilm lubrication during dry sliding wear, and their high neutron absorption cross‐sectional area.

Effect of Rolling Process Parameters on Transverse Cracks on the Surface of Q345 Steel

This article examines the evolutionary behavior of transverse surface cracks in Q345 steel during the hot‐rolling process under various rolling conditions. “V”‐shaped cracks are prefabricated on the billet surface for laboratory hot‐rolling tests, and a corresponding rolling model is developed to validate its accuracy. The slab rolling model is established based on actual onsite rolling process parameters. The aim is to analyze the effects of different rolling conditions on the surface crack morphology and aspect ratio. The results indicate that variations in roll diameter (1400, 1300, and 1200 mm) influence crack propagation, with cracks unfolding earlier when the roll diameter is 1400 mm. At varying initial rolling temperatures (1300, 1200, and 1100 °C), cracks begin to unfold earlier at the highest temperature of 1300 °C. When examining different friction coefficients (0.4, 0.5, and 0.6), cracks unfold earlier at the highest coefficient of 0.6. Similarly, at different rolling speeds (3, 4, and 5 m s−1), cracks unfolded earlier at the highest speed of 5 m s−1. Analysis of changes in crack depth and aspect ratio during rolling shows that the initial few passes have a greater influence on crack depth and unfolding. In the later stages of rolling, cracks continue to unfold, though the depth shows minimal variation, and the aspect ratio tends to approach zero.

Friction and Wear Resistance of Nanostructured TiNi Shape Memory Alloy

TiNi shape memory alloys with a superelastic effect are widely used in tribological interfaces requiring high wear resistance. One of the common approaches to reducing the wear of various metals is the application of severe plastic deformation (SPD), resulting in structural refinement and corresponding hardening. This paper investigates the tribological behaviour of a nanostructured Ti49.3Ni50.7 shape memory alloy produced using SPD. The friction and wear characteristics of the alloy at room temperature are compared in the coarse-grained, nanostructured, and nanostructured aged states. Through hardness measurement and transmission electron microscopy, it is shown that the transformation of a coarse-grained state into a nanostructured state increases wear resistance and hardness, reduces the coefficient of friction, and changes the friction mechanism. Formed nanoparticles during ageing in a nanostructured state further increase wear resistance.

Enhancing Water Lubrication in UHMWPE Using Mesoporous Polydopamine Nanoparticles: A Strategy to Mitigate Frictional Vibration.

Establishing a persistent lubrication mechanism and a durable tribo-film on contact surfaces is identified as crucial for improving the tribology and vibration characteristics of polymer materials under water-lubricated conditions. This study focuses on enhancing tribological performance and reducing frictional vibrations in ultrahigh molecular weight polyethylene (UHMWPE) through the incorporation of mesoporous polydopamine (MPDA) nanoparticles. In the experiments, MPDA nanoparticles were synthesized and blended with UHMWPE to create UHMWPE/MPDA composites. The interactions between these composites and zirconia (ZrO2) ceramic balls under water lubrication were examined. The results show that when the MPDA content of the composite is 1.5 wt %, the coefficient of friction and wear rate are reduced by 40% and 52% compared with those of pure UHMWPE, respectively. This notable enhancement helped to mitigate friction-induced vibrations, particularly those caused by intermittent sticking and slipping motions. MPDA nanoparticles were shown to act as reservoirs for water, releasing and replenishing water based on the loading conditions, which sustained continuous water-based lubrication at the composite surfaces. Additionally, the surface deformation behavior of the composite material is significantly weakened, which provides a more stable friction surface. This work introduces a novel approach to enhance the interface stability of polymers in water-lubricated environments, offering guidance for developing advanced materials and reducing friction and wear in engineering applications.

Enhanced tribological performance of PLA/CNC composites: A comparison with phenolic resin and nylon

PLA has been developed to replace plastic because it is degradable. For more advanced applications, more research is needed on PLA. This study investigates the tribological properties of phenolic resin, nylon, and PLA/CNC composites under varying sliding distances and loads. Both phenolic resin and nylon demonstrate exceptional wear resistance and stable friction coefficients. PLA/CNC composites exhibit improved wear resistance, showing a 17% reduction in friction coefficient at a 3 wt.% CNC content. While the wear volume of PLA/CNC composites increases with sliding distance, the addition of CNC enhances PLA’s self-lubricating properties and overall wear resistance. The correlation between dissipated energy and wear volume confirms that higher CNC content significantly improves the durability of PLA. These findings suggest that CNC has considerable potential as an additive to enhance the tribological performance of PLA composites, making it a valuable material for various applications requiring superior wear resistance.

Non-Amontons frictional behaviors of grain boundaries at layered material interfaces

Against conventional wisdom, corrugated grain boundaries in polycrystalline graphene, grown on Pt(111) surfaces, are shown to exhibit negative friction coefficients and non-monotonic velocity dependence. Using combined experimental, simulation, and modeling efforts, the underlying energy dissipation mechanism is found to be dominated by dynamic buckling of grain boundary dislocation protrusions. The revealed mechanism is expected to appear in a wide range of polycrystalline two-dimensional material interfaces, thus supporting the design of large-scale dry superlubric contacts.

Interfacial interaction mechanism and theoretical bond strength model between UHPC-CA and steel bar

The bond property is the basis of the bear collectively load between the steel bar and Ultra-High Performance Concrete with Coarse Aggregate (UHPC-CA). In this paper, the theoretical calculation method of bond strength between UHPC-CA and high-strength steel bar is studied. The chemical adhesion strength, friction coefficient, and mechanical interlock process of the two were investigated respectively through the refined bond property tests. The failure model is established from the interlock failure characteristics, and the bond strength is obtained theoretically. Results show that the chemical adhesion strength and friction coefficient between UHPC-CA and steel bars are 0.07MPa and 0.5, respectively. The friction coefficient between UHPC-CA is 1.15. The interlock failure process of UHPC-CA and steel bars can be divided into three stages: uncracked stage, crack development stage, and split stage. The crack develops at an angle of 52° to the steel bar's axis and tends to stagnate at a height of 4.5 times the rib. A theoretical bond strength model is established and it is proved that the model is applicable not only to UHPC-CA but also to UHPC. This study can provide a theoretical basis for determining the anchorage length of steel bars in the design of UHPC-CA/UHPC structure, and can also provide a reference for the formulation of relevant standards.

Advanced Machine Learning and Experimental Studies of Polypropylene Based Polyesters Tribological Composite Systems for Sustainable Recycling Automation and Digitalization

Digitalization and automation are emerging solutions to the complex problems of recycling. In this research work, the experimental and Python based Archard deep learning wear rate models are introduced regarding recycling automation and composite tribological systems optimization. The optimum polyester fibers (PESF) of length of 3-3.5 mm were used for fabrication of polypropylene (PP)-PESF composite systems. The deformation, high texture, asperities, and micro-cracks were observed during scanning electron microscope and machine-learning studies. The lowest experimental value of abrasive wear of 3.0 × 10-6 mm3/Nm was observed for PP. Comparatively, higher experimental values of abrasive wear of the PP-PESF composites are found in the range of 4.35 × 10-6 to 4.7 × 10-6 mm3/Nm due to presence micro-defects on the surface of composites. The experimental values of Coefficient of friction (COF) of PP and PP-PESF are found in the range of 0.70 - 0.8 and 1.1 - 1.3, respectively. The experimental values of abrasive wear and COF are found compatible with literature. Similarly, the simulated values of abrasive wear of PP and PP-PESF composites are predicted in the range of 4.8×10-7 to 3.75×10-7 mm3/Nm, respectively. The predicted values of PP and PP-PESF composite show better resistance towards abrasive wear. The proposed experimental and simulated (in terms of Python coding, machine learning, image processing, artificial intelligence, and deep learning studies) research work can be introduced industrially for automation as well as digitalization of grinding of PES waste, processing, tribological testing, and SEM characterization evaluations.

Mass discharge rate of granular flow in eccentric silos with variable side wall friction

There are many studies on the effect of side wall friction on mass discharge rate (MDR), but the physical mechanism is lacking. In this paper, by changing side wall friction of eccentric silos, the relationship between macroscopic MDR and microscopic frictional coefficient was established, and the regulation of MDR up to a range of 40 % was realized. Furthermore, it is revealed that the variation of MDR is caused by the change in geometric structure of free-fall arch (FFA). In addition, the velocity of particles on FFA is the same under different MDR. The reason is that under high frictional coefficient, the gravitational potential energy of particles is more dissipated in the rotational motion caused by resistance. This work explains for the first time the mechanism of the frictional coefficient on MDR, and provides a data reference for improving the theoretical model of MDR.

Enhancing dry sliding wear resistance of high-Mn austenitic steel by adding N

In this study, the wear resistance of two high-Mn austenitic steels, i.e., Fe−18.5Mn−7Cr−0.6C and Fe−18.5Mn−7Cr−0.6C−0.21N was tested in dry sliding friction on a disc friction and wear testing machine (MMU-5G). The wear behavior and microstructure evolution of the two tested steels were investigated. The results revealed that adding N enhanced the wear resistance of high-Mn austenitic steel due to the synergistic effects of hardness, wear hardening, and oxide layer. Interstitial N atoms increased the matrix hardness and decreased the stacking fault energy (SFE). The lower SFE facilitated wear hardening, and the active mechanical twins along with the higher dislocation density induced the formation of a thicker nanocrystalline layer with finer grains. The nanocrystalline layer with higher surface activity promoted the adsorption of a protective oxide layer. These factors decreased the surface roughness, coefficient of friction (COF), and wear rate of N-alloyed high-Mn austenitic steel. This study provided valuable insights into the application of N-alloyed high-Mn austenitic steels under dry sliding friction conditions.

Tribological behaviour of DIN 1.2740 hot working tool steel during mandrel mill stretching process

This study evaluates the tribological properties of DIN 1.2740 hot tool steel against Super Cr13 martensitic stainless steel at 700°C. The results show that the coefficient of friction (COF) ranged from 0.15 to 0.63, indicating moderate frictional interaction. The wear rate of DIN 1.2740 was observed to be low, suggesting good resistance to wear at high temperatures. The complex surface oxide layer that formed on the pin’s top surface, significantly reducing the COF and acting as a solid lubricant at elevated temperatures. The oxide layer was also fragile and unable to withstand the high sliding velocities and high loads. The steel exhibited a high surface roughness when subjected to increasing normal loads and increasing sliding velocities.