Friction Research Articles

Analysis of the Wear Parameters and Microstructure of High-Carbon Steel in Order to Identify Its Tribological Properties

Alloyed high-carbon steels are materials primarily intended for components operating under conditions of intense tribological wear. The carbides present in the microstructure of these materials significantly contribute to improving the wear resistance of such alloys. However, changes in the morphology of these precipitates can considerably alter the wear rate, leading to a deterioration in the properties of the materials. Therefore, this study aims to analyze the influence of several factors on the tribological wear of alloyed high-carbon steel. The research included friction tests under various load conditions and different sliding paths. Additionally, the samples were subjected to heat treatment to change the morphology of the observed precipitates. The tribological tests were conducted in a block-on-ring configuration under dry friction conditions. The tribological tests were analyzed statistically using analysis of variance (ANOVA). The results of the statistical analysis indicated that the primary factor influencing the observed differences between the samples was the heat treatment time of the material. Additionally, there were no significant statistical differences when pressure and friction path were varied. These findings, in conjunction with the SEM studies, allowed for the evaluation of the wear mechanism. The results demonstrated that, within the adopted tribological system, no alterations in the wear mechanism were observed with changes in test parameters. The observed differences in wear properties between the samples were found to be related to their heat treatment. The heat treatment resulted in alterations to the particle size distribution, with the annealing of the material at an elevated temperature leading to the dissolution of finer particles within the material. An increase in the average diameter of the carbide present in the material was observed to improve the wear resistance of the alloy tested.

Interparticle friction behaviors of kaolinite: Insights into macroscale friction from nanoscale

The friction behavior of widespread clay minerals is a major concern in many geo-engineering problems, such as the stability of soft soil foundations and the induction of seismic fault zones. The present work aimed to study the friction behaviors of kaolinite at the particle level using the molecular dynamics method. The effects of normal force (Fn), shear velocity (v), and interfacial water film on nanofriction were discussed. The “stick-slip” phenomenon and periodic evolution of friction forces (Ff) were observed in dry friction and became less pronounced with water lubrication. The dry Ff of kaolinite was found to be insensitive to Fn. However, wet Ff exhibited a linear increase with Fn and then transitioned to a non-linear relationship as slip displacement increases due to the continuous loss of water molecules from the interface during friction. Notably, at high loads (Fn ≥ 30 nN), the peak friction of wet kaolinite showed characteristics similar to dry friction. A velocity-strengthening behavior of kaolinite at high velocities was observed in both dry and wet conditions. The macroscale friction coefficients of kaolinite were predicted from nanofriction data and results showed good agreement with experimental values. This study lays the foundation for bridging micro- and macro-mechanical behaviors, suggesting a new pathway for acquiring precise macroscopic friction of minerals through cross-scale studies.

Weak solvability of elliptic variational inequalities coupled with a nonlinear differential equation

In this paper we establish existence, uniqueness, and boundedness results for an elliptic variational inequality coupled with a nonlinear ordinary differential equation. Under the general framework, we present a new application modeling the antiplane shear deformation of a static frictional adhesive contact problem. The adhesion process has been extensively studied, but it is usual to assume a priori that the intensity of adhesion is bounded by introducing truncation operators. The aim of this article is to remove this restriction.The proof is based on an iterative approximation scheme showing that the problem has a unique solution. A key ingredient is finding uniform a priori bounds for each iterate. These are obtained by adapting versions of the Moser iteration to our system of equations.

Tangential contact modeling to seal considering elastic-plastic for lubrication transition mechanism

Researches on the reciprocating seals lubrication under elastic-hydrodynamic lubrication (EHL) are mature, and leakage of failure criterion has been described with Couette flow for more than 30 years, which could not reflect to leakage mechanism in multiscale. Thus, it is necessary to explore seal leakage failure to focus on micro convex bodies of asperities model under contact pressure and cycle tangential friction stress in mixed lubrication. This is because convex bodies behaviors determine sealing effect and lubrication behaviors in microscale with subjecting to the dominant pressure. Interaction between convex bodies fatigue hysteresis curve and elastic-plastic strain are also calculated to explore sealing effect with leakage rate mechanism. We then design water seal at high pressure of 100 MPa with the speed of 0.1–1 m/s and medium temperature from 5 ℃ to 40 ℃. IWAN model of the convex bodies are calculated. Probability density function and Jenkin’s elements critical slip displacement are obtained. Convex bodies of radial and tangential deformation are also calculated through loading of contact pressure and friction stress with cycle strength coefficient to obtain seal fatigue lifespan. Ratio to seal stick and slip friction is calculated for evaluating the loading boundary. Seal leakage failure mechanism with fatigue characteristics is illustrated with macro lubrication parameters and micro convex bodies mechanics performance.

Shear strength characteristics of mixing slag-stone ballast reinforcement with tire geo-scrap using large-scale direct shear tests

AbstractUtilizing the ballast layer with more durable and stable characteristics can help avoid significant expenses due to decreased maintenance efforts. Strengthening the ballast layer with different types of reinforcements or substituting the stone aggregates with the appropriate granular materials could potentially help to achieve this goal by reducing the ballast deterioration. One of the exquisite and most effective solutions to eliminate these challenges is to use waste materials such as steel slag aggregates and useless tires. Utilizing these waste materials in the ballasted railway track will contribute to sustainable development, an eco-friendly system, and green infrastructure. So in a state-of-the-art insightful, the ballast aggregates, including a mixture of steel slag and stone aggregates, are reinforced with a novel kind of geo-grid made of waste tire strips known as geo-scraps. This laboratory research tried to explain the shear strength behavior of the introduced mixing slag-stone ballast reinforced with tire geo-scrap. To achieve this goal, a series of large-scale direct shear tests were performed on the ballast which is reinforced by tire geo-scrap and included various combinations of slag and stone aggregates. The concluded results indicate that the optimal mixing ratio is attained by a combination of 75% slag and 25% stone aggregates which is reinforced by tire geo-scrap at a placing level of 120 mm. In this case, the shear strength‌, internal friction angle, vertical displacement, and dilatancy angle of stone–slag ballast reinforced with geo-scraps exhibited average changes of + 28%, + 9%, − 28%, and − 15%, respectively.

The influence of selected grain size fractions of coal fly ash on properties of clay-cement mortars used for the flood levees construction

This study examines the influence of different grain size fractions of coal fly ash on the properties of clay-cement mortars used in flood levee construction. Dry aerodynamic separation and mesh sieving were used to obtain ultrafine, fine, and medium fractions of high-calcium and silica fly ash. The experimental results reveal that the rheological properties of fresh mortars are significantly influenced by these fractions. High-calcium fly ash mortars exhibit high reactivity and rapid increase in viscosity, with finer fractions showing the highest reactivity. Silica ashes show increased reactivity in the later stages of suspension hardening. Their spherical shape contributes to reducing internal friction during flow in initial technological operations. Furthermore, the compressive strength of hardened mortars improves as the particle size decreases for both ashes, resulting in a dense and uniform microstructure. The separation and fractionation of fly ashes contribute to the obtaining of fractions that influence the parameters of clay-cement suspension application on different scales. The results show the potential benefits of ash separation, which can bring advantages in terms of economic viability, engineering performance, and ecological sustainability.

Existence results for the time-incremental elastic contact problem with Coulomb friction in 2D

In this paper, the structure of the incremental quasistatic contact problem with Coulomb friction in linear elasticity (Signorini–Coulomb problem) is unraveled and sharp existence results are proved for the most general two-dimensional problem with arbitrary geometry and elasticity modulus tensor. The problem is reduced to a variational inequality involving a nonlinear operator which handles both elasticity and friction. This operator is proved to fall into the class of the so-called Leray–Lions operators, so that a result of Brézis can be invoked to solve the variational inequality. It turns out that one property in the definition of Leray–Lions operators is difficult to check and requires proving a new fine property of the linear elastic Neumann-to-Dirichlet operator. This fine property is only established in the case of the two-dimensional problem, limiting currently our existence result to that case. In the case of isotropic elasticity, either homogeneous or heterogeneous, the existence of solutions to the Signorini–Coulomb problem is proved for arbitrarily large friction coefficient. In the case of anisotropic elasticity, an example of nonexistence of a solution for large friction coefficient is exhibited and the existence of solutions is proved under an optimal condition for the friction coefficient.

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.

Flexural behavior and numerical simulation of reinforced concrete beams with a UHPC stay-in-place formwork

To overcome the shortcomings of traditional concrete structures such as long construction cycle, high construction cost and poor durability, seven composite beams with a UHPC stay-in-place formwork (UCB) and one reinforced concrete (RC) beam were designed. An experimental study was conducted to investigate the flexural behavior of composite beams under the static load. The research parameters include formwork thickness, reinforcement rate, and formwork surface treatment. The results revealed that roughening the surface of UHPC formwork has a positive impact on enhancing the integrity of composite beams. The utilization of UHPC stay-in-place formwork can effectively improve the stiffness, cracking load, and peak load of members. Compared with that of the RC beam, the cracking load and peak load of composite beams increased by 63% ~ 103% and 6% ~ 15%, respectively, and the yielding stiffness increased by 23% ~ 41%. Different from the RC beam, new cracks occurred on one side of the initial crack's end and continued to extend upwards rather than along the original crack. The existence of a significant quantity of tiny cracks in composite beams effectively slowed down the increase in the width of pre-existing cracks in the early stage of loading. Due to the multi-crack pattern exhibited by the UHPC formwork, the strain concentration of the steel bars was effectively mitigated. When subjected to the same load level, the strain of the longitudinal steel bars in composite beams was smaller than that of the RC beam. The formula for calculating the flexural bearing capacity of composite beams is established through theoretical analysis. In addition, the numerical model of the composite beam is established by the finite element method (FEM). The influence of the contact method of the UHPC-NC interface on the flexural performance of the composite beam is explored. The supplementary analysis of the parametric study of the reinforcement rate and the UHPC formwork thickness is carried out. When using ABAQUS for the numerical analysis of the composite beam, it is appropriate to adopt the cohesion model or the Tie model for the UHPC-NC interface, and it is not appropriate to use the Coulomb friction model.

Intelligent computing applications to study the tri-hybrid nanofluid past over the stretched surface

In this study, a recurrent neural network with the Levenberg-Marquardt backpropagation algorithm is used to examine the effects of various parameters on cooling mechanisms involving tri-hybrid nanofluid consisting of Al2O3, Cu, TiO2 and magnetohydrodynamic stagnation point flow. This research focus on nanofluid in the existence of an asymmetrically stretched disc in water, which plays an imprortant role for understanding heat transfer in addition to the dynamics of momentum and thermal boundary surface. Transform the complex partial differential system through suitable similarity transformations into the ordinary differential equations for numerical computing. These equations have been solved numerically by using the Adams method in Mathematica to generate datasets for various parameters.The current study demonstrates that the velocity profile rises with higher magnetic, velocity slip, and mass suction parameters. The fluid thermal level tends to decrease with an increase in mass suction parameters, whereas an increase in the magnetic parameter and Eckert number raises the fluid’s thermal level. Furthermore, it is noticed that the flow resistance and internal friction of the fluid are proportional to the viscosity parameter. The proposed scheme has shown its effectiveness in a wide range of scenarios and cases. This was achieved by comparing the mean square error metric for the squeezing flow tri-hybrid nanofluid problem with the obtained results. In addition, various statistical measures like state transitions, fitness assessments, error histograms, and regression analyses, provide further evidence of the solver’s robustness and reliability. The excellent agreement between the reference datasets and refined numerical solutions through the scheme showcases the method’s effectiveness, achieving remarkable accuracy levels ranging from 10-6 to 10-12.

Enhancing shear strength of sandy soil using zein biopolymer

Ecofriendly stabilization using various biopolymers has been explored to enhance the soil strength and the stability of geotechnical structures. This study investigates the improvement of shear strength characteristics in sandy soils treated with a novel protein-based biopolymer, zein. Poorly- and well-graded sands are treated with three different biopolymer contents (1, 2, and 3 %) and cured for 1–28 days. Direct shear tests are conducted under four normal stresses to evaluate the shear behavior and strength parameters of treated and untreated sands. The treated sands exhibit higher peak shear stress and more brittle behavior than the untreated sands due to the formation of biopolymer gel between the soil particles. The treated specimens show a greater improvement in shear strength over longer curing periods, with variation based on soil gradation. After curing for 28 days, apparent cohesion and internal friction angle significantly increase, from 8.1 to 257 kPa and from 26 to 45.4⁰, respectively. Poorly graded sands demonstrate a greater improvement in shear strength compared to well-graded sands, owing to the higher pore spaces available for biopolymer filling and bonding. Thus, incorporating zein biopolymer can significantly enhance the shear strength characteristics of sandy soil, providing a sustainable alternative for soil stabilization in geotechnical engineering.

Plastic Limited Numerical Modelling on Contact Friction Effects of Steel–Concrete Connection for Composite Bridges

This research employs plastic limit analysis to examine load combinations, contact interactions, and friction effects on steel–concrete connections. A nonlinear finite element model was developed using ABAQUS 2021, incorporating the concrete damage plasticity model and contact friction interactions. The model’s validity was confirmed through laboratory experiments. Results indicate that contact elements and friction between the top flange, concrete slab, and studs significantly influence structural behavior. Unlike conventional push-out tests, real deck–slab connections exhibit different load-displacement responses due to the self-weight and additional loads, such as vehicular traffic. Under horizontal loading, extensive failures with large deformations along the studs occur, while vertically compressive loads lead to failures around the connections.

Phase transition and internal friction behaviors in Mn-doped Co-V-Ga shape memory alloys

Shape memory alloys with a high abundance of mobile interfaces exhibit remarkable internal friction (IF) behaviors, which can be utilized for the reduction of noise and vibration. In this study, we systematically investigate the martensitic transformation and internal friction behaviors in the Mn-doped Co53V35–xGa12Mnx (x = 0 - 10) polycrystalline alloys. Our findings indicate that using Mn to replace V results in decreased transformation temperatures but increased thermal hysteresis. The addition of Mn enhances magnetic exchange interaction, leading to a gradual enhancement in magnetization difference across martensitic transformation, thereby compromising the transformation entropy change and arresting the martensitic transformation. At a frequency of 0.4 Hz, the intensity of transformation IF peak is enhanced from 0.124 to 0.178 with increasing the Mn content from 0 to 4.5 %, as a result of deteriorated geometrical compatibility between austenite and martensite due to the addition of Mn. Furthermore, hydrogenation treatments substantially improve both the peak intensity and frequency dependence of peak position for the relaxation-type IF, demonstrating the great contribution from hydrogen-twin boundary interaction.

Current-carrying friction behavior of CrN coatings under the influence of DC electric current discharge

CrN coatings are renowned for their low friction coefficients, high chemical inertness, excellent corrosion resistance, and substantial hardness, making them ideal for the tribological demands of bearings and gears in electric vehicles. This study investigated the current-carrying friction behavior of CrN coatings when sliding against steel balls under both non-electrified and electrified conditions. The friction coefficient (CoF), wear volume, wear type, and mechanism of the coating were reported by adjusting the direct current (DC) intensity and lubrication status. The findings indicate that while the current significantly exacerbates substrate wear during dry friction, its impact on the CrN coating is minimal. Even at a maximum DC current of 1.5 A, the wear rate of CrN coating during dry friction is only 1.9 × 10−4 mm3·(N·m)−1, representing a reduction by 79.1 % compared to the steel substrate. This effect is further pronounced when lubricated with PAO oil. The wear of CrN coating shows minimal change even as the current increased, and surface wear remains very slight. At a current of 1.5 A, the wear rate of CrN coating decreases to as low as 9.7 × 10−6 mm3·(N·m)−1, indicating a reduction by 98.7 % compared to its substrate. It is observed that under electrified conditions, the oxidation and degradation of CrN coating are accelerated, thereby resulting in the formation of a loose and low-hardness Cr2O3 oxide layer on the surface. The oxide layer is primarily attributable to the deterioration in frictional properties of the CrN coating under electrified conditions. Finally, CrN coatings exhibit minimal changes in tribological behavior under electrified conditions, thereby offering effective protection for substrates against electrical damage. Therefore, CrN coatings are ideal for applications involving electrical contacts.

Mechanical behaviour and macro-micro failure mechanisms of frozen weakly cemented sandstone under different stress paths

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure.

Optimal mine pitwall profiles in jointed anisotropic rock masses

ABSTRACT A new methodology based on the limit analysis upper bound method for the topological optimisation of slopes is presented, to determine geotechnically optimal slope profiles in anisotropic jointed rock masses. The methodology accounts for the effects of discontinuities such as joints, bedding planes, and tension cracks. We applied this methodology to the context of open pit mines, with the goal of achieving geotechnically optimal pitwall profiles. The optimal profiles maximise the Overall Slope Angle (OSA) while maintaining a prescribed Factor of Safety (FoS) and satisfying the geometric constraints imposed by benches and ramps. The method, implemented in the software OptimalSlope, utilises direction-dependent cohesion and internal friction angle parameters to replicate the effect of joints on slope stability. Key inputs include joint orientation, non-persistence, and probability of occurrence. We tested the methodology on a Mexican open pit mine to be excavated into Cretaceous siltstone featuring eight different joint sets and a primary bedding plane. Optimal pitwall profiles were determined for various combinations of bedding dip angles (0°, 15°, 30°, 45°, 60°, 75°, 90°) and mine pitwall orientations (hanging wall, footwall, side walls), considering the three-dimensional kinematics of the joints through anisotropic functions of cohesion and friction angle. Results indicate that the optimal pitwall profiles generally exhibit higher OSA compared to planar profiles with the same FoS, except in one bedding dip direction. Additionally, stability analyses performed using Rocscience Slide2 independently verified the FoS values of the optimal profiles.

Wear behavior of electron beam remelting modified Ni/WC thermal spray coatings

Ni/WC composite coatings were prepared by combining thermal spraying and electron beam remelting. Characterization methods such as SEM, EBSD and XRD were used. The effect of electron beam remelting beam current on the corrosion and wear resistance of Ni/WC composite coatings was investigated. The microstructure showed that hard carbides and borides such as W2C, Cr23C6, and M3B were generated within the remelted coating. Compared to the thermal spray specimens, the hardness of the 16 mA specimen was increased by a factor of 1.47, and the hardness of the 22 mA specimen was also increased by a factor of 1.14. The results of the corrosion experiments showed that the 16 mA specimen had the lowest corrosion current density and the highest corrosion potential, which showed the best corrosion resistance. Wear experiments were carried out by using SiC balls as the counterbodies. The results showed that the wear resistance of both 16 mA and 22 mA specimens under dry friction with 3.5 % NaCl solution conditions was improved compared to the thermal spray coating. The 22 mA specimens showed more obvious subsurface damage. The wear mechanism of thermal spray coatings is mainly abrasive, and the wear mechanism of remelted coatings is mainly abrasive and adhesive.

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.

Peridynamics modelling of projectile penetration into concrete targets

A non-ordinary state-based peridynamics (NOSB-PD) model is proposed to simulate the projectile penetration into concrete targets. In this model, the Kong-Fang concrete material model recently proposed is firstly implemented into the NOSB-PD framework to describe the complex dynamic behavior and failures in concrete material subjected to penetration loading, and then an improved point-to-volume discrete frictional contact model is proposed to simulate the physical interaction between projectile and target. After the mesh-free discretization and explicit time integration, the proposed NOSB-PD model is used to numerically predict two sets of projectile penetration experiments into low-strength and high-strength concrete targets. And numerical predictions are found to be in good agreements with corresponding test data including penetration depth, projectile deceleration, deformation of projectile and failures in concrete targets.

Nonlinear friction dynamics of water-lubricated bearings under transient shocks considering cavitation and turbulence effects

This study proposes a transient elastohydrodynamic mixed lubrication (EHML) model for water-lubricated bearings (WLBs) that incorporates cavitation and turbulence effects to evaluate the nonlinear friction dynamic performance under transient shock loads. The generalized average Reynolds equation is discretized using the control volume technique (CVM), and the constrained system is solved using the Fischer-Burmeister-Newton-Schur (FBNS) method. The validity of the model is verified by a comparison of experimental data from published literature. On this basis, the effects of cavitation, turbulence, shock load amplitude, direction, time, and rotational speed on WLB nonlinear friction dynamics characteristics are investigated. The results show that cavitation induces hydrodynamic loss under transient shock conditions, significantly increases contact time and load, and exacerbates the hydrodynamic instability phenomenon. In contrast, the turbulence effect effectively reduces frictional contact. The stability of WLBs under transient shock conditions is closely related to the load offset angle. Reducing the load offset angle improves the anti-shock stability of the bearings. Nevertheless, an increase in the amplitude and duration of the shock load may result in a deterioration of the frictional contact behavior. Increasing the rotational speed appropriately favors accelerating the lubrication regime transition and improving WLB’s anti-shock stability. This study provides a reference for enhancing WLB anti-shock performance and optimizing structural design.