Friction Research Articles

A COMPARATIVE STUDY OF THE SURFACE OF FACTORY AND HAND-MADE LOOPS ON TITANIUM-MOLYBDENUM ORTHODONTIC ARCHWIRE

The most important part of the brackets, used in orthodontic treatment, is the archwire, which, when activated, generate light and long-lasting biomechanical forces that make the teeth move. Different manufacturers offer ready-made expensive solutions for orthodontists - archwire with loops along the length of the wire of different shape, which increases the cost of treatment. However, orthodontic practice is strictly individual, depending on the patient’s orthodontic problems, the stages and methods of treatment.Orthodontists often have to choose between expensive archwires with pre-made loops or using an archwire that they can manually bend in the right places depending on the patient’s individual characteristics and specific needs. In this case, the orthodontist’s decision depends on preserving the quality of the archwire surface. The surface roughness of the orthodontic archwire plays an important role in the bracket-archwire complex and is an essential factor that determines the effectiveness of the guided movement of the teeth along the arch. Surface roughness not only affects the efficiency of sliding mechanics, due to frictional effects, but also corrosion behaviour and aesthetics. A comparison of the surface characteristics of Ti-Mo archwire - with factory and hand-made loops is made. The surface of the archwire in the bending zones of the loops was investigated by SEM analysis and Surface roughness analysis. The analysis of the results shows that manual bending practically does not change the surface of the archwire, does not introduce additional defects that increase the contact friction, as well as create conditions for faster deterioration of properties and the undesirable breakage of the archwire. Research results give orthodontists confidence that the manual bending process does not degrade the quality of the archwire surface. The hand-bent archwire preserves the possibility of trouble-free movement in the braces when tightening or loosening during the different stages of treatment.

On the dynamics of transporting rolling cylinders

AbstractA common, yet hazardous, method of transporting cylindrical tanks used to carry compressed gas involves rolling both tanks at opposite angles of inclination to the vertical. By propelling one of the tanks while maintaining point contact between the tanks, both tanks can be moved such that their centers of mass move in a straight line. The purpose of this paper is to explore this locomotion mechanism. First, the problem of supporting an inclined cylinder in point contact with a rough surface is examined. The analysis shows that dependent on the geometry of the cylinder and the coefficient of static friction, a wide range of angles of inclination are feasible. The presence of non-integrable constraints on the motion of the rolling cylinder is explored using the concept of a holonomy. The problem of transporting two cylinders using the aforementioned mechanism is then analyzed with the help of Frobenius’ integrability criterion for constraints and numerical simulations. The results show the mechanical advantage of transporting a pair of cylinders, the range of possible angles of inclination, and the forces needed to sustain the motion.

Influence of Plasma Arc Current and Gas Flow on the Structural and Tribological Properties of TiN Coatings Obtained by Plasma Spraying

This study investigates the development of TiN-based coatings using plasma spraying technology, focusing on how plasma arc current and working gas flow rate affect the coatings’ structural-phase composition and mechanical–tribological properties. The research highlights the potential and effectiveness of plasma spraying for TiN coatings. Results from scanning electron microscopy and nanoindentation tests show that the TiN coatings have a dense microstructure with strong adhesion. Tribological testing demonstrated that coatings deposited at a 250 A arc current displayed the lowest coefficient of dry friction and the lowest porosity (2.13%) compared to those deposited at 350 A and 450 A arc currents, which exhibited higher porosity (up to 10.45%).

Theoretical investigation of the resistance effect of embedded isolation piles on tunneling-induced lateral ground movements

This paper presents an isolation pile–soil lateral interaction model that considers not only the relative linear sliding at the pile-soil interface but also the pile group–soil interaction. The model allows for the calculation of the pile–soil interaction force using the elastic continuum method combined with the displacement compatibility relationship at the pile–soil interface, thus enabling the total lateral ground displacement to be obtained. The proposed method is validated by comparisons with the elastic foundation method (EFM) and the boundary element method (BEM). The advantages of the proposed method in calculating the lateral ground deformation resisted by isolation piles are demonstrated. The mechanical mechanism of the isolation pile’s lateral resistance effect on ground deformation can be summarized as follows: the combination of positive and negative resistance effects drives the lateral ground displacements along the depth direction from the original inhomogeneity caused by the tunnel excavation to a relatively homogeneous state. The soil parameters including Poisson’s ratio, internal friction angle and ground volume loss; the isolation pile parameters including the distance of the tunnel axis from the pile axis, the pile length, the buried depth of the pile top and the relative pile bending stiffness; and isolation pile–soil interface parameters including relative pile shaft–soil stiffness and relative pile tip–soil stiffness all exert a significant influence on the lateral resistance effect of the isolation pile. In light of that the resistance effects at different depths below the surface are not uniform, it is of the utmost importance to assess the resistance performance of the isolation pile in accordance with the location and lateral deformation requirements of the protected structure in actual engineering.

Fully coupled thermal-structural-vibration characteristics of 3-axis machine tools with complex hybrid linear axis-spindle systems considering structural nonlinearities

For machine tools composed of functional components bonded by joints with structural nonlinearities, the load- and temperature-dependent nonlinear restoring force,stiffness, and frictional heat generationfrom the jointdetermine its complex dynamic fully coupled thermal-structural-vibration characteristics. In response, in this work, considering the vibration feedback dominated by the structural vibration and employing a partition-based closed-loop iterative algorithm, a fully coupled thermal-structural-vibration model that characterizes the nonlinear coupling between temperature and mechanical fields is developed with the joint as the link. The multi-body dynamics model of the whole machine tool, considering the flexibility of the screw shaft, spindle, and joint nonlinearity, characterizes the milling dynamics influenced by structural vibration and regeneration effects. The global thermal resistance network model with dynamic heat flux, viscosity-temperature effect, and time-varying thermal resistanceis establishedto characterize the thermal characteristics. The partition-based closed-loop iterative algorithm is employed to realize the multi-field coupling and consider the moving heat source and the load distribution change caused by the reciprocating moving joint. Considering the changes in contact angle and contact deformation caused by preload, dynamic load, and thermal effect, load- and temperature-dependent nonlinear joint restoring force and stiffnessare developed. Based on the viscosity-temperature effects and the change of contact friction caused by thermal expansion and dynamic load, the load- and temperature-dependent nonlinear joint frictional heat generation is calculated. The milling load from tool-workpiece interaction is calculated, and the influence of multi-field coupling on regenerative chatter is explored. The proposed model was experimentally verified, andthe effectof parameterswas numerically investigated. The results show that the dynamic milling load excites the whole machine tool vibration, and for every 10 μm increase in cutting depth, the radial amplitude of the tool nose increased by at least 1 μm. The nonlinear coupling between temperature and mechanical field significantly affects the system response, and the joint contact stiffness dominates the multi-field coupling behavior.

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.

Fine analysis and size optimization of spherical hinge in swivel construction

Contact stress and friction torque are the two primary mechanical responses of a spherical hinge. In general engineering practice, the calculation methods for contact stress and friction in spherical hinges often involve simplifying the spherical hinge into a planar hinge. To accurately analyze the stress state of the spherical hinge, it is essential to establish a detailed model. In this study, 17 groups of spherical hinge models were developed. The support radius, curvature radius, and thickness of the spherical hinge are considered influencing factors, while the maximum contact stress, friction torque, and amount of steel used are treated as responses. A three-factor, three-level, and three-response design is implemented. Using the response surface method, optimization design is conducted, resulting in two proposed optimization schemes. The maximum contact stress is reduced by 40.10% and 10.91%, respectively, while the friction torque is decreased by 0.82% and 26.50%, respectively. The maximum error between the predicted and calculated values is 7.04%. This indicates that the model presented in this study possesses sufficient predictive accuracy and can effectively guide the selection of spherical hinge dimensions.

Two-parameter dynamics and multistability of a non-smooth railway wheelset system with dry friction damping.

A deep understanding of non-smooth dynamics of vehicle systems, particularly with dry friction damping offer valuable insights into the design and optimization of railway vehicle systems, ultimately enhancing the safety and reliability of railway operations. In this paper, the two-parameter dynamics of a non-smooth railway wheelset system incorporating dry friction damping are investigated. The effect of the crucial parameters on the complexity of the evolution process is comprehensively exposed by identifying different dynamic responses in the two-parameter plane. In addition, the multistability and the various routes transition to chaos for the system are also discussed. It is found that dry friction induces highly complex dynamics in the system, encompassing a range of behaviors such as periodic, quasi-periodic, and chaotic motions. These intricate dynamics are a direct result of the interplay between multiple parameters, such as speed and damping coefficients, which are critical in determining the system's stability and performance. The presence of multistability further complicates the system, resulting in unpredictable transitions between different motion states.

Cooperative Object Transport Via Non-Contact Prehensile Pushing by Magnetic Forces

Abstract Cooperative robot systems are an essential candidate for object transportation solutions. They offer cost-efficient and flexible operation for various types of robotic tasks. The benefits of cooperative robot systems have triggered the improvement of the object transportation field. In this study, a new way of transporting objects by cooperative robots is presented. The proposed method is performed by the pushing action of the magnetic forces of the robots. The permanent magnets mounted on the mobile robots and the cart create this repelling force. The rectangular object carrier cart equipped with passive caster wheels can be manipulated on flat terrains easily and be assigned to carry different shapes of objects. Using a carrier cart has the advantage of eliminating the vertical loads on the robots. Controlling a non-contact pushing method offers a low computational burden since simple velocity and position updates are adequate for operation management. Compared with the other methods of object transportation systems, the non-contact pushing method provides a faster operation with less sensitivity to control errors. Both simulations and real-world experiments are conducted and the performances are given comparatively with a generalized frictional contact object-pushing method. The results show that the proposed method provides 10.48% faster and 20.03% more accurate object transportation compared to the frictional contact method. It is envisioned that the presented method can be a promising candidate for object transportation tasks in the industry.

Structure and Properties of the Electroexplosive Coating of the TiB2-Ag System after Electron Beam Treatment

A coating of the TiB2-Ag system was formed through the use of sequential operations of electroexplosive spraying and electron beam processing. The values of electrical conductivity (62.0 MS/m), Vickers microhardness (0.251-0.265 GPa at the point of measurement on a silver matrix and 25-32 GPa at the point of measurement at inclusions of boride phases), nanohardness (4.48 ± 0.76 GPa) were determined), Young’s modulus (116±29 GPa), wear parameter under dry friction-sliding conditions (1.2 mm3/N • m) and friction coefficient (0.5). Switching wear resistance during accelerated tests was 7000 on and off cycles with an electrical resistance of 10.01 - 11.76 LiOhm. The thickness of the coatings is 100 microns. The coatings are formed by a silver matrix with inclusions of titanium borides located in it with three types of sizes: nanocrystalline, submicrocrystalline and microcrystalline. Quantitatively, in the structural composition among titanium borides, titanium diboride and silver (56 wt. %) are formed predominantly (41 wt. %), while other titanium borides account for 3 wt. %. Structural transformations are described using complementary methods of X-ray phase analysis, scanning and transmission electron microscopy.

Simplified assessment of structures with clutching inertia-friction systems by equivalent linearization methods

The innovative Clutching Inertia System (CIS), has garnered increasing recognition for its effectiveness in mitigating structural vibrations. To enhance the efficiency of passive CIS, introducing suitable energy dissipation mechanisms for the rotation inertia component is imperative. This study delves into the dynamic behavior of CIS, augmented with additional friction damping. Initially, the influence of supplementary friction damping within the CIS framework is examined through a dynamic model of a Single-Degree-of-Freedom (SDOF) system, integrated with the CIS and incorporating the Coulomb friction model. Subsequently, to streamline the dynamic analysis of the CIS and optimize the friction force thereby enhancing control efficiency while minimizing inactive durations, the paper introduces two distinct Equivalent Linearization Methods (ELMs). Furthermore, an assessment of the CIS’s dynamic performance, subjected to various external excitations, is presented. The findings highlight the crucial role of supplemental friction damping in reducing the inactivity of CIS and enhancing its overall control effectiveness. The employed ELMs demonstrate commendable accuracy and practicality for both response assessment and CIS performance optimization. In essence, the CIS, when integrated with supplemental friction damping, exhibits superior performance in suppressing structural displacement responses across diverse excitations, particularly in longer-period structures. Conversely, a more pronounced efficacy in managing structural acceleration responses is observed in structures with shorter periods. The study concludes that for specific structural applications, enhancing supplemental friction damping is more advantageous for vibration control than increasing the CIS’s inertia.

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.

Laboratory Study of Interface Friction between Sand and Steel Surfaces

Abstract In this study, results have been reported from a series of laboratory tests to determine the interface friction angle of steel surfaces with sand through modified direct shear testing. For completion, steel surfaces with different surface geometry to replicate the roughness have been slid against various sands compacted at different relative densities under both dry and wet conditions. The standard square shape direct shear box has been modified into circular and rectangular boxes to sufficiently enhance the contact area and to subsequently quantify its effect on interface friction angle. A mild steel interface of smooth and rough texture with a groove depth of 0.2 mm and tipping at an angle of 90° has been used in this study. The analysis of results revealed that the interface friction angles obtained from the standard direct shear box agree closely with those obtained from both modified rectangular and circular shear boxes. However, the ratio of the interface friction angle from the modified apparatus and soil’s angle of internal friction significantly depends upon the roughness of the surface in contact with the sand, its median particle size, and is independent of the effects of box size, soil’s relative density, and dry or wet condition. A comparison between existing well-accepted guidelines and current observations has been presented for use by the practicing engineers dealing with soil-structure interaction.

Investigating the compaction and the mechanical behaviors of coal gangue as subgrade filler and constructing highway subgrade in practice

Using coal gangue as subgrade filler (CGSF) can address the accumulated issues of coal mine waste, but also save the constructing costs, which has the important ecological and engineering practical value. The well-graded limit of CGSF was captured based on the fractal model grading equation (FMGE). The large-scale vibration compaction test (LCT) shows that particle grading has a remarkable influence on the compaction of CGSF, with the increase of fine particle content, the dry density of sample first increases and then decreases. On this basis, the optimal range of particle grading was obtained. A series of large-scale triaxial tests (LTT) were conducted to investigate the mechanical behaviors of CGSF. The results shown that (1) the peak deviatoric stress shows a well-quadratic correlation with the fractal dimension. The optimal grading range of CGSF captured by LTT and LCT is basically the same, hence the suggestion of acquiring the optimal grading through LCT was given. (2) Increasing the compaction degree (DC) can significantly improve the strength of CGSF if DC is smaller, while when DC is greater, the strength improved by increasing DC will not be significant. (3) The grading and DC have a significant impact on the cohesive force of CGSF, while have little effect on internal friction angle. In addition, the research results provide good guidance for the constructing of a highway subgrade in practice.

Stick–slip oscillations in the low feed linear motion of a grinding machine due to dry friction and backlash

Stick–slip oscillations in the low feed linear motion of a grinding machine due to dry friction and backlash

Debris Flow Simulations for Hazard, Vulnerability and Risk Assessment in the Karakorum Mountain ranges, northern Pakistan

The Karakorum mountainous ranges in northern Pakistan have frequently witnessed devastating debris flows with damaging impacts on surrounding communities and infrastructure. Debris flow runout modeling and hazard assessment are crucial to develop and implement effective mitigation and adaptation measures. In this study, debris flow runout modeling using multiple scenarios of slope failures is carried out for hazard and risk assessments in the Karimabad watershed of the Hunza Valley in northern Pakistan. A 3D numerical simulation tool RAMMS was used to estimate the hazard intensity parameters (runout distance, flow velocity and height) along the debris flow track, based on the Voellmy model. To calibrate the model inputs, a back analysis of the Haiderabad stream debris flow event of 26 July 2022 has been conducted based on the estimated initial volume and the known runout distance. The calibrated values of the dry friction coefficient μ=0.07 and turbulent coefficient ξ=550 m/s2 were utilized for the three potential release areas. Different initial volumes were considered, and the results were combined to determine the debris flow runout distance and other intensity parameters for each scenario. The failure of three selected release areas could potentially block or divert the river Hunza. The integration of RAMMS parameters mainly flow velocity and height into hazard mapping assists in the demarcation of the area and elements at risk which are exposed to the potential impacts of debris flows. The derived debris flow hazard maps show that the road network including the KKH is exposed to debris flows. The impact of the debris flows on the surrounding communities and infrastructure is carried out through the vulnerability assessment and combined with the hazard assessment to derive the risk. Due to the intensive incision in the channels as the path for debris flow, the settlements and populations are less vulnerable to debris flow, however, poses a risk to the communication network and KKH. The study should assist the concerned agencies in developing and implementing debris flow risk mitigation strategies.

Variational inequalities of multilayer elastic contact systems with interlayer friction: Existence and uniqueness of solution and convergence of numerical solution

Inspired by the layered structure models in pavement mechanics research, in this study, a class of multilayer elastic contact systems with interlayer frictional contact conditions and deformable supporting frictional contact conditions on the foundation has been constructed. Based on the nonlinear elastic constitutive equations, the corresponding system of partial differential equations and variational inequalities are respectively introduced. Under the framework of variational inequalities, the existence and uniqueness of solutions for such models, along with the approximation properties of finite element numerical solutions, are proven and analyzed. The aforementioned conclusions provide fundamental and broadly applicable theoretical support for addressing mechanical problems in multilayer elastic contact systems within the framework of variational inequalities. Finally, the numerical experimental results based on the mixed finite element method also substantiate our theoretical conclusions.

Analysis and Calculation of Cross-contact Force between Strands of Multi-layer Conductor

Abstract As a key component of the transmission line, the inter-layer cross-contact force of the internal strand is an important factor affecting the mechanical properties of the conductor. In this paper, the cross-contact characteristics between the strands of multi-layer conductors are analyzed. According to the relationship between the contact force and the contact distance between the strands, the finite element simulation of different material strands of different conductors at different cross angles is carried out. Through the analysis, it can be seen that the cross angle between the strands and the material of the strands have a significant impact on the contact force. Then, based on the existing Hertz contact theory model, the relationship between the contact force and the contact distance between the strands is modified, and the contact force and contact distance models suitable for different cross angles of the conductor strands are obtained, that is, the modified Hertz contact model. According to the simulation results, combined with the modified Hertz contact model, the contact force coefficient between the strands is fitted, and the calculation formula of contact force and contact displacement is proposed. The formula can be applied to the calculation of contact force at any intersection angle between strands. The calculation formula provides theoretical support for the accurate structural calculation of the conductor, which is helpful to the analysis and calculation of the contact friction between the strands.

Failure criterion and damage evolution of high-strength geopolymer concrete under compression-shear composite loading after high temperatures

Geopolymer concrete (GPC) holds significant potential for building fire safety design due to its green, low-carbon, and high-temperature resistant properties. In practical applications, concrete structures often face multiaxial composite loads. Therefore, investigating the composite stress performance of high-strength geopolymer concrete (HGPC) after exposure to high temperatures is crucial for assessing structural damage and enhancing fire prevention measures. This paper examines the compressive shear performance of HGPC at various temperatures T (20°C, 200°C, 400°C, 600°C) and stress ratios k (0.15, 0.3, 0.45, 0.6). The study analyzes failure patterns, shear load-displacement curves, shear strengths and their components, and peak shear deformation. Failure criteria are proposed to describe the damage patterns of HGPC under compressive shear loading after high temperatures. Additionally, the damage evolution process is evaluated using the energy method. The results show that HGPC damage surfaces penetrate the coarse aggregate at room temperature under compression-shear composite loading but shift to the aggregate-mortar interface at 600°C. Shear stiffness, peak shear strength, and residual strength increase with higher stress ratios but decrease with rising temperatures. Temperature affects peak shear strength by over 95 %, significantly more than the stress ratio. The shear strength decreases more slowly than compressive strength up to 400°C but more rapidly beyond 400°C. The cohesive strength of HGPC decreases with increasing stress ratio under different temperatures, while contact friction strength exceeds 50 % of peak shear strength. Shear dilation strength generally increases, then decreases, peaking at k = 0.45. The failure criterion based on the modified twin shear unified strength theory aligns best with experimental results. Furthermore, an increased stress ratio retarded the development of damage evolution, which was first accelerated and then slowed with rising temperature.

Evaluation of static and rolling friction coefficients of granulated sugar using the discrete element method in a rolling mode rotating drum

PurposeThis research investigates the behavior of granulated sugar particles of different sizes in a rotating drum at varying speeds, using the discrete element method (DEM) as a mathematical modeling approach.Design/methodology/approachThe study conducted a data scan to determine both static and rolling friction coefficients. Based on benchmark studies, the Hertz–Mindlin contact model with rolling history elastic-plastic spring-dashpot (EPSD) and CDT (directional constant torque) models were employed to simulate the behavior of granulated sugar particles in a rotating drum under varying speeds.FindingsIn this research, the static and rolling friction coefficients presented the best values for granulated sugar near 0.60 and 1.5, respectively, applying the CDT model. The method demonstrated great accuracy in replicating experimental data.Originality/valueThis study enables comprehension of the behavior of the particles and particle system in a rotating drum at different speeds. The method may develop models that characterize and predict the main effects of particle systems to reduce project time and expense, especially in the food industry.