Rotational Friction Research Articles

Research on Monitoring Method of Mechanical Joint Rotational Friction in Bench Press Training

Bench press training seems to be the most common exercise for increasing upper-body strength and control among athletes, fitness enthusiasts, and wellness buffs. Bench presses are usually done by lying down on the bench with the back, shoulders, and buttocks in touch. The bench press training surveillance systems with technical advancements are rarely seen in the research domain. Therefore, this paper presents a novel bench press training monitoring method (BPTMM) by evaluating mechanical joint rotational friction using Internet of Things (IoT) sensors. The bench press is a common upper body strength-building and muscle-building conditioning exercise. The bench press and the squat and deadlift are the three primary lifts performed in powerlifting competitions. Artificial intelligence aids in risk prediction and suggests possible positions. There is a 96.8% accuracy rate in surveillance and categorization, according to the findings of the experiments.

A nanographene disk rotating a single molecule gear on a Cu(111) surface

On Cu(111) surface and in interaction with a single hexa-tert-butylphenylbenzene molecule-gear, the rotation of a graphene nanodisk was studied using the large-scale atomic/molecular massively parallel simulator molecular dynamics simulator. To ensure a transmission of rotation to the molecule-gear, the graphene nanodisk is functionalized on its circumference by tert-butylphenyl chemical groups. The rotational motion can be categorized underdriving, driving and overdriving regimes calculating the locking coefficient of this mechanical machinery as a function of external torque applied to the nanodisk. The rotational friction with the surface of both the phononic and electronic contributions is investigated. For small size graphene nanodisks, the phononic friction is the main contribution. Electronic friction dominates for the larger disks putting constrains on the experimental way of achieving the transfer of rotation from a graphene nanodisk to a single molecule-gear.

Seismic performance of combined rotational friction and flexural yielding metallic dampers

A feature of designing combined rotational friction and flexural yielding metallic dampers, which could be used for prefabricated structures, was presented. The proposed dampers were composed of two energy dissipation systems with the friction damper (FD) by achieving rotational friction and metallic damper (MD) by yielding in flexure. To investigate the seismic performance of the proposed FD-MD connection, low cyclic experiments of rotational friction damper specimen and proposed FD-MD connection specimen were put forward. According to the experimental results, behaviors in hysteretic curves validated that they possessed excellent comprehensive performance of friction and plastic energy-dissipating ability. Consequently, the proposed FD-MD connection was capable of providing an alternative for precast structures in high seismic regions.

Combined lubrication of surface texturing and copper covering for broaching tool

Broaching is widely used in the aerospace field owing to its high efficiency and heavy load. However, heavy-load cutting causes intense squeezing and friction in the tool-chip contact area, resulting in a lack of lubrication. Therefore, three textures (i.e., micro-pit, stripe, mesh) are prepared on the rake face of broaching tool with a laser processing technique to improve cutting performance. Afterward, textures are covered with copper using the reciprocating rotational friction to enhance the wettability and heat dissipation capacity of the broaching tool. Experiments approve that striped textures covered with copper reduce the cutting force by 14.6% and the cutting temperature decreases from 90.13 to 76.9 ℃, compared with non-textured cutting teeth. Obtained results indicate that the wettability of cutting fluid on the tool surface is significantly improved due to the capillary force of micro-pores generated by the copper covering, especially in the direction to the cutting edge. Furthermore, the copper debris absorbs heat quickly in the cutting areas and is subsequently taken away by chips and cutting fluids, thereby reducing the cutting temperature.

Shake table testing of braced and Friction-Added suspended ceilings and associated numerical study

Suspended ceilings have long been shown as one of the most fragile non-structural components during past earthquakes. Under high seismic application, suspended ceilings are often required to be restrained using ceiling braces. However, because of the complicated behavior of suspended ceilings under seismic loading, the efficiency of braced ceiling systems is still unclear, and effective performance-enhancing methods for suspended ceiling systems have not yet been established. In this study, shake table tests were first conducted for unbraced (or non-seismic) and braced suspended ceiling specimens. Despite the seismic bracing according to ASTM E580, substantial damage, comparable to the non-seismic ceiling specimen, was observed in the braced ceiling specimen because of the lack of rigid diaphragm action of the tested ceiling grid. In order to enhance the seismic performance of a non-seismic suspended ceilings cost-effectively, a novel rotational friction mechanism was added, and its effectiveness was experimentally evaluated. The proposed friction damper exhibited a stable hysteretic behavior under various input motions and effectively improved the seismic performance; only minor damage was observed at the ceiling perimeters. The friction damping parameters, such as the maximum static friction force, were experimentally calibrated, and an analytical model of the friction-added ceiling system was developed. A numerical case study was conducted to evaluate the applicability of the proposed friction-added ceiling system based on an extensive time history analysis of steel moment-frame buildings.

Continuous Drive Friction Welding of AISI 8630 Low-Alloy Steel: Experimental Investigations on Microstructure Evolution and Mechanical Properties

Abstract Continuous drive friction welding (CDW) is a state-of-the-art solid-state welding technology for joining metallic components used in aerospace, oil and gas, and power generation industries. This study summarizes the results of mechanical and microstructural investigations on a modified AISI-8630 steel subjected to CDW. The effects of welding process parameters, including rotational speed, friction, and forge forces, during CDW were explored to determine an optimum welding condition. The mechanical properties of the weld, and microstructural characteristics across different regions of the weld were measured and examined. The microstructure characterization results suggest that the weld zone (WZ) experiences temperatures above the Ac3 and the thermo-mechanically affected zone (TMAZ) experiences temperatures between Ac1 and Ac3 of the material. Investigations with electron backscatter diffraction (EBSD) demonstrated the occurrence of strain-induced dynamic recrystallization in the weld. The weld demonstrated higher yield and ultimate tensile strengths at the expense of ductility and hardening capacity compared to the base metal (BM). The strain-hardening profiles of the welds exhibited a dual-slope characteristic, an indication of different levels of plastic deformation experienced by the constituent phases (i.e., martensite, bainite and ferrite) present in the microstructure. The maximum strength-to-ductility combination and static toughness values were obtained for the weld produced under the highest rotational speed, maximum friction force and an intermediate forge force of 1200–1400 rpm, 375–425 kN, and 600–650 kN, respectively.

Effectiveness of Damping Devices on Coupling Beams of 15-story Building Based on Nonlinear Analysis Procedures

In recent years, damping device has been experimentally studied to replace diagonally reinforced coupling beams, to mitigate rebar congestion problem. This study focuses on evaluating the effectiveness of various damping devices in a high-rise building. Type of damping devices evaluated are Viscoelastic Damper (VCD) and Rotational Friction Damper (RFD), with study case of a 15-story reinforced concrete apartment building with a dual system (column-beam and shear walls). The analysis used is a nonlinear time history analysis with 11 pairs of ground motions matched to the Indonesian response spectrum based on ASCE 41-17 and ASCE 7-16. In this analysis, each damper will be varied with a different position, namely the first model, the damper will be installed on the entire floor and in the second model, the damper will be installed on the 5th floor to the 9th floor, which is the floor with the largest drift. The results show that the model using both dampers increase the level of structural performance globally and locally in the building, reducing the level of damage to the structural elements. But between the two dampers, the coupling beam that uses RFD is more effective than using VCD in improving building performance. The damper on the coupling beam has a good role in dissipating earthquakes and in terms of ease of installation.

Facile Measurement of the Rotation of a Single Optically Trapped Nanoparticle Using the Diagonal Ratio of a Quadrant Photodiode

Optical tweezers are a powerful tool for exploring physical properties of particles in various environments through analysis of their dynamics in a trapping potential. Analysis of the trapped particle’s position is often done using interferometric back-focal-plane detection microscopy in which interference between the trapping laser and the light interacting with the trapped particle is projected on a quadrant photo-diode (QPD). The QPD measurements are almost universally the voltage ratios between the transverse components of the detector (left/right; up/down) that are calibrated to ascertain particle positions and orientations (i.e., rotation). In this paper, we demonstrate how measuring the diagonal ratio of the QPD allows tracking the spinning and orbital motion of optically trapped objects with enhanced sensitivity compared to the conventional transverse ratio and reveals additional information about particle dynamics. The diagonal ratio “balances” the signal from opposite sides of the QPD, allowing common mode noise reduction and increased measurement sensitivity of the rotating nanospheres at frequencies from below 200 Hz to above 15 kHz. We show that the variability in particle rotation rates is due to slight differences in the aspect ratio of the nanoparticles. We also measure in situ a gradual acceleration in the spinning frequency of trapped nanoparticles due to photothermal shedding of surface ligands and the resulting decrease of rotational friction in solution. The accelerating particles spin at rates exceeding 30 kHz and are eventually “optically printed” onto the glass coverslip on top of the liquid cell enclosure. The diagonal ratio is a simple, readily available, and powerful enabler for measuring rotational dynamics with a 5-fold sensitivity increase over conventional QPD measurements. This affords opportunities for controlling the orientational dynamics of trapped nanoparticles, which is crucial for various applications, including nanoscale mechanical motors.

Development of design method for precast concrete frame with dry-connected rotational friction dissipative beam-to-column joints

To realize a beam-to-column joint for precast concrete (PC) frames with simple details, adjustable performance, and desirable seismic performance, an innovative dry-connected rotational friction dissipative beam-to-column joint (DRFDBJ) is proposed in this study. To validate the advantages of introducing DRFDBJs into PC frame structures, PC frame with DRFDBJs (NPCF) is proposed and considered as the research object. This investigation highlighted on (1) validating the advantages of the DRFDBJ and NPCF, (2) revealing the critical design parameters of the NPCF, and (3) developing a high-efficiency design method for the NPCF. Based on parametric analyses of 300 NPCF study cases and three monolithic reinforced concrete frame study cases, the seismic performance of NPCF is investigated with emphasizing on the control effect. Based on the results, the critical design parameters of the NPCF are identified to be sliding moment ratio (ρ) and sliding moment distribution pattern (SMDP). The rational type of SMDP for the seismic design of NPCF is recommended to be the uniform cumulative SMDP. The quantitative relationship between number of stories and rational value of ρ is also recommended. Subsequently, a design method with high efficiency and compatibility is proposed for the NPCF, and two NPCFs are successfully designed using this method, thus further validating the advantages of the DRFDBJ and the reliability of the proposed design method.

Seismic performance assessment of a super high-rise twin-tower structure connected with rotational friction negative stiffness damper and lead rubber bearing

In this paper, a novel rotational friction negative stiffness damper (RFNSD) composed of negative stiffness device (NSD) and rotational friction dampers (RFDs) is proposed to develop flexible connection for improving the seismic performance of an asymmetrical super high-rise twin-tower connected structure. The prototype structure is rigidly connected by long-span steel truss, and shaking table test has shown that the rigid connection between the towers and the truss corridor generally cause buckling of steel truss members and structural damage on the connected floors. To mitigate seismic responses of the truss corridor and the towers, the rigid connection is replaced by flexible ones using the proposed RFNSD and lead rubber bearing (LRB). The working principle of RFNSD is introduced and the theoretical force-displacement model is derived. The numerical model for the proposed flexible connection is presented and detailed three-dimensional finite element models for the rigidly and flexibly connected structures are established. Then by nonlinear time history analysis, seismic responses of the models under three-directional excitations are analyzed, and the effect of flexible connection’s design parameters is discussed. The results show that the developed flexible connection can obviously mitigate the dynamic responses and structural damages. As the stiffness of the pre-tensioned spring in NSD increase, the dynamic response of the steel truss connection corridor would be further decreased. The RFDs can effectively control the increased deformation of the flexible connection caused by the NSD, and promotes the energy dissipation capacity. The model with the flexible connections presents good seismic performance, indicating the effectiveness of the proposed RFNSD.

Numerical investigation of two degree-of-freedom galloping oscillation of a cylinder attached with fixed fairing device

Fairing is one of the most effective devices to suppress vortex-induced vibration (VIV) of marine risers. However, when the rotational friction coefficient of the fairing device is too high to rotate, severe galloping oscillations occurs. In this paper, a two-dimensional mass-spring-damping system was constructed based on the commercial software ANSYS. The galloping mechanism and the two degree-of-freedom (DOF) galloping characteristics of the fairing were studied by numerical methods. In particular, the influence of the natural frequency ratio of the in-line (IL) direction and the cross-flow (CF) direction on the galloping oscillation was discussed. The mass ratio of the riser-fairing system for which the simulations were performed was 1.7, and the damping ratio was 0.003. The Reynolds number based on the cylinder diameter and the inflow velocity was 1000. The range of reduced velocities based on the natural frequency in the CF direction was 1.76–18.52. The results showed that the activation of the inherent modes of the structure and the reattachment of the shear layer in the wake had an important contribution to the generation of the galloping. The movement in the IL direction could promote the reattachment of the shear layer to a certain extent, thereby expanding the scope of the galloping conditions. When the natural frequency ratio was equal to 1 or 2, a “double peak” phenomenon was found in the vibration amplitude curve in the CF direction. In the 2-DOF vibration, the fairing moved in the shape of an “8″ or a drop-shaped trajectory in most cases. On the whole, the interaction between the movement of the fairing in the IL direction and the movement in the CF direction could not be neglected, and the natural frequency ratio also significantly affected the vibration characteristics.

Friction welding of pure titanium-AZ31 magnesium alloy: Characterization and simulation

Friction stir welding (FSW) is a solid-state joining process that is still effectively utilized for joining Mg alloys, Ti alloys, and many other similar and dissimilar materials. Application and dissimilar joining of titanium to magnesium are very attractive in the automobile industry due to the reduction in automobile weight and fuel consumption. In this study, parameter optimization of friction welding on the shear strength of pure commercial titanium to AZ31 magnesium alloy joint by response surface methodology (RSM) was carried out. Rotation speed, friction pressure, and forging pressure on three levels were considered as the variable parameters in welding for a friction time of 4 s and a fixed forge time of 8 s. The torsion test results showed that the best shear strength (103.285 MPa) is related to the sample with optimum parameters, namely, a friction pressure of 50 MPa, forging pressure of 40 MPa, and rotation speed of 1300 rpm. Analysis of variance (ANOVA) was used to investigate the capability of the expanded model. The ANOVA results also showed that among the parameters, rotation speed and friction pressure significantly affect the shear strength. The reason is that high rotation speed and friction pressure can result in rapid transformation for achieving axial displacement stability and escalation of temperature.

Improving the tribological performance of a biodegradable lubricant adding graphene nanoplatelets as additives

This research is based on the investigation of the tribological properties of a biodegradable polymeric ester lubricant (BIOE) additivated with two different pristine graphene nanoplatelets (GnPs), named as GnP7 and GnP40. These GnPs have lateral sizes of 7 and 40 μm, and thickness of 3 and 10 nm, respectively. Four different nanoadditive loadings: 0.015, 0.035, 0.055 and 0.075 wt% have been used. Stability of nanolubricants has been investigated using the visual control and the refractive index evolution during time, revealing a slightly better stability for the nanolubricants formulated with the largest lateral size graphene nanoplatelets (GnP40). The influence of the thickness and lateral size of these carbon-based nanoadditives on the antifriction and antiwear capabilities of BIOE is analysed. For this purpose, rotational friction tests were taken with the eight nanolubricants under a 20 N working load and 340 m sliding distance. All nanolubricants showed friction coefficients and worn area lower than those previously reported for the unadditivated BIOE. As regards friction, the ideal loading for both GnPs was 0.055 wt% GnP, being the best anti-friction behaviour obtained using GnP40 as additive (up to 26% reduction), whereas the 0.055 wt% GnP7/BIOE nanolubricant leads to the best anti-wear capability with wear reductions up to 56%. Finally, from Raman microscopy and roughness assessments on the worn surfaces, it can be determined that the good tribological performance of nanolubricants is owing to the protective film formation and surface repairing mechanism.

Impact of Variable Speed on Collective Movement of Animal Groups

The collective dynamics and structure of animal groups has attracted the attention of scientists across a broad range of fields. A variety of agent-based models have been developed to help understand the emergence of coordinated collective behavior from simple interaction rules. A common, simplifying assumption of such collective movement models, is that individual agents move with a constant speed. In this work we critically re-asses this assumption. First, we discuss experimental data showcasing the omnipresent speed variability observed in different species of live fish and artificial agents (RoboFish). Based on theoretical considerations accounting for inertia and rotational friction, we derive a functional dependence of the turning response of individuals on their instantaneous speed, which is confirmed by experimental data. We then investigate the interplay of variable speed and speed-dependent turning on self-organized collective behavior by implementing an agent-based model which accounts for both these effects. We show that, besides the average speed of individuals, the variability in individual speed can have a dramatic impact on the emergent collective dynamics: a group which differs to another only in a lower speed variability of its individuals (groups being identical in all other behavioral parameters), can be in the polarized state while the other group is disordered. We find that the local coupling between group polarization and individual speed is strongest at the order-disorder transition, and that, in contrast to fixed speed models, the group’s spatial extent does not have a maximum at the transition. Furthermore, we demonstrate a decrease in polarization with group size for groups of individuals with variable speed, and a sudden decrease in mean individual speed at a critical group size (N= 4 for Voronoi interactions) linked to a topological transition from an all-to-all to a distributed spatial interaction network. Overall, our work highlights the importance to account for fundamental kinematic constraints in general, and variable speed in particular, when modeling self-organized collective dynamics.

Inter-relationship between microstructure evolution and mechanical properties in inertia friction welded 8630 low-alloy steel

The evolution of microstructure and mechanical properties in AISI 8630 low-alloy steel subjected to inertia friction welding (IFW) have been investigated. The effects of three critical process parameters, viz. rotational speed, friction and forge forces, during welding of tubular specimens were explored. The mechanical properties of these weld joints, including tensile and Charpy V-notch impact were studied for determining the optimum welding parameters. The weld joints exhibited higher yield strength, lower hardening capacity and ultimate tensile strength compared to base metal (BM). The maximum strength and ductility combination was achieved for the welds produced under a nominal weld speed of ~ 2900–3100 rpm, the highest friction force of ~ 680–720 kN, and the lowest axial forging load of ~ 560–600 kN. The measured hardness distribution depicted higher values for the weld zone (WZ) compared to the thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ) and BM, irrespective of the applied welding parameters. The substantial increase in the hardness of the WZ is due to the formation of microstructures that were dominated by martensite. The observed microstructural features, i.e. the fractions of martensite, bainite and ferrite, show that the temperature in the WZ and TMAZ was above Ac3, whereas that of the HAZ was below Ac1 during the IFW. The fracture surface of the tensile and impact-tested specimens exhibited the presence of dimples nucleating from the voids, thus indicating a ductile failure. EBSD maps of the WZ revealed the formation of subgrains inside the prior austenite grains, indicating the occurrence of continuous dynamic recrystallisation during the weld. Analysis of crystallographic texture indicated that the austenite microstructure (i.e. FCC) in both the WZ and TMAZ undergoes simple shear deformation during IFW.

Rotational Friction Correlated with Moiré Patterns in Strained Bilayer Graphene: Implications for Nanoscale Lubrication

Energy conservation of graphene nanodevices requires frictional dissipation management for their high surface area to volume rates, and rotational motion besides sliding scenarios appear frequently. Here, the rotational friction between graphene layers is investigated by molecular dynamics simulations with a validated graphene-spring model. It shows that the interlayer frictional torque drops an order of magnitude and approaches superlubricity with the emergence of Moiré patterns (MPs). Further analysis reveals that the incommensurate interface of MPs tunes the local energy, which cancels each other out with relative rotation, resulting in ultralow interlayer energy barriers. Accordingly, for bilayer systems with biaxially stretched substrates, a significant torque reduction can be achieved when the size of MPs matches that of the graphene flake. This study would provide new insight into the lubrication of rotatable nanomechanical systems.

Predicting the ultimate tensile strength of AISI 1045 steel and 2017-T4 aluminum alloy joints in a laser-assisted rotary friction welding process using machine learning: a comparison with response surface methodology

Welding metal alloys with dissimilar melting points makes conventional welding processes not feasible to be used. Friction welding, on the other hand, has proven to be a promising technology. However, obtaining the welded joint’s mechanical properties with characteristics similar to the base materials remains a challenge. In the development of this work, several of the machine learning (ML) regressors (e.g., Gaussian process, decision tree, random forest, support vector machines, gradient boosting, and multi-layer perceptron) were evaluated for the prediction of the ultimate tensile strength (UTS) in joints of AISI 1045 steel and 2017-T4 aluminum alloy produced by rotary friction welding with laser assistance. A mixed design of experiments was employed to assess the effect of the rotation speed, friction pressure, and laser power over the UTS. Furthermore, the response surface methodology (RSM) was employed to determine an empirical equation for predicting the UTS, and contours maps determine the main interactions. A total of 48 specimens were employed to train the regressors; the 5-fold cross-validation methodology was used to find the algorithm with greater precision. The gradient boosting regressor (GBR), support vector regressor (SVR), and Gaussian processes regressors present the highest precision with a less than 3% percentage error for the laser-assisted rotary friction welding process. The GBR and SVR capability exceed the RSM’s accuracy with a coefficient of determination (R2) greater than 90.9 versus 83.2%, respectively.

Study on mechanical and tribological properties of cerium oxide/fluorine rubber composites

In order to study the effect of nanoscale cerium oxide (CeO2) on the basic mechanical properties of binary fluorine rubber (FKM), especially the tribological properties at different temperatures, CeO2/FKM composites were prepared by mechanical blending and hot molding process. The hardness test, tear test, uniaxial tension test, room-temperature rotational friction test and high-temperature reciprocating friction test of FKM and CeO2/FKM were performed. The surface morphology of the two materials after being rubbed was observed, and the rubber surface changes were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that CeO2 particles can increase the hardness, matrix strength and resistance to external damage of rubber. Compared with pristine FKM, the tensile strength, elongation at break, anti-wear and anti-friction properties of CeO2/FKM composites have been effectively improved, and the enhancement of anti-wear properties of CeO2 reinforced FKM is more obvious under the condition of high temperature (200 °C). Therefore, the composites prepared by blending CeO2 with FKM can effectively improve the basic mechanical properties and tribological properties of FKM.

Research on the Nonlinear Characteristic of Flow in the Electro-Hydraulic Servo Pump Control System

In an electro-hydraulic servo system, the system flow is used as an intermediate variable to control the output displacement/force/speed of the actuator, and it plays the role of a medium for energy transmission and conversion. Therefore, the control of the system flow is the essence of state control for the system actuator. The purpose of this paper is to study the non-linear characteristics of pump control system flow and pave the way for high-performance control of the system. Based on the flow partition idea, the system output flow is divided into the dead zone, load zone, and saturation zone. We establish a mathematical model of the hydraulic system to analyze and study the effect of the nonlinear characteristics of the servo motor and the positive displacement pump on the system flow partition characteristics. We focus on the effects of the positive displacement pump shear flow internal leakage, pressure difference flow internal leakage, oil compression, servo motor rotation friction, and servo motor torque reserve rate on the system flow output, and analyze the partition characteristics of the system flow under different working conditions. We provide a theoretical basis for a high-precision control strategy for a hydraulic system.

Study on seismic performance of prefabricated self-centering beam to column rotation friction energy dissipation connection

Under severe earthquakes, a significant number of unexpected plastic hinges and brittle failure were found in conventional rigid beam to column welded connections of steel frames. To improve the seismic performance of steel frames, an innovative prefabricated self-centering beam to column (SCBC) connection was proposed and experimentally validated in this paper. The SCBC connection consisted of disc springs at the bottom flange of beam and a rotation friction hinge (RFH) at the beam end. The bottom disc springs could not contact with slab systems and provided restoring moment, whereas the RFH was designed to dissipate seismic energy. Firstly, its configuration form and design methodology were introduced. Then cyclic tests of a 1/4 scale SCBC connection specimen was carried out and the responses of the SCBC connection was compared to that of the RFH. Finally, the restoring force model of the SCBC connection was established through theoretical analysis. The experimental and analytical results demonstrated full flag-shaped hysteretic curves of the SCBC connection under cyclic loadings, verifying the desirable energy dissipation capacity and reliable self-centering capability of the SCBC connection. The calculation results based on the restoring force model were in good agreement with the test results, showing that the proposed restoring force model could reasonably predict the hysteretic behavior of the SCBC connection.