Maximum Static Friction Coefficient Research Articles

An experimental and numerical study on the shear performance of friction-type high-strength bolted connections used for CLT-steel hybrid shear walls

One type of friction-type high-strength bolted connections (FHBCs) was developed to connect steel frames to the infilled cross-laminated timber (CLT) shear walls. In the FHBC, an opening was cut in the CLT near the wall-to-beam interface. Two predrilled holes existed within the CLT panel, running vertically from the bottom surface of the opening to the wall-to-beam interface. Two slotted holes were also predrilled on the top flange of the steel beam. Two high-strength bolts were attached to the upper anchor plate installed in the opening and the bottom anchor plate placed below the top flange of the steel beam. By applying the pretension force on the bolts, the CLT panel was pressed against the steel beam, forming the static friction force to resist the shear force along the wall-to-beam interface. In the study, cyclic tests were conducted to evaluate the friction properties of the interface between the infilled CLT wall and the steel beam. The CLT-steel friction coefficient was carefully investigated, which was a critical parameter for determining the maximum static friction force of the FHBCs. Three-dimensional solid finite element models were developed to predict the load-slip behaviors of the FHBCs, and their multi-stage load-slip behaviors were analyzed using the step-by-step method. It is found that the CLT-to-steel interface can perform with considerable shear-resisting capacity and shear stiffness in the pre-sliding friction as well as stable energy-dissipating capacity in its post-sliding behavior. The maximum static friction coefficient and the dynamic friction coefficient of the interface are recommended as 0.55 and 0.50, respectively. When the pretension force is enhanced from 40 kN to 80 kN, for the FHBCs with the three-layer CLT and those with the five-layer CLT, their ultimate shear-resisting capacity increases by 75.85% and 35.67%, respectively. The load-slip curves from the FHBC models exhibit a similar pre-sliding behavior with considerable shear stiffness and shear-resisting capacity. Whereas, the numerical load-slip curves of the post-sliding stage are distinctive between the FHBCs with the three-layer CLT and those with the five-layer CLT.

Study on the shear-slip process and characteristics of fracture in shale

To clarify the shear-slip process and characteristics of fault, we conducted triaxial shear tests driven by displacement on shale samples with prefabricated sawcut and natural fractures, and the acoustic emission (AE) technology was used to monitor the shear-slip process in real-time. According to the test results, the shear-slip process and mechanical characteristics of sawcut and natural fractures were analyzed. The test results indicate that the shear-slip process of fractures can be divided into four stages, improving the confining pressure will cause more serious plastic failure in the shear-slip process, and the increase of roughness will make the phenomenon of “stress drop” more obvious, which is closely related to the earthquake occurrence. Confining pressure and roughness all have implications for the stress thresholds of each stage. With the transition of shear-slip stages, the effects of confining pressure and roughness on the shear-slip of fractures are more drastic. The maximum static friction coefficient μ0 increases with initial roughness increasing and is independent of confining pressure. Due to the strain-strengthening effect of fracture slip, the average value of dynamic friction coefficient μd under simple shear deformation is greater than the maximum static friction coefficient μ0. Based on AE response characteristics, microcracks development, and rupture scale during the shear-slip process were also explored. AE events are mainly distributed along the inclined fracture. The AE response in different shear-slip stages displays pronounced differences, and the AE evolution and macro mechanical characteristics of fractures show significant time-synchronization. The variation of peak frequency can reflect the rupture scale transformation and the influence of confining pressure and roughness. Additionally, the differences in the morphological evolution of sawcut and natural fractures are mainly reflected in the wear pattern, degree and the rock debris attach amount. Finally, we also discussed the micro-deformation mechanism of asperities during the shear-slip process. This work may provide a reference for the research of fault activation and slip in shale reservoirs.

Visualization of stick-slip shear failure process of granite by 3D reconstruction technique and DEM

Understanding the mechanism of stick-slip instability of faults is of great significance for earthquake forecast and seismic fortification. In this paper, combined with the 3D reconstruction technology and discrete element method (DEM), the stick-slip shear failure process is visualized and the evolution mechanism of each stage of stick-slip process is studied. First, the 3D morphology scanning tests are carried out to define the 3D topography of the sample interface, which is imported into PFC3D to generate particle assembly, and micro-parameters of the particle assembly are calibrated by the experimental results. Second, the loading conditions are applied to the particle assembly, the stick-slip instability of the simulated fault occurs spontaneously, and the evolution of fault displacement and velocity distribution during the whole stick-slip period are studied. Third, the effects of normal stress, shear loading rate and interface roughness on stick-slip instability are investigated. Finally, nine parameters related to the steady-state friction coefficient, namely normal stress, natural density, Young's modulus, Poisson's ratio, maximum static friction coefficient, reference slip velocity, reference friction coefficient, a-b and slip velocity, are selected to establish the steady-state friction coefficient forecast model based on back propagation neural network (BPNN), and the relative importance analysis of relevant parameters is also implemented. Our research is helpful to reveal the seismogenic mechanism.

Flexible and Wireless Normal‐Tangential Force Sensor Based on Resonant Mechanism for Robotic Gripping Applications

AbstractThe ability to detect both normal and tangential forces is essential for robotic tactile systems, while most available sensors implement this function at the cost of complex electrode structure and wiring. Here a fully flexible sensor for wireless detection of normal and tangential force based on resonant mechanism is reported. The components of the sensor are designed and optimized to meet the requirement, and the sensor shows good sensitivity, hysteresis characteristics, response time, and stability in the wired test. Wireless operation is carried out through inductive coupling, and the collected spectrum of reflection coefficient can reflect both normal force and tangential force information. In the case of individual input, the sensitivity is −0.19 MHz kPa−1 to normal force in the range of 0–200 kPa, and −0.031 dB kPa−1 to tangential force in the range of 0–50 kPa. As proofs of concept, maximum static friction coefficient tests and robotic gripping experiments are demonstrated for preliminary determination of surface roughness and material identification respectively. In particular, a total recognition accuracy of 92.5% is achieved by random forest‐based machine learning for balls with different materials in the gripping experiment.

Friction Mechanism and Characteristics of Reticle Based on Contact Theory

Abstract With the development of integrated circuits, the structure of chips becomes more and more complex, and the processing cost increases accordingly. To improve the productivity of lithography, the acceleration of the reticle stage should be increased to reduce the positioning time. However, the increase of acceleration will cause the relative slip between the reticle and the vacuum chuck, which seriously affects the accuracy and the product yield of lithography. To suppress the slippage, the friction mechanism and the characteristics between the reticle and the chuck are studied in this article. First, based on the Kogut–Etsion contact model and the Majumdar–Bhushan (MB) fractal contact model, the maximum static friction coefficient model between nano-scale surfaces was established. Then, the surface morphology parameters of reticle and chuck adsorption surface were obtained by atomic force microscopy (AFM) scanning. Finally, the maximum static friction force experiments show that the MB model is more suitable for the study of friction mechanism between reticle and vacuum chuck, and the model is more instructive for the suppression of reticle slip.

Fabrication of Silica Nanoparticle Monolayer Arrays Using an Anodic Aluminum Oxide Template.

Non-close-packed (NCP) silica nanoparticle monolayer arrays (SNMA) on ordered porous anodic aluminum oxide (AAO) templates were fabricated for the first time by a novel two-step spin-coating technique. The obtained NCP-SNMA-AAO was composed of silica nanoparticles (average primary particle size of 440 nm) and well-organized nanopores on the AAO substrates. NCP-SNMA-AAO with a supporting ratio of 87% silica nanoparticles showed a hydrophilic surface (water contact angle of 51.0°), while the original AAO substrate shows a hydrophobic surface (water contact angle of 107.9°). The maximum coefficient of static friction was decreased by 29% (0.327 → 0.233). The coefficient of dynamic friction was also decreased by 20% (0.281 → 0.226). We found that controlling the silica supporting ratio using the two-step spin-coating technique is an effective approach for surface modification of an AAO substrate.

An Optimal Wet Friction Plate Inspired by Biological Surface Patterns

It is found that many biological organisms exhibit superior adhesion characteristics in wet environments. It has been observed that the foot pads of tree frogs and katydids are consist of a number of closely arranged polygons, most of them are hexagonal. In this paper, the common structure of two kinds of biological foot pad was extracted to model the bionic surface structure of friction plates. The friction plate prototypes were also prepared. Through the multivariate orthogonal regression design, the optimum parameter combination of the friction performances of the prototypes of the bionic plates has been obtained. The hexagonal circumcircle size is 10 mm, the groove width is 1 mm, and the hexagonal diagonal angle is 90°. Then the maximum static friction coefficient, dynamic friction coefficient and wear amount of the optimal friction plate were tested and compared with the control group friction plates. The comparative analysis of the experiment findings demonstrated that the bionic structure with hexagonal ring grooves can significantly improve the friction performance of the friction plates.

A simple experiment to measure the maximum coefficient of static friction with a smartphone

The aim of this study is to measure the maximum coefficient of static friction with a smartphone. To reach this aim a very simple experiment with few materials was designed. Different from conventional experiments, the smartphone was used like an angle meter to determine the slope angle. The experiment in this study can be more practical than the conventional ones. It also requires easily accessible materials. We think that teachers and students should carry out this experiment as a group or demonstration activity in their classrooms.

On the Temperature Effect on the Parameters of the Specific Friction Force of Metals

Temperature relationships of the maximum coefficient of static friction, maximum specific static friction force, and its parameters τ0 and β at the ball-plane contact are experimentally investigated. A ball indenter with a radius of 0.5 mm made of ZlM80 alloy contacted a flat gold sample (99.99%). The range of contact loads was 0.5–4 mN, and the temperature range was 24–160°C. The experiments have shown that the coefficient of friction, specific friction force, and parameter β increase with increasing temperature, while parameter τ0 decreases.

Experimental Study on the Influence of the Third Medium on the Wheel/rail Maximum Static Friction Coefficient

Experimental Study on the Influence of the Third Medium on the Wheel/rail Maximum Static Friction Coefficient

Analytical study of friction coefficients of pomegranate seed as essential parameters in design of post-harvest equipment

Friction coefficients (static friction coefficient (SFC) and dynamic friction coefficient (DFC)) of pomegranate seed on different structural surfaces (glass, aluminum, plywood, galvanized steel and rubber) as affected by moisture content (4–21.9% (d. b.)) and sliding velocity (1.4–16 (cm/s)) were investigated. Analysis of variance (ANOVA) was performed to determine the effect of main treatments and their interactions on SFC and DFC. Significance of single or multiple effect of the main treatments with five levels was assessed using Duncan’s multiple range test (DMRT). To predict SFC and DFC, multiple linear regression (MLR) modeling technique was applied for each type of structural surface. The goodness of fit of each MLR model was evaluated using statistical parameters: coefficient of determination, root mean square error and mean relative deviation modulus. Results showed that the minimum and maximum SFC or DFC were in minimum and maximum moisture content on glass and rubber surface, respectively. ANOVA table indicated the significant effect of main treatments and their interactions on SFC and DFC at significance level of 1% (P<0.01). According to DMRT results, SFC linearly increased as moisture content increased and DFC increased also linearly as individual or simultaneous increment of moisture content and sliding velocity occurred, for all experimental conditions. According to the obtained statistical parameters, both SFC and DFC were properly predicted by means of MLR modeling technique.

Thermomechanical modeling and transient analysis of sliding contacts between an elastic–plastic asperity and a rigid isothermal flat

To investigate thermomechanical contacts between an elastic–plastic sphere and a rigid flat, simulations with slip rates ranging from 0.1m/s to 10m/s were performed. As interfaces with strong interfacial bonding but weak substrate were specifically targeted, slip initiation was treated as shear failure of the softer material in numerical simulations. The simulations show that both sliding friction coefficient and friction stress are significantly dependent on slip rate while the maximum static friction coefficient is independent of that. Moreover, the energy release during the transition from full stick to full slip is comparable to the shear fracture energy of the material.

An Improvement Proposal to the Static Friction Model

Friction is a force acting against the relative motion between two surfaces in contact. This phenomenon is present in all mechanical systems and has a great impact on the control area. The design of mechatronic systems and the compensation techniques require a broad knowledge of the effects that friction produces. The phenomenon has two well-defined phases: static friction presents before the motion between the surfaces in contact is clearly visible, while kinetic friction appears when that motion at large scale has already started. There are different friction models for each of those phases. In this work we propose an improvement to the static friction models, which consist in assuming that the maximum static friction coefficient is no more a constant but a function of the rate of change of the external force that produces the motion. After explaining and justifying the proposal, the procedure for obtaining the parameters of the new model is mentioned. At the end, an experimental study on a direct-drive motor allows us to validate the proposed model.

굴삭기용 주차 브레이크의 마찰 판 제작방법에 따른 마찰특성 분석

The parking brake embedded in track driving motor for driving an excavator is composed of wet type multi-friction discs. This type parking brake can be designed more compact because the combination of some sheets of friction discs generate great braking power, and also it has good braking characteristic and long life time because it works in the oil. In this study, we analyzed torque characteristic of the parking brake through simulations and performed experiments by use of 3-kinds of paper friction sheet manufactured by different pressing methods. And, we compared the maximum static friction coefficient and torque characteristic with the simulation results and confirmed the optimal manufacturing process through this result.

대형 굴삭기용 주차 브레이크의 마찰 특성 분석

The parking brake is one of the essential units embedded in track driving motor for forward and backward motion of an excavator. It is composed of multi-friction discs. When the hydraulic motor stops, the multi-friction discs closely stick to the facing discs by acting of multi-spring forces. So, the friction forces generate the braking force by compressing the cylinder barrel of hydraulic motor. In this study, we combined the multi-friction discs to two kinds of spring which have different spring force, and the maximum torque measured at the rotational starting point of hydraulic motor through gradually increasing the rotational torque of load side hydraulic motor by use of 1 and 2 sheets of friction plates. And, under this experimental condition, the maximum coefficient of static friction and the characteristics of paper friction sheet were analyzed. The obtained experimental results will be applied to the design of parking brake system for producing large size excavator in the 85-ton weight class.

Research for a Projectile Positioning Structure for Stacked Projectile Weapons

One of the key technologies of stacked projectile weapons is projectile positioning. However, the present projectile positioning structures have their respective advantages and shortcomings. A new structure based on the self-locking principle is put forward in this paper and verified as feasible by static analysis if the proper material and structural parameters are chosen. In order to check the strength and verify the feasibility of the structure under launch conditions, the multibody contact finite element model of the structure is established, coupled with dynamic load in the interior ballistic cycle. According to simulations and analysis, the projectile positioning structure is feasible and the strength of the projectile can meet the strength requirement for launch conditions. For different maximum static friction coefficients, simulations show that an increase in the maximum static friction coefficient between the contact surfaces of the positioning ring and barrel improves the positioning performance, but an increase in the maximum static friction coefficient between the contact surfaces of the positioning ring and projectile worsens. On the basis of great computation, it is found that an increase in the upper thickness and height of the positioning ring improves the positioning performance, but an increase in the lower thickness worsens the positioning performance. Further, a lower thickness affects the positioning performance more greatly. As a result, the positioning ring will be thin and light to improve the positioning performance. Compared with other positioning structures, the new structure has little influence on the ballistic performance and is a good application prospect.

108 超音波非接触物体搬送に関する基礎研究

In this study authors measure both of the maximum coefficients of static friction while a vibration board vibrates and it doesn't, and examine the effect of decrease of friction by vibration. In this case, four kinds of small metal blocks instead of powder and grains are used because the study is fundamental research. As a result it is found that the maximum coefficient of static friction decreases with increasing the amplitude, and finally settles down about constant value. And also, the same tendency and the rate of decrease for these metal blocks can be seen.

An experimental investigation of fretting fatigue in Ti-6Al-4V: the role of contact conditions and microstructure

A systematic investigation of the fretting fatigue behavior of the titanium alloy Ti-6Al-4V in both the mill-annealed (MA) and the solution-treated and overaged (STOA) conditions was carried out. A sphere-on-flat fretting fatigue device was used that facilitated real-time control and monitoring of all the relevant parameters such as the contact geometry, contact (normal and tangential) loads, and bulk alternating stress. While different sets of experiments were conducted to examine the influence of the bulk stress, the tangential load, and the normal load, respectively, on fretting fatigue response, the effect of microstructure on fretting fatigue was explored with experiments on the acicular, Widmanstätten, and martensitic microstructures as well. In experiments where the contact loads were maintained constant and the bulk stress was varied, fretting reduced the fatigue strength of Ti-6Al-4V. For this case, the “strength reduction factor” was higher for the experiments with higher tangential loads. For cases where the bulk stress and the normal or the tangential loads were maintained constant, lower fretting fatigue lives were obtained at larger tangential loads and at smaller normal loads. Of all the microstructures studied, preliminary results on the martensitic structure suggest an enhanced fretting fatigue resistance, compared to the basic STOA or the MA microstructure. Using the measured maximum static friction coefficient for Ti-6Al-4V, the experimentally observed contact and stickzone radii were found to exhibit good agreement with analytical predictions. Furthermore, conditions for crack initiation were determined through the application of the recently developed adhesion model for fretting fatigue. The model predictions of weak adhesion and crack initiation were validated with experimental observations of stick-slip behavior and fretting fatigue failures, respectively.

Thermoelastic instabilities in the sliding of conforming solids

To investigate thermomechanical contacts between an elastic–plastic sphere and a rigid flat, simulations with slip rates ranging from 0.1 m/s to 10 m/s were performed. As interfaces with strong interfacial bonding but weak substrate were specifically targeted, slip initiation was treated as shear failure of the softer material in numerical simulations. The simulations show that both sliding friction coefficient and friction stress are significantly dependent on slip rate while the maximum static friction coefficient is independent of that. Moreover, the energy release during the transition from full stick to full slip is comparable to the shear fracture energy of the material.