Maximum Static Friction Force Research Articles

An Experiment on the Dwell Time Effect of Rubber Seal O-Rings: Friction Force in Intermittent Reciprocating Motion

The adhesive force between two contact surfaces often leads to an increase in the friction force of the rubber seal O-ring after a certain dwell time, forming dwell time effects and affecting the reliability of sealing. The dwell time effect may result in substantial instability with respect to the frictional behavior of rubber O-rings, which needs to be carefully taken into account in the design of rubber seals. Therefore, in this paper, the dwell time effect of the friction force was studied experimentally for intermittent reciprocating rubber seal O-rings coupled with stainless steel 316L and a sealing air medium. The friction force of three kinds of rubber materials, including fluorine rubber (FPM), silicone rubber (SI), and nitrile rubber (NBR), was measured under different dwell times, compression ratios, and seal pressure. The results showed that there was a rolling frictional force, and the second peak value of the frictional force caused by the O-ring’s rolling under shear action and after the maximum static frictional force was observed at the starting stage of reciprocating motion. For FPM O-rings, the rolling friction force was much greater than the maximum static frictional force at about four times the value of the compression ratio at 9% and seal pressure at 0; moreover, the force was much greater at greater compression ratios. The dwell time effect was significant in the friction forces of rubber O-rings. The friction force increases with an increase in dwell time. The increase in maximum static friction force exceeded 50% after 5 dwell days. The increase in seal pressure led to the disappearance of the rolling friction feature and the rapid increase in friction during the starting stage. Under gas seal pressure conditions, the dwell time effect still led to a significant increase in friction force. The obtained results might provide guidance for the material selection of sealing designs.

Interface friction between neighbor diamondene nanoribbons: A molecular dynamics study

Due to its unique carbon-carbon bond topology, diamondene exhibits different frictional properties compared to pristine graphene. This study evaluates the friction properties of diamondene ribbon (DR) for potential applications in the design of dynamic nanodevices. For a DR sample on a DR substrate at a specific temperature, it has a maximum static friction force (MSFF) that is about 38 times greater than that of a graphene counterpart with the same size. The rate of MSFF to the contact surface demonstrates the shear strength of a material. As an intrinsic property, the shear strength between DRs measures approximately 3.58 MPa at 10 K, which is much greater than that between graphene ribbons. When the pulling force on the DR sample exceeds MSFF, the sample undergoes a period of acceleration before reaching a stable sliding velocity. The viscous damping coefficient between DRs increases with increasing pulling force on the DR sample while decreasing with increasing temperature. The dynamic friction force behaves in a temperature-dependent manner due to the unstable bond topology of DRs at high temperatures. These studies address previous research lack regarding friction between carbon materials.

Friction behavior of 3D printed flexible cavity structure at low-speed condition

This study aims to study the changes in surface friction of flexible cavities produced by 3D printing under different internal pressures. An inflatable flexible air cavity fabricated using 3D printing technology and made of Tough-PLA and TPU95A materials was used as the experimental object. This study conducts low-speed friction tests on flexible surfaces under two conditions: different load pressure and different internal pressure. The experimental results show that under the same load conditions, the average sliding friction force between the contact surfaces with a contact area of only 16 cm2 increases by approximately 1 N as the air pressure increases, while the maximum static friction force increases by approximately 2–6 N. The inflatable cavity changes the friction of the contact surfaces under the influence of different internal air pressures. Through roughness measurements and microphotographs of the contact surfaces under different internal air pressures, it was found that the main reason is that the internal air pressure changes the surface roughness of the contact surface, thereby changing the friction between the contact surfaces. This study demonstrates a novel way to control the friction between flexible material contact surfaces. It has broad prospects and great significance for the future application of 3D printing flexible materials in the contact friction control of robot grippers and flexible joints and the lightweight of brakes.

Analysis of water droplet motion on hydrophobic surfaces with different microstructures

AbstractThe influence of material surface microstructure on interface properties is crucial for the preparation and development of special functional materials. In this paper, polydimethylsiloxane‐based superhydrophobic surfaces of varying roughness and surface energy are prepared using the template method and a spraying technique, and the effect of surface microstructure on lateral friction is studied using a lateral friction detection system. The experimental results indicate that as the surface roughness of a sample decreases, it is observed that the water droplets transition from a Cassie state to a Wenzel state. When the roughness changes from 4.619 μm, reduce to 3.512 μm, the maximum static friction force increases from 33.59 μN increased to 51.52 μN. The lateral sliding friction force ranges from 15.87 ± 1.9 μN increases to 40.91 ± 1.2 μN. For a given surface roughness, when the surface energy is reduced, the water droplets on the surface can be seen to transition from a Wenzel state to a Cassie state, the maximum static friction force increases from 19.32 μN dropped to 9.23 μN, and the lateral sliding friction force increases from 15.26 ± 1.6 μN dropped to 3.47 ± 2.1 μN. However, this behavior is distinct from that observed when changing the roughness of the sample. Studying the influence of the surface microstructure on the lateral friction force observed at a solid–liquid interface can provide important insights into novel geometries that may be used in new, advanced functional surfaces.

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.

Correction : Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

Correction : Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

On the issue of evaluating the effectiveness of the anti-slip profile of machine structures

Profiles with anti-slip grooves can be used for the design and modernization of machines, but the magnitude of the anti-slip effect for such profiles has not yet been fully studied. At the same time, among the causes of injuries to transport passengers, slipping on bearing contact surfaces is not uncommon. The existing scientific literature gives some idea of the factors influencing tribocontact with the macro-dimensions of surfaces. This served as the basis for the mathematical description in the article of the factorial effect on the anti-slip efficiency of the grooved profile. For this purpose, two indicators were identified that take into account the influence of the shape and number of profile irregularities. With the help of modeling tribocontact with profiles of different corrugation in the SolidWorks Motion environment, calculated values of the maximum static friction force were obtained. These values were compared with the calculated values of performance indicators, as a result of which a conclusion was made about the adequacy of the mathematical description of the factors. Keywords: machine structures, grooved profile, anti-slip surface properties, anti-slip efficiency, tribocontact, coefficient of friction, macro-dimensions

Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

State-and-rate friction in contact-line dynamics.

In order to probe the dynamics of contact-line motion, we study the macroscopic properties of sessile drops deposited on and then aspirated from carefully prepared horizontal surfaces. By measuring the contact angle and drop width simultaneously during droplet removal, we determine the changes in the shape of the drop as it depins and recedes. Our data indicate that there is a force which opposes the motion of the contact line that depends both on the amount of time that the drop has been in contact with the surface and on the withdrawal rate. For water on silanized glass, we capture the experimentally observed behavior with an overdamped dynamical model of contact-line motion in which the phenomenological drag coefficient and the assumed equilibrium contact angle are the only inputs. In this case, the damping coefficient decreases with increasing velocity of the contact line. For other liquid-substrate pairs, the observed contact-line motion suggests that a maximum static friction force is important in addition to damping. The dependence on time of contact and withdrawal rate, reminiscent of rate-and-state friction between solid surfaces, is qualitatively consistent across three substrate-liquid pairs.

Static friction coefficient depends on the external pressure and block shape due to precursor slip

Amontons’ law states that the maximum static friction force on a solid object is proportional to the loading force and is independent of the apparent contact area. This law indicates that the static friction coefficient does not depend on the external pressure or object shape. Here, we numerically investigate the sliding motion of a 3D viscoelastic block on a rigid substrate using the finite element method (FEM). The macroscopic static friction coefficient decreases with an increase in the external pressure, length, or width of the object, which contradicts Amontons’ law. Precursor slip occurs in the 2D interface between the block and substrate before bulk sliding. The decrease in the macroscopic static friction coefficient is scaled by the critical area of the precursor slip. A theoretical analysis of the simplified models reveals that bulk sliding results from the instability of the quasi-static precursor slip caused by velocity-weakening local friction. We also show that the critical slip area determines the macroscopic static friction coefficient, which explains the results of the FEM simulation.

Experimental Study on Interfacial Friction Characteristics of Reinforced Clay.

Clay is one of the important base materials in slope restoration. The adhesion of clay-rock interface plays a decisive role in the repairing effect on rock slopes. Fibers and polymers are widely used as a clay improvement method in rock slope repair. In this paper, the friction effect of sisal fiber and polyvinyl acetate (PVAc)-reinforced clay was studied through the design of an indoor rock-like interface sliding model test. Using modelled test results and scanning electron microscope (SEM) images, the reinforced clay was analyzed. The test results showed that the critical sliding angle and maximum static friction force of clay decreased with the increase of moisture content. An excess of fiber content and moisture content weakens the coupling effect of fiber-anchoring clay. Fiber content of 0.8% and PVAc content of 2% had the best effect on enhancing the sliding resistance of clay and provided good adhesion for dangerous interfaces of rock slope at 35° and 45°, respectively. PVAc formed a three-dimensional networked elastic membrane structure to improve the skid resistance and dynamic friction coefficient of the clay. The results provide an effective way for soil improvement and ecological restoration.

Dynamic Friction-Slip Model Based on Contact Theory

In ultra-precision positioning equipment, the positioning accuracy is affected by the friction characteristics, especially the pre-slip stage. At present, the research on friction mainly includes contact theory and the dynamic friction process. There is no time variable in contact theory models, so they only apply to the stage of static contact, while the establishment of a friction dynamics model depends on parameter identification and cannot reflect the influence of a rough morphology and load. Therefore, neither theory can elucidate the ultra-precise slip mechanism. In this paper, maximum static friction force, tangential stiffness, and tangential damping models of contact surfaces were deduced through fractal contact theory. By substituting the contact parameters into the modified LuGre model, a dynamic slip model of the mask was established. Finally, the above model was verified by a reticle dynamic slip measurement system. The experimental results showed that in the pre-slip stage of the reticle, with an increase in the normal external load, the slippage of the reticle decreased. The theoretical value calculated by the model was basically consistent with the experimental value, and the slippage of the reticle mainly originated from the tangential deformation and relative sliding of the contact surface. With the increase in the normal external load, the proportion of the tangential deformation in the sliding of the entire contact surface was larger. For the change in slippage during different motion stages, the theoretical value was close to the experimental value after eliminating system errors such as vibration and fiber bending, which proved the correctness of the model in this paper.

Displacement Linearity Improving Method of Stepping Piezoelectric Platform Based on Leg Wagging Mechanism

It is difficult to obtain linear output displacements for stepping piezoelectric platform due to their discontinuous outputs. Inspired by the theory that the maximum static friction force is greater than the sliding friction force, in this letter, we propose a bipedal alternating inertial actuation mode (BAIAM) to improve the displacement linearity of the stepping platform. The output displacements are measured, the linear fitting is carried out by the least square method, the correlation coefficient and linear fitting function are used to evaluate the displacement linearity, and the correlation coefficients of the forward and backward motions are calculated as 0.9998 and 0.9999 in BAIAM, respectively, which verifies the effectiveness of the proposed method. The closed-loop experiments in BAIAM are also carried out, and the steady-state errors for the target position of ±40 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m within ±0.2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m in the point-to-point positioning control experiments are achieved. The experimental results confirm that the developed platform can be applied to precision fields requiring a large travel range, planar two-degree-of-freedom motion, and linear outputs.

Nano-friction phenomenon of Frenkel–Kontorova model under Gaussian colored noise

The nano-friction phenomenon in a one-dimensional Frenkel–Kontorova (FK) model under Gaussian colored noise is investigated by using the molecular dynamic simulation method. The role of colored noise is analyzed through the inclusion of a stochastic force via a Langevin molecular dynamics method. Via the stochastic Runge–Kutta algorithm, the relationship between different parameter values of the Gaussian colored noise (the noise intensity and the correlation time) and the nano-friction phenomena such as hysteresis, the maximum static friction force is separately studied here. Similar results are obtained from the two geometrically opposed ideal cases: incommensurate and commensurate interfaces. It was found that the noise strongly influences the hysteresis and maximum static friction force and with an appropriate external driving force, the introduction of noise can accelerate the motion of the system, making the atoms escape from the substrate potential well more easily. Interestingly, suitable correlation time and noise intensity give rise to super-lubricity. It is noteworthy that the difference between the two circumstances lies in the fact that the effect of the noise is much stronger on triggering the motion of the FK model for the commensurate interface than that for the incommensurate interface.

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.

Discontinuous dynamics of an asymmetric 2-DOF friction oscillator with elastic and rigid impacts

• An asymmetric 2 DOF oscillator with elastic and rigid impacts is investigated. • Negative feedback forces and nonlinear spring of cubic term are considered. • Switching conditions of motion at separation boundaries are explored. • Several typical motions are simulated numerically by MATLAB software. In this paper, by using flow switching theory of discontinuous dynamical systems , the discontinuous dynamic behavior of a 2-DOF (two-degree-of-freedom) friction oscillator with elastic impact and rigid impact on different sides is investigated. For the 2-DOF friction oscillator, when the direction of object’s velocity changes, the negative feedback works and the inequality of maximum static friction force and kinetic friction force leads to the existence of flow barriers. In addition, the elastic impact and rigid impact can change motion states of object, resulting in the discontinuity of this 2-DOF system. Considering the multiple motion states of object and better analyzing the equation of object’s motion, the phase space of each object is divided into different motion domains and boundaries in relative and absolute coordinates by means of the discontinuities resulted from the friction and impact. Moreover, because the elastic impact exists in a time period, there will be a variety of motion behaviors coexisting, such as elastic and rigid impacts occur simultaneously. With that in mind, in absolute coordinate system, the phase space of the system is divided in six cases according to whether there are stick motion and stuck motion. Based on flow switching theory, the switching conditions at discontinuous boundaries for all possible motions are given by using G-functions, and it should be noted that the vanishing conditions of the sliding motion become more complicated due to the existence of flow barriers at speed boundaries. Through defining the switching sets on separation boundaries, the mapping structures are further introduced to demonstrate the global dynamic behavior and periodic motions. For a better understanding of the object’s motion and the switching criteria at separation boundaries, the numerical simulation method is used to demonstrate several typical motions such as passable motion, sliding motion, grazing motion, stick motion (elastic impact), rigid impact and periodic motions etc. The results obtained have reference value for the optimization design and noise control of mechanical systems with gap couplings and negative feedbacks.

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.

A new approach of using Lorentz force to study single-asperity friction inside TEM

Taking advantage of the magnetic field inside transmission electron microscope (TEM), a unique Lorentz-force-actuated method for quantitative friction tests was developed via a commercial electromechanical holder. With this approach, a submicron-sized silver asperity sliding on a tungsten flat punch was actuated by Lorentz force due to electrical current through the punch, with the normal force imposed by the built-in transducer of the holder. The friction force was determined by tracking the elastic deflection of the fabricated cantilever from in situ video. Through correlating the friction behavior with the microstructural evolution near the silver-tungsten interface, we revealed that even when the relative motion commenced with the plastic deformation of the silver asperity, the interface can still sustain the further increasing static friction force. Exactly following the arrival of the maximum static friction force, the sliding occurred at the interface, indicating the transition from static to dynamic friction. This work enriches our understanding of the underlying physics of the dynamic friction process for metallic friction behavior.

Experimental Analysis of Frictional Characteristics of the Interface between Gantry Crane Wheels and Rails under Submerged Rail Conditions

The purpose of this paper is to clarify the influence of rail submergence that occurs at the quay on the frictional characteristics of the interface between gantry crane wheels and rails. The characteristics serve as a basis for the dynamic simulation analysis of cranes that run away due to wind and crane designs. An experimental analysis system developed uniquely by the authors was used to carry out this research. Wheel was pressed to submerged rail, then the rail was slid. The friction force generated between the wheel and the rail was measured. This experimental analysis was conducted for contact pressure conditions that the ratios of the maximum Hertzian contact pressure to the yield stress of the material of the rail are approximately 1.76, 2.12 and 2.39. Under these various contact pressures, the ratio of the maximum static friction force under submergence conditions to the same friction force under dry conditions increased slightly. In contrast, when contact pressure conditions were nearly identical, the dynamic friction force under submergence and dry conditions was about same. Finally, the ratio of the dynamic friction coefficient to the static friction coefficient as a reference for designing cranes was shown and discussed.

Nano-friction phenomena in driven Frenkel-Kontorova model with stochastic excitation

In this paper, the effects of a Gaussian white noise excitation on the one-dimensional Frenkel-Kontorova (FK) model are studied by the stochastic Runge-Kutta method under two different types of substrate cases, i.e. incommensurate case and commensurate case. The noise excitation is considered through the inclusion of a stochastic force via a Langevin molecular dynamics approach, and we uncover the mechanism of nano-friction phenomenon in the FK model driven by the stochastic force. The relationship between the noise intensity and the nano-friction phenomenon, such as hysteresis, maximum static friction force, and the super-lubricity, is investigated by using the stochastic Runge-Kutta algorithm. It is shown that with the increase of noise intensity, the area of the hysteresis becomes smaller and the maximum static friction force tends to decrease, which can promote the generation of super-lubricity. Similar results are obtained from the two cases, in which the ratios of the atomic distance to the period of the substrate potential field are incommensurate and commensurate, respectively. In particular, a suitable noise density gives rise to super-lubricity where the maximum static friction force vanishes. Hence, the noise excitation in this sense is beneficial to the decrease of the hysteresis and the maximum static friction force. Meanwhile, with the appropriate external driving force, the introduction of a noise excitation can accelerate the motion of the system, making the atoms escape from the substrate potential well more easily. But when the chain mobility reaches a saturation state (&lt;i&gt;B&lt;/i&gt; = 1), it is no longer affected by the stochastic excitation. Furthermore, the difference between the two circumstances lies in the fact that for the commensurate interface, the influence of the noise is much stronger and more beneficial to triggering the motion of the FK model than for the incommensurate interface since the atoms in the former case are coupled and entrapped more strongly by the substrate potential.