scholarly journals Multiscale study of the dynamic friction coefficient due to asperity plowing

Friction ◽  
2020 ◽  
Author(s):  
Jianqiao Hu ◽  
Hengxu Song ◽  
Stefan Sandfeld ◽  
Xiaoming Liu ◽  
Yueguang Wei
Keyword(s):  
Friction Coefficient ◽  
Surface Friction ◽  
Multiscale Approach ◽  
Normal Contact ◽  
Dynamic Friction Coefficient ◽  
Dislocation Plasticity ◽  
One Step ◽  
Dynamics Simulations ◽  
Single Contact ◽  
Nanoscale Level

AbstractA macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities. Therefore, the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear. In this work, we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs. Subsequently, to estimate the friction coefficient of rough surfaces, we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model. By employing the present multiscale approach, we used the size, rate, and orientation effects, which originated from nanoscale dislocation plasticity, to determine the dependence of the macroscale friction coefficient on system parameters, such as the surface roughness, separation, loading velocity, and direction. Our model predicts an unconventional dependence of the friction coefficient on the normal contact load, which has been observed in nanoscale frictional tests. Therefore, this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level.

Adhesive Effects on Dynamic Friction for Unlubricated Rough Planar Surfaces

2004 ◽  
Author(s):  
Xi Shi ◽  
Andreas A. Polycarpou
Keyword(s):  
Friction Coefficient ◽  
Mean Value ◽  
Friction Model ◽  
Major Influence ◽  
Dynamic Friction ◽  
Friction Behavior ◽  
Friction Forces ◽  
Normal Contact ◽  
Continuous Contact ◽  
Dynamic Friction Coefficient

As the size of contacting and sliding tribosystems decrease, intermolecular or adhesive forces become significant partly due to nanometer size surface roughness. The presence of adhesion has a major influence on the interfacial contact and friction forces as well as the microtribosystem dynamics and thus influences the overall dynamic friction behavior. In this paper, a dynamic friction model that explicitly includes adhesion, interfacial damping and the system dynamics for realistic rough surfaces was developed. The results show that the amplitude and mean value of the time varying normal contact and friction forces increase in the presence of adhesion under continuous contact conditions. Also, due to the attractive nature of adhesion, its presence delays or eliminates the occurrence of loss of contact. Furthermore, in the presence of significant adhesion, dynamic friction behavior is significantly more complicated compared to the no adhesion case, and the dynamic friction coefficient predictions may be misleading. Thus, it is more appropriate to discuss dynamic friction force instead of dynamic friction coefficient under dynamic conditions.

Adhesive Effects on Dynamic Friction for Unlubricated Rough Planar Surfaces

2006 ◽  
Vol 128 (4) ◽  
pp. 841-850 ◽  
Author(s):  
Xi Shi ◽  
Andreas A. Polycarpou
Keyword(s):  
Friction Coefficient ◽  
Mean Value ◽  
Friction Model ◽  
Major Influence ◽  
Dynamic Friction ◽  
Friction Behavior ◽  
Friction Forces ◽  
Normal Contact ◽  
Continuous Contact ◽  
Dynamic Friction Coefficient

As the size of contacting and sliding tribosystems decrease, intermolecular or adhesive forces become significant partly due to nanometer size surface roughness. The presence of adhesion has a major influence on the interfacial contact and friction forces as well as the microtribosystem dynamics (microtribodynamics) and thus influences the overall dynamic friction behavior. In this paper, a dynamic friction model that explicitly includes adhesion, interfacial damping, and the system dynamics for realistic rough surfaces was developed. The results show that the amplitude and mean value of the time varying normal contact and friction forces increase in the presence of adhesion under continuous contact conditions. Also, due to the attractive nature of adhesion, its presence delays or eliminates the occurrence of loss of contact. Furthermore, in the presence of significant adhesion, dynamic friction behavior is significantly more complicated compared to the no adhesion case, and the dynamic friction coefficient predictions may be misleading. Thus, it is more appropriate to discuss dynamic friction force instead of dynamic friction coefficient under dynamic conditions.

scholarly journals A Simple Mechanistic Model for Friction of Rough Partially Lubricated Surfaces

2021 ◽  
Vol 69 (3) ◽  
Author(s):  
Gianluca Costagliola ◽  
Tobias Brink ◽  
Julie Richard ◽  
Christian Leppin ◽  
Aude Despois ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Friction Coefficient ◽  
Mechanistic Model ◽  
Applied Pressure ◽  
Real Contact Area ◽  
Experimental Measurements ◽  
Dynamic Friction ◽  
Real Contact ◽  
Dynamic Friction Coefficient ◽  
Direct Measurements

AbstractWe report experimental measurements of friction between an aluminum alloy sliding over steel with various lubricant densities. Using the topography scans of the surfaces as input, we calculate the real contact area using the boundary element method and the dynamic friction coefficient by means of a simple mechanistic model. Partial lubrication of the surfaces is accounted for by a random deposition model of oil droplets. Our approach reproduces the qualitative trends of a decrease of the macroscopic friction coefficient with applied pressure, due to a larger fraction of the micro-contacts being lubricated for larger loads. This approach relates direct measurements of surface topography to realistic distributions of lubricant, suggesting possible model extensions towards quantitative predictions.

Study on the Mechanical Properties and Handle of PTT/Wool Blended Fabrics

2010 ◽  
Vol 150-151 ◽  
pp. 1810-1813
Author(s):  
Guang Biao Xu ◽  
Lian Ying Zhao ◽  
Fu Mei Wang
Keyword(s):  
Mechanical Properties ◽  
Friction Coefficient ◽  
Surface Friction ◽  
Maximum Load ◽  
Wool Fabrics

The low-stress properties of PTT/wool blended fabrics were investigated by comparing with PET/wool blended fabrics. The results show that, the elongation of PTT/wool fabrics at the maximum load is higher, especially in filling wise, which means PTT/wool fabrics have better elastic. The bending hysteresis, shearing rigidity and shearing hysteresis of PTT/wool fabrics are higher than those of PET/wool fabrics, determining the fabrics having good formability. PTT/wool fabrics are easier to be compressed, and has a little higher surface friction coefficient, giving the fabrics better feeling of softness and fullness. The hand values show that PTT/wool blended fabrics are softer, and have the good bulkiness but not as good as that of PET/wool fabrics.

Slip-Clutch Torque Estimation via Real-Time Adaptive Lookup Table

2021 ◽  
Vol 2 (2) ◽  
Author(s):  
Wenpeng Wei ◽  
Hussein Dourra ◽  
Guoming Zhu
Keyword(s):  
Friction Coefficient ◽  
Real Time ◽  
Mean Squared Error ◽  
Surface Friction ◽  
Lookup Table ◽  
Recursive Least Squares ◽  
Time Varying ◽  
Squared Error ◽  
Output Torque ◽  
Clutch Torque

Abstract Transfer case clutch is crucial in determining traction torque distribution between front and rear tires for four-wheel-drive (4WD) vehicles. Estimating time-varying clutch surface friction coefficient is critical for traction torque control since it is proportional to the clutch output torque. As a result, this paper proposes a real-time adaptive lookup table strategy to provide the time-varying clutch surface friction coefficient. Specifically, the clutch-parameter-dependent (such as clutch output torque and clutch touchpoint distance) friction coefficient is first estimated with available low-cost vehicle sensors (such as wheel speed and vehicle acceleration); and then a clutch-parameter-independent approach is developed for clutch friction coefficient through a one-dimensional lookup table. The table nodes are adaptively updated based on a fast recursive least-squares (RLS) algorithm. Furthermore, the effectiveness of adaptive lookup table is demonstrated by comparing the estimated clutch torque from adaptive lookup table with that estimated from vehicle dynamics, which achieves 14.8 Nm absolute mean squared error (AMSE) and 2.66% relative mean squared error (RMSE).

scholarly journals Experimental Study on the Transition between Static and Kinetic Frictions of Steel/Shale Pairs

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Qin Lian ◽  
Chunxu Yang ◽  
Jifei Cao
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
Critical Distance ◽  
Dynamic Friction ◽  
Stick Slip ◽  
Dynamic Friction Coefficient ◽  
The Coefficient Of Friction ◽  
The Difference ◽  
Stick Slip Motion ◽  
Insight Into

The transition between static and kinetic frictions of steel/shale pairs has been studied. It was found that the coefficient of friction decreased exponentially from static to dynamic friction coefficient with increasing sliding displacement. The difference between static and dynamic friction coefficients and the critical distance Dc under the dry friction condition is much larger than that under the lubricated condition. The transition from static to dynamic friction coefficient is greatly affected by the normal load, quiescent time, and sliding velocity, especially the lubricating condition. Maintaining continuous lubrication of the contact area by the lubricant is crucial to reduce or eliminate the stick-slip motion. The results provide an insight into the transition from static to dynamic friction of steel/shale pairs.

scholarly journals Dynamic characteristics of the gear-rotor system in compressed air energy storage considering friction effects

2021 ◽  
Vol 12 (1) ◽  
pp. 677-688
Author(s):  
Xinran Wang ◽  
Wen Li ◽  
Dongxu Hu ◽  
Xingjian Dai ◽  
Haisheng Chen
Keyword(s):  
Energy Storage ◽  
Friction Coefficient ◽  
Dynamic Characteristics ◽  
Surface Friction ◽  
Rotor System ◽  
Compressed Air ◽  
Contact Temperature ◽  
Tooth Surface ◽  
Compressed Air Energy Storage ◽  
Rotating Speed

Abstract. The tooth surface friction effects and the resulting tooth surface contact temperature are important factors for the dynamic characteristics of a gear-rotor system in compressed air energy storage (CAES). Therefore, a 3∘ of freedom finite-element model of the system is set up in which the lubrication state of the gear pair, tooth surface friction, contact temperature of the tooth surface, backlash and unbalanced excitation are considered. The friction coefficient is calculated according to the variation of the lubrication state, and the tooth surface contact temperature is derived based on the friction coefficient. The tooth profile deformation caused by the change in the contact temperature is calculated, and the resulting effects on backlash and comprehensive meshing stiffness are considered. The influence of rotating speed, torque load and viscosity of lubricating oil on the system response is studied, and the variation of the friction coefficient, flash temperature of the tooth surface, pressure of the tooth surface and so on are discussed in detail. The results indicate that when the friction coefficient is derived according to the variation of the lubrication state, the variation of the contact temperature of the tooth surface with rotating speed is quite different from that calculated based on a friction coefficient which is set artificially. This leads to a new variation of the dynamic response of the gear-rotor system, and the method of stabilizing the operation of the system is put forward based on the optimization curve for the operation of the system. The results obtained in this paper will provide a reference for the study and design of a gear-rotor system in CAES.

scholarly journals Chaos phenomenon and stability analysis of RU-RPR parallel mechanism with clearance and friction

2018 ◽  
Vol 10 (1) ◽  
pp. 168781401774625 ◽  
Author(s):  
Yulei Hou ◽  
Yi Wang ◽  
Guoning Jing ◽  
Yunjiao Deng ◽  
Daxing Zeng ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Contact Force ◽  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Force Model ◽  
Obvious Effect ◽  
Normal Contact ◽  
Rotational Degrees Of Freedom ◽  
The Stability ◽  
Baumgarte Stabilization

The chaos phenomenon often exists in the dynamics system of the mechanism with clearance and friction, which has obvious effect on the stability of the mechanism, then it is worthy of attention for identifying the relationship between the friction coefficient and the stability of the mechanism. Two rotational degrees of freedom decoupled parallel mechanism RU-RPR is taken as the research object. Considering the clearance existing in the revolute pair, Lankarani–Nikravesh contact force model is used to calculate the normal contact force, and the Coulomb friction force model is used to calculate the tangential contact force. The dynamics model is established using Newton–Euler equations, and the Baumgarte stabilization method is used to keep the stability of the numerical analysis. Then, the equations are solved using the fourth adaptive Runge–Kutta method, and the effect of the revolute pair’s clearance on the dynamic behavior is analyzed. Poincare mapping is plotted, and the bifurcation diagrams are analyzed with varying the friction coefficient corresponding to different values of clearance size. The research contents possess a certain theoretical guidance significance and practical application value on the analysis of the chaotic motion and its stability in the dynamics of the parallel mechanism.

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