The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

Sliding speed calculation of the Wenchuan earthquake fault using the Doppler effect

Currently,the fault sliding speed functions or source–time functions used in theoretical seismogram calculations have only produced theoretical results;that is,the results of the fault speed–time functions have been obtained only from theoretical studies,and have not been validated using the measured data.This paper signifi cantly improves the method for calculating fault sliding speed using the Doppler eff ect,from the following four perspectives.First,the paper theoretically demonstrates how to confirm that the seismic waves received in some frequency bands by two diff erent receivers are emitted by the same source.Second,the paper proposes a method to determine the similarity of seismic waves received by two diff erent receivers in some frequency bands;it applies the relative change at the two receivers in Fourier amplitude standard deviation in some frequency bands,and determines that similar seismic waves are emitted by the same frequency bands.Third,to eliminate the interference of reflected and refracted waves,this study uses fault sliding time S-wave records for data processing.Finally,the paper replaces the long-time Fourier transform with short-time Fourier transform to enhance the positioning accuracy of fault sliding times.Based on these perspectives,the paper systematically summarizes a general methodology for calculating the fault sliding speed using the Doppler effect.This method is employed to calculate the fault sliding speed of the Wenchuan earthquake;the calculations reveal that there is a general correlation between the fault sliding speeds of the Wenchuan earthquake and the seismic moment changes.The results confi rm that the sliding speed of the Wenchuan earthquake fault possesses the characteristics of abrupt change,whereby a sudden increase in the sliding speed is followed by a rapid decrease.Generally,the sliding speed is not fast,and sometimes,no sliding occurs.There are obvious diff erences from the currently used sliding speed functions,such as the Haskell function,bell-shaped function,exponential function,and triangular function.To determine the fault sliding speed using the Doppler eff ect,only the earthquake records and locations of the epicenter and receivers are required,instead of using unknown crust parameters.In short,the proposed calculation method has clear physical meaning,and the required parameters are easier to obtain.

Adaptive Gain Tuning Rule for Nonlinear Sliding-mode Speed Control of Encoderless Three-phase Permanent Magnet Assisted Synchronous Motor

In this paper, an adaptive gain tuning rule is designed for the nonlinear sliding mode speed control(NSMSC) in order to enhance the dynamic performance and the robustness of the permanent magnet assisted synchronous reluctance motor(PMa-Syn RM) with considering the parameter uncertainties. A nonlinear sliding surface whose parameters are altering with time is designed at first. The proposed NSMSC can minimize the settling time without any overshoot via utilizing a low damping ratio at starting along with a high damping ratio as the output approaches the target set-point. In addition, it eliminates the problem of the singularity with the upper bound of an uncertain term that is hard to be measured practically as well as ensures a rapid convergence in finite time, through employing a simple adaptation law. Moreover, for enhancing the system efficiency throughout the constant torque region, the control system utilizes the maximum torque per ampere technique. The nonlinear sliding surface stability is assured via employing Lyapunov stability theory. Furthermore, a simple sliding mode estimator is employed for estimating the system uncertainties. The stability analysis and the experimental results indicate the effectiveness along with feasibility of the proposed speed estimation and the NSMSC approach for a 1.1-k W PMa-Syn RM under different speed references, electrical and mechanical parameters disparities, and load disturbance conditions.

Influence of Normal Load,Sliding Speed and Ambient Temperature on Wear Resistance of ZG42CrMo

To investigate the wear resistance of ZG42CrMo in industrial application,the wear behaviors under different normal loads,sliding speeds and ambient temperatures were simulated by an MMU-5G abrasion tester to acquire the friction coefficients and wear rates,with the morphology of worn surface observed by scanning electron microscopy（SEM） and chemical composition of worn surface and debris analyzed by X-ray energy dispersive spectroscopy（EDS）.Combine with the theory of tribology,finally the regular of environmental factors’ influence on material wear behaviors is determined.The results show that the increase of load decreases wear resistance significantly,when the pressure reaches a certain extent,severe spalling occurs on the worn surface;the changes of speed result in the changes of size of abrasive debris,and then effect the wear behaviors,in the increasing process of speed,the wear rate increases firstly and then decreases;the rise of temperature causes changes in wear mechanism,bring forth oxidation film on the worn surface,which leads to significant improvement of the wear resistance of materials under high temperature compared to that under low temperature

Effect of sliding speed on elevated-temperature wear behavior of AISI H13 steel

Elevated-temperature wear tests were performed on AISI H13 steel under 50 and 100 r/min at 400–600℃.Through examining the morphology,structure and composition of worn surfaces as well as the microhardness at subsurfaces,the wear mechanisms in various sliding conditions were explored.H13 steel exhibited totally different elevated-temperature wear behavior at two sliding speeds while the high sliding speed would seriously deteriorate its wear resistance.During sliding at two sliding speeds,the wear rate of H13 steel decreased first and then rose with the increase in temperature and the wear rate reached the lowest value(lower than 1×10^(–6)mm^(3)/mm)at 500℃and 50 r/min.The wear rate at 600℃was lower than that at 400℃for 50 r/min,but the wear rate at 600℃was higher than that at 400℃for 100 r/min(except for 50 N).At 50 r/min,the wear rate decreased first and then increased with the increase in load.However,at 100 r/min,the wear rate monotonically increased with increasing load and reached 33×10^(–6)mm^(3)/mm at 600℃and 150 N,where severe wear occurred.In the other sliding conditions,severe wear did not appear with wear rate lower than 5×10^(–6)mm^(3)/mm.Oxidative mild wear merely prevailed at 500℃and 50 r/min and oxidative wear appeared in the other sliding conditions except for 600℃and 150 N,where severe plastic extrusion wear prevailed.The effect of sliding speed on wear behavior was attributed to the changes of tribo-oxide layers.During elevated-temperature sliding,tribo-oxide particles were more readily retained to form protective tribo-oxide layers on worn surfaces at the lower sliding speed than at the higher sliding speed,so as to protect from wear.

Model predictive current control for PMSM driven by three-level inverter based on fractional sliding mode speed observer

Based on the fractional order theory and sliding mode control theory,a model prediction current control(MPCC)strategy based on fractional observer is proposed for the permanent magnet synchronous motor(PMSM)driven by three-level inverter.Compared with the traditional sliding mode speed observer,the observer is very simple and eases to implement.Moreover,the observer reduces the ripple of the motor speed in high frequency range in an efficient way.To reduce the stator current ripple and improve the control performance of the torque and speed,the MPCC strategy is put forward,which can make PMSM MPCC system have better control performance,stronger robustness and good dynamic performance.The simulation results validate the feasibility and effectiveness of the proposed scheme.

Friction and wear properties of in-situ synthesized Al_2O_3 reinforced aluminum composites

Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al2O3 composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al2O3 composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al2O3 composites includes abrasive wear, adhesive wear and oxidation wear.

Determination of the Friction Coefficient in the Flat Strip Drawing Test

Current work is focused on the influence of friction in deep drawing process. Friction measurements were also conducted using a modified tribotester based on strip sliding between tools. Four different tool surfaces were tested under similar contact conditions regarding contact area, normal pressure, sliding speed, lubricant and surface characteristics to calculate the friction coefficient between the tool surface and a high strength low alloy steel sheet HSLA 380. The results showed that friction coefficient varies over a wide range with different lubricating conditions and different sliding velocities. For some sliding velocities, the coefficient of friction is stable and low, while for others it is unstable and higher. Results of the experiments reveal that this novel tribotester is a very useful tool to evaluate and compare the friction between steel sheet and tool surfaces in alloyed steel for cold working applications. The outcomes have only small dispersion within the different test series, which indicates a stable process with good repeatability. The test method enables comparison of different surface finishes and treatments, lubricants and coatings in terms of friction and galling under conditions similar to those found in sheet metal forming processes. The four different types of surfaces considered for this study were grinded, polished, nitrided and quenched/tempered. The main difference among the tested tools in this work was the surface roughness, which was found to have a strong influence on friction.

Effect of Bagasse ash reinforcement on the wear behaviour of Al-Cu-Mg/Bagasse ash particulate composites

The effect of Bagasse ash （BAp） particle reinforcement on the wear behavior of Al-Cu- Mg alloy has been studied. Bagasse ash particles were varied from 0 wt pct-10 wt pct with interval of 2 wt pct. Unlubricated pin-on disc tests were conducted to examine the wear behaviour of the aluminium alloy/Bagasse ash particulate composites. The tests were conducted at varying loads, from 5 to 20 N and sliding speeds of 1.26 m/s, 2.51 m/s, 3.77 m/s and 5.02 m/s for a constant sliding distance of 5000 m. The results showed that the wear rates of the A1-Cu-Mg/BAp composites are lower than that of the matrix alloy and further decrease with increasing Bagasse ash content. Wear rate increases as the sliding speed and applied load increase. The microstructure of the worn surface revealed that a large amount of plastic deformation appeared on the surface of the unreinforced alloy. While Bagasse ash reinforced Al-Cu-Mg alloy showed worn out surface that is not smooth, and grooves, scratches and parallel lines were observed. A combination of adhesion and delamination wear was in operation. These results show that improve wear properties is achievable for the aluminium alloy by the addition of Bagasse ash particles as reinforcement material.