Forced stick-slip oscillations allow the measurement of the friction force: Application to paper materials

Different methods for measuring the friction forces are investigated in this paper. We consider the paper-on-paper contact as an example of application. We first underline several drawbacks for the two main standard methods, namely the inclined and horizontal plane methods. In particular, the horizontal plane test method often involves stick-slip oscillations that make the measurement of the friction force impossible. We then propose a method for characterizing these oscillations and removing their influence on the friction force measurement. The comparison of the proposed method to standards suggests that our proposed method delivers measurements that are much more accurate and repeatable. We finally discuss the validity of averaging the friction force measured during the sliding movement.     

Atomic-scale study of friction and energy dissipation

This paper presents an analysis of the interaction energy and various forces between two surfaces, and the microscopic study of friction. Atomic-scale simulations of dry sliding friction and boundary lubrication are based on the classical molecular dynamics (CMD) calculations using realistic empirical potentials. The dry sliding of a single metal asperity on an incommensurate substrate surface exhibits a quasi-periodic variation of the lateral force with two different stick-slip stage involving two structural transformation followed by a wear. The contact area of the asperity increases discontinuously with increasing normal force. Xe atoms placed between two atomically flat Ni surfaces screen the Ni-Ni interaction, decrease the corrugation of the potential energy as well as the friction force at submonolayer coverage. We present a phononic model of energy dissipation from an asperity to the substrates.     

高速切削过程测温方法综述

切削温度与加工精度和刀具磨损密切相关,高速切削过程中切削温度随着材料,刀具,切削用量的选择不同而呈现出与普通切削过程不同的变化规律.本文归纳了高速切削当中切削温度的测定方法,并指出了各种方法的优缺点及适用性.     

铜铁合金复合摩擦材料高温摩擦行为

研究高速列车用铜铁合金复合摩擦材料的高温摩擦磨损性能。在PlintTE77高温疲劳试验机上对该材料进行高温摩擦磨损性能测试 ,并对摩擦后的磨痕进行了微观组织分析     

Test verification of an extensometer for deformation measurement of high temperature straight pipes

In order to measure deformations of high temperature pipes, an extensometer is designed and verified by experiments. Firstly, the structure and working principle of the extensometer are described. Then experiments both in the laboratory and on site are carried out to prove stability and accuracy of the extensometer. Results from experiments are compared with the calibrating values, and they are in good agreement. The operating condition of the main steam pipe is evaluated by the on-site test. Conclusions can be drawn that the designed extensometer has reliable stability and high accuracy and can be used for measuring deformations of high temperature pipes in power plants.     

Double-integrator control for precision positioning in the presence of friction

In order to achieve good performance in precision positioning systems where friction is present, a straightforward approach is using single-integrator controllers to suppress the effect of friction. In this paper, double-integrator (DI) control, in which two integrators are involved, is proposed to enhance controller gain at lower frequencies. A new integral anti-windup scheme is developed for the DI control and is shown to be effective. Performance of a DI controller is compared with that of a proportional-integral-derivative controller (I-PD) and a pole-placement-with-integration controller (PPI) by experiment on a slide system driven by a dc motor. In the system, the dc motor has brushes that give rise to friction, and all other frictional contacts are removed by frictionless aerostatic support. Because of the unmodeled high frequency dynamics caused by aerostatic dynamics, closed-loop bandwidth with the I-PD controller is limited at a lower value than in the cases with the DI and PPI controllers. With the three controllers having parameters for similar closed-loop bandwidths, the DI controller gives uniform closed-loop responses to step inputs of different heights, while for the other two controllers the responses are obviously dependent on the height of the step inputs.     

Method for continuous detection of different friction and wear regimes and application to the behaviour of ceramics at high temperature

This paper describes tests carried out on a tribometer functioning at high temperature and equipped to record continuously the various test parameters, namely, the normal applied load, the tangential friction force, the differential movement of the contact surfaces, and the temperature of the sample. Dry friction tests, conducted on two aluminas of different purities, showed different degradation regimes at both 20 and 800°C. Thus, three successive periods of functioning were identified and correlated with transitions in the mechanism of degradation of the surfaces or in the mechanism of interfacial adaptation in the contact. The first period corresponds basically to the adaptation mechanisms of the interfaces with no wear material generated. The two subsequent periods demonstrate the degradation mechanisms of the surfaces leading to the production of more or less wear material and resulting in different states of equilibrium between production, recirculation, and loss of wear debris through the contact.     

Stabilization of high frequency chatter vibration in fine boring by friction damper

Friction damper has been found successful to prevent high frequency chatter occurring at more than 10,000Hz, and causing problem of reduced tool life in fine boring operation. The new damper is characterized by simple structure that consists of an additional mass attached to the main vibrating structure with small piece of permanent magnet. The principle is straightforward in which Coulomb and viscous frictions dissipate vibration energy at the interface between the damper and main vibrating structure. The damper needs no tuning, and is effective at high frequency. The paper first introduces a typical design of the friction damper with experimental proof by cutting tests of its effectiveness in eliminating the high frequency chatter in fine boring, and assuring normal tool life of the cutting edge. Theoretical and experimental analyses are introduced for understanding the fundamental principle and characteristics of the new damper. The new damper is effective for boring tools, which vibrate at frequency more than 5,000Hz.     

Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel

Abstract

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s^?1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.     

Tribological behavior of reciprocating friction drive system under lubricated contact

The dynamic friction and wear behaviors are investigated in reciprocating friction drive system using a 0.45% carbon steel pair. The effects of various operating parameters on the traction force, stick and slip time, and friction modes are examined under the lubricated contacts. Moreover, the critical operating conditions in classifying three friction modes are also established. Results show that the fluid friction induced by the shearing of lubricant dominates the variation of traction force and produces the positive slope γ at the first period of slip in the traction force–relative sliding velocity curve. The γ value decreases at higher driver speed during stick-slip motion due to the thicker fluid film and shear thinning effect. The γ value increases due to the asperity interactions as the friction region is transferred from stick-slip to sticking with normal load from 196 to 980 N. Furthermore, it is also found that the static friction force is independent of stick time for the tangential loading rate ranged from 1.12 to 16.8 s⁻¹. The transition region produces the severest wear under the different driver speeds, but the wear is insensitive to the friction regions and the severe wear only occurs at higher normal load due to the action of Hertzian contact.     

Positioning and tracking of a linear motion stage with friction compensation by fuzzy logic approach

In this paper, the development of a fuzzy controller that compensates for nonlinear friction in a linear motion stage is presented. The experimental work and instrumentation set up is presented for this research. Based upon a nonlinear friction model, friction parameters were estimated from experimental results. Simulation and experimental validation on a ball-screw mechanism is presented, showing the effectiveness of the proposed controller. Furthermore, it is shown that the proposed fuzzy control scheme offers several implementation advantages such as smaller control effort, and reduced effect of measurement noise. Moreover, the fuzzy logic methodology displays superior performance when compared to a conventional PID controller. It also shows good and robust tracking with respect to system parameters variation.     

摩擦火花瞬时高温对中高碳钢中碳的影响

选取42CrMo、60Si2Mn、GCr153种常见的中高碳钢理论分析和检测验证两方面对高速打磨过程中摩擦火花瞬时高温是否会对中高碳钢表面形成脱碳层,从而影响中高碳钢中碳含量的检测进行探讨、验证。结果表明高速打磨过程中摩擦火花瞬时高温无法达到中高碳钢表面脱碳所需的温度,并且在实际检测中标准物质11次测试结果的RSD在0.499%~0.698%,测试结果的平均值和认定值的差值均在标准样品证书的不确定度范围内。因此高速打磨过程中摩擦火花瞬时高温不会影响中高碳钢中碳含量的检测。     

Apparatus for the high temperature measurement of the Seebeck coefficient in thermoelectric materials

The Seebeck coefficient is a physical parameter routinely measured to identify the potential thermoelectric performance of a material. However, researchers employ a variety of techniques, conditions, and probe arrangements to measure the Seebeck coefficient, resulting in conflicting materials data. To compare and evaluate these methodologies, and to identify optimal Seebeck coefficient measurement protocols, we have developed an improved experimental apparatus to measure the Seebeck coefficient under multiple conditions and probe arrangements (300 K-1200 K). This paper will describe in detail the apparatus design and instrumentation, including a discussion of its capabilities and accuracy as measured through representative diagnostics. In addition, this paper will emphasize the techniques required to effectively manage uncertainty in high temperature Seebeck coefficient measurements.     

PZN-PT based smart probe for high temperature fluid viscosity measurements

A smart sensing system is proposed for high-temperature (up to 90 °C) viscosity measurement of viscous fluids. The proposed sensing system is based on a smart cantilever probe on which a new generation of piezoelectric materials, relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3−x)PbTiO(3) (PZN-PT), is bonded. The proposed system utilizes a PZN-PT single crystal for actuation and a laser displacement sensor for vibration detection. By analyzing the vibrational properties of the cantilever probe, the viscosity of measured fluids at different temperatures (up to 90 °C) were extracted. Lab tests were carried out to verify and evaluate the effect of this system on high-temperature measurements. Results show a consistent agreement with theoretical analysis. In comparison to the existing high-performance piezoelectric material, lead magnesium niobate-lead titanate solid solution (1−x)[Pb(Mg1/3Nb2/3)O3]−x[PbTiO3] (PMN-PT), PZN-PT has a steady performance at high temperatures and shows more reliability. The proposed sensing system can be applied to real-time monitoring of viscous fluids in high-temperature environments, such as vehicle cooling systems, power plant cooling tower fluid monitoring, and other heat transfer systems.     

Effect of temperature and load on three-body abrasion of cermets and steel

The effect of temperature and load on three-body abrasion resistance has been examined for stainless steel, Cr₃C₂-Ni cermet, plain WC-Co hardmetal and yttria stabilized zirconia doped WC-based composites. Series of tests at various tribo-conditions were performed on a recently developed device. Coefficient of friction and materials response to abrasive actions have been analyzed and positive effect of zirconia addition on materials wear resistance has been shown. The low wear rates of ZrO₂ containing cermets are due to lower susceptibility of zirconia to transgranular crack propagation, smaller mean free path between ceramic grains and formation of lubricating glazed silica-rich layer.     

Apparatus for monitoring the resistivity of the hydration of cement cured at high temperature

A resistivity apparatus was developed to investigate the early hydration processes of cementitious materials cured at elevated temperatures. The apparatus consists of a temperature control system, resistivity measurement system, and automatic data acquisition system. The temperature control of the resistivity apparatus was ±0.5°C. Three parallel measurements varied by approximately 5%, which shows that the apparatus was reliable and reproducible. By monitoring the electrical resistivity of fresh cement, the hydration process was characterized. The developed device may provide valuable insights into the mechanisms of cement hydration at high curing temperatures. In addition, increased curing temperature accelerates the setting process and strength development of the cement. However, high temperature has negative effects on compressive strength of the material.     

Experimental mathematical model as a generalization of sensitivity analysis of high temperature spectral emissivity measurement method

The development of an experimental mathematical model describing temperature state of the sample during high temperature spectral emissivity measurement is introduced. Dimensional analysis of the measurement process gives the physical dimensionless quantities and sensitivity analysis of the measurement process provides the large set of performed model experiments. Evaluated experimental mathematical models are presented including their accordance with model experiments. Established equations are generalization of sensitivity analysis of high temperature spectral emissivity measurement method and can be used for computation of spectral emissivity total uncertainty.     

高速切削中切削温度研究方法

切削热与切削温度的产生和影响是高速切削技术研究的重要内容。高速切削过程中的温度检测技术与研究方法是在传统切削速度加工相关技术基础上的发展与创新。归纳了高速切削中切削温度实验测定方法和数值计算方法,指出了各种方法的优缺点及适用性。     

高速干式飞刀的切削温度模型

根据传热学和金属切削原理等,建立高速干式飞刀的切削温度模型,推导出多因素切削温度的计算公式,该模型的建立为进一步分析高速干式滚齿切削温度及切削机理奠定了基础。