Thermomechanical wear modelling

It is assumed that the contact between bodies in sliding motion produces a stress field and frictional heat source that may induce severe wear from material yielding or fracture. For this situation, a thermomechanical wear model is used to develop a wear transition equation for identifying the dominant factors that will reduce or control such wear, by employing thermoelasticity analyses and contact mechanics. This equation is used to construct wear maps for ease of analysis. Studies are used to substantiate the thermomechanical wear model with experimental results that emphasise the transition from mild to severe wear for dry and lubricated metallic and ceramic sliding contacts under load.     

湿式多片摩擦离合器接排过程热结构耦合分析

针对船用齿轮箱湿式多片摩擦离合器,考虑摩擦片与摩擦片座外花键、对偶片与离合器齿轮内花键间摩擦力作用,分析了摩擦片副间的正压力和花键齿间摩擦力的分布规律,并计算了摩擦片副的热流密度及对流换热系数;利用ANSYS建立了多对摩擦片副的热弹接触有限元分析模型,通过瞬态热结构耦合分析,得出接排过程中摩擦片副间温度云图及温度沿径向、轴向分布规律,同时分析了摩擦片的热弹变形及片间接触压力。     

Processes in heat dynamics and modelling of friction and wear (dry and boundary friction)

Theoretical postulates of heat dynamics and modelling of friction and wear are formulated based on a system of equations including basic dependences of friction behaviour on load, velocity, time and temperature.     

盘式制动器摩擦磨损热动力学研究进展

摩擦磨损热动力学是制动器失效分析和设计的重要理论依据,对选择摩擦副材料也有指导作用．因此从分析摩擦热对制动器摩擦副的影响着手,总结了盘式制动器摩擦磨损热动力学的数学、物理模型,并对制动摩擦表面温度场和应力场的计算方法进行分析比较,评述了盘式制动器摩擦磨损热动力学的研究进展,并对今后主要研究工作进行了展望．     

Thermomechanical aspects of mixed friction in concentrated contacts

Important aspects of partial elastohydrodynamic lubrication are discussed. For heavily loaded counterformed machine parts such as cams and followers, gear teeth, and ball- and roller-bearing elements working in the mixed friction regime, thermomechanical effects on the micro scale have been investigated. The temperature distribution resulting from friction has been determined, assuming that an axially symmetrical source of heat occurs on the peak of the contacting asperity.The thermal deformations and stresses in interacting asperities are obtained with the finite element method. A statistical analysis of the thermomechanical quantities has been carried out. Conclusions about the temperatures and the thermal stresses in contacting asperities have been formulated. A thermoelastic coupling of the interacting rough surfaces has been proposed as a mechanism of the scuffing mode of failure in concentrated contacts.     

脉冲电化学加工表面形貌与摩擦磨损

通过对脉冲电化学、电火花以及机械加工形成的不同表面形貌的对比，来分析加工表面形貌与摩擦磨损之间的影响关系。结果表明：脉冲电化学加工表面具有较小的摩擦系数和很好的抗磨损性能。     

Features of wear of brittle inorganic materials during friction and abrasive machining

Laser confocal microscopy reveals fatigue cracking under the surface of silicate glass upon friction and abrasive machining. Surface cracking is also registered and its maximum depth is determined, indicating that its longitudinal cross section has an irregular profile. The stage of fatigue wear of the glass corresponding to debris nucleation shouldbe visualized. It is established that the mass wear rate and the maximum surface cracking depth are correlated: once a definite sliding velocity is reached, the cracking becomes deeper and the wear rate intensifies in both types of tests. The obtained results prove that several wear mechanism can occur simultaneously during abrasive machining of brittle inorganic materials, namely, brittle chipping, low-cycle fatigue, thermomechanical fracture, and local melting (under critical loading conditions).     

Third body effects on friction and wear during fretting of steel contacts

Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track.     

Magnetization of friction surfaces and wear particles by tribological processes

The relationship between magnetization of a friction surface and wear phenomena is discussed for the case of rubbing of nickel on nickel. Experiments were performed by sliding-friction tests of the pin-on-block type. Magnetization of the friction surface was estimated by measuring changes in the magnetic flux density with a Tesla meter, and the effects of lubrication and various normal loads on changes in the magnetic flux density were examined. Also, the magnetic flux density of wear particles was examined for single particles and particle aggregates. The magnetization of the friction surface was found to be related to surface damage by transfer (adhesion). Individual wear particles and aggregates of fine wear particles were all magnetized in one direction by tribological action, showing that wear particles and transfer particles on the friction surface are the principal source of magnetization.     

Prediction of the occurrence of wear by friction force-displacement curves

If a contacting body is moved in the tangential direction in very small steps a rapid increase of the friction force can be observed during the early stages of motion. No transition to a constant value representing the kinetic friction was observed during the investigation of steel surfaces. The friction force increased, though at a more moderate rate. At this stage of movement wear will occur. Investigations with oil-lubricated surfaces showed similar increases. No increase was observed with MoS₂ or PTFE lubrication. It is suggested that the behaviour of the friction force after the transition displacement indicates whether deterioration of the surfaces will occur. If the movement does not exceed the transition displacement no wear occurs.     

Mechanism-based modeling of friction and wear

Equations for “predicting” friction and wear that product design engineers can readily apply require new methods to develop. These include the following. 1. The planned cooperation of several technical disciplines.

2. The selection of a well studied system.

3. Parametric equations (models) for the observed friction or wear behavior, including all variables known by an interdisciplinary group.

4. Data that cover a wide range (e.g. several decades) of most relevant variables.

5. Methods for adjusting parameters in the models to closely match the data. The results of three research efforts are discussed in terms of the prospects for developing equations either by curve fitting the data or by describing underlying phenomena involved in the sliding process. Finally, possible contributions of several technical disciplines toward modeling the conditions for scuff prevention are suggested.     

Advances in friction and wear mechanisms

This review considers what inferences regarding the mechanism of wear can be derived from recent investigations into the functioning of machine elements operating under conditions representative of engineering practice. Among the subjects discussed are particle analysis, surface texture effects, stress system, thermal effects, chemical aspects of wear, and ehd effects     

Effect of friction cycles on wear particle generation of carbon nitride coating against a spherical diamond

The in-situ observations of wear particle generation of carbon nitride coating on silicon repeatedly sliding against a spherical diamond have been studied in terms of the critical friction cycles and normal loads. An environmental scanning electron microscope (E-SEM), in which a pin-on-disk tribotester was installed, has in-situ provided direct evidence of when and how the wear particle generation do occur during the repeated sliding of carbon nitride coating against a spherical diamond. The in-situ observations of non-conductive carbon nitride coating are therefore available free from surface charging with controllable relative humidity. The repeated sliding tests at a sliding speed of 50 μm/s have been carried out with the purpose of observing the ‘No wear particle generation’ region when varying normal load from 10 to 250 mN. It appears that until 20 friction cycles, the maximum Hertzian contact pressure P_max for ‘No wear particle generation’ can be improved from 1.39 Y to 1.53 Y if silicon is coated by carbon nitride with a thickness of 10 nm, where Y is defined as the yield strength of silicon. The applicable enlargement of the ‘No wear particle generation’ region of carbon nitride coating has therefore been comparatively discussed with the silicon substrate from the view points of the friction coefficient and the specific wear rate. The mode transition maps have also been summarized for the repeated sliding of carbon nitride coating in terms of ‘No wear particle generation’, ‘Wear particle generation by microcutting’ and ‘Wear particle generation by microcutting and microfracturing’ three typical modes.     

Numerical analysis of heat generation and temperature field in reverse dual-rotation friction stir welding

A 3D model is developed for numerical analysis for heat generation, temperature field, and material flow in reverse dual-rotation friction stir welding (RDR-FSW) process. The reverse rotation of the assisted shoulder and the tool pin is considered to determine the heat generation rate. Friction heat, plastic deformation heat, and their partition coefficients are analyzed. Due to the tool pin and assisted shoulder being separated and reversely rotated independently, the temperature difference between the advancing and retreating sides is weakened. The reverse material flow is beneficial to the uniformity of both the temperature and microstructure at the advancing and retreating sides. The calculated temperature profiles agree well with the corresponding experimentally measured values.     

The friction and wear properties of nylon

The effects of temperature on the friction of nylon are examined at various sliding velocities. Maximum friction values are obtained, but it is found that when specimens slide continuously at various velocities, the magnitude of the maximum friction varies with the velocity, while when specimens slide alternately at 10 and 0.1 mm s⁻¹, nearly the same maximum value is obtained. In the latter case, the displacement of the friction-velocity curves at various temperatures along the velocity axis can give a master curve while in the former case this is impossible.

The effects of temperature, velocity and load on the wear of nylon are also examined. Minimum values of the wear are obtained in all cases, whereas maximum values of the friction are obtained. The mechanism of such behaviour is discussed.     

环一块摩擦磨损试验机设计研究

在滚动摩擦磨损实验技术中,摩擦系数和摩擦力是影响摩擦的重要参数,为了测量环块摩擦的特性本文设计了环块摩擦磨损试验机。本试验机中负荷模块可以实现对摩擦系数的测量试验,减小了体积;机械传动部件简单,降低了润滑剂的使用;采用闭环反馈响应系统,运动精度和测量精度都得到了提高;采用单片机编程技术对摩擦后的反馈信号进行实时采集;该试验机能够在低温环境下运行;试样夹紧装置结构简单,为实验试样的装卸提供了方便;并按照标准选则装配零件和按标准绘出了机构装配图。     

High temperature wear of asbestos-reinforced friction materials

The high temperature (480 °–570 °F) wear of two commercial asbestosreinforced friction materials was investigated by dynamometer testing. Wear rate constants were evaluated at different temperatures; the activation energy for the wear of each material was obtained under different loads and speeds. The results strongly support a pyrolysis mechanism proposed previously for wear at elevated temperatures.