Frictional resistance characteristics of a capsule inside the intestine for microendoscope design

The design of the capsule body for a self-propelled endoscope is important from the frictional resistance point of view. The motivation of this work was to gain a better understanding of the effect of capsule shape on the frictional resistance of the capsule inside a small intestine. Special experimental set-ups were built to investigate the frictional resistance of the capsule and the viscoelastic deformation characteristics of the small intestine specimen of a pig. Tests were performed with capsules of various shapes and dimensions. Experimental data showed that a smooth cylindrical capsule geometry resulted in the least frictional resistance due to the shape and relatively small surface area. Also, it was found that the variation of frictional resistance of the capsule was closely related to the local change in the viscoelastic property of the intestine due to the heterogeneity of the internal structure of the intestine.     

Dependence of the frictional coefficient on the antifrictional-component concentration in the working layer of a slip bearing

We know that variation in the antifrictional-component concentration affects the frictional coefficient. The relation between factors affecting the frictional properties in the production of antifrictional materials is considered in a complete factorial experiment.     

Friction force microscopy as a probe of molecular relaxation on polymer surfaces

The scan-velocity dependence of friction force microscopy (FFM) is characterized on nominally-dry gelatin films and related to the rate dependence of dissipative molecular relaxations. For a range of scanning-parameter values the measurement itself affects the frictional characteristics of the films: imparted frictional energy populates molecular conformations from which more dissipative relaxations occur. Variations in frictional dissipation tens of nanometers in lateral size are quantified as histograms of the number of image pixels versus frictional force. Histogram breadth and symmetry apparently reflect the energy dispersion of molecular relaxations.     

Numerical study of thermal conditions for a oil-cooled friction pair of a multidisc brake

The thermal load of an oil-cooled frictional pair in the multidisk brake of a mine truck is numerically investigated. The formation of the temperature field at frictional contact and within the frictional bodies is considered. The influence of various operational and structural parameters on the thermal load is analyzed.     

Indirect Cutting Force Measurement Considering Frictional Behaviour in a Machining Centre Using Feed Motor Current

In machine tools, friction exists between the table and the guideways, and in ballscrews. In this paper, feed motor current is measured by a hall effect current sensor. It is used to calculate the motor torque which, in turn, is the frictional torque at steady state. Some frictional phenomena are studied in feed drive systems of a horizontal machining centre, such as the relationship between feedrate and frictional torque, the relationship between frictional torque and table feed position, and the slideway cover effects on frictional torque. Considering all these frictional phenomena, the relationship between the feed force and the feed motor current is obtained. Feed force can be estimated well from the feed motor current considering frictional behaviour. The relationship between the cutting force and the feed motor current is slightly different during up milling and down milling, because y(vertical) directional cutting force changes the frictional force.     

静止销和旋转圆盘间的稳态温度新算法

无油润滑压缩机的十字头滑块／滑道、唇形密封／轴和凸轮／挺杆等摩擦副间的摩擦温度往往是影响其工作性能的最主要参数。基于摩擦学机敏结构材料的新思路，这类摩擦副可视为静止柱销和运动圆盘基本摩擦副的集成。文中提出了这种基本摩擦副摩擦温升的一维简单算式和二维有限差分分析。计算结果同国外已发表试验数据吻合很好。     

Frictional heating of a half-space with cracks. I. Single or periodic system of subsurface cracks

The paper deals with the two-dimensional problem of frictional heating for an elastic half-space containing one or a system of periodic subsurface cracks. The generation of frictional heating in the region of contact is estimated by the use of sliding speed, frictional coefficient and contact pressure. The problem is reduced to a pair of singular integral equations which are solved numerically. The influence of the location of cracks on the stress intensity factor is investigated.     

Modeling of Frictional Resistance of a Capsule Robot Moving in the Intestine at a Constant Velocity

Capsule robot is the direction for future development of capsule endoscopy. The imperfection of friction model between the capsule robot and the intestine has been one of the biggest obstacles of its development. Uniform motion is the main mode of the capsule robot in the intestine. However, the frictional resistance variation of the capsule robot in this period has not been understood completely until now. This is the research content in the paper. First, some experiments are conducted to measure actual frictional resistance with a homemade experiment platform. Next, the model of the frictional resistance at a constant velocity is established based on the hyperelasticity of the intestinal material and the interactive features between the capsule robot and the intestine. At last, the theoretical result of the model is proved to be reasonable by simulation analysis. The model is efficient to describe the frictional resistance variation at a constant velocity and can be seen as another kind of stick–slip motion. The work is hoped to perfect the friction model between the capsule robot and the intestine and contribute to the development of the capsule robot.     

Analysis of the dissimilar interface frictional constraints during the upsetting process

A thermo-elastic-plastic coupling model combined with frictional functions is proposed to analyse the plastic upsetting of a cylinder, accounting for dissimilar interface frictional constraints. The flow stress of the deforming workpiece is considered as a function of strain, strain rate and temperature, and the properties of the interface frictional constraints are approached through the use of two continuously varying functions which are presented in terms of the amount of the workpiece deformation.The effects of various combinations of dissimilar interface frictional constraints at the top and bottom die surfaces on the temperature, strain and strain rate distributions are investigated. The asymmetrical flow inducing uneven billet profiles, together with the variations in top and bottom die surface loads, are predicted. The results obtained are consistent with the observations of upsetting experiments.     

Dynamics in the Bridged State of a Magnetic Recording Slider

A novel region of tribological interaction is explored by inducing near contact between the magnetic recording slider and disk. In this study, we performed frictional measurements over a wide range of subambient air pressure and disk rotation rate. Since the slider is supported over the disk by an air bearing, it has been found that cycling from ambient to subambient and then back up to ambient pressure over several minutes of time forms a frictional hysteresis loop. The high-friction branch of the loop, referred to as the bridged state, is characterized by an average frictional displacement and resonant vibration of the suspension mount assembly. The bridged state is currently employed for accelerated wear testing of magnetic slider/disk/lubricant systems. Future magnetic recording systems designed to operate at increasingly lower physical spacing will need to take into account these frictional forces which accompany the incipient contact between the lubricated disk and slider with finite surface roughness. A single degree of freedom model is solved to determine the equivalent dynamic friction force on the slider as an impulse series with random impulse frequency and amplitude from the measured frictional displacement in the bridged state. The mean slider-disk spacing in the bridged state is derived from the experimental friction force, the spacing probability density function, and the adhesion stress from the Lifshitz model for dispersion interaction energy.     

Analytical model development for the prediction of the frictional resistance of a capsule endoscope inside an intestine

For the purpose of optimizing the design of the locomotion mechanism as well as the body shape of a self-propelled capsule endoscope, an analytical model for the prediction of frictional resistance of the capsule moving inside the small intestine was first developed. The model was developed by considering the contact geometry and viscoelasticity of the intestine, based on the experimental investigations on the material properties of the intestine and the friction of the capsule inside the small intestine. In order to verify the model and to investigate the distributions of various stress components applied to the capsule, finite element (FE) analyses were carried out. The comparison of the frictional resistance between the predicted and the experimental values suggested that the proposed model could predict the frictional force of the capsule with reasonable accuracy. Also, the FE analysis results of various stress components revealed the stress relaxation of the intestine and explained that such stress relaxation characteristics of the intestine resulted in lower frictional force as the speed of the capsule decreased. These results suggested that the frontal shape of the capsule was critical to the design of the capsule with desired frictional performance. It was shown that the proposed model can provide quantitative estimation of the frictional resistance of the capsule under various moving conditions inside the intestine. The model is expected to be useful in the design optimization of the capsule locomotion inside the intestine.     

Seizure of elastic material sliding through a rigid die

Mechanisms causing frictional locking due to the interaction between normal load and frictional force are described. The particular type of jamming produced when an elastic material is pushed between fixed rigid plates is discussed in detail. Experiments, using rubber as the elastic material and aluminum for the rigid plates, support a theoretical analysis of this effect.     

表面粗糙度和润滑油黏度对活塞裙-缸套摩擦副润滑性能的影响

以一多缸内燃机为对象,研究表面粗糙度和润滑油黏度对活塞裙-缸套摩擦副润滑性能的影响。建立活塞二阶运动方程与平均Reynolds方程相结合的活塞裙-缸套摩擦副润滑分析模型。活塞二阶运动方程采用Broyden方法求解,应用有限差分法进行活塞裙-缸套摩擦副的润滑分析。结果表明,表面粗糙度对活塞裙-缸套摩擦副润滑性能影响不明显,而随润滑油黏度增加,活塞裙-缸套摩擦副的最小油膜厚度、摩擦力和摩擦功率增加,最大油膜压力在进气和排气行程随润滑油黏度变化比较明显,在其他行程变化较小。     

摩擦焊接初始阶段的摩擦机制及摩擦系数

对影响摩擦焊接初始阶段温度场的摩擦机制及摩擦系数进行了实验研究。结果表明：在摩擦焊接初始阶段，摩擦表面的摩擦机制主要为粘着摩擦，在外缘区域存在着氧化摩擦。文中还通过回归方法建立了ＧＨ２１３２材料摩擦焊接初始阶段摩擦系数与摩擦压力、摩擦速度及表面温度之间的经验公式。     

Numerical analysis of rolling-sliding contact with the frictional heat in rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.     

橡胶线接触摩擦规律的研究

由于橡胶磨损机理与摩擦机理之间密切相关,因此,对橡胶摩擦机理及其规律的了解将有助于深入了解橡胶磨损机理.本文通过对橡胶在线接触下摩擦机理和规律的研究发现:橡胶线接触的主要摩擦机理是粘附,橡胶线接触的摩擦系数随时间周期性变化,并随法向载荷增大而略有下降,且基本不随滑动速度而变化.     

Deformation of frictional joints under the action of a compressive force and arbitrary torque

A method is proposed for calculating the deformation of frictional joints under the action of a compressive force and torques in three perpendicular planes. The calculation results are compared with experimental data.     

Prediction of the frictional coefficient between a hard protuberance and a soft metal surface

Sliding contact is investigated between a soft metal surface (duralumin) and a hard protuberance ball (steel). The frictional coefficient in this case does not obey Amonton's law of friction, and it increases with an increase of normal load. The experimental value of the frictional coefficient agrees well with the calculated one. In the calculation, the variation of work-hardened depth corresponding to normal force is taken into consideration. It is confirmed that the normal force dependence of the frictional coefficient is generated from the contact pressure determined by the work-hardened depth corresponding to normal force, and from the ploughing effect.     

Stress and strain and damage during frictional strengthening treatment of flat steel surface with a sliding cylindrical indenter

Frictional strengthening treatment of a flat steel surface with a cylindrical indenter is considered. A finite-element model of the process is developed. The parameters of stress and strain of the treated material are calculated, and the accumulated deformation in the surface layers is evaluated as a function of the number of frictional load cycles and the coefficient of friction. The type of changes in the target value of plastic deformation along the depth of the frictionally treated surface layer is compared to the experimentally calculated distribution of microhardness and density of dislocations in the surface layer. On the basis of evaluation of damage on the surface of frictional contact, restrictions on using the developed finite-element model for analyzing actual frictional treatment are considered.