Search

The recent COVID-19 pandemic involved in increased hand hygiene to prevent virus transmission. There are a lot of hand hygiene products available on the market but if are frequently used they may alter skin barrier integrity and function. This aspect can be important in daily living activities that involve gripping, feeling and manipulating objects. In this paper the authors studied the influence of the frequently hand disinfection on the friction behavior of the finger skin. Commercially available alcohol-based hand sanitisers were used to perform repeated skin disinfection and the coefficient of friction (COF) was measured on three healthy subjects by using a steel cylinder laterally sliding on the finger tip skin. The preliminary results showed that for all test subjects the coefficient of friction significantly decrease, up to 50%, when frequently hand sanitisers are used compared to daily “dry” skin condition.

Shape Memory Alloys (SMA) have been researched extensively in the past forty years. The different available compositions of these alloys can make them suitable for certain applications with specific requirements. The increasing demand for high precision machinery and equipment brought forward the need to search for alloys that that can perform better under stress than conventional materials. This is the case of Shape Memory Alloys. As their name suggests, these alloys can regain their initial shape after being subjected to external stresses, up to a specific degree. Due to the research carried out over the past two decades on these alloys, they became better known and more accessible, being tested in order to be integrated in various applications. One such application consists of using a shape memory alloy formed into disc springs in order to optimize the preloading of angular contact ball bearings. The tests were conducted using a device especially developed for this research, with the purpose of recording the friction torque evolution and the preload induced by disc springs during the operation of the rolling bearings in order to assess the possibility of using elastic elements for active ball bearings preloading systems.

The authors investigated analytically, and experimentally the friction torque in a modified 51100 thrust ball bearing. The operating tests and modeling were made at very low axial load in lubricated conditions by using only three balls and a standard steel cage. Two analytical friction moments in the ball–cage contacts based on the friction in the hydrodynamic lubricant film, were developed. An analytical methodology to evaluate the film thickness in the ball – cage contacts was developed, as well. The experiments were conducted by using spin–down method for two viscosities and for rotational speeds between 60 and 240 rpm. Both experiments (with three balls without cage, and three balls mounted in the cage) have been made to validate the proposed models.

Human hands perform daily different tasks and the fingers skin comes in contact with many surfaces and objects. Grip task of objects can be performed by using different combination of the fingers. Precision grip task is influenced by several factors which decide the grip force of the individuals performing the task. This study aims to evaluate in vivo the coefficient of friction (COF) between a steel cylinder and the skin of fingers’ phalanges from both hands for three healthy subjects. The experiments were realized in a reciprocating-sliding contact with normal loads of 1 N and 2 N and sliding speed of 1 mm/s. Also, indentation tests were realized in order to determine the skin deformation of the fingers phalanges under normal loads. The indentation results show that distal phalanges (fingertip) play a significant role in deciding the grip force. The friction tests reveal that the coefficient of friction varies between 0.3 and 1.1 along the fingers phalanges according to the age, gender and skin structure of the test subjects. The distal phalanges of index and middle fingers showed the highest value of the coefficient of friction in the case of the subjects that mainly use the right hand. These aspects can be considered in developing devices for grip and sensing tasks applications.

In this paper the authors theoretically investigated the influence of the hydrodynamic rolling friction forces in greased ball-race contacts at low loads. Two IVR-EHL transitions equations for hydrodynamic rolling friction forces have been applied to the ball-race contacts in a modified thrust ball bearing by using three types of greases having base oil viscosities between 40 mm2/s and 1000 mm2/s. Based on the total friction torque analytically estimated and experimentally determined has been evidenced the influence of the hydrodynamic rolling friction force on the total friction torque as the most important parameter for both proposed transition equations. The theoretical values of the total friction torque have been experimentally validated. The experiments was realized with a modified tree ball thrust bearing, without cage in a range of speed between 60 rpm and 400 rpm and for a normal load of 1.422 N for each ball.

In this paper the authors presented a methodology to study the viscoelastic behavior of the human finger tissue by using the indentation process with a steel ball and indentation speed between 0.02 mm/s to 4 mm/s. Considering that at very low speeds the viscoelastic effects can be neglected, an effective Young’s modulus of the human finger as function of the indentation force was determinate based on the Hertzian equation and validated with experimental data. The influence of the indentation speed on both, the indentation force and depth, was studied and a mathematical model was proposed. The authors observed that the normal force resulting from the indentation process increase with speed due to an important damping effect in the finger tissue. Also, based on the Hertzian contact model the contact pressure during the indentation process has been calculated.

To determine the friction forces and friction coefficient in dry and lubricated conditions between steel and a triol crosslinked polyurethane, the authors developed a new experimental method consist in sliding of a steel cylinder on a plate polymer sample in the direction of the cylinder axis. By using this method the experiments were realized on a deformed path in the polymer sample by maintaining the same pressure distribution between the contact elements during the experiments. The experiments were realized with normal load between 1 N and 8 N and a cyclic linear speed having values between 1mm/s and 10 mm/s. Were determined the friction forces and friction coefficients in dry and lubricated contacts. An analytical model to evaluate the friction force in the cylinder – polymer contact surface has been developed and a good correlation with the experiments was obtained.

Vibration based fault detection and diagnose analysis is a well established field in machine or monitoring supervision. The vibration diagnose is also suited for the miniature ball bearings monitoring. The typical balls size starts at 3 mm with the bearing outer diameter of maximum 20 mm. Ball bearings of this size are ideal for precision mechanisms, they are able to carry light loads and they are perfect for handheld medical equipment and tools which must be very small but also very precise and durable. The paper presents experiments carried out on a fully instrumented universal CETR micro-tribometer at room temperature. The tested miniature ball bearing, lightly loaded and operating at low speeds, is subjected to dry and lubrication conditions with two different oil viscosities. A comparative study is realized concerning the vibration diagnose potential using the FFT analysis of the bearing acquired signals. Statistical analysis of the vibration signals is a key point in the detection of the overall vibration level of bearings lubricated with oils of different viscosities.

The authors investigated experimentally the friction torque in a thrust ball bearing operating at very low axial load and lubricated with mineral oils. The experiments were conducted using spin-down methodology and the results were compared with the theoretical values determined by the SKF methodology for friction torque. The values of the friction torque obtained in the experiments are higher than the analytical values obtained with SKF equations, the differences being explained by the important influence of the friction in balls–cage contacts.

Some of the aspects of the vehicle suspension limiting performances from stress and vibrations point of view have been explored in this study. The vehicle is modeled as two DOF system and the suspension is considered a passive one. 3D CATIA model was built for both the spring and spring-damper ensemble, neglecting the tire influence. This can reasonably covers the studies of geometries and forces (bending or tensile stress), masses and stiffnesses (meaning vibration profiles). The theoretical analysis on the vibration behaviour of the spring-damper ensemble, regarded as the vehicle suspension, suggests a convenient operation regime at low frequencies below 15 Hz, if the damper piston displacement is limited.

Based on a theoretical model and an experimental methodology for defining the friction torque for lubricated conditions in a modified thrust ball bearing having only three balls, the authors experimentally investigated the influence of the lubricant parameter Λ on friction torque for mixed IVR (isoviscous rigid) and EHL (elastohydrodynamic) lubrication conditions. The experiments were conducted using ball diameters of 3 mm, 3.97 mm and 6.35 mm loaded at 0.125 N, 0.400 N and 0.633 N. Two oils of viscosity 0.08 Pa·s and 0.05 Pa·s were used and rotational speed was varied in the range 60–210 rpm to obtain a lubricant parameter Λ varying between 0.3 and 3.2. The experiments confirmed that the measured friction torque can be explained using hydrodynamic rolling force relationships respecting the transition from an IVR to an EHL lubrication regime.

The prehension of the small objects with the human fingers is depending on the friction and adherence between finger’s skin and object’s surface. The design of finger pads for robotic and prosthetic hands must simulate both the human finger friction and adherence and elastic deformation, especially for small objects. In this paper, the authors have experimentally investigated the friction forces and friction coefficients in a dry sliding contact tribosystem using Microtribometer CETR UMT-2. A steel cylinder was sliding on the human finger with speeds between 0.5 to 10 mm/s at normal loads up to 10 N. The results showed that the friction coefficient increases with the sliding speed and decreases with the normal load. Also, it was evidenced the presence of the adherence and sliding zones during the laterally cyclic movement of steel cylinder as function of the normal loads and sliding speeds. A general equation for the friction coefficient as function of sliding speed and normal load has been obtained. Therefore, the experimental results offer important information to select the adequate artificial skin materials for robotic finger pads, often overlooked, with relatively simple shapes and mechanical properties typically used.

The authors theoretically investigated and then validated the power loss generated both by sliding and rolling in a modified thrust ball bearing with 3 balls operating at low axial load and grease lubrication. Based on ball forces and moment equilibrium, it has been determined the tangential forces on contact ellipses. The hydrodynamic rolling friction forces have been determined by using Biboulet & Houpert’s methodology considering base oil viscosity of the grease. Total power loss has been obtained as a sum of two components: power loss generated by sliding and power loss generated by rolling. Also, total friction torque has been theoretically determined and, as an alternative method, the total power loss has been calculated as a product between total friction torque and angular speed. Finally, based on previously experimental results, the power loss has been validated as the product between experimentally total friction torque and angular speed. A good correlation between the power losses determined by all three methods for 100, 200, 300 and 400 rpm have been obtained.

Based on a theoretical model and an experimental methodology for defining the rolling resistance moments in a modified thrust ball bearing having only 3 balls, the authors experimentally investigated the influence of the Hertzian contact pressure on rolling resistance moments between a ball and a race. The experiments were realized with balls having diameters between 1.588 mm and 4.762 mm with maximum Hertzian pressure between 0.2GPa and 1GPa, operating for rotational speed between 60rpm to 210 rpm. The experiments evidenced that the measured values of the rolling resistance moments have higher values that the theoretical hysteresis and curvature rolling resistance moments for low contact pressure. By increasing of the contact pressure to 1GPa the experimental values for rolling resistance moments are in good agreement with the theoretical models.

Modeling large nonlinear elastic deformation of elastomers is an important issue for developing new materials. Particularly, this is very promising for design and performance analysis of dielectric elastomers (DEs). These “smart materials” are capable of responding to an external electric field by displaying significant change in shape and size. In this paper, finite element method (FEM) was used to simulate the mechanical behavior of soft elastomers on uniaxial tension. Experimental data from uniaxial tensile tests were used in order to calibrate hyperelastic constitutive models of the material behavior. The constitutive model parameters were evaluated in ABAQUS/CAE. The 3D-model simulation results of a dumbbell shaped specimen at uniaxial tension shows very good correspondence with experimental data.

The vibration analysis aims to extract features from the measurements in order to be used for fault detection and diagnosis. Vibration response measurement is an important and effective technique for the detection of the defects in rolling element bearings. The corresponding analysis methods operate in the time domain, in the frequency domain and recently in the time-frequency domain. A quantitative determination of the defect severity and its development are useful to be determined in order to estimate the remaining useful ball bearing life. Experimental data from a bearing with a defect are collected by an accelerometer then processed to identify the passing time of a ball over a defect. The paper presents a computation model corroborated to an experimental investigation to establish the defect length of a ball bearing inner race.

Based on a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing having only 3 balls and presented in [2], the authors experimentally investigated the influence of the ball diameter on friction torque when operating in mixed and full film lubrication conditions and maintaining the normal load, the race curvature and oil viscosity constant. The experiments were realized using ball diameters between 7.938 mm and 3 mm corresponding to maximum Hertzian pressure between 0.264 GPa and 1 GPa and a rotational speed between 60 rpm to 240 rpm. The experiments confirmed that the measured friction torque can be explained using hydrodynamic rolling force relationships respecting the transition from IsoViscous Rigid (IVR) to ElastoHydrodynamic Lubrication (EHL) regime presented in [2].

Authors propose a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing, operating in mixed and full film lubrication conditions. The friction torque was measured at low loads and large Λ parameter range using a spin-down method. A comprehensive analytical bearing torque model is described using elastic rolling resistance, curvature effects, inertia forces, disc-air resistance and ball-races hydrodynamic rolling forces, the latter explaining 98% of the final bearing torque. Several sets of hydrodynamic rolling force relationships respecting the transition from IVR to EHL lubrication regime were tested. Final numerical results are shown to be very close to the experimental ones in both full film and mixed lubrication conditions.

The economic, energetic and ecological indicators of combustion of water-oil emulsions and water-coal dust suspensions on a test installation are presented in this paper.

In this paper, the authors present a new methodology to study the viscoelastic behaviour of the human finger. The methodology is based on experimental research consisting of a finger's indentation with a small steel cylindrical object for various indentation speeds. The tests were realized on a CETR UMT-2 Tribometer for indentation speed between 0.02 mm/s and 4 mm/s with a normal load of up to 22 N. Using the force-deformation diagrams recorded at the smallest indentation speed determined the elastic modulus of the human finger according to an adapted Hertzian model. By considering the increasing of the indentation force with indentation speed, the viscous component of the human finger was evidenced. The power dissipated in the finger tissue as a result of the prehension process has been obtained as a function of indentation speed and indentation depth. In addition, a general equation for the prehension force as a function of indentation speed and indentation depth has been obtained. The results of this study will be relevant for selection of the specific elastomers used in biomimetic hands., info:eu-repo/semantics/publishedVersion

To use the elastomers as a interfacial surface in the prehension systems, the authors experimentally determined the elastic deformation and sliding friction of a plane elastomer sample in contact with small steel roller for normal loads up to maximum 9 N and linear speed of 0.1 mm/s. The experiments were realized on a Tribometer CETR UMT 2, by using two procedures: firstly was determined the Young’s modulus of the elastomer by indentation with a steel roller with normal loads between 1 and 9 N and secondly was determined the friction forces in sliding of the steel roller on elastomer sample with normal loads between 1 and 5 N. On contact surfaces was experimentally determined the total friction force including both elastic deformation force and sliding force. Also, an analytical model for friction force has been developed., (undefined), info:eu-repo/semantics/publishedVersion

To determine the rolling friction resistance in the micro rolling systems we developed a new micro tribometer consisting in a driving rotational disc in contact with 3 microballs which sustain an inertial driven rotational disc. The driving disc has a constant rotational speed and his rotational motion is transmitted to the inertial driven disc by rolling friction forces, developed in the rolling contacts between the microballs and the inertial disc. When the rotational speed of the inertial driven disc becomes constant, the driven disc is stopped and the inertial driven disc starts a deceleration process until it completely stops due to friction. A camera monitors the angular position of the inertial driven disc, from the start of the deceleration process to his completely stop (the spin-down method). An analytical model based on the integration of the inertial disc motion equation, including both rolling frictions in the rolling contacts and the friction between the inertial disc and air has been developed. The equation of the inertial disc angular position, as function of the time was obtained considering two hypothesis: (i) in the first hypothesis it was considered that rolling friction torque does not depend on rotational speed in dry contacts; (ii) in the second hypothesis it was considered a linear dependence between rolling friction torque and rotational speed for dry contacts. Experimental investigations using the new microtribometer with three 1.588 mm diameter stainless steel microballs, for a range of rotational speed between 30 rpm and 210 rpm and for normal contact loads between 8 mN and 33 mN confirm the validity of the hypothesis of constant friction torque in dry conditions. Based on the hypothesis of constant friction torque, the rolling friction torque in the contacts between the microballs and the two discs having values between 1.8 μNmm and 7.2 μNmm have been obtained with the new microtribometer. Also, rolling friction coefficients having values between 0.0002 and 0.0004 have been obtained.

In this paper an automotive full synthetically lubricant is tested on a four ball machine. A new data acquisition system is developed, based on tensometric strain gauges principle. In order to interpret the data statistically (signal to noise ratio, skewness and kurtosis etc.) and to directly display the values of the instantaneous friction coefficient, a LabVIEW interface is created. The effect of the sustaining rolling bearing on the mean friction torque and instantaneous friction coefficient between the rotating upper ball and the three stationary balls of the four ball machine's testing device is also evaluated. For the synthetically motor oil the last non-seizure load (LNSL), initial seizure load (ISL), and the weld points (WP) were established. The new data acquisition system and interface allow the exact prediction of lubricant film seizure. The experimental values of the friction coefficient correspond as order of magnitude with those from literature.

Friction torque in an angular contact ball bearing is dependent on the motion of the balls, lubricant viscosity and quantity, rotational speed and applied loads. To evaluate the friction torque in a ball bearing, the SKF methodology includes the geometrical parameters, lubricant viscosity and type of lubrication, operation speeds and applied loads (radial and axial). As is indicated in the SKF catalogue, the above-mentioned methodology can be used for applied loads equal to or larger than the recommended minimum load indicated. For very low applied loads and for dry or limit conditions, the SKF catalogue doesn't indicate the adequate models to estimate the friction torque. Also, the presence of the cage is not directly included in the SKF methodology. Based on the spin down methodology, the authors performed experimental investigations on a 7205B modified angular contact ball bearing, by using only three balls with and without the cage. Experimental friction torques on the outer race has been obtained in dry conditions and the results were compared with the results obtained from the SKF catalogue. Important differences have been obtained. Also, it was evidenced that at very low loads the presence of the cage leads to an increase in the friction torque with more than one order of magnitude.

We developed a theoretical model and an experimental procedure to investigate the rolling friction coefficient in a micro rolling tribosystem. The procedure we suggest is based on the integration of the free oscillation equations of a microball on a spherical surface. The rolling friction coefficient was evaluated on the basis of the number and amplitude of the experimentally determined ball oscillations. The influence of condensing atmospheric water on the rolling friction coefficient at the level of rolling micro tribosystems was also determined.

The development of dependable software for mechatronic systems can be a very complex and hard task. For facilitating the obtaining of dependable software for industrial controllers, some powerful software tools and analysis techniques can be used. Mainly, when using simulation and formal verification analysis techniques, it is necessary to develop plant models, in order to describe the plant behavior of those systems. However, developing a plant model implies that designer takes his (or her) decisions concerning granularity and level of abstraction of models; approach to consider for modeling (global or modular); and definition of strategies for simulation and formal verification tasks. This paper intends to highlight some aspects that can be considered for taking into account those decisions. For this purpose, it is presented a case study and there are illustrated and discussed very important aspects concerning above exposed issues., info:eu-repo/semantics/publishedVersion

The design of mechatronic systems is a multidisciplinary task that involves skills from mechanic, electronic and informatics areas. Recently, the expertise from such different fields is able to communicate and exchange the necessary contribution to successful design solutions, through a myriad of internet tools available. The introduction of internet of services on the design of mechatronic systems, mainly when teams, with different skills, operate in different geographic places, has contributed to flawlessly integrate better and interoperable final solutions. The design of mechatronic systems without errors that operate without failures - is an important contribution to such goal. Safe behavior of mechatronic systems is crucial, mainly, in what concerns human safety. The correct behavior of those systems can be improved by the development of safe software for their controllers using some analysis techniques. Among them, Formal Verification (FV) is able to guarantee the best results. One of the main gaps using this technique is the difficulty of obtaining adequate plant models, in a systematic way, because this task is, usually, related with high level of expertise of designers and, in industry, this fact causes some difficulties for using those methods and tools. The work presented in this paper is a part of a larger project developed in the context of Software as a Service (SaaS) platform. It is intended to develop a systematized approach in order to obtain meaningful plant models out of existing CAD data, from Autodesk Inventor (or CATIA), and translate those models to formatted files according to input data of the UPPAAL model checker (because it allows dealing with time variable).The main idea is to obtain, systematically, plant models for Formal Verification purposes, considering that nowadays companies with different CAD systems are using increasingly often STEP-File format. A solution for this specific problem is explored and presented in this paper., info:eu-repo/semantics/publishedVersion

This paper presents a new method and criterion for predicting the occurrence of the interruption of a kinematic joint contact in a multi-bar mechanism. The method is based on the elastic interactions in the tribosystems of the joints with imposed clearances. The method was used in a four-bar mechanism with clearance in the joint formed from the coupler and the rocker. The analytical results were experimentally confirmed by measurement of the acceleration of the rocker.

The piston ring is one of the main elements in an internal combustion engine. Together with the cylinder sleeve, the piston ring has two basic functions: (1) contacting the cylinder sleeve to prevent the gases formed above the piston from migrating to the crankcase and (2) as a translation couple, formed of the piston-ring and cylinder-sleeve assembly. Complex tribological phenomena occur in the piston-ring and cylinder-sleeve tribosystem, according to variations in sliding speed, gas pressure, and temperature. This paper presents a method of calculation of the thickness of the lubricant film in the piston-ring and cylinder-sleeve tribosystem, using the Reynolds equation, integrated in specific conditions. According to the Newtonian behaviour of the lubricant, the shear stresses in the lubricant film between the piston ring and cylinder sleeve are determined. A computational procedure to determine flash temperatures in the piston-ring and cylinder-sleeve tribosystem is presented. The theoretical results, including film thickness, sliding speed, gas pressure, and flash temperatures for a complete crankshaft cycle are also presented.

The paper investigates the elastohydrodynamic lubrication of concentrated contacts in a rolling bearing operating at moderate speeds. Two base oils with different characteristics, additivated with low-density polyethylene were used as lubricants. Rheological and tribological tests were performed to study the influence of temperature, polymer concentration, and bearing speed. The influence of the addition of a polymer component on the film-forming properties and on wear under high pressure was examined in a four-ball test rig. Experimental data show that the polymer concentration added to the base oil plays an important role in obtaining greater film thicknesses and in preventing wear in elastohydrodynamic contacts.

Polymers as lubricating oil additives can play a significant role in tribological phenomena. The main effect of the polymer addition is an increase in the lubricant viscosity and film thickness at high operating temperatures. Rheological and tribological tests were performed to determine the influence of the polymer concentration, temperature, and speed on the lubricant viscosity and elastohydrodynamic film formation capacity. A mineral oil additive with a low density polyethylene was investigated. The rheological behavior of the tested lubricants was first studied for shear rates ranging from 10 to 103 s−1. The low-voltage electrical resistance method was also used to estimate the lubricant film thickness formed between the rollers and the raceways in a tapered roller bearing. These experimental investigations have shown that 0.5 percent of low density polyethylene in oil is an optimal concentration which produces the highest viscosity and thickest lubricant film and hence improves the lubrication of mac...

This research was focused on the damping capacity study of two types of silicone rubbers proposed as layers within total lumbar disc prostheses of ball-and-socket model. In order to investigate the damping capacity, the two silicone rubber types mainly differing by the molecular mass of polymeric matrix and the filler content, as was emphasized by scanning electron microscopy and differential scanning calorimetry, were subjected to free vibration testing. Using an adapted experimental installation, three kinds of damping testing were realised: tests without samples and tests with three samples of each type of silicone rubber (69 ShA and 99 ShA). The free vibration tests were performed at a frequency of about 6 Hz using a weight of 11.8 kg. The relative damping coefficient was determined by measuring of two successive amplitudes on the vibrogram and calculating of the logarithmic decrement. The test results with silicone rubber samples showed a relative damping coefficient of 0.058 and respectively 0.077, whilst test results without samples showed a relative damping coefficient of 0.042. These silicone rubbers were found to have acceptable damping properties to be used as layers placed inside the prosthetic components.

The use of analysis techniques for industrial controller's analysis, such as Simulation and Formal Verification, is complex on industrial context. This complexity is due to the fact that such techniques require sometimes high investment in specific skilled human resources that have sufficient theoretical knowledge in those domains. This paper aims, mainly, to show that it is possible to obtain a timed automata model for formal verification purposes, considering the CAD model of a mechanical component. This systematic approach can be used, by companies, for the analysis of industrial controllers programs. For this purpose, it is discussed, in the paper, the best way to systematize these procedures, and this paper describes, only, the first step of a complex process and promotes a discussion of the main difficulties that can be found and a possibility for handle those difficulties. A library for formal verification purposes is obtained from original 3D CAD models using Software as a Service platform (SaaS) that, nowadays, has become a common deliverable model for many applications, because SaaS is typically accessed by users via internet access.

The authors investigated experimentally and theoretically the friction torque in a modified thrust ball bearing having only 3 balls operating at low axial load and lubricated with NGLI-00 and NGLI-2 greases. The experiments were made by using spin-down methodology and the results were compared with the theoretical values based on Biboulet&Houpert's rolling friction equations. Also, the results were compared with the theoretical values obtained with SKF friction model adapted for 3 balls. A very good correlation between experiments and Biboulet_&_Houpert's predicted results was obtained for the two greases. Also was observed that the theoretical values for the friction torque calculated with SKF model adapted for a thrust ball bearing having only 3 balls are smaller that the experimental values.

A procedure has been developed to determine both the value of the ball's angular velocity and the angular position of this velocity, according to the normal loads in a linear system with four contact points. The program is based on the variational analysis of the power losses in ball-races contacts. Based on this the two kinematics parameters of the ball (angular velocity and angular position) were determined, in a linear system type KUE 35 as function of the C/P ratio.

This paper presents an experimental technique to investigate the electromechanical properties of silicone dielectric elastomers actuated with high DC electric fields. A non-contact measurement technique is used to capture and monitor the thickness strain (contraction) of a circular film placed between two metallic disks electrodes. Two active fillers such as silica (10, 15 and 30 wt%) and barium titanate (5 and 15 wt%) were incorporated in order to increase the actuation performance. Thickness strain was measured at HV stimuli up to 4.5 kV and showed a quadratic dependence against applied electric field indicating that the induced strain is triggered by the Maxwell effect and/or electrostriction phenomenon as reported in literature. The actuation process evidences a rapid contraction upon HV activation and a slowly relaxation when the electrodes are short-circuit due to visco-elastic nature of elastomers. A maximum of 1.22 % thickness strain was obtained at low actuating field intensity (1.5 V/pm) comparable with those reported in literature for similar dielectric elastomer materials.

A new methodology to determine experimentally the Young's modulus of the human fingers has been developed by the authors. The methodology consist in the experimentally variation of the elastic deformation for the finger in contact with a steel cylinder normal loaded from zero to 10 N. The Hertzian model for elastic deformation specific to a point contact between a cylindrical object and the index finger has been used to curve fitting the experimental curve for elastic deformation of the finger in the vicinity of imposed forces from 0.5N to 10 N. Values between 0.07 MPa and 0.2 MPa for Young's modulus of the finger have been obtained, in agreement with the values determined by the other authors using ball finger contacts or finger plane surface contacts.

A complex analytical model for the starvation mechanism in ball-race contacts, in correlation with thermal effects, has been developed. From the theoretical results it was found that in high speed, mist-lubricated ball bearings, the reduction factor of the film thickness by starvation and thermal effects can be computed in correlation with the ball-race lateral oil meniscus thicknesses. Experimental investigations of 7206 C angular contact ball bearings, operating between 5000 and 35 000 min −1 , are in good correlation with the theoretical results when only starvation and inlet shear heating have been included. When the ball bearing temperature increases, both the theoretical and experimental results show that starvation occurs at smaller ball-race lateral oil meniscus thicknesses, by decreasing the oil viscosity.

A complex theoretical model for friction loss computation in high speed angular ball bearings has been presented. The theoretical model includes the dynamic and kinematic interactions in the angular ball bearings with numerical integration of the ball and cage motion equations. The shear stresses on the elliptical surfaces are determined by an original bidimensional Theological model in the elastohydrodynamic regime hypothesis and for the cage-race interactions an experimental model has been determined. Some theoretical elliptical sliding speeds, shear stresses and power losses have been determined for 7206 C angular contact ball bearings in the range from 5000 to 35000 rev min −1 . Both theoretical and experimental outer-race torques have been determined and a good correlation between 5000 and 26000 rev min −1 is determined.

A new model to estimate all friction losses between the balls and the circular — arch grooves races (two contact ball screw) has been developed. Based on the equilibrium of the forces and moments acting on the ball, the sliding forces between ball and both screw and nut races are determined without integrating the shear stress on contact ellipses. The sliding forces include the rolling forces on the two contacts, the friction moments due to the races curvature, the elastic resistance moments in ball-races contacts, the contact force between the balls and the friction moment between the balls. The program was adapted for a ball — screw system and the influences of the speed and load on total friction torque were investigated. The efficiency of the system was computed and good agreement with the research literature was obtained.