Gary Barber

Friction and wear in high speed sliding with and without electrical current

High speed sliding with electrical current has been studied frequently due to its many important industrial applications. In this paper, a friction test machine with the capacity up to 75 m/s sliding speed and 100 A current was constructed, and friction and wear performance of a carbon-graphite material under high speed sliding with and without current was studied. The effects of the load, sliding speed and electrical current on the tribological behavior of the tested material were investigated. The wear debris was examined by SEM. Test results showed different friction and wear performance of the test material with and without current.

Tool life and wear mechanism of uncoated and coated milling inserts

Abstract A systematic study was conducted for face milling inserts cutting 4140 preheat treated steel. The flank wear of uncoated C5 carbide insert, as well as TiN, TiAlN, and ZrN coated inserts was evaluated and ranked. Tool life was expressed as the function of cutting speed and feed. This information is useful for production optimization. Wear mechanisms of attrition, abrasion, mechanical fatigue, and thermal fracture were identified and were represented by wear maps. The TiN and TiAlN coatings provided significant improvement in tool life. The ZrN coated inserts performed about as well as the uncoated C5 carbide inserts.

Numerical analysis for the elastic contact of real rough surfaces

The elastic contact of rough surfaces and the subsurface stresses caused by the contact have been analyzed by means of a numerical model based on fast Fourier transforms (FFT) and minimization of complementary energy. The elastic contact has been modeled mathematically as a linear complementarity problem and solved by a robust algorithm, Conjugate Gradient Method, while the force-displacement relation is determined through a FFT approach. After solving for the pressure distribution, the subsurface stress field is obtained by calculating the stresses due to the application of a point force, and then integrating over the contact region. In comparison with the matrix based method published in recent years, the numerical approach presented in this study is more efficient, more stable and requires less memory. It has great potential in application to problems with general contact geometry and three-dimensional surface roughness. The results show that high frequency roughness could lead to very sharp impulses a...

A study of flank wear in orthogonal cutting with internal cooling

Internal cooling is being paid more and more attention as a means to overcome the limitations of cutting fluids. The purpose of this paper is to investigate the effects of internal cooling on the flank wear of cutting tools in orthogonal cutting. A flank wear model for a cutting tool in orthogonal cutting is presented which is based on previous wear models and includes the normal stress and the effect of thermal softening. The effects of internal heat sink intensity and heat sink area on the flank wear of the cutting tool in orthogonal cutting are demonstrated.

The effect of operating conditions on heavy duty engine valve seat wear

Abstract Engine valve seat wear affects engine performance. To improve valve quality and life is a common goal for both valve and engine manufacturers. By performing tests on a valve seat wear simulator, the effect of cycles, load and temperature on heavy duty intake valve/insert seat wear was investigated. The test temperatures ranged from 180 to 650 °C, the number of cycles was varied from 150 000 to 3 420 000, and the test loads were applied from 6615 to 24 255 N. The relationship of valve and insert seat wear as a function of cycles, load and temperature was experimentally established. A load dependent wear transition was found to exist and suggests different wear mechanisms operating in these different regions. Higher temperatures produced lower seat wear, which was attributed to parting agents or oxide films and valve head deformation. The intake valve/insert (Silcrome 1/Silcrome XB) seat wear mechanisms were found to be a complex combination of adhesion, shear strain and abrasion. Shear strain or radial flow was found to be an important valve seat wear mechanism from the microstructure analysis of cross-sectioned valve seats, and two-dimensional and three-dimensional worn seat profiles. The oxide films which formed during testing were found to play a significant role. They can prevent the direct metal to metal contact and reduce the coefficient of friction on the seat surface, thus reducing adhesive wear and deformation controlled wear.

Engagement of a Rough, Lubricated and Grooved Disk Clutch ith a Porous Deformable Paper-Based Friction Material

The engagement of wet clutches was simulated using Bergers model (1997) and torque equations. Influencing parameters were studied such as surface roughness, fluid viscosity, friction characteristics, material permeability, moment of inertia, groove area ratio and Youngs modulus. One big concern for the wet clutch engagement is engagement time which affects the friction generated heat and thus the temperature. Another major concern is the torque response that is of importance to study clutch shudder. Surface roughness, viscosity and friction curves affect the engagement time and torque response. The moment of inertia has a big influence on the engagement time rather than the torque. Permeability, groove area and Youngs modulus have less effect on the torque than the other parameters. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

An Experimental Study of Bearing and Thread Friction in Fasteners

An experimental procedure is proposed for studying the underhead and thread friction in fasteners. The effective bearing friction radius, the underhead friction coefficient, and the thread friction coefficient are experimentally determined for fasteners with standard hexagonal heads and for flanged head fasteners. Hence, greater accuracy has been achieved in determining the value of the torque components that are consumed in overcoming friction in threaded fasteners. This would lead to a more reliable torque-tension correlation and would enhance the safety and quality of bolted assemblies. A design of experiment procedure is presented in order to investigate the effect of fastener material class, the thread pitch, and the fastener size on thread friction coefficient. For the underhead bearing friction, an experimental model is presented in order to determine the effect of the radii ratio of the contact area on the bearing friction radius.

Bearing Friction Torque in Bolted Joints

Formulas are developed for calculation of the effective radius of the bearing friction forces on the rotating contact surface in threaded fasteners. These formulas provide a more accurate estimation of the underhead bearing friction torque component in threaded fastener applications. This enhances the reliability, safety, and quality of bolted assemblies, especially in critical applications. It is well known that the torque-tension correlation in threaded fasteners, and the resulting joint clamping force, is highly sensitive to friction torque components: under the turning head and between threads. This analysis focuses on the bearing friction torque component under the turning head of a threaded fastener. Furthermore, it analyzes the error contained in the current practice when an approximate value, equal to the mean contact surface radius, is used instead of the actual bearing radius. New formulas for the bearing friction radius are developed for a mathematical model of a bolted joint using four different scenarios of the contact pressure distribution under the rotating fastener head or nut. The effect of the radially varying sliding speed over the rotating contact surface is analyzed and compared with a constant-friction-coefficient scenario. Numerical results and error analysis are presented in terms of a single nondimensional variable, namely, the radii ratio between the outside and the inside bearing area.

Analysis of asymmetrical cold rolling with varying coefficients of friction

Abstract In this research, asymmetrical cold rolling was produced by the difference in the coefficient of friction between rolls and sheets rather than the difference of roll radius or rotation speeds. The influence of friction coefficient ratio on the cross shear deformation, rolling pressure and torque was investigated using slab analysis. The results showed that the shear deformation zone length increased with the increase of the friction coefficient ratio. The rolling force decreased only under the condition that the friction coefficient ratio increased while the sum of the friction coefficients was held constant. As the reduction per pass was increased, the shear deformation zone length increased and the rolling force also increased. An increase of the front tension resulted in a decrease of the shear deformation zone length. An increase of back tension, however, led to an increase of the shear deformation zone length. The reduction of rolling torque for the work roll with higher surface roughness was greater than that for the work roll with lower surface roughness.

Thread Friction Torque in Bolted Joints

In this paper, formulas are developed for the calculation of the effective thread friction radius in fasteners, in order to determine the thread friction torque component. Due to the lack of exact formulas in the literature, current practice uses the average value of the minor and major thread radii, as an approximation, for determining the thread friction torque component. Results provided by these formulas are compared with those given by the current practice that uses the average value of the minor and major thread radii, instead of the exact value. It is well known that the torque-tension relationship in threaded fastener applications is highly sensitive to the friction torque components: between threads, and under the turning fastener head or nut. Even moderate variations or inaccuracies in determining the friction torque components would significantly impact the fastener tension and the joint clamp load. High accuracy in the estimation of the friction torque components is critical, as it directly affects the reliability, safety, and the quality of bolted assemblies. This analysis focuses on the thread friction torque component. The new formulas for the thread friction radius are developed for a mathematical model of a bolted joint using five assumed scenarios of the contact pressure between male and female threads. Because of the fact that the variation in the sliding speed of various points on a thread surface is insignificant, a uniform thread friction coefficient is used in the analysts. However, a contact area weighted average value is used for the thread friction coefficient. Numerical results and error analysis are presented in terms of a single nondimensional variable, namely, the ratio between the major and minor thread radii.