Maximum Subsurface Stress Research Articles

Research on Elastic Composite Cylindrical Roller Bearing Contact Fatigue Based on the Subsurface Stress

In order to study the elastic contact fatigue problems of composite cylindrical roller bearing, through the three stages of contact fatigue crack initiation, propagation, and ablating of cylindrical roller bearing theoretically analyzed, the subsurface stress is one of the factors of contact fatigue damage. By finite element method and theoretical analytic method with solid cylindrical roller bearing contact surface, the size and distribution of shear stress are analyzed, and comparing the calculation results of two methods, the comparison results show that the finite element method to calculate the bearing contact problem is scientific and reasonable. Through the finite element method of cylindrical roller bearing and elastic composite cylindrical roller bearing subsurface shear stress and equivalent stress on the surface of numerical analysis, the calculation results show that the subsurface stress value of elastic composite cylindrical roller bearings was 31.65% smaller than that of ordinary cylindrical roller bearings, and the distribution of the maximum subsurface stress value of elastic composite cylindrical roller bearings was shallower than that of cylindrical roller bearings. The elastic composite cylindrical roller bearings have significant advantages over cylindrical roller bearings in terms of subsurface stress and have stronger resistance to contact fatigue damage. The finite element method is used to analyze the subsurface stress of elastic composite cylindrical roller bearings with different filling degrees. The results show that the subsurface shear stress and equivalent stress values of elastic composite cylindrical roller bearings with filling degrees of 55% to 65% are maintained at a relatively low level, and the depth of the maximum stress is minimal, which is basically distributed on the surface of the rolling body. The magnitude and distribution of subsurface stresses in elastic composite cylindrical roller bearings provide a reference for more reasonable structural design.

Numeric simulation of steel twin disc system under rolling-sliding contact

Various mechanical parts come into high-load rolling and sliding contact at the contact surface. Even with technological advancements, mechanical failures still occur. Rolling-sliding mechanical contact issues are the primary cause of over 90 % of surface and subsurface metallic failures and they are only becoming worse. Using discretised continuum 2D finite element methods (FEM), this research investigates the parametric contact effect of a steel twin disc system subjected to rolling-sliding contact at varied surface friction and comprehensive load condition. The equivalent von Mises stress distribution, contact pressure distribution and shift position of maximum subsurface stress on the contour region are all influenced by changes in compressive load and coefficient of friction, according to a numerical surface-to-surface contact simulation performed with Abaqus at mean Hertzian pressure. The maximal equivalent stress, for a given load, reaches a peak in the subsurface and moves farther away from the surface when the coefficient of friction decreases and comes close to the contact surface when the coefficient of friction increases. Consistency is shown by the analytical and numerical results.

Relationship between subsurface stress and wear particle size in sliding contacts during running-in

The results of an experiment set using a pin-on-disk rig on samplers made of ST37 disk and bearing steel pin are reported to characterize the wear rate of the specimen, weight loss, friction coefficient behavior, and wear particle size during running-in. Using the equations of subsurface stress for spherical contact, the location and value of maximum subsurface stress in the running-in period in three dimensions is predicted. The results indicate that there exists a relation between the size of the detached particles and the location at which the maximum subsurface shear stress occurs. Based on wear particles’ SEM images, there is a direct relationship between the size of the wear particles with the applied load, applied speed, and the initial surface roughness. It is shown that increasing the load and speed results in a rise in the friction coefficient, which affects the magnitude and location of the maximum subsurface shear stress. The latter is responsible for the nucleation and propagation of subsurface cracks.

Lubrication Performance of Helical Gear Pair Under Dynamic Load Based on Local Involute Profile

Abstract The tribological properties of gear interface have been widely concerned in the past decades. In this study, based on the local involute profile and crown modification, a thermal elastohydrodynamic lubrication model is proposed for a helical gear pair. To discuss the influences of dynamic load on the tribological properties of helical gear pair, the dynamic mesh force of tooth surface is obtained by torsional vibration model. The influences of working conditions and surface roughness on the tribological properties of helical gear pair are investigated. The tribological properties are evaluated in terms of the average film thickness, friction coefficient, mechanical power loss etc. Results show that the dynamic effect of gears has a significant effect on the tribological properties, especially at a specific speed, such as resonance speed. In order to simulate gear lubrication accurately, it is recommended to adopt local involute tooth profile and consider tooth profile modification to calculate geometric clearance. The influence of input rotation speed on the dynamic characteristics and tribological properties of gear is more significant than that of input torque. The surface roughness significantly changes the distribution of interface pressure and film thickness. With the increase of roughness amplitude, the local fluctuation amplitude of pressure and film thickness increase and the dry contact occurs at the end of contact line. Meanwhile, the maximum subsurface stress moves toward the tooth surface, especial for the high frequency engineering roughness. This local stress concentration is harmful to the fatigue life of gear meshing process.

Relative fatigue life prediction of high-speed and heavy-load ball bearing based on surface texture

In this paper, a new calculation method of relative fatigue life considering surface texture on high-speed and heavy-load ball bearing is presented. Rolling bearing quasi-dynamics, micro-TEHL analysis, non-Gaussian surface simulating technique and stress analysis with FEM are combined to obtain the relative fatigue life. The maximum subsurface stress with the new method are compared with data in inference, the relative error is 3.9%, which caused by decreasing surface stress under high speed. The non-Gaussian surface textures effect on surface pressure and shear stress are studied, which show transverse texture perpendicular to entrainment direction is helpful to form film because of the increasing hydrodynamic effect, and decrease the pressure and shear stress, but longitudinal texture has an opposite effect. Non-Gaussian parameters effects on relative fatigue life are researched, which display relative fatigue life increase with the increase of transverse texture, and decrease with the increasing longitudinal texture. The increasing skewness and curtosis can bring the decrease of relative fatigue life, but the relative fatigue life is beneficial as skewness is negative and curtosis is small, which is helpful for bearing life. Finally, the whole relative fatigue life of inner race and balls are given.

Sliding contact problems involving inhomogeneous materials comprising a coating-transition layer-substrate and a rigid punch

This paper proposes a semi-analytical model for the two-dimensional contact problem involving a multi-layered elastic solid loaded normally and tangentially by a rigid punch. The solid is comprised of a homogeneous coating and substrate joined together by a graded elastic transition layer whose material properties exhibit an exponential dependence on the vertical coordinate. By applying the Fourier transform to the governing boundary value problem, we formulate analytic expressions for the stresses and displacements induced by the application of line forces acting both normally and tangentially at the origin. The superposition principle is then used to generalise these expressions to the case of distributed normal and tangential tractions acting on the solid surface. A pair of coupled integral equations are further derived for the parabolic stamp problem which are easily solved using collocation methods.The primary aim of this paper is to provide insight into the likely behaviour of graded materials under the combined effects of surface pressure and shear stress. In this study, the assumption of Coulomb friction is invoked and the effects of material gradation, coating/interlayer thickness and friction coefficient upon the contact footprint and sub-surface stress field are investigated in great detail. The results we obtain suggest that the thickness of the transition layer as well as the combined thickness of the coating and transition layer have a significant effect on the maximum sub-surface stress attained through contact. This indicates that small changes in the composition of the coating can lead to significant differences in material behaviour. We additionally find that an increase in the amount of friction present in the contact can cause dramatic changes in the pattern of the stress field and can give rise to a much larger maximum stress. This effect can be offset somewhat under certain conditions by changing the thickness of the transition layer.To the best of the authors belief, this work represents the first attempt made to characterise the effects of friction on the sub-surface stress field within a graded elastic material.

Enhancement of a simplified model for maximum stress prediction

A simplified model for rapid estimation of maximum subsurface stress was previously reported by the authors. That model was found to predict the upper bound of the maximum von Mises stress in each layer below any surface with good accuracy. In this work, the model is enhanced by quantifying the difference between the predicted upper bound and the maximum stress for a specific rough surface. This is done by evaluating stress predictions for real rough surfaces, sinusoidal surfaces, ideal textured surfaces, and real rough surfaces with imposed computer generated texture. The difference between the predicted upper bound and the surface-specific maximum stress is found to be related to that surface’s roughness. The origin of this relationship is investigated in terms of apparent contact area. The enhanced simplified model provides an efficient means of estimating maximum stress in rough surface contact.

A Multi-Scale System Analysis and Verification for Improved Contact Fatigue Life Cycle of a Cam-Roller System

Surface distress in the form of contact fatigue is encountered in cam-roller systems. The contact fatigue appears to be initiated at micrometer-scale subsurface region. High stress is a result of the macro-scale requirement on the cam-roller motion event that produces high contact loads due to inertia of the roller and its follower link. Sliding of the roller and its impact onto the cam surface further compounds the detrimental effect of contact load. While conventionally a Hertz contact stress analysis can be used in ascertaining contact stress and maximum subsurface von Mises stress, it generally underestimates the stress when compared to the micrometer-scale subsurface stresses due to the presence of surface roughness. Contact analyses of cam and roller with rough surfaces are performed to examine the effects of two surface treatments. These involve surface finishing process in which a surface is rendered smooth, and the addition of a coating to the roller surface. Measurements of such cam and roller surfaces are used in micro-contact analysis module of a Surface Distress Analytical Toolkit to examine the effect of surface finish and coating on maximum subsurface stress. It is found that smooth surface provides a 53% reduction in maximum subsurface stress. The analysis also shows that the addition of coating further reduces subsurface stress nearly 7%. The impact of the combined treatment of the surface is an increase in contact fatigue life of the cam-roller system by nearly two orders of magnitude. The above findings are confirmed by laboratory tests using six rollers with various degrees of finishing processes, and with and without addition of coating to the surfaces. Examination of the rollers indicates a general improvement in roller performance due to addition of coating. Most notably, the combination of finishing process and coating was found to provide the best contact fatigue life since the corresponding rollers showed no observable wear even after testing for 2161h, or the same number of cycles accumulated over about 500,000 truck miles.

Prediction of subsurface stress in elastic perfectly plastic rough components

Understanding and anticipating the effects of surface roughness on subsurface stress in the design phase can help ensure that performance and life requirements are satisfied. One approach used to address this problem is to simulate contact between digitized real, machined surfaces, and then analyze the predicted subsurface stress field. Often, elastic-perfectly plastic contact models are used in these simulations because of their relative computational efficiency. Reported here is an analysis of the magnitude and location of maximum stress predicted using an elastic-perfectly plastic model. Trends are identified which then enable estimation of the upper bound of the simulation results based on surface discretization, operating conditions, and material properties. These estimations can be used as an effective and efficient tool for rapid prediction of maximum subsurface stress in real surface contact.

Chromium oxide coatings applied to magnetic tape heads for improved wear resistance

This paper reports on an investigation of the wear of chromium oxide based very thin films. Linear data tape Advanced Digital Recording (ADR™) heads coated with 20- and 40-nm thick chromium oxide films have been tested subject to temperature/humidity matrix of 10 to 40°C/10 to 80% in order to assess the wear behaviour of the coating as a function of environment. The tested heads were analysed at various stages of wear, by use of optical microscopy (OM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The results show that the most severe damage occurs at the highest relative humidity (80% RH) and for a given humidity, at the lowest temperature (10°C). Inversely, stain transferred from the tape to the head surface predominates at the lowest humidity (10% RH). Stain therefore appears to protect the coating against wear with the degree of protection increasing with the temperature. The wear process differs according to the coating thickness. This is attributed to the location of the maximum subsurface stress with respect to the coating/substrate interface. It is shown that this maximum stress occurs below the interface for 20 nm and at the interface for 40 nm thick coatings. This correlates to different observed wear modes.

Use of the Inverse Approach to Investigate the Stresses in Rough Elastohydrodynamic Contacts

The inverse approach, described in detail in a companion paper, is applied to two contacts. The first is a line contact with transverse roughness; the second a point contact with an ellipticity ratio of four containing an isolated transverse surface feature. In each case the surface profile was monitored as the operating conditions became more severe. These profiles were used to define the surface in a multi-level EHL solver and the pressures and subsurface stresses calculated. After allowing for the build up of residual stress, the maximum subsurface stress was compared with the yield strength of the rough surface. Good agreement was obtained indicating, first, that EHL theory is accurate for the rolling case examined and, second, that the Hooke-Venner hypothesis of equivalence between roughness effects in line and point contacts is valid.

Effects of Friction on Contact of Transverse Ground Surfaces

The two-dimensional plane-strain sliding contact of a smooth rigid roller on a transverse ground rough surface is analyzed. The rough surface is idealized as an elastic half-space with periodic roughness modeled as cylindrical ridges oriented transverse to the sliding direction. The contact problem is solved using a numerical iterative method in which each asperity contact is treated as a micro-Hertz contact, and the exact treatment of asperity interaction is included. The subsurface stress field is calculated using Westergaard stress functions. The subsequent analysis compares the rough surface stress fields with the corresponding smooth Hertz contact to evaluate the influence of surface roughness and friction on the subsurface stress distributions. The results show that the real area of contact is less than the corresponding smooth surface Hertz contact area, and the magnitude of the actual localized maximum contact pressure is always greater than the corresponding smooth surface contact pressure. The asperity level subsurface effective stresses are greater in magnitude than the maximum subsurface stress due to the macro-Hertz contact for low coefficients of friction, and for high coefficients of friction the maximum effective stresses occur on the bulk material surface.