Surface Distress Research Articles

Effect of Sliding Friction on Contact Stresses for Multi-Layered Elastic Bodies With Rough Surfaces

The stress distributions associated with frictionless and smooth surfaces in contact are rarely experienced in practice. Factors such as layers, friction, surface roughness, lubricant films, and third body particulate are known to influence the state of stress and the resulting rolling contact fatigue life. A numerical technique for evaluating the subsurface stresses arising from the two-dimensional sliding contact of two elastic bodies with real rough surfaces has been developed, where an elastic body contacts with a multi-layer surface under both normal and tangential forces. The presence of friction and asperities within the contact region causes a large, highly stress region exposed to the surface. The significance of these near-surface stresses is related to modes of surface distress leading to surface eventual failure (Mao et al., 1997).

Detection and Monitoring of Cracks in Asphalt Pavement Under Texas Mobile Load Simulator Testing

The Texas mobile load simulator (TxMLS) is a newly developed accelerated pavement testing device used to evaluate pavement performance under real trafficking loads. This evaluation is performed by applying trafficking loads and monitoring surface distress, such as cracking and rutting, in conjunction with a number of other measurements of the pavement, such as those conducted with the falling weight deflectometer, multidepth deflectometer, strain gauge, pressure cells, and seismic (stress-wave) tests. A procedure for monitoring the progressive degradation of the asphalt surface was developed using the spectral-analysis-of-surface-waves (SASW) technique. This procedure was applied with the TxMLS and proved to be equally effective. SASW tests that were performed intermittently between trafficking phases on trafficked and untrafficked areas show ( a) the effect of temperatures and frequencies on the asphalt moduli, ( b) the importance of temperature and frequency corrections in analyzing the degradation of the asphalt surface layer, and ( c) the long-term trends in surface-wave velocities (and hence, moduli) of the surface layer with increasing number of load applications. It was found that stiffness of the asphalt layer in the longitudinal direction was progressively reduced under trafficking. Concurrently, surface cracking progressively increased. The reduction in longitudinal stiffness occurred at a faster rate than the crack growth. In contrast, the reduction in the stiffness of the asphalt layer in the transverse direction was slower, probably because the main mode of cracking was transverse. The feasibility of using SASW testing as a predictor of degradation and imminent cracking was confirmed with these studies.

Étude expérimentale et théorique du microgrippage dans les contacts élastohydrodynamiques

This paper describes experimental research conducted on a high-speed twin-disk machine. The twin-disk machine, originally designed to simulate the operation of gears, is used at high speed and low load to simulate the operation of high-speed rolling bearings at the inner ring - rolling element contact. Operating conditions, ie, rolling and sliding speeds, contact pressure, lubricant, temperature, disk material combination and surface finish are typical of aerospace practice. The lubricant used in these tests is a tetra ester of five centistoke viscosity at 100 °C, qualified for use in gas turbine engine lubrication systems under the MIL-L-23699 specifications. In the experimental procedure, the scuffing limit is reached by increasing progressively the sliding speed, other operating conditions such as the normal load and the rolling speed being kept constant. The evidence of disk scuffing is a sudden increase of the friction force, which stops automatically the machine at an earlier stage of the damage process. Moreover, a model to estimate the surface and subsurface temperature distribution in the contacting bodies is presented and used to complement our experimental results. Scuffing damages at sliding speeds of up to 40m.s −1 have been obtained. A total of 32 tests have been carried out. Damages observed on the surface of the disks after tests at very high sliding speeds, appear to be similar in nature to those of the inner raceway of rolling bearings subject to skidding. They consist of transfer of component surface material in microscopic patches from a location on one contacting surface to a location on the other contacting surface. The scuffing limits of two material combinations (M50-M50 and M50-16NCD13), for two mean rolling speeds (25 and 50 m/s), three maximum Hertz pressures (0.5, 0.8 and 1 Gpa) and three oil feed temperatures (40, 80 and 120 °C) are presented and discussed. Finally, from this experimental and theoretical investigation, it is proposed to call ‘micro-scuffing damage’ the surface distress observed as a consequence of skidding.

Reproducing the Kinematic Conditions for Automotive Valve Train Wear in a Laboratory Test Machine

The positions of maximum wear on the surfaces of automotive cams and followers have been found to be characterized by low velocities of the point of contact over the surface in question, in combination with significant sliding velocities and thin oil films. The modelling of these critical conditions has now been extended to examine the significance of low contact velocities in two internationally accepted engine tests for the evaluation of the anti-wear properties of lubricants in valve train systems. Calculations of the contact dwell times and the corresponding sliding distances against the opposing surfaces indicate that the particular susceptibility to wear and surface distress in these systems arises from the extreme values of these parameters experienced by particular points on the surfaces during each rotation of the cam. The conditions on the follower surfaces appear to be more severe than on the cams in this respect. It is shown that kinematic conditions representative of the more severe parts of the operating cycles of the engine tests can be reproduced in a modified Amsler two-disc machine, thus enabling the use of small, flat test specimens, which are accessible to a wide range of advanced surface analysis instruments, to facilitate the study of lubricant anti-wear additive film formation.

Defining and Serving Clients for Pavements

Total client satisfaction is a goal toward which any service or product provider, including pavement engineers, should strive. If this is to be achieved, the clients for pavements must be well identified, as should be the measures to be used for judging their satisfaction. The key sets of pavement clients are defined, in relation to the different classes of pavements, including roads, off-road areas, airfields, and railbeds. The means by which effective pavement management can serve clients is then addressed. Next, some possible measures of client satisfaction are identified, including ride quality, surface distress, structural adequacy, surface friction, surface drainage, noise, user delays, and life-cycle cost-effectiveness. The degree of importance for different client-measure combinations is suggested, as well. The technologies available for characterizing the measures are described briefly, and some examples are given. Finally, the results of a simple pilot study to determine the relative value of the measures of road user client satisfaction are related; they suggest that on a scale of 0 to 100, ride quality would contribute about 25 percent to overall customer satisfaction, surface distress nearly 20 percent, and all the other measures between about 5 and 10 percent each.

Defining and Serving Clients for Pavements

Total client satisfaction is a goal toward which any service or product provider, including pavement engineers, should strive. If this is to be achieved, the clients for pavements must be well identified, as should be the measures to be used for judging their satisfaction. The key sets of pavement clients are defined, in relation to the different classes of pavements, including roads, off-road areas, airfields, and railbeds. The means by which effective pavement management can serve clients is then addressed. Next, some possible measures of client satisfaction are identified, including ride quality, surface distress, structural adequacy, surface friction, surface drainage, noise, user delays, and life-cycle cost-effectiveness. The degree of importance for different client-measure combinations is suggested, as well. The technologies available for characterizing the measures are described briefly, and some examples are given. Finally, the results of a simple pilot study to determine the relative value of th...

Development of Automated Road Inspection Vehicle for Nondestructive Evaluation of Road Surface Condition

An ever-growing need exists for a fast, objective, and relatively inexpensive automated road inspection system. Unlike traditional methods of road inspection, the proposed automated road inspection system relies on video images and distance tracking systems housed within a survey vehicle. The road inspection vehicle is capable of acquiring full field road surface distress information at speeds in excess of 85 km/hr. Only two individuals are needed to drive the towing vehicle and trailer along the appropriate roadways where a surface analysis is required and to operate the acquisition equipment. This type of road inspection process eliminates the need to class a road for inspection and greatly increases safety levels when compared with the traditional road inspection methods. Acquisition of roadway surface distress information is accomplished using the shadow moire method. The shadow moire method has been proven to be a fast and accurate means of measuring out-of-plane surface deformation. This method is relatively inexpensive and requires minimal maintenance while providing accurate results. The objective of this research is to refine or improve, or both, the various subsystems that form the integrated prototype system.

Development of Automated Algorithms for Pavement Condition Survey

Image processing and analysis techniques have been successfully applied to the evaluation of some types of pavement surface distress, including longitudinal, transverse, and alligator cracking. Many efforts have been made to develop automated evaluation for other types of distress patterns, but, due to the complexities of these distress types, the results were not as positive as for those distresses mentioned above. The main objectives are to develop image segmentation and classification methods to isolate distress features, and to develop the back-propagation neural network model to recognize block cracking and potholes, in addition to alligator, longitudinal, and transverse cracking. It was observed that longitudinal, transverse, alligator, and block cracking were accurately recognized, and the analytical system has a success rate of 93 percent for potholes. Preliminary results indicate that the proposed approach is very positive and has great potential for integration into an automated system for pavement distress evaluation.

Development of Automated Algorithms for Pavement Condition Survey

Image processing and analysis techniques have been successfully applied to the evaluation of some types of pavement surface distress, including longitudinal, transverse, and alligator cracking. Many efforts have been made to develop automated evaluation for other types of distress patterns, but, due to the complexities of these distress types, the results were not as positive as for those distresses mentioned above. The main objectives are to develop image segmentation and classification methods to isolate distress features, and to develop the back-propagation neural network model to recognize block cracking and potholes, in addition to alligator, longitudinal, and transverse cracking. It was observed that longitudinal, transverse, alligator, and block cracking were accurately recognized, and the analytical system has a success rate of 93 percent for potholes. Preliminary results indicate that the proposed approach is very positive and has great potential for integration into an automated system for pavem...

Development of Automated Road Inspection Vehicle for Nondestructive Evaluation of Road Surface Condition

An ever-growing need exists for a fast, objective, and relatively inexpensive automated road inspection system. Unlike traditional methods of road inspection, the proposed automated road inspection system relies on video images and distance tracking systems housed within a survey vehicle. The road inspection vehicle is capable of acquiring full field road surface distress information at speeds in excess of 85 km/hr. Only two individuals are needed to drive the towing vehicle and trailer along the appropriate roadways where a surface analysis is required and to operate the acquisition equipment. This type of road inspection process eliminates the need to class a road for inspection and greatly increases safety levels when compared with the traditional road inspection methods. Acquisition of roadway surface distress information is accomplished using the shadow moiré method. The shadow moiré method has been proven to be a fast and accurate means of measuring out-of-plane surface deformation. This method is relatively inexpensive and requires minimal maintenance while providing accurate results. The objective of this research is to refine or improve, or both, the various subsystems that form the integrated prototype system.

Digital image processing as a tool for pavement distress evaluation

The information obtained through accurate condition assessment of pavement surface distress data is needed as an essential input to any decision making process concerning pavement management policy. At the same time technological advances in automated inspection systems provide the opportunity to automate the collection and evaluation of the pavement surface condition. In this paper a method developed jointly by the Laboratories of Highway Engineering and Photogrammetry of the National Technical University of Athens is described and proposed. The method involves digital image processing techniques to provide suitable digital imagery as input to specialised software developed especially for this project. This software determines objectively and fully automatically the type, the extent and the severity of surface crackings for flexible road pavements. The proposed method presenten substantial agreement, when compared with systematic visual ratings of existing pavement crackings carried out according to the internationally accepted requirements for airfield and road pavement of the Federal Aviation Administration (FAA).

Continuous Monitoring of Smith Shocks after Lubrication Failure

Contacting surfaces can give rise to short pressure pulses (Smith shocks) when asperities interact and the resulting high-frequency vibrations, detected by accelerometers, can indicate surface distress to allow condition monitoring. Previous work had been limited by the test technique used so in this work vibration was recorded directly to computer memory to give a clearer idea of vibration patterns after failure of lubrication.

The influence of asperity statistics on surface distress and spalling life of Hertzian contacts: Tallian, T.E. Tribol. Trans. (Jan. 1993) 36 (1), 35–42

The influence of asperity statistics on surface distress and spalling life of Hertzian contacts: Tallian, T.E. Tribol. Trans. (Jan. 1993) 36 (1), 35–42

The Influence of Asperity Statistics on Surface Distress and Spalling Life of Hertzian Contacts

Recent spalling life prediction models emphasize the role of surface defects in spalling life. Surface distress microspalling in asperity dimensions is one of the main sources of these defects. This paper describes surface distress defect formation in rolling contact using the Greenwood-Williamson surface roughness model. The defect distribution obtained is incorporated into the spalling fatigue life model recently proposed by the author, and the resulting life predictions are evaluated. The paper illustrates the influence on life of several asperity statistics, EHD film thickness ratio, traction, material fatigue properties, and pre-service defects.

Effect of Roughness and Sliding Friction on Contact Stresses

The stress distributions associated with smooth surfaces in contact are rarely experienced in practice. Factors such as surface roughness, lubricant films, and third body particulates are known to influence the state of stress and the resulting rolling contact fatigue life. This paper describes a numerical technique for evaluating the complete subsurface field of stress resulting from the elastic contact of nonconforming rough bodies, based on measurements of their profile. The effect of sliding friction is included. The presence of asperities within the contact region gives rise to high shear stresses near the surface. Realistic coefficients of friction for lubricated sliding contacts (i.e., μ ≈ 0.1) causes the “smooth body” shear stresses to interact with the asperity stresses to produce a large, highly stressed region exposed to the surface. The significance of these near-surface stresses is discussed in relation to modes of surface distress which lead to eventual failure of the contacting surfaces.

A Comparison of Fatigue Failure Morphology Between TiN Coated and Uncoated Lubricated Rollers

In this study two series of morphological fatigue tests were con-ducted with a two disk machine for TiN coated rollers as well as uncoated rollers. Surface examinations showed that 1 mu;m TiN coated surfaces underwent principally elastic deformation without coating debonding. However, uncoated surfaces were heavily deformed even after a shorter contact cycle. For the uncoated rollers, cross-sectional micrographs revealed the presence of many near-surface microcracks at an asperity scale nearly parallel to the surface. It is believed that these microcracks are initiated by asperity interaction. Metallographic examinations of the uncoated subsurface revealed a. thin layer of dark etching region corresponding to the microcrack failure region. For the coated roller, few cracks were found and the dark etching region was absent. The hard coating minimizes the surface distress and suppresses the initiation of microcracks. This explains why the fatigue life is enhanced with a thin hard coating. Cross-sectional transmission electron microscopy (XTEM) study showed a. coherent interface structure for the coated specimens. The interface after rolling and sliding contact exhibited no clear boundary compared to that of the as-deposited coating. This may indicate that a good coating adhesion can be maintained during the current concentrated contact tests.

Laser-based pavement condition monitoring system.

A laser-based pavement condition monitoring system (PCMS) provides the longitudinal roughness, transverse deformation, and surface distress ofaroad simultaneously. The longitudinal roughness is detected by three displacement sensors based on laser trigonometry. The transverse deformation is measured by a structured light method utilizing a planar light pattern.The surface distress is recorded by a slit-camera. Data acquisition instruments as well as data processing and storage units are installed on a vehicle and the measurement is performed in thenormal traffic flow (up to 100km/h).

Appreciable improvements in oil film formation and surface durability of gears with tooth profile modification.

The influence of tooth profile modification on the surface durability of spur gears has been studied using mirror-like finished gears with a high accuracy (≒0.1 μm Rmax, JIS M 00 class). In order to explain the effectiveness of tooth profile modification, the durations of the elastohydrodynamic lubrication (EHL) condition at the point of contact were measured utilizing an electric resistance method. The results clearly show that the duration of the EHL condition on gear pairs with tooth profile modification have been improved, especially at the beginning and the end points of contact. Even when low hardness gears are used, it is necessary to modify the tooth profile in order to form the lubricating oil film between the meshing teeth and to reduce the surface distress.

Appreciable improvements in oil film formation and surface durability of gears with the tooth profile modification.

The influence of tooth profile modification on the surface durability of spur gears has been studied by using mirror-like finished gears with a high accuracy(=0.1μm Rmax, JIS M 00 class). In order to explain the effectiveness of tooth profile modification, the durations of the elastohydrodynamic lubrication condition (EHL) at the point of contact were measured by utilizing an electric resistance method. The results clearly showed that the duration of the EHL condition on gear pairs with tooth profile modification were improved, especially at the first and the last points of contact. Even though low hardness gears are used, it is necessary to modify the tooth profile in order to form the lubricating oil film between the meshing teeth, and to reduce the surface distress.

Elastic Stresses Below Asperities in Lubricated Contacts

The presence of contacting asperities in lubricated rolling bearings modifies the subsurface stress field strongly in the neighborhood of the surface and, to a lesser extent, at larger depths where the maxima of the shear or von Mises stress of a smooth Hertzian contact normally exist. The near surface stresses are of importance because they may result in micropitting, a mode of surface distress which leads to the eventual fatigue failure of the contacting surfaces. A mathematical method is presented in this paper which allows the statistical calculation of important parameters (maximum von Mises stress or maximum shear stress amplitude) of the stress fields generated under elastically deforming asperities during their passage through a lubricated contact. The asperities themselves are modelled using estimates of the surface spectral moments obtained from single-profile trace measurements. The method is applicable to both isotropic and anisotropic rough surfaces. Moreover, the important effect of the shear surface tractions, including tractions over the asperities, is contained in the analysis. Computed examples are presented for different surface textures and film thicknesses in the case of a deep groove ball bearing. Finally, a qualitative attempt is made to correlate features of these stress fields with the presence of surface pitting, and the limitations of the analysis are discussed.