Michael N. Kotzalas's research while affiliated with The Timken Company and other places

Publications (20)

Article
Mechanical systems that operate in agricultural, construction, and mining and mineral processing applications typically operate in debris-containing and thin-film lubrication environments. Consequently, the lives of rolling element bearings in these applications are often limited by surface fatigue arising from thin-film lubrication, damage from th...
Article
Preloading the rolling elements of a rolling element bearing beyond their yield limit will result in subsurface plastic strains in the deformed material. These plastic strains are manifested in the form of a three-dimensional state of residual stresses. In this analysis a two-dimensional plane strain J2 based plasticity model with two different har...
Article
In this investigation an elastic–plastic Voronoi finite element (EPVFE) model for rolling contact fatigue of Hertzian line contact was developed. The EPVFE model coupled with damage mechanics approach is used to investigate rolling contact fatigue (RCF) of tribo-components. Mises based plasticity model with kinematic hardening was employed to incor...
Article
Full-text available
Wind turbines have had various limitations to their mechanical system reliability owing to tribological problems over the past few decades. While several studies show that turbines are becoming more reliable, it is still not at an overall acceptable level to the operators based on their current business models. Data show that the electrical compone...
Article
Brittle flaking, micropitting, and smearing are life-limiting wear modes of critical bearing positions in wind turbine gearboxes. Whereas micropitting and smearing are caused by roller/raceway sliding in thin film lubricant conditions, the origins of brittle flaking are less understood. Bearings experiencing low load conditions at high speeds and r...
Conference Paper
The standard rolling contact fatigue life calculations currently in use by the rolling bearing industry is based on the first occurrence of subsurface-initiated spalling of a raceway or roller surface. However, wind turbine gearbox roller bearings have been suffering from another damage mode, which manifests itself as micro-pitting. The micro-pitti...
Article
Repair and remanufacture has become an accepted method to extend bearing useful life in many applications, including positions within off-highway construction and mining vehicles. However, it has not been an easy task for equipment owners to become confident in the use of repaired bearings, nor has it been an easy task for engineers to select the p...
Article
Typically, the contact of two rough bodies is transformed into an equivalent rough surface contacting a flat. Due to the mathematics involved, this was usually conducted for surfaces assumed to be Gaussian, where distribution of peaks and valleys are equal. These assumptions were acceptable when dealing with ground surfaces, which are typically Gau...
Book
For the last four decades, Tedric Harris' Rolling Bearing Analysis has been the "bible" for engineers involved in rolling bearing technology. Why do so many students and practicing engineers rely on this book? The answer is simple: because of its complete coverage from low-to high-speed applications and full derivations of the underlying mathematic...
Article
The original two-parameter Weibull distribution used for rolling element bearing fatigue tends to greatly underestimate life at high levels of reliability. This fact has been proven for through hardened ball, cylindrical and spherical roller bearings, as well as linear ball bearings, by other researchers. However, to date this has not been done wit...
Article
Recently, the trend has been toward the use of the full subsurface stress field in rolling element bearing fatigue life prediction (stress field-based life models). By using the stress field-based bearing life models, more accurate assessments of such things as fitting practice and thermal treatments on the bearing performance are achieved. However...
Article
Traction measurements, like any other physical testing, contain variability associated with the test rig, test samples, and data acquisition systems. These natural sources of variation increased when simulating contacts with spin velocity in the most common rolling and sliding test conditions. Averaging the results within one test sequence with spi...
Article
Friction and heat generation in oil-lubricated ball bearings is mainly the result of sliding in the ball-raceway contacts and agitation of the lubricant in the free space between the balls, cage. and bearing rings. Endurance of a ball bearing is highly dependent on the thicknesses of the oil films which serve to separate the balls from the raceways...
Article
Recently, the trend has been toward the use of the full subsurface stress field in rolling element bearing fatigue life prediction (stress field-based life models). By using the stress field-based bearing life models, more accurate assessments of such things as fitting practice and thermal treatments on the bearing performance are achieved. However...
Article
Typically, the life of a component containing rolling contacts is defined as the rime to the initiation of a fatigue spall. Initiation of a spall does nor always cause the component to stop performing its designed function. Operating the component past the initiation of a spall increases the hear generation rates and vibrations, eventually leading...
Article
According to the standard method for calculation of life ratings for rolling contact bearings, failure is considered to occur at the initiation of the first spall in a rolling component surface. While this is acceptable for most bearing applications, in many applications bearing operation may effectively continue for a period of time during which s...
Article
Cylindrical roller bearings which support thrust and/or moment loading in addition to predominant radial loading have flanges on both the inner and outer rings to accommodate the thrust loading carried by the rollers. The roller thrust loading causes roller tilting and friction moments about the rotating axis perpendicular to both the bearing and r...

Citations

... where n is the load-deflection exponent, which is equal to 3/2 for ball bearing [54]. ki and ko represent the contact stiffness between the rolling element and the inner and outer raceways, respectively, which are calculated by Equation (6) according to [8,54] as follows: When a ball passes over a localized defect, the clearance of the bearing assembly suddenly changes compared to the normal bearing case, as illustrated in Figure 1c,d. ...
... The contact resistances of the spindle components contacting surfaces are denoted as R cHS (housing-sleeve), R cHF (housing-flange), R cSB (sleeve-bearings), R cBF (bearingflange), and R cBSh (bearings-shaft). The calculation method for the contact thermal resistance of solid-solid interfaces (such as the bearing outer ring and the bearing seat contact) was carried out based on the author's presented methodology in previous studies [20,21] as well as other studies in the literature [22,23]. ...
... On the other hand, the tangential friction force induces subsurface cracks of raceways to propagate towards to the surface and finally leads to material peeling [6,7]. In rolling element bearings, the local tangential friction force varies greatly at different azimuths of roller-raceway contact [8], which is called friction force distribution in this paper. Thus, obtaining the uneven friction force distribution between rollers and raceways accurately allows the engineers to correctly determine the heat generation rate and locate the weak area facing fatigue or wear failure in rolling element bearings. ...
... That is to say that the appearance the HAB and LAB marks the end of the fatigue life of the bearing, regardless of the build-up compressive residual stress. Some studies showed that the development of compressive residual stresses, associated with the decay of the steel matrix, would not lead to an increase of fatigue strength, but rather is an indication of the fatigue damage process which eventually lead to failure, [49][50][51]. Different types of fatigue damage and microstructure alternation are further illustrated in the stress-live plot in Fig. 15. Included in this plot are the results reported in [46] which were obtained by running tests under good lubrication on an axially loaded angular contact ball bearing (mean diameter of 39 mm) made of standard bearing steel (AISI 52100 martensite) and design with an over-rolling stress cycling frequency of 1.3 kHz. ...
... They require power levels O(10 −3 − 10 1 ) W dependent on data rates and system architecture (Moschitta & Neri 2014). While turbines can achieve such power levels (Tong 2010), they are susceptible to wear and friction within their bearing assemblies, and not favorable alternatives for decades of use without maintenance (Guo et al. 2009;Doll et al. 2010;Tong 2010). Hydrokinetic energy harvesters based on flow-induced vibration (FIV) avoid the use of bearings or gears altogether, shifting the primary failure to structural fatigue. ...
... Bumping injuries are mainly pitting phenomena caused by the collision of tough metal bodies with each other [45]. Figure 2b illustrates a schematic diagram of the wear bump injury of the inner ring on a wind turbine gearbox bearing. ...
... Moreover, extreme slip occurred for low load and high speed conditions because of concomitant contact area reduction and traction loss at the roller-raceway interfaces. Based on a literature review related to the study of the phenomenon of micro-pitting in wind turbine gearbox roller bearings, a proposed test scheme could be created from which a method to predict the risk of micro-pitting might be determined [39]. The tribology of three marine energy conversion devices, namely, offshore wind turbines, tidal turbines, and wave machines has been reviewed [40]. ...
... For some applications, sliding bearings are not an option since frequent start-stops are necessary and/or hydraulic systems are not viable. Rolling element bearings can be improved by the use of coatings [31][32][33][34]. Since coatings involve additional costs, this option is not considered for some applications. ...
... The material parameters utilised in the ELKP material model are elastic modulus 'E' , yield strength 'S y ', kinematic yield strength 'σ k ', and plastic modulus 'M', which are nominally derived from extensive experimental data of fatigue tests. It is believed that the idealisation of the ELKP material model from torsional testing data is feasible for finite element analysis of rolling contact fatigue and is utilised by different researchers [10,[59][60][61][62] for RCF modelling. Figure 6a shows a generic representation of the stress-strain curve for ELKP relationships whose simulation parameters are acquired from the torsional testing of standard AISI 52100 bearing steel. ...
... It is well known that this subsurface plastic deformation involves a forward flow of material parallel to rolling direction, which causes compressive residual stresses in the axial and circumferential direction [8,9]. The deep zone residual stresses arise due to the decomposition of parent microstructure and accumulation of non-uniform plasticity [10] during RCF. Earlier studies [3,11,12] reported that the life span of bearing elements during operation can be altered due to deep zone compressive residual stresses (CRS). ...