Asperity Research Papers - Academia.edu (original) (raw)

Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaus-sian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions.

- by and +2
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- Tribology (Engineering), Internal Combustion Engines, Lubrication, Tribology

It is necessary to develop an analytical solution in order to combine predictions with measured tribolog-ical parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time-efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel-Silicon Carbide wear-resistant coating of choice in high performance motorsport.

Linear elastic fracture mechanics (LEFM) integrated with the interference of fracture surface asperities has been formulated. The asperities are considered to simulate the influence of the microstructures and possibly oxide debris. The applied stress/load-crack opening displacement (COD) relationships in several cases have been derived. In the original LEFM, the stress-COD relationship is represented by a straight line passing through the origin of the stress-COD plot. The insert of one asperity results in a deviation of the stress-COD response from the LEFM relationship, leading to the exhibition of an inflection point (first contact point, σop), a larger slope, and a residual COD. In the case of two asperities, the slope and the residual COD of the stress-COD relationship become further larger, and two inflection points emerge. A general stress-COD expression in the case of multiple asperities has been derived. The slope of the stress-COD equation, the residual COD, and the minimum COD all increase with increasing number of asperities for a given loading condition, resulting in a smaller ΔCOD and Δσeff. The number of the inflection points is the same as that of the asperities. To the authors' knowledge, this paper is the first to derive analytically an applied stress-COD curve with a gradual variation below σop, caused by the asperity-/roughness-, or oxide-induced crack closure.

- by Daolun Chen
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- Materials Engineering, Mechanical Engineering, Civil Engineering, Microstructure

Se abordó el comportamiento microestructural del acero AISI 1045 endurecido mediante la Deformación Plástica Superficial por rodillo, Se establece el mecanismo de endurecimiento del acero por el deslizamiento de los granos en la red cristalina y se demuestra el fenómeno de la acritud, la cual es producto del tensionamiento de los granos cuando el material es sometido al tensionamiento de su estructura cristalina. Se establece el procedimiento experimental realizado después que las probetas fueron sometidas al proceso de deformación.

- by Isnel Rodriguez Gonzalez
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- Materials Science, Microstructure, Plastic deformation, Asperity
- by Selim A. Oleksowicz
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- Mechanical Engineering, Materials Science, Mathematical Modeling, Wear

This work presents an analysis of the transient creep deformation of a hemisphere in contact with a rigid flat, loaded by a constant force. The analysis is based on extensive finite element simulations, using a Garofalo creep law. Motivated by the simulations, an analytical framework is derived. Starting from the trivial case of a cylinder, the analytical framework can be generalized by exchanging a few functionals; this will describe the spherical geometry under analysis. The necessary functionals are derived by using a combination of analytical and empirical models. The resulting model accurately predicts the creep evolution of arbitrary asperities for a wide parameter range, requiring only the bulk material parameters. The results are interpreted in view of transient friction effects with creep as their possible cause.

- by Randolf Mock
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- Materials Engineering, Mechanical Engineering, Wear, Creep

The effect of contact loading of single surface irregularities, i.e. asperities, as an underlying mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Spalls in the teeth flanks of driving gear wheels were investigated for typical spalling crack initiation properties. The spalling entry angle was documented and some spalls with a convex entry tip were found. The residual surface stresses of the used teeth, with spalls, were measured with the hole drilling technique. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three dimensional contact model was required. The material description included J 2-plasticity with isotropic and linear hardening. The simulation included residual stresses from material heat treatment. The first roll cycle introduced plastic deformation which altered the residual stresses. Thus, the stress results were captured during a second roll cycle. The most important result was that asperities will serve as local stress raisers in the contact surfaces. The computed stress cycle at the asperity was compared to stress cycles that gave ring/cone cracks at point loaded experiments. The principal stress trajectory into the material was compared to the cross-section profiles of the spalling entry and ring/cone crack. The surface stress profile at the asperity was compared to the convex surface profiles of the spalling tip and ring/cone crack. The asperity deformation and change in residual surface stresses from moderate plastic deformation during rolling were estimated.

- by Marten Olsson
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- Materials Engineering, Mechanical Engineering, Modeling, Finite element method

活断層の分布と形態から地震の規模や震源の位置を予測できる。活断層系内の連鎖地震や空白域に注意する必要がある。特に、震源になる危険のあるアスペリティ部分の監視が必要である。

- by Hitoshi Koide
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- Earthquake, Active Faults, Asperity, Active Fault Studies

Contact of geometric asperities across rough faults causes perturbations to the shear traction resolved on a fault surface that could potentially deflect the local slip direction. Slickenlines, which record the relative displacement of opposing sides of a fault, may therefore be sensitive to fault surface geometry. To investigate the relationship between fault geometry, shear traction and slip, we use ground-based LiDAR to measure the orientations of slickenlines defined by centimeter-amplitude corrugations on three fault surfaces. Slickenline rakes measured in the mean plane of each fault rarely vary by more than a few degrees. Deviations from the mean rake do not correlate with the fault surface topography at scales up to a few meters, but a weak correlation may be present at larger scales. Slip directions are therefore insensitive to any shear traction perturbations from the contact of geometric asperities at small scales. This observation is consistent with scale-dependent deformation. We show that the roughness of fault surfaces implies that short wavelength asperities fail inelastically because of flattening during fault slip. A crossover to elastic deformation occurs at lengths of 10 −2 to 10 0 m, which defines the minimum dimension of a strength asperity that influences the displacement field. The roughness at the crossover length scale corresponds to the typical thickness of fault rocks in the fault core suggesting that fault rock thickness is related to the crossover length scale. The data requires that multiple processes combine to produce the fault surface geometry. We reconcile the variety of processes with the consistent surface roughness scaling by noting that all of the processes are governed in different ways by the elastic limit of rock.

- by Emily Brodsky
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- Earth Sciences, Geology, Stress, Physical sciences

We have studied differences in ground motion and fault rupture characteristics between surface rupture and buried rupture earthquakes. We found that the ground motion generated by buried rupture in the period range around 1 second is on average 1.5 times larger than the average empirical relationship. In contrast, ground motion from earthquakes that rupture the surface is 1.5 times smaller in the same period range. This phenomenon is considered to be caused by differences in fault rupture process between the two types of earthquakes. To examine possible reasons of the above effect we analyzed source slip distribution data derived from waveform inversions, and divided them into two groups: surface rupture and buried rupture earthquakes. It was found that the large slip areas (asperities) of surface rupture earthquakes are concentrated in the depth range shallower than about 5 km. In contrast, large slip areas of buried rupture earthquakes are spread over the depth deeper than 5 km. We also found that the total rupture area of buried rupture earthquakes is 1.5 times smaller than that of surface rupture earthquakes having the same seismic moment, and that deep asperities have about 3 times larger effective stress drops and 2 times higher slip velocities than shallow asperities. These observations are verified by numerical simulations using stochastic Green's function method.

- by Paul Somerville
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- Earth Sciences, Distributed Data Mining, Numerical Simulation, Depth

The great Tohoku-oki earthquake (Mw 9.0) on 11 March 2011 was accompanied by nearly 100 large foreshocks and aftershocks (M ≥ 6.0) in the Northeast Japan forearc. In this study we relocated 77 of these large events using three different velocity models. An updated three-dimensional velocity model significantly reduced the travel-time residuals in the earthquake relocation. We found that the large thrust earthquakes are generally located in or around high-velocity patches, suggesting that the generation of the large thrust earthquakes is controlled by structural heterogeneities in the megathrust zone. The high-velocity patches may represent asperities in the megathrust zone where the subducting Pacific plate and the overriding Okhotsk plate may be coupled strongly. Many non-thrust earthquakes occurred in the crust of the overriding Okhotsk plate, indicating that the stress field there has been changed by the Tohoku-oki mainshock. The present results may improve our understanding of the subduction dynamics and seismotectonics of the Northeast Japan arc.

- by Dapeng Zhao
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- Geology, Geochemistry, Geophysics, Tectonophysics

In this study, seismic data recorded during the period 01/01/1996 to 09/01/2009 has been used to evaluate the seismic hazard potential along the Alborz region, Northern Iran. The technique of mapping local recurrence time, T L, is used to map major asperities, which are considered as the areas with maximum hazard. We calculated T L from a and b values which are in turn derived from the frequency–magnitude relation constants within a radius of 30 km about every corner point of a 10-km spacing grid. Since b value is inversely related to applied stress, the areas with lowest b values and/or shortest T L are interpreted to locate the asperities or the areas of maximum seismic hazard. To test this method, we computed T L map using seismic catalogues before and after the 2004 Baladeh earthquake of M w 6.2. The local recurrence time map before the earthquake shows anomalously short T L in the epicentral region of the Baladeh earthquake a decade before its occurrence. The T L map after the earthquake indicates that this large event has redistributed the applied stress in the Alborz region. The microseismicity of the region after the Baladeh earthquake, however, suggests that there are two anomalies in T L map positioned in Alborz. The places where these anomalies are observed can be considered as the areas with maximum seismic hazard for future large earthquake in the Alborz region.

- by Mohammad Tatar
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- Geophysics, Seismic Hazard, Pattern Recognition, Stress
- by Changjiang WU
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- Multidisciplinary, Geophysical, Subduction Zone, Asperity