The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
David Nowell - One of the best experts on this subject based on the ideXlab platform.
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an elastic plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
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An elastic–plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
Daniel M. Mulvihill - One of the best experts on this subject based on the ideXlab platform.
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Studies of frictional interface behaviour: experiments and modelling
2012Co-Authors: Daniel M. MulvihillAbstract:Predictive models of structures containing frictional joints presently suffer from poor descriptions of interface behaviour at the joints. This thesis aims to address this shortfall by furthering the physical understanding of parameters affecting interface behaviour such as friction and contact stiffness. Aspects of friction and contact stiffness relevant to the characterisation of fretting joints are investigated by a combined modelling and experimental approach. Friction and wear behaviour in gross-slip fretting are investigated by in-line and rotational fretting tests. New 3D topography parameters are found to be useful in the analysis of surfaces during fretting. Wear-scar shape is found to be dependent on material. A phenomenon whereby friction increases during the gross-slip phase of individual cycles is found to be due to wear-scar interaction primarily through the interference of local features distributed over the contact area. These features are similar in size to the applied fretting stroke. A simple model to explain the behaviour is put forward which shows that wear-scar shape determines the form of the friction variation.A finite-element (FE) model of the interaction of an elastic-plastic Asperity Junction is used to predict sliding friction coefficients. The modelling differs from previous work by: permitting greater Asperity overlaps, enforcing an interface shear strength, and allowing material failure. The results are also used to predict friction coefficients for a stochastic rough surface. The magnitudes of the predicted friction coefficients are generally representative of experimental measurements. Results suggest that friction arises from both plasticity and tangential interface adhesion.Contact stiffness is studied for both fretting and non-fretting. A technique to isolate the true interface stiffness from results derived from load-deflection data is developed by comparing experimental and FE results. In the fretting wear case, comparison of tangential contact stiffness results in the literature with FE results reveals an interface whose compliance dominates the response to the extent that stiffness is proportional to contact area. In fretting tests such as this, wear debris is thought to be a factor contributing to high interface compliance. Non-fretting experiments performed here show that, at higher pressures, interface domination is reduced as the contact approaches the smooth case. Experiments are performed where contact stiffness is measured simultaneously by both ultrasound and digital image correlation. The effect of normal and tangential loading upon the contact stiffness (normal and tangential) is investigated. Experimental evidence showing that ultrasound measures an ‘unloading’ stiffness while DIC measures a ‘loading’ stiffness is obtained for the case of tangential loading where the ‘DIC stiffness’ decreases with increasing tangential load whereas the ‘ultrasound stiffness’ remains approximately constant. On average, ultrasound gives magnitudes 3.5 and 2.5 times stiffer than the DIC results for the normal and tangential stiffness cases, respectively. The difference in magnitudes can largely be physically explained, and is relatively small considering the significant differences between the techniques. Therefore, both methods can claim to give valid measurements of contact stiffness – though each has its own limitations which are outlined herein.
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an elastic plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
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An elastic–plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
Mehmet E. Kartal - One of the best experts on this subject based on the ideXlab platform.
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an elastic plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
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An elastic–plastic Asperity interaction model for sliding friction
Tribology International, 2011Co-Authors: Daniel M. Mulvihill, Mehmet E. Kartal, David NowellAbstract:A finite-element model of the interaction of an elastic–plastic Asperity Junction based on cylindrical or spherical asperities is used to predict sliding friction coefficients. The modelling differs from previous work by permitting greater Asperity overlaps, enforcing an interface adhesional shear strength, and allowing material failure. The results of the modelling were also used to predict friction coefficients for a stochastic rough surface. The asperities were based on the titanium alloy Ti-6Al-4V, and the magnitudes of the predicted friction coefficients were generally representative of experimental measurements of sliding friction. The results suggest that friction arises from both plasticity and tangential interface adhesion.
S D Glaser - One of the best experts on this subject based on the ideXlab platform.
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Asperity generation and its relationship to seismicity on a planar fault a laboratory simulation
Geophysical Journal International, 2017Co-Authors: P A Selvadurai, S D GlaserAbstract:Author(s): Selvadurai, PA; Glaser, SD | Abstract: Earthquake faults, and all frictional surfaces, establish contact through asperities. A detailed knowledge of how asperities form will enable a better understanding of the manner in which they communicate during foreshock failure sequences that are observed, leading to the larger main shock. We present results of experiments where a pressure sensitive film was used to map, size and measure the magnitudes of the normal stresses at asperities along a seismogenic section of a laboratory simulated fault. We measured seismicity acoustically and foreshocks were found to be the result of localized Asperity failure during the nucleation phase of gross fault rupture. Since surface roughness plays an important role in how asperities are formed, two Hurst exponents were measured to characterize a highly worn interface using roughness profiles: (i) long wavelength estimates (H ~ 0.45) and (ii) short wavelength estimates (H ~ 0.8-1.2). The short wavelength roughness estimates were computed at the scale of single Asperity Junction points. Macroscopically, the number of asperities and real contact area increased with additional application of normal force while the mean normal stress remained constant. The ratio of real to nominal contact area was low - ranging from 0.02 l Ar/A0 l 0.05-predicting that the asperities should be elastically independent of each other. Results from the pressure sensitive film showed that asperities were closely spaced and could not be treated as mechanically independent. Larger asperities carried both higher levels of average normal stress and higher levels of normal stress heterogeneity than smaller ones. Using linear stability theorem, the critical slip distance on foreshocking asperities was estimated to be d0 ~ 0.65-3 μm. The critical slip distance d0 was ~1.8-11.5 per cent of the premonitory slip needed to initiate gross fault rupture of the interface (20-40 μm) and the overall slip necessary to initiate gross fault rupture was on the order of the average Asperity diameter (52 μm). Foreshocks may be due to a change in the critical slip distance, at localized sections of the fault, caused by the two distinct roughness profiles measured at short and long length scales.
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Asperity generation and its relationship to seismicity on a planar fault: A laboratory simulation
eScholarship University of California, 2017Co-Authors: P A Selvadurai, S D GlaserAbstract:Earthquake faults, and all frictional surfaces, establish contact through asperities. A detailed knowledge of how asperities form will enable a better understanding of the manner in which they communicate during foreshock failure sequences that are observed, leading to the larger main shock. We present results of experiments where a pressure sensitive film was used to map, size and measure the magnitudes of the normal stresses at asperities along a seismogenic section of a laboratory simulated fault. We measured seismicity acoustically and foreshocks were found to be the result of localized Asperity failure during the nucleation phase of gross fault rupture. Since surface roughness plays an important role in how asperities are formed, two Hurst exponents were measured to characterize a highly worn interface using roughness profiles: (i) long wavelength estimates (H ~ 0.45) and (ii) short wavelength estimates (H ~ 0.8-1.2). The short wavelength roughness estimates were computed at the scale of single Asperity Junction points. Macroscopically, the number of asperities and real contact area increased with additional application of normal force while the mean normal stress remained constant. The ratio of real to nominal contact area was low - ranging from 0.02 < A /A < 0.05-predicting that the asperities should be elastically independent of each other. Results from the pressure sensitive film showed that asperities were closely spaced and could not be treated as mechanically independent. Larger asperities carried both higher levels of average normal stress and higher levels of normal stress heterogeneity than smaller ones. Using linear stability theorem, the critical slip distance on foreshocking asperities was estimated to be d ~ 0.65-3 μm. The critical slip distance d was ~1.8-11.5 per cent of the premonitory slip needed to initiate gross fault rupture of the interface (20-40 μm) and the overall slip necessary to initiate gross fault rupture was on the order of the average Asperity diameter (52 μm). Foreshocks may be due to a change in the critical slip distance, at localized sections of the fault, caused by the two distinct roughness profiles measured at short and long length scales. r 0 0
Jeanfrancois Molinari - One of the best experts on this subject based on the ideXlab platform.
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on the debris level origins of adhesive wear
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Ramin Aghababaei, D H Warner, Jeanfrancois MolinariAbstract:Every contacting surface inevitably experiences wear. Predicting the exact amount of material loss due to wear relies on empirical data and cannot be obtained from any physical model. Here, we analyze and quantify wear at the most fundamental level, i.e., wear debris particles. Our simulations show that the Asperity Junction size dictates the debris volume, revealing the origins of the long-standing hypothesized correlation between the wear volume and the real contact area. No correlation, however, is found between the debris volume and the normal applied force at the debris level. Alternatively, we show that the Junction size controls the tangential force and sliding distance such that their product, i.e., the tangential work, is always proportional to the debris volume, with a proportionality constant of 1 over the Junction shear strength. This study provides an estimation of the debris volume without any empirical factor, resulting in a wear coefficient of unity at the debris level. Discrepant microscopic and macroscopic wear observations and models are then contextualized on the basis of this understanding. This finding offers a way to characterize the wear volume in atomistic simulations and atomic force microscope wear experiments. It also provides a fundamental basis for predicting the wear coefficient for sliding rough contacts, given the statistics of Junction clusters sizes.
