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- Bartkowiak, T., et al.
(författare)
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Establishing functional correlations between multiscale areal curvatures and coefficients of friction for machined surfaces
- 2018
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Ingår i: Surface Topography: Metrology and Properties. - 2051-672X. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this research is to determine the strengths of correlation, and their variation with scale, between friction coefficients and topographic characterization parameters, calculated using statistical representations of multiscale areal curvatures. The surfaces are created by milling and manual polishing. Coefficients of friction were measured during bending under tension tests. Surfaces were measured with a white light interferometer. Curvature tensors were calculated using a normal based method adapted for multiscale analysis. Three different regions were analyzed from each of eight samples. Curvature tensor parameters: principal, mean, and Gaussian curvatures were calculated for scales between 0.78 and 47.08 μm. These statistical measures of the curvatures were regressed against the coefficient of friction. Three different analyses were performed, taking into account entire curvature distributions, only negative or positive values and curvatures of top heights. Strong correlations (R2 > 0.85 for many and as large as 0.96) were found for the standard deviations for all four curvature measures when entire distributions were considered. These results suggest that the frictional responses of surfaces could be related to the variance of their topographic curvatures. Average curvature parameters correlate strongly with coefficients of friction for negative values. Curvatures calculated from top regions present strong correlations for both mean and standard deviation of maximal, mean and Gaussian curvatures. This supports the use of multiscale curvature tensor methods for characterizing interactions between surface topography and tribological performance.
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- Brown, Christopher A., et al.
(författare)
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Multiscale analyses and characterizations of surface topographies
- 2018
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Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 67:2, s. 839-862
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Tidskriftsartikel (refereegranskat)abstract
- This work studies multiscale analyses and characterizations of surface topographies from the engineering and scientific literature with an emphasis on production engineering research and design. It highlights methods that provide strong correlations between topographies and performance or topographies and processes, and methods that can confidently discriminate topographies that were processed or that perform differently. These methods have commonalities in geometric characterizations at certain scales, which are observable with statistics and measurements. It also develops a semantic and theoretical framework and proposes a new system for organizing and designating multiscale analyses. Finally, future possibilities for multiscale analyses are discussed.
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- Giblin, S. R., et al.
(författare)
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Pauling Entropy, Metastability, and Equilibrium in Dy2Ti2O7 Spin Ice
- 2018
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 121:6
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Tidskriftsartikel (refereegranskat)abstract
- Determining the fate of the Pauling entropy in the classical spin ice material Dy2Ti2O7 with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice-the dipolar spin ice model-predicts an ordering transition at T approximate to 0.15 K, but recent experiments by Pomaranski et al. suggest an entropy recovery over long timescales at temperatures as high as 0.5 K, much too high to be compatible with the theory. Using neutron scattering and specific heat measurements at low temperatures and with long timescales ( 0.35 K/10(6) s and 0.5 K/10(5) s, respectively) on several isotopically enriched samples, we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Furthermore, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez et al. are, after all, essentially correct: The short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.
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