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Alessandro Caporali - One of the best experts on this subject based on the ideXlab platform.
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Average Strain Rate in the italian crust inferred from a permanent gps network ii Strain Rate versus seismicity and structural geology
Geophysical Journal International, 2003Co-Authors: Alessandro Caporali, Silvana Martin, Matteo MassironiAbstract:SUMMARY High-quality, weekly solutions for the coordinates of 45 permanent GPS stations spanning 1–6 years and covering the Alpine Mediterranean area are used to estimate a horizontal velocity field aligned with the ITRF2000 velocity datum. After subtracting model velocities for the Eurasian Plate, we show that the residual velocity field north of the Apennines, in the Adriatic/Dinaric region, describes a NNE-trending tectonic flow with a negative velocity gradient, from 6 mm yr−1 NE of the Apennines to virtually zero NE of the Dinarids. In the Calabria region we observe a divergent pattern, with NNW orientation, which turns to west as one moves north, towards Tuscany. Very small residual velocities are observed for stations in the Sardinia Corsica block, Spain, Southern France and north of the Alps. This regional pattern of velocities defines areas of intraplate Strain. On the basis of good station coverage and of a Strain Rate value above a threshold, we define five provinces: Calabria, Central Apennines, both in the extensional regime, and North Adriatic, Eastern Alps and South Adriatic, under compression. We show that the orientations of the principal Strain Rate axes agree with the stress pattern that is inferred from local seismicity. A comparison of the geodetically determined Strain Rate with the Strain Rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface Strain. For example, the Umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large, but concentRated over a short time interval, so that the equivalent coseismic Strain Rate was larger than the value observed geodetically. On Average, depending on the assumptions on the seismogenic volume and time span, 70–100 per cent of the surface Strain seems to be accommodated by the release of seismic moment in the upper Italian crust.
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Average Strain Rate in the italian crust inferred from a permanent gps network i statistical analysis of the time series of permanent gps stations
Geophysical Journal International, 2003Co-Authors: Alessandro CaporaliAbstract:SUMMARY Time-series of the horizontal coordinates of 21 GPS stations of the EUREF Permanent Network in the Alpine Mediterranean area with three or more years of continuous tracking have been computed with the intent of estimating velocities and their uncertainties, taking into account the detailed structure of their noise. The power spectral densities demonstRate that coloured noise, mostly flicker (1/f ) noise, can be present at frequencies below 6 cycle yr −1 , while at higher frequencies the spectrum tends to a regime of white (i.e. frequency-independent) noise. This statistical information is used to obtain more accuRate estimates of station velocities and of their uncertainties than by the standard least-squares method. Following an approach well known in the analysis of time-series of frequency standards, the stability of each time-series is computed as a function of time, in the sense of a two-sample Allan variance. The power spectral density of the time-series is used to infer the variance of the change in the slope, with 1σ probability, of two consecutive, equal-length batches of a given time-series, and this as a function of the length of the batch. The power spectral density of each time-series is then converted into an autocorrelation function. Taking into account the correct correlations of pairs of samples as a function of their lag, the slope of each time-series is estimated by the least-squares method, with a non-diagonal weight-matrix. We show that in all the examined cases the uncertainties in the velocities computed taking into account the detailed noise spectrum are larger by a factor of 4 ± 1 than the formal uncertainties obtained by the least-squares method under the assumption of pure white noise. Estimating the slope of a time-series taking into account the autocorrelation of the samples yields velocities not significantly different from those obtained assuming uncorrelated samples. We conclude that the reason for the velocity uncertainty estimated by the standard least-squares method being unrealistically small is the neglect of the cumulative effect of uncorrelated and correlated noise. Neglecting the correlated noise does not, however, affect the velocity. Earlier investigations based on more limited (<3 yr) data sets have resulted in non-unique conclusions as to the time decrease of the velocity uncertainty with time, and the noise spectrum of the time-series. We find that the velocity uncertainty does decrease as the time-series increases, and the value of the velocity uncertainty can be predicted from the power spectral density, as the length of the time-series increases. The time-series are finally analysed in the space domain. After removal of common errors, typically represented by sinusoids of annual period, correlation coefficients are computed for pairs of stations and plotted as a function of their distance. We find that the time-series already decorrelate at very short distances (<100 km). This suggests that random errors affecting the coordinates of clusters of stations such as, for example, atmospheric refraction or mismodelling of the orbits are negligible in our time-series. The estimates of the velocities and uncertainties of the permanent stations obtained by spectral analysis form the basis for a subsequent investigation of the present-day, large-scale Strain Rate field in the Alpine Mediterranean area, which is implied by these scattered surface displacements.
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Average Strain Rate in the Italian crust inferred from a permanent GPS network – II. Strain Rate versus seismicity and structural geology
Geophysical Journal International, 2003Co-Authors: Alessandro Caporali, Silvana Martin, Matteo MassironiAbstract:SUMMARY High-quality, weekly solutions for the coordinates of 45 permanent GPS stations spanning 1–6 years and covering the Alpine Mediterranean area are used to estimate a horizontal velocity field aligned with the ITRF2000 velocity datum. After subtracting model velocities for the Eurasian Plate, we show that the residual velocity field north of the Apennines, in the Adriatic/Dinaric region, describes a NNE-trending tectonic flow with a negative velocity gradient, from 6 mm yr−1 NE of the Apennines to virtually zero NE of the Dinarids. In the Calabria region we observe a divergent pattern, with NNW orientation, which turns to west as one moves north, towards Tuscany. Very small residual velocities are observed for stations in the Sardinia Corsica block, Spain, Southern France and north of the Alps. This regional pattern of velocities defines areas of intraplate Strain. On the basis of good station coverage and of a Strain Rate value above a threshold, we define five provinces: Calabria, Central Apennines, both in the extensional regime, and North Adriatic, Eastern Alps and South Adriatic, under compression. We show that the orientations of the principal Strain Rate axes agree with the stress pattern that is inferred from local seismicity. A comparison of the geodetically determined Strain Rate with the Strain Rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface Strain. For example, the Umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large, but concentRated over a short time interval, so that the equivalent coseismic Strain Rate was larger than the value observed geodetically. On Average, depending on the assumptions on the seismogenic volume and time span, 70–100 per cent of the surface Strain seems to be accommodated by the release of seismic moment in the upper Italian crust.
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Average Strain Rate in the Italian crust inferred from a permanent GPS network – I. Statistical analysis of the time-series of permanent GPS stations
Geophysical Journal International, 2003Co-Authors: Alessandro CaporaliAbstract:SUMMARY Time-series of the horizontal coordinates of 21 GPS stations of the EUREF Permanent Network in the Alpine Mediterranean area with three or more years of continuous tracking have been computed with the intent of estimating velocities and their uncertainties, taking into account the detailed structure of their noise. The power spectral densities demonstRate that coloured noise, mostly flicker (1/f ) noise, can be present at frequencies below 6 cycle yr −1 , while at higher frequencies the spectrum tends to a regime of white (i.e. frequency-independent) noise. This statistical information is used to obtain more accuRate estimates of station velocities and of their uncertainties than by the standard least-squares method. Following an approach well known in the analysis of time-series of frequency standards, the stability of each time-series is computed as a function of time, in the sense of a two-sample Allan variance. The power spectral density of the time-series is used to infer the variance of the change in the slope, with 1σ probability, of two consecutive, equal-length batches of a given time-series, and this as a function of the length of the batch. The power spectral density of each time-series is then converted into an autocorrelation function. Taking into account the correct correlations of pairs of samples as a function of their lag, the slope of each time-series is estimated by the least-squares method, with a non-diagonal weight-matrix. We show that in all the examined cases the uncertainties in the velocities computed taking into account the detailed noise spectrum are larger by a factor of 4 ± 1 than the formal uncertainties obtained by the least-squares method under the assumption of pure white noise. Estimating the slope of a time-series taking into account the autocorrelation of the samples yields velocities not significantly different from those obtained assuming uncorrelated samples. We conclude that the reason for the velocity uncertainty estimated by the standard least-squares method being unrealistically small is the neglect of the cumulative effect of uncorrelated and correlated noise. Neglecting the correlated noise does not, however, affect the velocity. Earlier investigations based on more limited (
V. A. Mel'nikova - One of the best experts on this subject based on the ideXlab platform.
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Low temperature stress relaxation of nanocrystalline nickel
Journal of Materials Science, 1995Co-Authors: L. I. Trusov, T. P. Khvostantseva, V. A. Solov'ev, V. A. Mel'nikovaAbstract:Stress relaxation in nanocrystalline nickel within the temperature range 523–673 K in a uniaxial compression regime is studied in the present investigation. The results obtained for coarser grained nickel are given for comparison. An Average Strain Rate of nanocrystalline nickel within the investigated range of temperatures is 1.75 × 10−5–3.03 × 10−5s−1. The presence of two types of stress relaxation dependencies are shown. The most likely Strain mechanism is grain boundary sliding controlled by grain boundary diffusion for temperatures between 623 and 673 K.
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Stress relaxation following heating of nanocrystalline nickel
Nanostructured Materials, 1994Co-Authors: L. I. Trusov, T. P. Khvostantseva, V. A. Solov'ev, V. A. Mel'nikovaAbstract:Stress relaxation of nanocrystalline nickel within the range of temperatures from 523 to 673K (0.17–0.27·Tm) in the regime of uniaxial compression is studied. The results obtained for nickel with more coarse grains are given for comparison. An Average Strain Rate of nanocrystalline nickel within the investigated range of temperatures is 1.75·10−5–3.03· 10−5s−1. The presence of two types of stress relaxation dependencies is shown. The most probable mechanism of plastic Strain is grain boundary sliding controlled by grain boundary diffusion for 623–673K. At lower test temperatures, 523–573K, a plastic Strain occurs by the powder law creep according to the Weertman model.
Philip E. Wood - One of the best experts on this subject based on the ideXlab platform.
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Laminar mixing of shear thinning fluids in a SMX static mixer
Chemical Engineering Science, 2006Co-Authors: Shiping Liu, Andrew N. Hrymak, Philip E. WoodAbstract:Abstract Flow and mixing of power-law fluids in a standard SMX static mixer were simulated using computational fluid dynamics (CFD). Results showed that shear thinning reduces the ratio of pressure drop in the static mixer to pressure drop in empty tube as compared to Newtonian fluids. The correlations for pressure drop and friction factor were obtained at Re MR ⩽ 100 . The friction factor is a function of both Reynolds number and power-law index. A proper apparent Strain Rate, area-weighted Average Strain Rate on the solid surface in mixing section, was proposed to calculate pressure drop for a non-Newtonian fluid. Particle tracking showed that shear thinning fluids exhibit better mixing quality, lower pressure drop and higher mixing efficiency as compared to a Newtonian fluid in the SMX static mixer.
John S Carpenter - One of the best experts on this subject based on the ideXlab platform.
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Strain Rate sensitivity and activation volume of cu ni metallic multilayer thin films measured via micropillar compression
Applied Physics Letters, 2012Co-Authors: John S Carpenter, A Misra, Michael D Uchic, Peter M AndersonAbstract:Micropillar compression testing with repeated jumps in Strain Rate is used to circumvent inherent difficulties associated with nanoindentation and tensile testing of free-standing films. Application to sputtered 21 nm/21 nm Cu/Ni multilayer thin films with a cube-on-cube texture reveals an Average Strain Rate sensitivity (m = 0.014) and activation volume (V = 17 b3), comparable to nanocrystalline face-centered cubic metals. Yet, m increases by ∼50% and V decreases by 70% with increasing Strain, opposite to trends reported for nanotwinned Cu. The large, Strain-dependent shifts in m and V are dependent on the underlying misfit dislocation structure of Cu/Ni interfaces.
Alain Molinari - One of the best experts on this subject based on the ideXlab platform.
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Validation of an interaction law for the Eshelby inclusion problem in elasto-viscoplasticity
International Journal of Solids and Structures, 2005Co-Authors: Sebastien Mercier, Nicolas Jacques, Alain MolinariAbstract:The non linear Eshelby problem is considered for an elastic viscoplastic inclusion. An approximate solution has been proposed by Molinari et al 1997 who have postulated a simplified interaction law. With this interaction law, the Average Strain Rate in the inclusion can be related to the far field loading prescribed in the matrix. In the present work, the matrix and the inclusion have elastic-viscoplastic behavior described by a non-linear Maxwell law. Comparisons between predictions derived from the interaction law and finite element results are performed. It is observed that the approximate solution is in good agreement with numerical results as far as Average Strain Rates and stresses are considered in the inclusion. Various inclusion shapes, material parameters and loading conditions are taken into account.
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Validation of an interaction law for the Eshelby inclusion problem in elasto-viscoplasticity
International Journal of Solids and Structures, 2005Co-Authors: Sebastien Mercier, Nicolas Jacques, Alain MolinariAbstract:The nonlinear Eshelby problem is considered for an elastic viscoplastic inclusion. An approximate solution has been proposed by [Molinari et al., 1997. On the self-consistent modelling of elastic–plastic behavior of polycrystals. Mech. Mater. 26, 43–62] who have postulated a simplified interaction law. With this interaction law, the Average Strain Rate in the inclusion can be related to the far field loading prescribed in the matrix. In the present work, the matrix and the inclusion have elastic-viscoplastic behavior described by a nonlinear Maxwell law. Comparisons between predictions derived from the interaction law and finite element results are performed. It is observed that the approximate solution is in good agreement with numerical results as far as Average Strain Rates and stresses are considered in the inclusion. Various inclusion shapes, material parameters and loading conditions are taken into account.
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Validation of the tangent formulation for the solution of the non-linear Eshelby inclusion problem
International Journal of Plasticity, 2004Co-Authors: Alain Molinari, F El Houdaigui, Laszlo S. TothAbstract:Abstract An extension of the Eshelby problem for non-linear viscous materials is considered. An ellipsoidal heterogeneity is embedded in an infinite matrix. The material properties are assumed to be uniform within the ellipsoid and in the matrix. The problem of determining the Average Strain Rate in the ellipsoid in terms of the overall applied Strain Rate is solved in an approximate way. The method is based on the non-incremental tangent formulation of the non-linear matrix behavior [Acta Metall. 35 (1987) 2983]. In the present work this approximate solution is verified with a good agreement by comparing to finite element calculations for various inclusion shapes and loading conditions.
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Averaging Models for Heterogeneous Viscoplastic and Elastic Viscoplastic Materials
Journal of Engineering Materials and Technology-transactions of The Asme, 2001Co-Authors: Alain MolinariAbstract:Averaging models are proposed for viscoplastic and elastic-viscoplastic heterogeneous materials. The case of rigid viscoplastic materials is first discussed. Large deformations are considered. A first class of models is based on different linearizations of the nonlinear local response. A second class of models is obtained from approximate solutions of the nonlinear Eshelby problem. In this problem, an ellipsoid with uniform nonlinear properties is embedded in an infinite homogeneous matrix. An approximate solution is obtained by approaching the matrix behavior with an affine response. Using this solution of the nonlinear Eshelby problem, the Average Strain Rate is calculated in each phase of the composite material, each phase being represented by an ellipsoid embedded in an infinite reference medium. By adequate choices of the reference medium, different averaging models are obtained (self-consistent scheme, nonlinear Mori Tanaka model…). Finally, elasticity is included in the modelling, but with a restriction to small deformations.
