Groundwater recharge from rainfall is a major input into aquifers, especially in arid and semi-ar... more Groundwater recharge from rainfall is a major input into aquifers, especially in arid and semi-arid areas, where little or no surface water exist. However, estimation of rainfall recharge is not an easy task as it is highly variable spatially and temporally. In arid areas, recharge occurs indirectly after rainfall-runoff accumulates in low lands such as Wadis and percolates the aquifer. The method proposed in this study to estimate rainfall recharge is based on soil-water budget model and utilizing geoprocessing tools in GIS. It uses digital elevation model (DEM), land-cover and rainfall distribution to estimate runoff accumulation in low lands. The soil-water budget model is then applied to estimate the groundwater recharge in areas of runoff accumulation. The proposed methodology was applied on Qatar karst aquifer as a case study. The spatial resolution of raster maps was 350 by 350 m and the temporal resolution is one day. Results obtained in this study for the hydrological year 2013/2014 show the total groundwater recharge is approximately 14 million m 3 , and concentrated more in the northern part of Qatar. The method can be applied on any arid region.
Polycrystalline yield surfaces of metals are a good way to characterize the anisotropy of plastic... more Polycrystalline yield surfaces of metals are a good way to characterize the anisotropy of plastic deformation. The evolution of these surfaces is impossible to accurately reproduce without taking into account the evolution of the material microstructure such as texture development. In this paper, a numerical computation of yield surfaces using the viscoplastic ϕ-model is proposed. Results concerning face-centered cubic metals subjected to a plane strain compression test are presented. The influence of several mechanical parameters (strain hardening, strain rate sensitivity coefficient and accumulated deformation) on subsequent yield surfaces evolution is studied. The analysis of the change in the shape and size of the yield surfaces shows that the results depend strongly on the parameter ϕ which controls the strength of the interactions in the polycrystal. In addition, the predictions are compared to the widely used viscoplastic self-consistent model as well as to experimental yield loci taken from the literature for various aluminum alloy sheets. A fairly good qualitative agreement between our ϕ-model results and the experimental ones is found. The probable links between the parameter ϕ and the microstructural features such as the stacking fault energy and the grain size of the polycrystal are also briefly discussed.
In this work, we propose the used of the new viscoplastic φ -model to predict texture evolution i... more In this work, we propose the used of the new viscoplastic φ -model to predict texture evolution in hcp metals. We will compare our results to those predicted by the viscoplastic self-consistent (VPSC) model. In both approaches, elasticity is neglected and crystallographic shearing is the only mechanism assumed to cause plastic deformation. Axisymmetric compression test is performed for different values of the parameters controlling the grain interaction strength for both approaches. Predicted stress-strain curves, texture evolution and slip activity are compared and conclusions are drawn. We show that the φ -model allows for correct prediction while it is much easier to formulate and to numerically implement.
ABSTRACT High Jc superconducting oxides can be obtained by processing polycrystalline powders to ... more ABSTRACT High Jc superconducting oxides can be obtained by processing polycrystalline powders to achieve high degrees of densification and sharp crystallographic textures characterized by the conducting crystallographic planes lying parallel to the direction of the current flow (i.e., in the plane of a conducting tape or parallel to the axis of a wire). In the present study, we investigate the densification and texture evolution in a Pb doped Bi—Sr—Ca—Cu oxide (BSCCO) under axisymmetric and plane strain (channel die) compression. Experimental measurements of the microstructural evolution, including crystallographic texture and grain morphology, are presented as a function of the degree of deformation and densification. The orientations of the conducting planes (c planes) are shown by measured X-ray pole figures and analyses of these orientations are given for both tests. A model based on crystal plasticity theory is proposed to simulate the inelastic deformation and texturing of the BSCCO oxide. Predicted textures, under both axisymmetric and plane strain compression, agree well with the experimental observations. Analysis of the predicted orientation distribution of the cplanes with respect to the loading direction suggests that the most desirable texture for a high overall critical current density can be obtained by axisymmetric compression, but textures that should lead to high Jc's are also obtained through plane strain compression.
Clinical Orthopaedics and Related Research, Aug 1, 2011
Background Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear re... more Background Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear resistance than conventional UHMWPE but lower strength and toughness. To produce crosslinked UHMWPE with improved mechanical properties, the material can be treated before crosslinking by tension to induce molecular alignment (texture). Questions/purposes We asked how (1) the microstructure of UHMWPE evolves when subjected to tension and (2) whether the new microstructure (texture) increases strength and toughness. Methods We analyzed microstructure evolution of UHMWPE by small-and wide-angle xray scattering and scanning electron microscopy. We then developed a method to characterize the local strength and toughness of undeformed and textured UHMWPEs by means of nanoscratch tests along and perpendicular to the specimen axis. In three samples we determined the scratch characteristics in terms of deformation mode, coefficient of friction (l), and viscoelastic recovery (r). Results Before the tensile process, the scratch behavior of UHMWPE was characterized by a l ranging from 0.64 to 0.68, no cracking, and r ranging from 0.58 to 0.60. Microfibrillar morphologic features resulted from the tensile process. The new microstructure had an increased strength (r = 0.78) and decreased toughness (cracking + l = 0.77) perpendicular to the fibril axis and decreased strength (r = 0.53) and increased toughness (no cracking + l = 0.55) parallel to the fibril axis. Conclusions Textured UHMWPE behaves like a fiber composite with high strength and toughness in well-defined directions. However, the effect of crosslinking on these specific properties is unknown and therefore it is important to verify that the properties are retained. If wear resistance of crosslinked-textured UHMWPE is at least as high as that of crosslinked UHMWPE, novel medical devices made of crosslinked-textured UHMWPE could be developed and clinically tested.
International Journal of Solids and Structures, 2004
We propose to use the physically-based mechanical threshold stress (MTS) model for the analysis o... more We propose to use the physically-based mechanical threshold stress (MTS) model for the analysis of adiabatic shear band spacing in HY-100 steel and Ti-6Al-4V alloy. Based on existing works, we use the perturbation method to determine the instability modes and their corresponding spacing. To validate our results, we compare them to those obtained using the phenomenological, and widely used, Johnson-Cook and power law models. We notice that the shear band spacing depends on the constitutive relation employed. We also compared the results from our analytical analysis to the available experimental ones. We show, for the first time, that the MTS model yields good results for adiabatic shear band spacing, particularly for the case of Ti-6Al-4V alloy.
Different equivalent circuit models can be found in the literature to describe the electrical per... more Different equivalent circuit models can be found in the literature to describe the electrical performance of PV panels. Among all the models, the one diode models are widely used. However the determination of the electrical parameters of these models is not an easy task. In this paper, the particle swarm optimization (PSO) method was applied to extract the equivalent circuit parameters of PV panels. The PSO method was implemented in Matlab to calculate the series and shunt resistances of two modified one-diode models used to determine the electrical performance of a photovoltaic panel. The PSO method allowed us to plot I-V curves close to those provided by the PV manufacturer and proved to be a good approach capable of working with any electrical model.
ABSTRACT. Because of the trend in the industry to smaller sheet thickness and higher stroke rates... more ABSTRACT. Because of the trend in the industry to smaller sheet thickness and higher stroke rates, modeling of blanking requires the development of advanced material models. Large plastic strain, high strain rate effects, adiabatic heating and the associated ...
Groundwater recharge from rainfall is a major input into aquifers, especially in arid and semi-ar... more Groundwater recharge from rainfall is a major input into aquifers, especially in arid and semi-arid areas, where little or no surface water exist. However, estimation of rainfall recharge is not an easy task as it is highly variable spatially and temporally. In arid areas, recharge occurs indirectly after rainfall-runoff accumulates in low lands such as Wadis and percolates the aquifer. The method proposed in this study to estimate rainfall recharge is based on soil-water budget model and utilizing geoprocessing tools in GIS. It uses digital elevation model (DEM), land-cover and rainfall distribution to estimate runoff accumulation in low lands. The soil-water budget model is then applied to estimate the groundwater recharge in areas of runoff accumulation. The proposed methodology was applied on Qatar karst aquifer as a case study. The spatial resolution of raster maps was 350 by 350 m and the temporal resolution is one day. Results obtained in this study for the hydrological year 2013/2014 show the total groundwater recharge is approximately 14 million m 3 , and concentrated more in the northern part of Qatar. The method can be applied on any arid region.
Polycrystalline yield surfaces of metals are a good way to characterize the anisotropy of plastic... more Polycrystalline yield surfaces of metals are a good way to characterize the anisotropy of plastic deformation. The evolution of these surfaces is impossible to accurately reproduce without taking into account the evolution of the material microstructure such as texture development. In this paper, a numerical computation of yield surfaces using the viscoplastic ϕ-model is proposed. Results concerning face-centered cubic metals subjected to a plane strain compression test are presented. The influence of several mechanical parameters (strain hardening, strain rate sensitivity coefficient and accumulated deformation) on subsequent yield surfaces evolution is studied. The analysis of the change in the shape and size of the yield surfaces shows that the results depend strongly on the parameter ϕ which controls the strength of the interactions in the polycrystal. In addition, the predictions are compared to the widely used viscoplastic self-consistent model as well as to experimental yield loci taken from the literature for various aluminum alloy sheets. A fairly good qualitative agreement between our ϕ-model results and the experimental ones is found. The probable links between the parameter ϕ and the microstructural features such as the stacking fault energy and the grain size of the polycrystal are also briefly discussed.
In this work, we propose the used of the new viscoplastic φ -model to predict texture evolution i... more In this work, we propose the used of the new viscoplastic φ -model to predict texture evolution in hcp metals. We will compare our results to those predicted by the viscoplastic self-consistent (VPSC) model. In both approaches, elasticity is neglected and crystallographic shearing is the only mechanism assumed to cause plastic deformation. Axisymmetric compression test is performed for different values of the parameters controlling the grain interaction strength for both approaches. Predicted stress-strain curves, texture evolution and slip activity are compared and conclusions are drawn. We show that the φ -model allows for correct prediction while it is much easier to formulate and to numerically implement.
ABSTRACT High Jc superconducting oxides can be obtained by processing polycrystalline powders to ... more ABSTRACT High Jc superconducting oxides can be obtained by processing polycrystalline powders to achieve high degrees of densification and sharp crystallographic textures characterized by the conducting crystallographic planes lying parallel to the direction of the current flow (i.e., in the plane of a conducting tape or parallel to the axis of a wire). In the present study, we investigate the densification and texture evolution in a Pb doped Bi—Sr—Ca—Cu oxide (BSCCO) under axisymmetric and plane strain (channel die) compression. Experimental measurements of the microstructural evolution, including crystallographic texture and grain morphology, are presented as a function of the degree of deformation and densification. The orientations of the conducting planes (c planes) are shown by measured X-ray pole figures and analyses of these orientations are given for both tests. A model based on crystal plasticity theory is proposed to simulate the inelastic deformation and texturing of the BSCCO oxide. Predicted textures, under both axisymmetric and plane strain compression, agree well with the experimental observations. Analysis of the predicted orientation distribution of the cplanes with respect to the loading direction suggests that the most desirable texture for a high overall critical current density can be obtained by axisymmetric compression, but textures that should lead to high Jc's are also obtained through plane strain compression.
Clinical Orthopaedics and Related Research, Aug 1, 2011
Background Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear re... more Background Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear resistance than conventional UHMWPE but lower strength and toughness. To produce crosslinked UHMWPE with improved mechanical properties, the material can be treated before crosslinking by tension to induce molecular alignment (texture). Questions/purposes We asked how (1) the microstructure of UHMWPE evolves when subjected to tension and (2) whether the new microstructure (texture) increases strength and toughness. Methods We analyzed microstructure evolution of UHMWPE by small-and wide-angle xray scattering and scanning electron microscopy. We then developed a method to characterize the local strength and toughness of undeformed and textured UHMWPEs by means of nanoscratch tests along and perpendicular to the specimen axis. In three samples we determined the scratch characteristics in terms of deformation mode, coefficient of friction (l), and viscoelastic recovery (r). Results Before the tensile process, the scratch behavior of UHMWPE was characterized by a l ranging from 0.64 to 0.68, no cracking, and r ranging from 0.58 to 0.60. Microfibrillar morphologic features resulted from the tensile process. The new microstructure had an increased strength (r = 0.78) and decreased toughness (cracking + l = 0.77) perpendicular to the fibril axis and decreased strength (r = 0.53) and increased toughness (no cracking + l = 0.55) parallel to the fibril axis. Conclusions Textured UHMWPE behaves like a fiber composite with high strength and toughness in well-defined directions. However, the effect of crosslinking on these specific properties is unknown and therefore it is important to verify that the properties are retained. If wear resistance of crosslinked-textured UHMWPE is at least as high as that of crosslinked UHMWPE, novel medical devices made of crosslinked-textured UHMWPE could be developed and clinically tested.
International Journal of Solids and Structures, 2004
We propose to use the physically-based mechanical threshold stress (MTS) model for the analysis o... more We propose to use the physically-based mechanical threshold stress (MTS) model for the analysis of adiabatic shear band spacing in HY-100 steel and Ti-6Al-4V alloy. Based on existing works, we use the perturbation method to determine the instability modes and their corresponding spacing. To validate our results, we compare them to those obtained using the phenomenological, and widely used, Johnson-Cook and power law models. We notice that the shear band spacing depends on the constitutive relation employed. We also compared the results from our analytical analysis to the available experimental ones. We show, for the first time, that the MTS model yields good results for adiabatic shear band spacing, particularly for the case of Ti-6Al-4V alloy.
Different equivalent circuit models can be found in the literature to describe the electrical per... more Different equivalent circuit models can be found in the literature to describe the electrical performance of PV panels. Among all the models, the one diode models are widely used. However the determination of the electrical parameters of these models is not an easy task. In this paper, the particle swarm optimization (PSO) method was applied to extract the equivalent circuit parameters of PV panels. The PSO method was implemented in Matlab to calculate the series and shunt resistances of two modified one-diode models used to determine the electrical performance of a photovoltaic panel. The PSO method allowed us to plot I-V curves close to those provided by the PV manufacturer and proved to be a good approach capable of working with any electrical model.
ABSTRACT. Because of the trend in the industry to smaller sheet thickness and higher stroke rates... more ABSTRACT. Because of the trend in the industry to smaller sheet thickness and higher stroke rates, modeling of blanking requires the development of advanced material models. Large plastic strain, high strain rate effects, adiabatic heating and the associated ...
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