A contribution is given to the theoretical research on the stiffness of ceramic materials, under the approximation of the average stress field, the relation E = E0(1 -p)/(1+ 2.5p) is derived to describe the dependence...A contribution is given to the theoretical research on the stiffness of ceramic materials, under the approximation of the average stress field, the relation E = E0(1 -p)/(1+ 2.5p) is derived to describe the dependence of the modulus of etasticity on porosity. The prediction of this model is consistent with the experimental data from several ceramics such as reacting sintered Si3N4,MgO and MgAl2O3.展开更多
<span style="font-family:Verdana;">A series of colossal magneto resistance (CMR) materials with compositional formula Pr</span><sub><span style="font-family:Verdana;">0.5<...<span style="font-family:Verdana;">A series of colossal magneto resistance (CMR) materials with compositional formula Pr</span><sub><span style="font-family:Verdana;">0.5</span></sub><span style="font-family:Verdana;">Sr</span><sub><span style="font-family:Verdana;">0.5</span></sub><span style="font-family:Verdana;">Mn</span><sub><span style="font-family:Verdana;">1-x</span></sub><span style="font-family:Verdana;">Cr</span><sub><span style="font-family:Verdana;">x</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by sol-gel technique using pure metal nitrates as the starting materials. These samples were characterized structurally by X-ray diffraction, FTIR and SEM. All the </span><span style="font-family:Verdana;">samples exhibit orthorhombic structure without any detectable impurities.</span><span style="font-family:Verdana;"> The bulk den</span><span></span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">sities for all the compositions were measured from the pellets. The Young’s and Rigidity moduli, Poisson’s ratio and Debye temperature of all the compositions were calculated with the experimentally measured ultra</span><span style="font-family:Verdana;">sonic longitudinal and shear velocities at room temperature using pulse</span><span style="font-family:Verdana;"> transmission technique. As the materials are porous, zero porous elastic moduli have also been calculated using a well-known Hasselmann and Fulrath model. </span><span style="font-family:Verdana;">The observed variation of elastic moduli with varying chromium doping</span><span style="font-family:Verdana;"> concentration has been studied qualitatively.</span></span></span>展开更多
Nano-sized silicon carbide(SiC:0wt%,1wt%,2wt%,4wt%,and 8wt%)reinforced copper(Cu)matrix nanocomposites were manufactured,pressed,and sintered at 775 and 875℃in an argon atmosphere.X-ray diffraction(XRD)and scanning e...Nano-sized silicon carbide(SiC:0wt%,1wt%,2wt%,4wt%,and 8wt%)reinforced copper(Cu)matrix nanocomposites were manufactured,pressed,and sintered at 775 and 875℃in an argon atmosphere.X-ray diffraction(XRD)and scanning electron microscopy were performed to characterize the microstructural evolution.The density,thermal expansion,mechanical,and electrical properties were studied.XRD analyses showed that with increasing SiC content,the microstrain and dislocation density increased,while the crystal size decreased.The coefficient of thermal expansion(CTE)of the nanocomposites was less than that of the Cu matrix.The improvement in the CTE with increasing sintering temperature may be because of densification of the microstructure.Moreover,the mechanical properties of these nanocomposites showed noticeable enhancements with the addition of SiC and sintering temperatures,where the microhardness and apparent strengthening efficiency of nanocomposites containing 8wt%SiC and sintered at 875℃were 958.7 MPa and 1.07 vol%^(−1),respectively.The electrical conductivity of the sample slightly decreased with additional SiC and increased with sintering temperature.The prepared Cu/SiC nanocomposites possessed good electrical conductivity,high thermal stability,and excellent mechanical properties.展开更多
Experimental rock mechanics testing provides a controlled and effective method for measuring physical properties,their dependencies,and their evolution due to the addition of localized microcracks.To understand the co...Experimental rock mechanics testing provides a controlled and effective method for measuring physical properties,their dependencies,and their evolution due to the addition of localized microcracks.To understand the contributions of microcracks to first order changes in compliance,the behavior of initial undamaged properties of a material should be comprehensively investigated as a function of stress,load path,and load history.We perform a comprehensive study of elastic properties and their dependence on a variety of materials exhibiting nonlinearity,and varying levels of anisotropy in elastic stiffnesses.We programmatically perturb the testing environment of the specimens under triaxial stresses.Elastic moduli are measured within each test,and along multiple discrete loading paths for multistage tests as a function of stress,focusing on a set launch point.Four single stage triaxial tests per rock type are performed to calculate Mohr-Coulomb failure criteria,and ultrasonic velocities are captured during compression for establishing the upper bound of elastic behavior.Shear wave velocity for granite experiences a maximum value at a lower differential stress than maximum volumetric strain.Sandstone displays a similar trend at the highest confining pressure,while these two maxima converge under the lowest confining pressure.展开更多
文摘A contribution is given to the theoretical research on the stiffness of ceramic materials, under the approximation of the average stress field, the relation E = E0(1 -p)/(1+ 2.5p) is derived to describe the dependence of the modulus of etasticity on porosity. The prediction of this model is consistent with the experimental data from several ceramics such as reacting sintered Si3N4,MgO and MgAl2O3.
基金supported by the National Natural Science Foundation of China(Grant Nos.11102139&11472195)Natural Science Foundation of Hubei Province of China(Grant No.2014CFB713)
文摘An anisotropic micromechanical model based on Mori-Tanaka method is developed to calculate the effective elastic moduli
文摘<span style="font-family:Verdana;">A series of colossal magneto resistance (CMR) materials with compositional formula Pr</span><sub><span style="font-family:Verdana;">0.5</span></sub><span style="font-family:Verdana;">Sr</span><sub><span style="font-family:Verdana;">0.5</span></sub><span style="font-family:Verdana;">Mn</span><sub><span style="font-family:Verdana;">1-x</span></sub><span style="font-family:Verdana;">Cr</span><sub><span style="font-family:Verdana;">x</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by sol-gel technique using pure metal nitrates as the starting materials. These samples were characterized structurally by X-ray diffraction, FTIR and SEM. All the </span><span style="font-family:Verdana;">samples exhibit orthorhombic structure without any detectable impurities.</span><span style="font-family:Verdana;"> The bulk den</span><span></span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">sities for all the compositions were measured from the pellets. The Young’s and Rigidity moduli, Poisson’s ratio and Debye temperature of all the compositions were calculated with the experimentally measured ultra</span><span style="font-family:Verdana;">sonic longitudinal and shear velocities at room temperature using pulse</span><span style="font-family:Verdana;"> transmission technique. As the materials are porous, zero porous elastic moduli have also been calculated using a well-known Hasselmann and Fulrath model. </span><span style="font-family:Verdana;">The observed variation of elastic moduli with varying chromium doping</span><span style="font-family:Verdana;"> concentration has been studied qualitatively.</span></span></span>
基金the Deanship of Scientific Research(DSR)King Abdulaziz University,Jeddah,Saudi Arabia under grant No.(G:30-135-1441).The authors therefore acknowledge with thanks DSR for the technical and financial support.
文摘Nano-sized silicon carbide(SiC:0wt%,1wt%,2wt%,4wt%,and 8wt%)reinforced copper(Cu)matrix nanocomposites were manufactured,pressed,and sintered at 775 and 875℃in an argon atmosphere.X-ray diffraction(XRD)and scanning electron microscopy were performed to characterize the microstructural evolution.The density,thermal expansion,mechanical,and electrical properties were studied.XRD analyses showed that with increasing SiC content,the microstrain and dislocation density increased,while the crystal size decreased.The coefficient of thermal expansion(CTE)of the nanocomposites was less than that of the Cu matrix.The improvement in the CTE with increasing sintering temperature may be because of densification of the microstructure.Moreover,the mechanical properties of these nanocomposites showed noticeable enhancements with the addition of SiC and sintering temperatures,where the microhardness and apparent strengthening efficiency of nanocomposites containing 8wt%SiC and sintered at 875℃were 958.7 MPa and 1.07 vol%^(−1),respectively.The electrical conductivity of the sample slightly decreased with additional SiC and increased with sintering temperature.The prepared Cu/SiC nanocomposites possessed good electrical conductivity,high thermal stability,and excellent mechanical properties.
文摘Experimental rock mechanics testing provides a controlled and effective method for measuring physical properties,their dependencies,and their evolution due to the addition of localized microcracks.To understand the contributions of microcracks to first order changes in compliance,the behavior of initial undamaged properties of a material should be comprehensively investigated as a function of stress,load path,and load history.We perform a comprehensive study of elastic properties and their dependence on a variety of materials exhibiting nonlinearity,and varying levels of anisotropy in elastic stiffnesses.We programmatically perturb the testing environment of the specimens under triaxial stresses.Elastic moduli are measured within each test,and along multiple discrete loading paths for multistage tests as a function of stress,focusing on a set launch point.Four single stage triaxial tests per rock type are performed to calculate Mohr-Coulomb failure criteria,and ultrasonic velocities are captured during compression for establishing the upper bound of elastic behavior.Shear wave velocity for granite experiences a maximum value at a lower differential stress than maximum volumetric strain.Sandstone displays a similar trend at the highest confining pressure,while these two maxima converge under the lowest confining pressure.
