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Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si_(3)N_(4) ceramics:ab initio and quasi-harmonic Debye modeling

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Chinese Physics B 2012年第6期21卷 130-140页

作者：余本海陈东 College of Physics and Electronic Engineering Xinyang Normal University

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-*** ground-state parameters accord quite well with the experimental *** calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 *** α → β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 ***,the α → β transition occurs at 1600 K and 7.98 *** α-and β-Si3N4,the c axes are slightly more incompressible than the a *** conclude that β-Si3N4 is a hard material and ductile in *** the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 ***,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and *** features in these properties are observed at high *** calculated results are in good agreement with available experimental data and previous theoretical *** fundamental solid-state properties are reported at high pressure and high ***,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.

关键词： ab initio elastic constants phase transition poisson ratio

Strength and elastic properties of sandstone under different testing conditions

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Journal of Central South University of Technology 2007年第2期14卷 210-215页

作者：陈运平王思敬王恩志 State Key Laboratory of Hydroscience and Engineering Tsinghua University

A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10^(-5), 10^(-4) and 10^(-3)/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and poisson ratio display asymmetric 'X' shape with various strain, and the average unloading modulus is larger than the average loading modulus.

关键词： strain rate strength deformation modulus poisson ratio softening coefficient rock

Cellular Automata Model for Elastic Solid Material

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Communications in Theoretical Physics 2013年第1期59卷 59-67页

作者：董银峰张广财许爱国甘延标 National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics North China Institute of Aerospace Engineering

The Cellular Automaton(CA) modeling and simulation of solid dynamics is a long-standing difficult *** this paper we present a new two-dimensional CA model for solid *** this model the solid body is represented by a set of white and black particles alternatively positioned in the x-and *** force acting on each particle is represented by the linear summation of relative displacements of the nearest-neighboring *** key technique in this new model is the construction of eight coefficient *** and numerical analyses show that the present model can be mathematically described by a conservative ***,it works for elastic *** the continuum limit the CA model recovers the well-known Navier *** coefficient matrices are related to the shear module and poisson ratio of the material *** with previous CA model for solid body,this model realizes the natural coupling of deformations in the x-and ***,the wave phenomena related to the poisson ratio effects are successfully *** work advances significantly the CA modeling and simulation in the field of computational solid dynamics.

关键词： cellular automata poisson ratio elastic body

Stress and strain analysis on the anastomosis site sutured with either epineurial or perineurial sutures after simulation of sciatic nerve injury

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Neural Regeneration Research 2012年第29期7卷 2299-2304页

作者： Guangyao Liu Qiao Zhang Yan Jin Zhongli Gao Department of Orthopedics China-Japan Union Hospital Jilin University Changchun 130031 Jilin Province China Department of Ophthalmology Second Hospital Jilin University Changchun 130041 Jilin Province China

The magnitude of tensile stress and tensile strain at an anastomosis site under physiological stress is an important factor for the success of anastomosis following suturing in peripheral nerve injury treatment. Sciatic nerves from fresh adult cadavers were used to create models of sciatic nerve injury. The denervated specimens underwent epineurial and perineurial suturing. The elastic modulus （40.96 ＋ 2.59 MPa） and poisson ratio （0.37 ＋ 0.02） of the normal sciatic nerve were measured by strain electrical measurement. A resistance strain gauge was pasted on the front, back left, and right of the edge of the anastomosis site after suturing. Strain electrical measurement results showed that the stress and strain values of the sciatic nerve following perineurial suturing were lower than those following epineurial suturing. Scanning electron microscopy revealed that the sciatic nerve fibers were disordered following epineurial compared with perineurial suturing. These results indicate that the effect of perineurial suturing in sciatic nerve injury repair is better than that of epineurial suturing.

关键词： sciatic nerve injury epineurial suture perineurial suture strain electrical measurement anastomosis site tensile stress tensile strain elastic modulus poisson ratio biomechanics peripheral nerve injury neural regeneration

mechanical and thermodynamic properties of α-and β-Si3N4 ceramics： ab initio and quasi-harmonic Debye modeling

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Chinese Physics B 2012年第6期21卷 126-136页

作者：余本海陈东 College of Physics and Electronic Engineering Xinyang Normal UniversityXinyang 464000China

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4. The ground-state parameters accord quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K. The α → β phase transformation would not occur in a pressure range of 0-40 （3Pa and a temperature range of 0 300 K. Actually, the α → β transition occurs at 1600 K and 7.98 GPa. For α-and β-Si3N4, the c axes are slightly more incompressible than the a axes. We conclude that β-Si3N4 is a hard material and ductile in nature. On the other hand, β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0 - 010 GPa. Besides, the thermodynamic properties such as entropy, heat capacity, and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures. Significant features in these properties are observed at high temperature. The calculated results are in good agreement with available experimental data and previous theoretical values. Many fundamental solid-state properties are reported at high pressure and high temperature. Therefore, our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.

关键词： ab initio elastic constants phase transition poisson ratio