Anharmonic properties of 16 alkali halides and 4 alkali cyanides are investigated using long-range Coulomb and short-range Born-Mayer potentials starting from the nearest-neighbour distance and repulsive parameter. This study includes the prediction of second, third and fourth order elastic constants, the pressure derivatives of second and third order elastic constants and partial contractions at elevated temperatures. The results obtained in present investigations are in reasonable agreement compared with experimental studies.
Calculations were made to investigate the anharmonic properties of lead chalcogenides PbS, PbSe and PbTe at elevated temperatures by means of primary physical parameters viz. nearest-neighbour distance and hardness parameter using long- and short-range potentials. Higher-order elastic constants are computed up to their melting temperature for these crystals. The first order pressure derivatives of second- and third-order elastic constants, the second-order pressure derivatives of second-order elastic constants and partial contractions are also evaluated at different temperatures. As the experimental elastic constants are not available at high temperatures, hence our results were only compared with the available values obtained at room temperature. The nature of the elastic behaviour in these compounds was analyzed.
By means of density-functional theory with the generalized gradient approximation and using the virtual-crystal approximation, we report first-principles calculation results on the structural and elastic properties of Ti_{1-x}Zr_{x}N alloy. In order to gain some further information on the mechanical properties of Ti_{0.5}Zr_{0.5}N compound, we also calculated the Young modulus, Poisson ratio, and anisotropy factor. The variation of calculated unit cell parameter for Ti_{1-x}Zr_{x}N structure increases with Zr content x. A linear dependence of the elastic constants and the bulk modulus over a range of composition x is found. All the C_{ij} of Ti_{0.5}Zr_{0.5}N increase linearly with increasing pressure. The same behaviour is observed for the other compounds with Zr compositions x.
This paper presents an optimal boundary temperature control of thermal stresses in a plate, based on time-conformable fractional heat conduction equation. The aim is to find the boundary temperature that takes thermal stress under control. The fractional Laplace and finite Fourier sine transforms are used to obtain the fundamental solution. Then the optimal control is held by successive iterations. Numerical results are depicted by plots produced by MATLAB codes.
The main goal of the proposed paper is to present the results of the nitrogen ion implantation effects on mechanical and corrosion properties of NiTi shape memory alloy. Local pseudoelasticity phenomena of NiTi were determined using the ultra-low load applied system. The load-penetration depth curves show that lower nitrogen fluence improves mechanical properties in the near surface layer but higher ion fluence leads to degradation of pseudoelasticity properties. Corrosion resistance of NiTi in the Ringer solution was evaluated by means of electrochemical methods. The results of potentiodynamic measurements in the anodic range for implanted NiTi indicate a decrease of passive current density range in comparison with non-treated NiTi, without any signs related to Ni release. The results of impedance measurements recorded at the corrosion potential show a capacitive behaviour for all samples without clear predominance of one of them. It can be explained by the fact that this result concerns the first stage of corrosion exposition. It is shown that nitrogen ion implantation leads to formation of modified surface of improved physicochemical properties.
This study was addressed to use knowledge about the orthodontic system with numerical simulation of the finite elements method. For the first time we simulated the stresses on the orthodontic system and, in this manner, calculated the orthodontic force on the tooth. A 3D orthodontic model or orthodontic system was designed resembling moderate crowding in the dental arch with all supporting structures. CATIA V5 computer software was used to set up a model for the orthodontic system and ABAQUS was used for simulation of the stresses on the orthodontic system. Our attention was focused on the stresses on the tooth lateral incisor and its periodontal ligament. The results of the numerical simulation showed complex stresses on the tooth lateral incisor and its periodontal ligament. In this paper there is presented a calculation of the orthodontic force acting on the tooth lateral incisor due to the orthodontic wire. This orthodontic force was calculated from the stresses on the bracket. The calculated orthodontic force was in the area which is considered as the optimal orthodontic force for movement of the tooth.
First principles calculations on structural, elastic and thermodynamic properties of K₂S have been made using the full-potential augmented plane-waves plus local orbitals within density functional theory using generalized gradient approximation for exchange correlation potentials. The ground state lattice parameter, bulk moduli have been obtained. The second-order elastic constants, Young and shear modulus, Poisson ratio, have also been calculated. Calculated structural, elastic and other parameters are in good agreement with available data. The elastic constants and thermodynamic quantities under high pressure and temperature are also calculated and discussed.
The present paper concerns the elastic-plastic nanodeformation of Te-doped GaSb crystals grown by molecular beam epitaxy on the n-type of GaSb substrate. The conventional analysis of nanoindentation data obtained with sharp triangular (Berkovich) and spherical tip revealed the elastic modulus (E=83.07± 1.78 GPa), hardness (H=5.19±0.25 GPa) and "true hardness" (H_{T}=5.73±0.04 GPa). The registered pop-in event which indicates the elastic-plastic transition in GaSb crystal points towards the corresponding yield strength (σ_{Y}=3.8±0.1 GPa). The origin of incipient plasticity in GaSb crystal is discussed in terms of elastic-plastic deformation energy concept.
We present theoretical results showing dependence of Poisson ratio and biaxial relaxation coefficient on composition and atomic arrangement in wurtzite In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys. Our calculations reveal that the Poisson ratio determined for In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys subjected to a uniaxial stress parallel to the c axis of the wurtzite structure shows significant superlinear dependence on composition. The superlinear bowing in Poisson ratio is enlarged by the effect of In clustering. The biaxial relaxation coefficient determined for In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys subjected to a biaxial stress in the plane perpendicular to the c axis of the wurtzite structure changes superlinearly and linearly with x in In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N, respectively. The effect of In atom clustering results in sublinear dependence of the biaxial relaxation coefficient in both In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys.
Elastic anisotropy and acoustic attenuation in bulk material consisting of consolidated graphene nanoplatelets are studied. The material was prepared by spark plasma sintering, and exhibits highly anisotropic microstructure with the graphene nanoplatelets oriented perpendicular to the spark plasma sintering compression axis. The complete tensor of elastic constants is obtained using a combination of two ultrasonic methods: the through-transmission method and the resonant ultrasound spectroscopy. It is shown that the examined material exhibits very strong anisotropy both in the elasticity (the Young moduli in directions parallel to the graphene nanoplatelets and perpendicular to them differ by more than 20 times) and in the attenuation, where the dissipative effect of the internal friction in the graphene nanoplatelets combines with strong scattering losses due to the porosity. The results are compared with those obtained for ceramic-matrix/graphene nanoplatelet composites by the same ultrasonic methods.
An attempt to evaluate mechanical properties changes (superelastic phenomena) in the shape memory NiTi alloy (austenitic form) due to ion implantation (N^{+}, fluences of 1 × 10^{17} and 4 × 10^{18} cm^{-2}) has been made. We applied the differential scanning calorimetry technique and spherical indentation (micro- and nanoindentation scale) test to study superelastic effect. The results of investigations of selected functional properties, i.e. characteristic temperatures, total and recovered penetration depth on the implanted and non-implanted NiTi samples are presented.
We study the heteroepitaxial growth of thin layers by means of the modified phase-field model with the incorporated anisotropy. The influence of elastic and surface energies on the layer growth is considered. For numerical solution of the model, an explicit numerical scheme based on the finite element method is employed. The obtained computational results with various anisotropy settings demonstrate the anisotropic thin-layer pattern growth.
We present theoretical study of the pressure coefficient of the light emission (dE_{E}/dP) in compressively strained zinc-blende InGaAs/GaAs and InGaN/GaN quantum wells, grown in a (001) direction. We investigate the contributions to dE_{E}/dP arising from (i) third-order (nonlinear) elasticity, (ii) nonlinear elasticity, originating from pressure dependence of elastic constants, and (iii) nonlinear dependence of elastic constants on composition in InGaAs and InGaN alloys. The obtained results indicate that the use of nonlinear elasticity is essential for determination of dE_{E}/dP in the strained InGaAs/GaAs and InGaN/GaN quantum wells, while the inclusion of the nonlinear dependence of elastic constants on composition of InGaAs and InGaN alloys does not improve agreement between the theoretical end experimental values of dE_{E}/dP in the considered structures.
The phases chemical composition and micromechanical properties in single crystal of Ni-based superalloy with chemical composition of 12.1 Al, 5.3 Cr, 9.4 Co, 0.8 Nb, 0.9 Ta, 0.7 Mo, 2.5 W, 0.7 Re and Ni-balance (in at.%) were changed during hard cyclic viscoplastic deformation at room temperature. The method we used based on the Bauschinger effect. The changes in the dendritic microstructure and chemical composition were characterized by scanning electron microscopy and energy dispersive spectrometry. The phases micromechanical properties evolution were characterized by nanoindentation. The results show that the cumulative strain or strain energy density increase arouse the interdiffusion of atoms between the different phases and the phases equilibrium in SC was changed. It is established that the interdiffusion rate depends on elements atoms activation energy. The new γ-γ'-eutectic pools were formed in the primary dendrites region (with fine γ/γ'-phase) and as result the length of newly formed dendrites was decreased significantly. The maximal and plastic depth of nanoindentation were measured and the corresponding micromechanical properties of phases calculated.
The plastic behavior of face-centered cubic metals was investigated over a wide range of strain and testing temperature. The experimental stress-strain data were described using both macroscopic and microscopic, well-established relationships. The characteristics of these descriptions are discussed and compared with each other. The analysis of the characteristics leads to a definition of the low and high temperature deformation regions, where the kinetics of both the dislocation-multiplication and the dislocation-annihilation (recovery) are different. For pure aluminum, it is shown that the boundary between these two regions occurs at a homologous temperature of the order of ≈ 0.5 T_{m} where T_{m} is the absolute melting temperature. From this analysis, correlations are also drawn between the macroscopic parameters describing the stress-strain relationship and the fundamental characteristics of the microscopic processes both at room temperature and elevated temperatures.
First principles study of structural, elastic properties and anisotropy effect on the mechanical parameters of the zinc-blende boron nitride has been performed using the pseudopotential plane wave method based on density functional theory with the Teter and Pade exchange-correlation functional of the local density approximation. The equilibrium lattice constant, molecular and crystal densities, bond length, the independent elastic constants, bulk modulus and its pressure derivatives, compressibility, shear modulus, internal strain parameter, isotropy factor, compliance constants, the Debye temperature, Young's modulus, Poisson's ratio, the Lamé constants and sound velocity for directions within the important crystallographic planes of this compound are obtained and analyzed in comparison with the available theoretical data reported in the literature.
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