Values Of Stiffness Constants Research Articles

Physical properties of new MAX phase borides M2SB (M = Zr, Hf and Nb) in comparison with conventional MAX phase carbides M2SC (M = Zr, Hf and Nb): Comprehensive insights

In this article, a detailed study of the recently synthesized MAX phase borides M2SB (M = Zr, Hf and Nb) has been performed via first principles technique. Investigation of mechanical properties, elastic anisotropy, optical properties, dynamical stability and thermal properties are considered for the first time. The estimated values of stiffness constants and elastic moduli are found in good agreement with available results. The Vickers hardness is also calculated using Mulliken population analysis. The electronic density of states and charge density mapping are used to explain the variation of stiffness constants, elastic moduli and hardness parameters among the studied ternary borides. The Nb2SB compound is found to show the best combination of mechanical properties. Mixture of covalent and ionic bonding within these borides is explained using Mulliken population analysis. The direction dependent values of Young's modulus, compressibility, shear modulus and Poisson's ratio are visualized by 2D and 3D representations and different anisotropic factors are calculated. The important optical constants are calculated and analyzed. The metallic nature of the studied borides is confirmed from the density of states (DOS) and optical properties. The reflectivity spectra reveal the potential use of Zr2SB as coating materials to diminish solar heating. The studied borides are dynamically stable as confirmed from the phonon dispersion curves. The characteristic thermodynamic properties have also been calculated and analyzed. The physical properties of corresponding 211 MAX phase carbides are also calculated for comparison with those of the titled ternary borides.

Mechanical, optical and high-temperature magnetic properties of Sn-substituted Mg–Zn ferrites

ABSTRACT Sn-substituted Mg–Zn ferrites (0 ≤ x ≤ 0.10) have been synthesized using conventional ceramic technique and the mechanical, optical and high-temperature magnetic properties were studied. The formalism of elastic constants was assessed based on FTIR data. The mechanical stability was confirmed from the obtained values of stiffness constants. The bulk modulus, shear modulus and Young’s modulus have been estimated for different Sn concentrations. The Poisson’s ratio and Pugh ratio confirmed the brittleness character of the studied compounds. The Debye temperature was also calculated. The optical band gap has been calculated from diffuse reflectance spectra. The magnetization curves measured at different temperatures revealed the significant effect of temperature on the magnetic properties of the considered compositions. A second-order phase transition of ferrimagnetic to paramagnetic phase was observed in temperature-dependent magnetization vs. applied field and magnetic moment curves. The Curie temperature was observed to decrease owing to Sn substitution.

Mechanical properties of graphene-CNT van der Waals heterostructures: a molecular dynamics study

We find stiffness properties of van der Waals heterostructures made of graphene and carbon nanotubes (CNTs) using molecular dynamics (MD) simulations. The variation of the stiffness tensor is studied at different temperatures for structures with changing CNT density, and orientations. Orthotropic structures with unidirectional CNTs have high stiffness ∼300–500 GPa, in one direction. Structures with transverse isotropy show stiffness of ∼150–350 GPa along two mutually perpendicular directions. The orthotropic structures also show greater stiffness with increasing CNT density, while the others are insensitive to it. In general,the stiffness constant values are decrease as temperatures increase. The results can aid in determining useful heterostructure configuration for a particular application and in finding overall stiffness of devices having additional components.

Physical strength and Opto-electrical conductivity of L-Serine Phosphate single crystal for structural and photonics devices fabrication

ABSTRACT Optically transparent and mechanically good quality single crystal of L-Serine Phosphate (LSP) was grown by slow solvent evaporation technique. Optical Transmittance study was carried out by UV-Vis spectrophotometer. The optical Transmittance studies show the better transparency of the crystal in the ultraviolet and the entire visible region. Various optical constants such as optical band gap, absorption coefficient, extinction coefficient, reflectance, refractive index were calculated. Optical conductivity and electrical conductivity are also calculated using transmittance data. Important Mechanical properties of the grown crystal such as Vicker’s microhardness number, work hardening index, Yield strength, fracture toughness, brittleness index and elastic Stiffness constant values were determined using Vicker’s microhardness tester.

Structural and mechanical properties of diglycine perchlorate single crystals

Abstract Good quality diglycine perchlorate (DGPCL) single crystals were grown by slow evaporation solution growth method using the combination of glycine and perchloric acid in the ratio of 2:1. Single crystal X-ray diffraction and mechanical characterization of the grown single crystals of diglycine perchlorate were analyzed in this article. Lattice parameters, space group and crytal system were found from single crystal X-ray diffraction analysis. All the cell parameters and space group are in a good agreement with the reported values. Mechanical properties, such as Vicker’s microhardness number, work hardening index, standard hardness value, yield strength, fracture toughness, brittleness index and elastic stiffness constant values, were determined using Vicker’s microhardness tester.

Growth, structural and mechanical studies of phthalic acid single crystals grown in two different solutions

Good quality pure Phthalic acid single crystals were grown by slow evaporation solution growth method. Phthalic acid 1(PA1) crystals were grown in Ammonium Oxalate aqueous solution. From the aqueous solution of Ammonium Bromide, Phthalic acid 2 (PA2) crystals were grown. Single crystal x-ray diffraction and Mechanical characterizations of slow evaporation grown single crystals of PA1 and PA2 were analyzed in this article. Lattice parameters, space group and crytal system were found from Single crystal x-ray diffraction analysis. Optical tranmittance study reaveal the optical perfection of the crystals. Mechanical properties such as Vicker’s microhardness number, work hardening index, standard hardness values, Yield strength, fracture toughness, brittleness index and elastic Stiffness constant values were determined using Vicker’s microhardness tester.

Crystal growth, physical properties and computational insights of semi-organic non-linear optical crystal diphenylguanidinium perchlorate grown by conventional solvent evaporation method

A splendid nonlinear optical single crystals diphenylguanidinium perchlorate (DPGP) was lucratively grown by low cost solvent evaporation method with the dimensions of 8 × 4 × 2 mm3. Structural and morphological studies of grown crystal were confirmed using X-ray diffraction studies. The presence of diverse functional groups was identified using FTIR and RAMAN studies. The molecular structure of a grown crystal was inveterate by NMR studies. The optical transmittance of DPGP crystal was analyzed using UV–vis-NIR studies. Photoluminescence spectrum shows sharp, well defined emission peak at 388 nm. Thermal studies assign that adduct is stable with the melting point of 164 °C. Microhardness studies declare that DPGP crystal belongs to the soft material class and their yield strength and elastic stiffness constant values were evaluated. Photoconductivity studies revealed the negative photoconductive nature of DPGP crystal. Second harmonic generation (SHG) efficiency of the DPGP crystal was 1.4 times that of potassium dihydrogen phosphate. Etching studies were carried out for different etching time. The dielectric studies were performed at different frequency. Laser damage threshold properties of DPGP crystal were examined using Nd:YAG laser system. The HOMO-LUMO energy gap evident the charge transfer interaction of the molecule. The calculated first order hyperpolarizability value is 5 times greater than that of urea. Thus, the grown DPGP single crystals are well suited for NLO device fabrications.

Elastic properties of nanocrystalline aluminum substituted nickel ferrites prepared by co-precipitation method

NiAlxFe2−xO4 (x=0.0–1.0 in the step of 0.2) spinel ferrite system was prepared by the co-precipitation method. The elemental compositional stoichiometry, microstructure, infrared spectral and elastic properties have been carried out by means of energy dispersive analysis of X-ray (EDAX), scanning electron microscopy (SEM) and infrared spectroscopic (IR) measurements. Infrared spectra were carried out at room temperature in the wavenumber range of 300–800cm−1. The IR spectra show three major absorption bands. High frequency bands ‘ν1’ is assigned to the tetrahedral and low frequency bands ‘ν2’ is assigned to the octahedral complex. Small frequency bands ‘ν3’ is assigned to Al3+O−2 complexes. Force constant for the tetrahedral and octahedral site was determined by using IR data. Force constant used to calculate the stiffness constants (C11 and C12). Using the values of stiffness constants; elastic moduli such as Young’s modulus, bulk modulus, modulus of rigidity, Poisson ratio and Debye temperature were calculated.

Steady flow of smooth, inelastic particles on a bumpy inclined plane: Hard and soft particle simulations

We study smooth, slightly inelastic particles flowing under gravity on a bumpy inclined plane using event-driven and discrete-element simulations. Shallow layers (ten particle diameters) are used to enable simulation using the event-driven method within reasonable computational times. Steady flows are obtained in a narrow range of angles (13 degrees-14.5 degrees); lower angles result in stopping of the flow and higher angles in continuous acceleration. The flow is relatively dense with the solid volume fraction, nu approximately 0.5 , and significant layering of particles is observed. We derive expressions for the stress, heat flux, and dissipation for the hard and soft particle models from first principles. The computed mean velocity, temperature, stress, dissipation, and heat flux profiles of hard particles are compared to soft particle results for different values of stiffness constant (k). The value of stiffness constant for which results for hard and soft particles are identical is found to be k>or=2x10(6) mg/d, where m is the mass of a particle, g is the acceleration due to gravity, and d is the particle diameter. We compare the simulation results to constitutive relations obtained from the kinetic theory of Jenkins and Richman [J. T. Jenkins and M. W. Richman, Arch. Ration. Mech. Anal. 87, 355 (1985)] for pressure, dissipation, viscosity, and thermal conductivity. We find that all the quantities are very well predicted by kinetic theory for volume fractions nu<0.5. At higher densities, obtained for thicker layers (H=15d and H=20d), the kinetic theory does not give accurate prediction. Deviations of the kinetic theory predictions from simulation results are relatively small for dissipation and heat flux and most significant deviations are observed for shear viscosity and pressure. The results indicate the range of applicability of soft particle simulations and kinetic theory for dense flows.

Aging affects passive stiffness and spindle function of the rat soleus muscle

Aging affects many motor functions, notably the spinal stretch reflexes and muscle spindle sensitivity. Spindle activation also depends on the elastic properties of the structures linked to the proprioceptive receptors. We have calculated a spindle efficacy index, SEI, for old rats. This index relates the spindle sensitivity, deduced from electroneurograms recording (ENG), to the passive stiffness of the muscle. Spindle sensitivity and passive incremental stiffness were calculated during ramp and hold stretches imposed on pseudo-isolated soleus muscles of control rats (aged 4 months, n = 12) and old rats (aged 24 months, n = 16). SEI were calculated for the dynamic and static phases of ramp (1–80 mm/s) and for hold (0.5–2 mm) stretches imposed at two reference lengths: length threshold for spindle afferents discharges, L n (neurogram length) and slack length, L s. The passive incremental stiffness was calculated from the peak and steady values of passive tension, measured under the stretch conditions used for the ENG recordings, and taking into account the muscle cross-sectional area. The pseudo-isolated soleus muscles were also stretched to establish the stress–strain relationship and to calculate muscle stiffness constant. The contralateral muscle was used to count muscle spindles and spindle fibers (ATPase staining) and immunostained to identify MyHC isoforms. L n and L s lengths were not significantly different in the control group, while L n was significantly greater than L s in old muscles. Under dynamic conditions, the SEI of old muscles was the same as in controls at L s, but it was significantly lower than in controls at L n due to increased passive incremental stiffness under the stretch conditions used to analyze the ENG. Under static conditions, the SEI of old muscles was significantly lower than control values at all the stretch amplitudes and threshold lengths tested, due to increased passive incremental stiffness and decreased spindle sensitivity at L s. The muscle stiffness constant values were greater in old muscles than in controls, confirming the changes in elastic properties under passive conditions due to aging. Aging also altered the intrafusal fibers: it increased the mean number of intrafusal fibers and the contents in the slow, neonatal and developmental isoforms intrafusal of MyHC have been modified. These structural modifications do not seem great enough to counteract the loss of the spindle sensitivity or the spindle efficacy under passive conditions and after the nerve was severed. However, they may help to maintain the spindle afferent message under natural conditions and under fusimotor control.

Spin-wave resonance and magnetic anisotropy in FePt thin films

Ferromagnetic Resonance (FMR) measurements at room temperature and X-band microwave frequency were performed on polycrystalline FePt thin films with face-centered cubic structure. With the external field perpendicular to the film plane, the absorption fields H n of the odd and even spin-wave resonance modes n detected for the Fe 0.44Pt 0.56(45 nm)/Si(1 0 0) and Fe 0.51Pt 0.49(105 nm)/Pt(55 nm)/MgO(1 0 0) films, were found to obey the well-known H n × n 2 ratio, giving for these films the exchange stiffness constant values of 3.9×10 −8 and 4.4×10 –7 erg/cm, respectively. The study of the out-of-plane angular dependence of the absorption field of the uniform FMR mode allowed the measurement of the effective magnetic anisotropy constants of 5.3×10 6 , 6.4×10 6 , and 6.7×10 6 erg/cm 3, related, respectively, to the [1 1 1], [1 0 0], and [1 1 0] textures present in the films.

Dependence of DNA steady-state electric birefringence on field strength

Abstract A major task in our work has been to calculate the dependence of DNA steady-state electric birefringence on field strength for a ‘hinged bent rod’ (HBR) composed of two rod-like arms of length L with a restoring force proportional to the angle of bending at the hinge. The system is considered to have a permanent dipole moment due to asymmetric charge distribution with respect to its centre of diffusion. The electric and optical polarizability tensors of HBR macroions are also calculated. To calculate the electric birefringence, the statistical averages of the differential optical polarizability per molecule in the directions parallel and perpendicular to the applied electric field are made over all conformations as well as over all spatial orientations and all the velocities in the presence of the electric field. Using this approach, numerical calculations are carried out to achieve a fitting of electric birefringence experimental curves versus the square of the electric field for the sonicated and fractioned DNA and restriction enzyme fragments of DNA. It is shown that the HBR macroion presents a reversal of the birefringence sign at low electric fields for certain chain lengths, electric polarizability and stiffness constant values, in agreement with the experimental results obtained for DNA. It is observed that the HBR model adequately represents DNA elastic properties.