Papers by Keyword: Elastic Constant

Abstract: Theoretical and experimental investigations are being carried out on Cu based alloys due to their technologically important shape memory properties and pseudo-elasticity, which are intimately associated with the martensitic transformation. The transition between the two phases, martensite to austenite, is of continued interest in academics and in industry. The shape memory effect, superelastic properties and biocompatibility are being applied in a variety of fields. Cu based SMA system has large vibrational entropy, high damping capacity and good economic viability. All these make it a potential candidate in the field of sensors and actuators. The concurrent knowledge of the second order elastic constants (SOEC) and third order elastic constants (TOEC) enables a better understanding of the nonlinear elasticity exhibited by these alloys. We have used a model based on deformation theory and Keating’s potential scheme to obtain the expressions for TOEC of the above alloys. In this paper we have calculated the complete sets of six non-vanishing TOEC of Cu-Al-Ni, Cu-Al-Zn, Cu-Al-Be and Cu-Al-Pd and are presented along with the available experimental data. It is remarkable that all the third order elastic constants are negative, indicating an increase in the vibrational frequencies under stress, giving rise to an increase in the strain-free energy. The absolute values of the TOEC are large. This means that the bcc phase observed is considerably anharmonic. The TOEC C144 representing the shear mode has a smaller value than C111. Hence, the effect of pressure is much greater on longitudinal wave velocity than on the shear wave velocity in the above Cu based SMA. The mode Grüneisen parameters of the acoustic waves are determined based on the quasi-harmonic approximation method. The low temperature limit of the lattice thermal expansion and the Anderson– Grüneisen parameter of these alloys are also obtained.

Abstract: Strains around a constricted matrix dislocation in a coherent twin grain boundary in germanium is measured by a combination of high-resolution electron microscopy and geometric phase analysis. Whilst strains in the grains on either side of the twin boundary agree closely with the isolated dislocation case, significant additional strains are localized at the boundary plane. By comparing the stresses and strains across the boundary plane, values for the elastic modulus of the twin boundary are determined. They are found to exhibit a drastic decrease as compared to the bulk and this is interpreted in terms of the non-equilibrium configuration of the boundary.

Abstract: The temperature dependence of single-crystal elastic constants of L10-ordered single-crystals of FePd . A complete set of elastic constants has been determined with the resonance ultrasound spectroscopy technique. The compounds clearly show a tetragonal elastic anisotropy, c11 < c33 and c44 < c66. The temperature dependencies of the anisotropies are not simply explained by the variation of axial ratio (c/a) of the crystal.

Abstract: The use of non destructive techniques for the elastic characterization of isotropic materials is continuously increasing and those based on the modal vibration testing of plate-like specimens is very widespread. In the present paper, an optimized search procedure is proposed which allows the material constants of isotropic plates to be non-destructively identified from vibration testing data and using finite element analyses. The identification process is performed by an optimizing algorithm in which the error function to be minimized depends on the difference between the natural frequencies obtained by finite element analyses and the measured ones. In order to verify the proposed identification procedure a comparison with the results reported in literature has been made.

Abstract: Combining vibration testing and numerical method is a potential inverse technique for determining elastic constants of materials because of its nondestructive characteristic, single test, and producing average properties. In order to simplify the modeling processes and to reduce complicated derivation in the numerical method, the combination of finite element analysis and optimum design is adopted in this work. A finite element package, ANSYS, is used to do the modal analysis of the composite plate. A hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is used to search the possible elastic constants. After obtaining the natural frequencies of the composite plates from vibration testing, this inverse technique could predict the elastic constants of the composite plate. The inverse technique is verified by comparing with other methods and by determining the elastic constants of aluminum plates, and the excellence of including the hybrid genetic algorithm is proved. The results also indicate that the present technique could obtain very accurate elastic constants of composite plates.

Abstract: Using the first-principles calculation, the elastic constant C44 of Ag/Al multilayers with different modulation periods from 0.43 nm to 2.27 nm has been evaluated in order to examine the effect of atomic and electronic structures on it. With increasing modulation period, C44 decreases and becomes close to that obtained by the conventional mixing rule, however, the difference of 8 % still remains at the modulation period of 2.27 nm. As C44 correlates with the average interplanar spacing, the decrease of C44 can be explained by the decrease of the charge density in the stacking direction due to the increase of the average interplanar spacing. The difference in the electronic structure is included in the effect of atomic structure.

Abstract: A simple finite-element-based inverse method has been devised with the aim of characterizing the properties of isotropic but heterogeneous materials under load. The method has been implemented into the commercial finite element code ABAQUS via its User Material (UMAT) Subroutine to facilitate the process of material characterization. Verification of the method has been carried out using simulated examples and the results showed rapid convergence of the method with good accuracy. The method has also been applied successfully to actual mechanical testing of graphite which has a porous microstructure and hence inhomogeneous distribution of material properties.

Abstract: Any NDE process may be considered to involve three systems, each having a unique set of parameters that define its characteristics viz. (a) The Input to the material, (b) The material itself, and (c) The output response measured by the NDE system. Traditionally, the input and the material parameters are assumed known and numerous Forward Models have been developed that predict or estimate the output response function. Over the years, forward models are very well established and serve the key purpose, for improved interpretation of the, as well as to optimize the input parameters to obtain the desired, output response. The other two scenarios i.e. if the output response function in the form of measured data is available, to obtain one of system parameters, i.e. either the input function or the material properties, while the other one is assumed to be known are classified as Inverse Problems. Due to the availability of computational resources, the inverse problem solutions are becoming increasingly feasible. Typical applications include measurement of material properties such as modulus, viscosity, temperature, hardness and stress profiles, etc. This paper will discuss the different techniques and the kinds of problems that have been successfully addressed in the area of NDE and their implications on the expanding horizons in NDE.

Abstract: Using self-consistent effective-medium theory, we studied the complex elastic compliances of conducting disordered heterogeneous piezoelectric-polymer systems. The considered system is a random mixture of piezoelectric spheroids and polymer ones with the same orientation. The proximate cause of the effective elastic constants frequency dependencies was considered. The nature of the obtained spectra was analyzed.

Abstract: A list of monographs on internal friction, anelasticity, ultrasonic attenuation, relaxation phenomena in solids, and mechanical spectroscopy published in Soviet Union, Russia, and Ukraine is provided. A complete list of proceedings from international and Russian conferences is also given. This work is a valuable supplement to the Mechanical Spectroscopy - Suggested Reading Series.