Papers by Keyword: Elastic Properties

Abstract: Hierarchical honeycombs with sandwich cell walls are classified as advanced honeycomb structures with enhanced mass-specific mechanical properties. In this paper, we present a hierarchical honeycomb composed of corrugated sandwich cell walls and investigate its effective elastic response in terms of the nine elastic constants of orthotropic materials. An analytical model is employed to predict the elastic constants, which has been previously utilized for similar honeycombs with sandwich walls of solid homogenous cores. Numerical predictions were obtained through a finite element-based homogenization technique and used to validate the analytical model predictions for a range of design parameters. Results indicate that the optimal design increases the in-plane stiffness by up to 350%, while a reduction of 20% occurs for the out-of-plane shear stiffness.

Abstract: The aim of this work is the evaluation by non-destructive impulse excitation tests, the modulus of elasticity (E) and the transversal deformation modulus (G) of cross laminated bamboo (CLB). Tests were performed on twenty-three CLB specimens measuring: 12 mm (height), 40 mm (width) and 12 mm (length). Twelve specimens have two lamellas with fibers at 0 °, longitudinal direction, and one layer with fibers at 90 °, normal direction (N) and the other eleven specimens have two layers in the normal direction and one in the longitudinal direction (L). The tests were performed using the Sonelastic apparatus indicated for the estimation of the dynamic modulus of elasticity and the damping of materials by the impulse excitation technique. A software attached to the apparatus analyzes the acoustic wave generated, and from it, the dynamic modulus of elasticity is determined. In order to verify the significance of this estimation, semi-destructive, three-point bending tests were performed in a universal test machine, determining E and G. It was concluded that the estimation of the modulus of elasticity is very significant when compared with the semi-destructive tests, and this method can be used to estimate the elasticity modulus of the CLB with high precision (R² = 99% and p-value <0.001). Modulus of elasticity in the longitudinal direction were five times larger than those in the normal direction.

Abstract: A mixed numerical-experimental technique based on vibration tests is modified and applied to determine the elastic material properties of woven composites. This non-destructive technique consists of physical experiments, numerical modelling and material identification procedure. For the purpose of characterization, two carbon fiber panels were prepared by manual layout technology. An evaluation of the accuracy of woven composite elastic properties is executed comparing the numerical and experimentally obtained resonant frequencies.

Abstract: As a potential functional material in the perovskite family, the KCaF₃ on electronic structure, elasticity, Debye temperature and anisotropy are studied based on density functional theory (DFT). Above all, the structural parameters of KCaF₃ crystal are optimized. Then the elastic constants and Debye temperature are calculated. The results show that: (1) KCaF₃ is composed of covalent bonds, in which the Ca-F bond is stronger than K-F. (2) Ca atom mainly contributes for the electronic properties of KCaF₃. (3) The structural parameters of KCaF₃ is in fair agreement with the experimental data. (4) The anisotropy of KCaF₃ was analyzed from the pure and quasi waves, of which the longitudinal wave velocity in the direction of [100] is the larger than the others two directions ([110] and [111]). Finally, The homogenized elastic moduli (bulk modulus B, shear modulus G, Young's modulus E), Pugh and Poisson ratio, are obtained. This research is meaningful and thus to provides a good theoretical guidance for the design the new ABX₃-type material with better performance.

Abstract: In present paper the effect of inclusions with irregular shapes on the elastic material properties of two-phase composites is studied. The irregular shapes of the real inclusions were approximated using smooth three-dimensional structures. For this needs the images of the microscopic particles were numerically approximated through smooth structures using methods of the computer algebra and were used for the following FE studies. The reference elements with typical inclusions with irregular shapes were determined and used for calculation of the effective material properties.

Abstract: This paper presents a theoretical study using the full potential linearized augmented plane wave approach (FP-LAPW) based on the density functional theory (DFT) to predict the structural and electronic properties of RbCdF3 and TlCdF3 compounds. The exchange-correlation potential is treated by the local density approximation (LDA), generalized gradient approximation (GGA) and modified Beck-Johnson exchange potential (mBJ). The calculated structural properties such as the equilibrium lattice parameter, the bulk modulus and its pressure derivative are in good agreement with the available data. The obtained results for the band structure and the density of states (DOS) show that the RbCdF3 (TlCdF3) compound have an indirect band gap of 6.77 and 3.07 eV (5.70 and 3.66 eV) with TB-mBJ and WC method respectively. From the electronic transition from valence conduction bands to conduction bands the optical properties were calculated. The elastic constants were calculated using the energy deformation relationship, from these constants the other mechanical properties such as bulk modulus, shear modulus, Young modulus and Poisson ratio were calculate and comment. Lastly, the elastic anisotropy was discussed.

Abstract: In this work we investigated the structural, electronic and elastic properties of TlN, TlP, TlAs and TlSb compounds in the zinc-blende phase, the lattice parameter, bulk modulus, band structure, and elastic constants have been calculated by employing the full potential linearized augmented plane wave method based on density functional theory of the exchange-correlation potentials including local density approximation, PBE generalized gradient, and Wu-Cohen generalized gradient are used. Furthermore, the modified Backe-Johnson (mBJ) potential has been utilized for the calculation of the energy gap. The present results are compared with other available theoretical values obtained.

Abstract: The structural, elastic and anisotropic properties for rare earth manganites compound YMnO3 in ferromagnetic state with hexagonal structure, have been investigated using the ab initio calculations based on the density functional theory, this calculations were based on the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The agreement of the DFT (FP-LAPW) calculations including internal atomic relaxations, with the experimental data is very good. Other relevant quantities such as elastic constants, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factors, sound velocity, and Debye temperature have been calculated and discussed.

Abstract: Currently, composite materials composed of a matrix and reinforcing components are widely used as a structural material for various engineering devices designed to operate under extreme loads of different types. By modifying a composite with structure-sensitive inclusions, such as a single-wall carbon nanotube, the mechanical properties, especially elastic characteristics, of the resulting material can be significantly improved. The results of investigation of a single-walled carbon nanotubes chirality influence on its elastic properties are presented. Various configurations of nanotubes, such as zigzag and armchair are considered. The dependences of the nanotube bulk modulus and shear modulus of its diameter are shown.

Abstract: Finite-element simulation of the spatially reinforced composite material elastic properties is performed. The simulation models are built in two steps: first, a 4DL-reinforced material model simulating a perfect matrix/rod contact is built; second, an improved simulation model is developed, taking into account the possibility of separation between the composite components. Comparison is made between the results obtained numerically and those based on the existing analytical models. With these finite-element simulation models, it is possible to estimate the required composite elastic properties to be used when designing structural components based on those materials.