Explore the vast range of titles available.

The Leeb hardness test is a non-destructive and portable technique that can be used both in the laboratory and in-field applications. The main purpose of this study is to predict the dynamic elastic constants of the igneous and sedimentary rocks using Leeb dynamic hardness testing. For this purpose, three vital topics have been investigated and analyzed. First, the relationships between ultrasonic wave velocities and dynamic elastic constants with the Leeb hardness were investigated. Thereafter, by determining the rock quality index (IQ) using microscopic studies and by analyzing the quality index-porosity plot, the variation of the Leeb hardness values was studied. Eventually, the longitudinal waveform in rock samples with different quality indexes and Leeb hardness were analyzed. To achieve these outputs, 33 samples of igneous and sedimentary rocks with a wide range of physical, mechanical, and textural features were collected and tested. The results of the analyses show that in both igneous and sedimentary rocks, the dynamic modulus of elasticity (E d ) has a significant correlation with the Leeb hardness. Generally, based on the microscopic studies, it was observed that the existence of the porosity in sedimentary rocks and intercrystalline and intracrystalline fissures in igneous rocks sharply reduce the Leeb hardness and thus lead to changes in the form of the longitudinal waves.

We investigate the mechanical properties of proposed graphene-like hexagonal gallium nitride monolayer ( g -GaN) using first-principles calculations based on density-functional theory. Compared to the graphene-like hexagonal boron nitride monolayer ( g -BN), g -GaN is softer, with 40 % in-plane stiffness, 50 %, 46 %, and 42 % ultimate strengths in armchair , zigzag , and biaxial strains, respectively. However, g -GaN has a larger Poisson’s ratio, 0.43, about 1.9 times that of g -BN. It was found that the g -GaN also sustains much smaller strains before rupture. We obtained the second-, third-, fourth-, and fifth-order elastic constants for a rigorous continuum description of the elastic response of g -GaN. The second-order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson’s ratio monotonically decreases with increasing pressure. The sound velocity of a compressional wave has a minima of 10 km/s at an in-plane pressure of 1 N/m, while as a shear wave’s velocity monotonically increases with pressure. The tunable sound velocities have promising applications in nano waveguides and surface acoustic wave sensors.

The experimental work described in this paper was carried out in order to discover about the effects of petrographic characteristics on the ultrasonic pulse velocity and dynamic elastic constants of granitic rocks. For this, petrographic characteristics include the mean mineral grain size (MGS) and ratio of Quartz to Feldspar (Qz/Fl), ultrasonic pulse velocity include the P-wave (Vp) and S-wave velocity (Vs), and dynamic elastic constants include the elastic modulus (E) and Poisson’s ratio (ν) of ten different granitic rock were determined. By data analysis, correlations between Vp, Vs, E and ν with MGS and Qz/Fl were developed. It is concluded that the MGS and Qz/Fl have significant effects on the Vp, Vs, E and ν. Moreover, the results showed that MGS and Qz/Fl are in good accuracy for estimating the Vp, Vs and E, while there are no meaningful correlations between ν with MGS and Qz/Fl.

A macroscopic coupled stress-diffusion theory which accounts for the effects of nonlinear material behaviour, based on the framework proposed by Cahn and Larché, is presented and implemented numerically into the finite element method. The numerical implementation is validated against analytical solutions for different boundary valued problems. Particular attention is payed to the open system elastic constants, i.e. those derived at constant diffusion potential, since they enable, under circumstances, the equilibrium composition field for any generic chemical-mechanical coupled problem to be obtained through the solution of an equivalent elastic problem. Finally, the effects of plasticity on the overall equilibrium state of the coupled problem solution are discussed.

In this study, the mechano-chemical properties of aromatic polymer polyetheretherketone (PEEK) samples, irradiated by high energy electrons at 200 and 400 kGy doses, were investigated by Nanoindentation, Brillouin light scattering spectroscopy and Fourier-transform infrared spectroscopy (FTIR). Irradiating electrons penetrated down to a 5 mm depth inside the polymer, as shown numerically by the monte CArlo SImulation of electroN trajectory in sOlids (CASINO) method. The irradiation of PEEK samples at 200 kGy caused the enhancement of surface roughness by almost threefold. However, an increase in the irradiation dose to 400 kGy led to a decrease in the surface roughness of the sample. Most likely, this was due to the processes of erosion and melting of the sample surface induced by high dosage irradiation. It was found that electron irradiation led to a decrease of the elastic constant C11, as well as a slight decrease in the sample’s hardness, while the Young’s elastic modulus decrease was more noticeable. An intrinsic bulk property of PEEK is less radiation resistance than at its surface. The proportionality constant of Young’s modulus to indentation hardness for the pristine and irradiated samples were 0.039 and 0.038, respectively. In addition, a quasi-linear relationship between hardness and Young’s modulus was observed. The degradation of the polymer’s mechanical properties was attributed to electron irradiation-induced processes involving scission of macromolecular chains.

Using ab initio calculations, we have studied the structural, electronic and elastic properties of M 2 GeC, with M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Geometrical optimizations of the unit cell are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d -C p and M d -Ge p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C 44 , which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 8.41–8.50. We derived the bulk and shear moduli, Young’s moduli and Poisson’s ratio for ideal polycrystalline M 2 GeC aggregates. We estimated the Debye temperature of M 2 GeC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic constants of Ti 2 GeC, V 2 GeC, Cr 2 GeC, Zr 2 GeC, Nb 2 GeC, Mo 2 GeC, Hf 2 GeC, Ta 2 GeC and W 2 GeC compounds, and it still awaits experimental confirmation.

First-principles calculations on a huge configuration space of four different binary alloy systems reveal that stiffness and heat of formation are negatively and linearly correlated. A stiff test for stability This study asks a fundamental question: is the most thermodynamically stable atomic configuration of a material the hardest, stiffest or strongest form of that material? Or could some metastable configurations improve on that performance? Focusing on stiffness, the authors perform first-principles calculations on a huge configuration space of four different binary-alloy systems. They find that, at least in the systems they research, stiffness and heat of formation are negatively and linearly correlated. That is, the more stable a system is, the harder the material will be. The methods used here should, in principle, be applicable to the investigation of other relationships between stability and mechanical properties. Any thermodynamically stable or metastable phase corresponds to a local minimum of a potentially very complicated energy landscape. But however complex the crystal might be, this energy landscape is of parabolic shape near its minima. Roughly speaking, the depth of this energy well with respect to some reference level determines the thermodynamic stability of the system, and the steepness of the parabola near its minimum determines the system’s elastic properties. Although changing alloying elements and their concentrations in a given material to enhance certain properties dates back to the Bronze Age 1 , 2 , the systematic search for desirable properties in metastable atomic configurations at a fixed stoichiometry is a very recent tool in materials design 3 . Here we demonstrate, using first-principles studies of four binary alloy systems, that the elastic properties of face-centred-cubic intermetallic compounds obey certain rules. We reach two conclusions based on calculations on a huge subset of the face-centred-cubic configuration space. First, the stiffness and the heat of formation are negatively correlated with a nearly constant Spearman correlation 4 for all concentrations. Second, the averaged stiffness of metastable configurations at a fixed concentration decays linearly with their distance to the ground-state line (the phase diagram of an alloy at zero Kelvin). We hope that our methods will help to simplify the quest for new materials with optimal properties from the vast configuration space available.

In this article, expressions are derived for the Voigt, Reuss, and Hill estimates of the third-order elastic constants for polycrystals with either cubic or hexagonal crystal symmetry and orthorhombic physical symmetry. General forms of the fourth- and sixth-rank elastic stiffness and compliance tensors for crystal and physical symmetries are given. Explicit expressions are reduced from these tensors for the case of polycrystals exhibiting orthorhombic sample symmetry with either cubic or hexagonal crystallites. The estimated third-order elastic constants of the textured polycrystal are obtained in terms of second- and third-order single-crystal elastic constants and orientation distribution coefficients (ODCs), which are used to account for anisotropic physical symmetry. The acoustic nonlinearity parameter, β ¯ , is defined through combinations of the second- and third-order Voigt, Reuss, and Hill estimates of the elastic constants for a textured polycrystal. The model predicts that β ¯ is dependent on the type of averaging scheme used and the texture-defining ODCs. The model is quantitatively evaluated for polycrystalline iron, aluminum, and titanium using second- and third-order single-crystal elastic constants and experimentally measured ODCs. The interrelation between β ¯ and polycrystalline anisotropy offers potential for techniques associated with quantitative texture analysis.

In the present paper, we have investigated the phase transition and elastic properties of BeO at high pressure using three-body potential model (TBPM). The present interaction potential consists of long-range coulomb and three-body interactions and short-range overlap repulsion effective up to second neighbour ions. We have studied the phase transition from wurtzite ( B 4 ) to rock salt ( B 1 ) for BeO. The phase transition pressure ( P t ) obtained from this approach shows a respectably good agreement with experimental and other theoretical data. We have also computed the collapse of relative volume changes (Δ V ( P t )/ V (0)). Three-body potential model has also been used to derive the correct expressions for third-order elastic constants and pressure derivatives of second-order elastic constants for BeO.

The elastic properties of CdxNi1−xFe2O4 (x = 0.2, 0.4, 0.6 and 0.8) spinel ferrite system synthesized by wet-chemical technique, have been studied by infra-red spectroscopy and X-ray diffraction pattern analysis before (W) and after high temperature annealing (AW). The average particle size for wet-samples was within the range 4–5 nm, which is much lower than the average particle size found for AW samples (≈85 nm). The force constants for tetrahedral and octahedral sites determined by infrared spectral analysis, lattice constant and X-ray density values by X-ray diffraction pattern analysis; have been used to calculate elastic constants. The elastic moduli for W-samples are found to be larger as compared to AW samples, which are explained on the basis of grain size reduction effect. The average crystallite size calculated from elastic data is in agreement to that determined from X-ray diffraction data analysis.