Change In Bulk Modulus Research Articles

Lattice Thermal Conductivities of Yb(Cd1-xMgx)2Sb2 Analyzed via Debye-Callaway Model

YbCd2Sb2-based Zintl phases have been identified as promising materials for thermoelectric applications due to their high Seebeck coefficient and electrical conductivity. However, their high thermal conductivity limits their overall thermoelectric performance. To address this, Mg has recently been introduced as an alloying element at Cd atomic sites to reduce the lattice thermal conductivity of YbCd2Sb2 . Zhang et al. have reported a high zT (a figure-of-merit for the thermoelectric performance) of 1.4 at 700 K in Yb(Cd0.8Mg0.2)2Sb2. They have demonstrated that the high zT is due to significantly suppressed phonon transport, in other words, low lattice thermal conductivity. They attributed the significantly low lattice thermal conductivity to severely distorted lattices that could not be described even with the Debye-Callaway model. Here, the Debye-Callaway model and Callaway-von Baeyer model have been utilized to evaluate the effect of Mg alloying on the lattice thermal conductivity of Yb(Cd1-xMgx)2Sb2 (x = 0, 0.1, 0.2) by estimating their theoretical lattice thermal conductivities. We found that appropriately fitting the parameter included in the phonon relaxation rate (of the Debye-Callaway model), which represents a fractional change of bulk modulus to that of local bond length, could describe the significantly suppressed lattice thermal conductivities of Yb(Cd1-xMgx)2Sb2 (x = 0, 0.1, 0.2).

Influence of pressure-induced formation of dihydrogen bonds on lattice parameters, volume, and vibrational modes of ammonia borane.

The high-pressure phase of ammonia borane (NH3BH3) observed at ∼1.2GPa has been reported to result in pressure-induced formation of dihydrogen bonds at ∼4GPa. In this study, we performed high-pressure x-ray diffraction measurements on the high-pressure phase (up to ∼10.2GPa) using a He hydrostatic pressure medium to examine the influence of the formation of dihydrogen bonds on the lattice parameters and unit cell volume of NH3BH3. We observed a unique behavior in the pressure dependence of lattice parameters close to the pressure at which the dihydrogen bond was formed. The lattice parameters demonstrated hysteresis curves under compression and decompression conditions but the unit cell volume did not. Moreover, the pressure dependence of the unit cell volume could not be expressed using a single Birch-Murnaghan equation within an acceptable margin of error, thus suggesting a change in bulk modulus under compression. These results are considered to have originated from the pressure-induced formation of dihydrogen bonds. Moreover, high-pressure Raman scattering measurements and a simulation using density functional theory calculations revealed the vibrational modes of the high-pressure phase of NH3BH3. The results demonstrated that librational modes were enhanced by forming dihydrogen bonds. Moreover, the intramolecular stretching modes of BN, BH, and NH monotonically shifted with pressure, while the symmetrical in-plane bending modes of BH3 and NH3 split irrespective of the formation of dihydrogen bonds.

Evaluating the theoretical elastic properties of Li-Mn ferrites: A new approach

The ability to select the most suited ferrite materials for a given application necessitates understanding of their elastic characteristics. In the present communication, the elastic properties of Li–Mn–Co, Li–Mn–Ni and Li–Mn–Cu ferrite series were evaluated and predicted in terms of compositional parameters, for the first time. This has been carried out on the basis of Makishima-Mackenzie's theory, Rocherulle et al. model as well as Abd El-Moneim and Alfifi's approach. The compositional factors that are most important were assessed and correlated with experimental elastic properties. Moreover, the theoretically calculated values of elastic moduli, micro-hardness, and Poisson's ratio were compared with those determined experimentally from ultrasonic velocities and density measurements. It has been found that Abd El-Moneim and Alfifi's approach can be applied successfully to predict changes in bulk modulus of the investigated ferrite series. The calculated packing densities from Makishima-Mackenzie's theory and Rocherulle et al. model are suitable for predicting the data of experimental Poisson's ratio. A reasonable agreement between theoretical and experimental data of elastic moduli, and micro-hardness was achieved on the basis of Makishima-Mackenzie's theory.

Moduli variations in two-phase fluid rocks considering squirt flow and patchy saturation

The complex pore structure and fluid distribution in underground rocks bring difficulties to rock physics modeling and reservoir interpretation. The existence of cracks and ellipsoidal pores will cause squirt flow during wave propagation, and the fluid may be present as patchy saturation. By considering the effects of both squirt flow and patchy saturation, a new rock physics model is proposed. The fluids in inclusions include a soft fluid such as gas and a stiff fluid such as water. The novelty is that an explicit expression of patch saturation with frequency is introduced. Thus, the proposed model is helpful to analyze the variations of moduli with frequency caused by squirt flow and patchy saturation simultaneously. By comparison, the proposed model matches well with existed boundary models and covers all possible behavior of the moduli. Then, variations in moduli with water saturation and frequency are analyzed in detail, as well as the impact of patchy saturation on the attenuation induced by the squirt flow. The analysis shows that a small amount of gas contained in inclusions can cause a large change in moduli, especially the bulk modulus. The effect of patchy saturation on the moduli increases with the increasing frequency and when the frequency is low, the effect only occurs at very high water saturation. Besides, at high water saturation, the squirt flow can cause a sharp change in bulk modulus. The proposed model is helpful for understanding wave propagation in partially saturated rock with cracks.

Effect of pressure on mechanical and thermodynamic properties of Al<sub>7</sub>Cu<sub>2</sub>Fe phase

The band structures and elastic anisotropy of Al₇Cu₂Fe phase under various pressures are studied by using the Vienna ab-initio simulation package (VASP) based on density functional theory. The results show that Al₇Cu₂Fe phase is still metallic in the pressure range of 0 to 50 GPa and the pressure can improve the expansion of atomic orbital in the energy band. The elasti anisotropy in (100) and (010) planes of Al₇Cu₂Fe phase enhances with the increase of pressure, while the elasti anisotropy in (110) planes shows a fluctuating upward trend from 0 GPa to 50 GPa. Based on the quasi-harmonic Debye model, the changes of bulk modulus (B), Debye temperature (Θ_{<italic>D</italic>}), heat capacity (C_v and C_p) and thermal expansion coefficient (α) of Al₇Cu₂Fe phase with pressure and temperature are studied. The effects of applied pressure and temperature on thermodynamic properties of the Al₇Cu₂Fe phase is opposite. The values of B and Θ_{<italic>D</italic>} decrease with temperature and increase with the pressure. In addition, the variation trends of C_v, C_p and α under pressure and temperature are basically the same.

Eshelby instability pressure for nucleation of a phase change defect

The existence of a nucleation instability is demonstrated at the vanishing of the path-independent M integral in linear anisotropic elasticity so that a region that is arbitrarily small can grow at constant potential energy. It yields a quadratic equation for the critical pressure to balance the Eshelby dissipation and nucleate an inclusion undergoing both change in density and change in bulk modulus, and is independent of the radius of the defect. Regarding the shape of nucleation, the expression from Noether's theorem allows also a symmetry breaking mode as a penny-shape “pancake”, and by comparison of the M integrals for the pancake and the sphere, it would require a greater loss of potential energy of the system to nucleate a pancake, but less to grow it larger.

Quasi‐static confined uniaxial compaction of granular alumina and boron carbide observing the particle size effects

AbstractThe quasi‐static confined uniaxial compaction of granular alumina and boron carbide was studied, and the effect of triaxial stress on the materials as a function of increasing particle size was observed. The average particle sizes studied for granular alumina were 170 ± 63, 230 ± 55, 330 ± 67, and 450 ± 83 µm. The average particle size studied for granular boron carbide were 170 ± 40, 190 ± 34, 320 ± 59, and 470 ± 90 µm. The material response at hydrostatic pressure as a function of porosity, the bulk modulus as a function of hydrostatic pressure, and the transmission ratio as a function of applied load was evaluated for increasing particle size. For alumina, the increase in particle size resulted in an increase in strength for a fixed porosity, the bulk modulus of this material did not show clear particle size‐dependent trends, and the transmission ratio increased with increase in particle size. Conversely, for granular boron carbide, the hydrostatic pressure‐porosity curve shifted to the right with increasing particle size, the change in bulk modulus increased with increasing particle size, and no clear particle size‐dependent trends were observed when looking at the transmission ratio during the experiment. Post‐experiment scanning electron microscopy revealed that alumina powder fragmented from elongated shapes to block‐like structures, while boron carbide powder appeared more circular before the experiments and fragmented into smaller comminuted pieces. This paper discusses the implication of the work in the context of the limited experimental data in the field and the modeling of granular advanced ceramics behavior.

Analysis and prediction for elastic properties of quaternary tellurite Ag2O–V2O5–MoO3–TeO2 and WO3–B2O3–MgO–TeO2 glasses

Analysis and prediction have been carried out for elastic properties of quaternary tellurite xAg2O–(35–x)(0.5V2O5–0.5MoO3)–65TeO2 and xWO3–(75–x)B2O3–10MgO–15TeO2 glass systems. This has been achieved on the basis of Makishima–Mackenzie's theory, Rocherulle et al. model and Abd El-Moneim and Alfifi's approaches. It has been found that, both Makishima–Mackenzie's theory and Abd El-Moneim and Alfifi's approaches can be applied successfully to predict the compositional changes in elastic moduli of WO3–B2O3–MgO–TeO2 glasses. In case of Ag2O–V2O5–MoO3–TeO2 glasses, the best correlation between theoretical and experimental elastic moduli can be achieved if the effect of the basic structural units TeO4, TeO3, VO4, VO5, MoO4 and MoO6 is taken into account. In compared to Makishima-Mackenzie's theory, Rocherulle et al. model appears to be more applicable for predicting Poisson's ratio. Moreover, the compositional changes in bulk modulus are predictable from the molar volume.

Numerical prediction of in situ horizontal stress evolution in coalbed methane reservoirs by considering both poroelastic and sorption induced strain effects

As an organic-rich dual-porosity medium, coal distinctively manifests unique deformation and permeability evolution behaviors due to the adsorption/desorption induced matrix swelling and/or shrinkage. Being different from the elastic strain, the sorption induced strain shows a non-linear behavior with continuous sorbing gas injections, and these two types of strains are competing process of the volumetric change for coal. With primary gas depletion, the horizontal stress decreases within coalbed methane (CBM) reservoirs due to the in situ boundary confinement, namely, uniaxial strain boundary condition. However, the coal solid skeleton deformative behavior with primary depletion is not specifically clear due to the difficulty both in field and lab measurement of horizontal stress. This paper, based on a gas-solid coupling model incorporated with swelling effect, focuses on the horizontal stress variation with respect to the primary depletion under uniaxial strain condition. It was found the simulated results of volumetric change under the hydrostatic condition well agree with experimental data. The increase of horizontal stress for methane is four times as for helium, with injected pore pressure at 7.6 MPa. Also, the conceptual dual-material model is proposed to demonstrate the competing process of compression and swelling, which leads to the bulk modulus change of coal. It was found the Biot's coefficient can be larger than unity and be a variable during the primary depletion due to the swelling induced equilibrium negative bulk modulus.

Mechanical properties of Fe rich Fe–Si alloys: ab initio local bulk-modulus viewpoint

Fe-rich Fe–Si alloys show peculiar bulk-modulus changes depending on the Si concentration in the range of 0–15 at.%Si. In order to clarify the origin of this phenomenon, we have performed density-functional theory calculations of supercells of Fe–Si alloy models with various Si concentrations. We have applied our recent techniques of ab initio local energy and local stress, by which we can obtain a local bulk modulus of each atom or atomic group as a local constituent of the cell-averaged bulk modulus. A2-phase alloy models are constructed by introducing Si substitution into bcc Fe as uniformly as possible so as to prevent mutual neighboring, while higher Si concentrations over 6.25 at.%Si lead to contacts between SiFe8 cubic clusters via sharing corner Fe atoms. For 12.5 at.%Si, in addition to an A2 model, we deal with partial D03 models containing local D03-like layers consisting of edge-shared SiFe8 cubic clusters. For the cell-averaged bulk modulus, we have successfully reproduced the Si-concentration dependence as a monotonic decrease until 11.11 at.%Si and a recovery at 12.5 at.%Si. The analysis of local bulk moduli of SiFe8 cubic clusters and Fe regions is effective to understand the variations of the cell-averaged bulk modulus. The local bulk moduli of Fe regions become lower for increasing Si concentration, due to the suppression of bulk-like d–d bonding states in narrow Fe regions. For higher Si concentrations till 11.11 at.%Si, corner-shared contacts or 1D chains of SiFe8 clusters lead to remarkable reduction of local bulk moduli of the clusters. At 12 at.%Si, on the other hand, two- or three-dimensional arrangements of corner- or edge-shared SiFe8 cubic clusters show greatly enhanced local bulk moduli, due to quite different bonding nature with much stronger p-d hybridization. The relation among the local bulk moduli, local electronic and magnetic structures, and local configurations such as connectivity of SiFe8 clusters and Fe-region sizes has been analyzed. The ab initio local stress has opened the way for obtaining accurate local elastic properties reflecting local valence-electron behaviors.

Effects of strain rate and moisture content on the behaviour of sand under one-dimensional compression

The influence of strain rate and moisture content on the behaviour of a quartz sand was assessed using high-pressure quasi-static (10−3 s−1) and high-strain rate (103 s−1) experiments under uniaxial strain. Quasi-static compression to axial stresses of 800 MPa was carried out alongside split Hopkinson pressure bar (SHPB) experiments to 400 MPa, where in each case lateral deformation of the specimen was prevented using a steel test box or ring, and lateral stresses were recorded. A significant increase in constrained modulus was observed between strain rates of 10−3s−1 and 103s−1, however a consistently lower Poisson’s ratio in the dynamic tests minimised changes in bulk modulus. The reduction in Poissons ratio suggests that the stiffening of the sand in the SHPB tests is due to additional inertial confinement rather than an inherent strain-rate dependence. In the quasi-static tests the specimens behaved less stiffly with increasing moisture content, while in the dynamic tests the addition of water had little effect on the overall stiffness, causing the quasi-static and dynamic series to diverge with increasing moisture content.

Guiding ab initio calculations by alchemical derivatives.

We assess the concept of alchemical transformations for predicting how a further and not-tested change in composition would change materials properties. This might help to guide ab initio calculations through multidimensional property-composition spaces. Equilibrium volumes, bulk moduli, and relative lattice stability of fcc and bcc 4d transition metals Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag are calculated using density functional theory. Alchemical derivatives predict qualitative trends in lattice stability while equilibrium volumes and bulk moduli are predicted with less than 9% and 28% deviation, respectively. Predicted changes in equilibrium volume and bulk moduli for binary and ternary mixtures of Rh-Pd-Ag are in qualitative agreement even for predicted bulk modulus changes as large as +100% or -50%. Based on these results, it is suggested that alchemical transformations could be meaningful for enhanced sampling in the context of virtual high-throughput materials screening projects.

First-principles study on the effect of alloying elements on the elastic deformation response in β-titanium alloys

Theoretical deformation response of hypothetical β-titanium alloys was investigated using first-principles calculation technique under periodic boundary conditions. Simulation was carried out on hypothetical 54-atom supercell of Ti–X (X = Cr, Mn, Fe, Zr, Nb, Mo, Al, and Sn) binary alloys. The results showed that the strength of Ti increases by alloying, except for Cr. The most effective alloying elements are Nb, Zr, and Mo in the current simulation. The mechanism of bond breaking was revealed by studying the local structure around the alloying element atom with respect to volume change. Moreover, the effect of alloying elements on bulk modulus and admissible strain was investigated. It was found that Zr, Nb, and Mo have a significant effect to enhance the admissible strain of Ti without change in bulk modulus.

Structural investigation ofNp2Co17and analogue compounds under pressure

The structural behavior of Np2Co17 is investigated by means of high-pressure diamond-anvil compression measurements and is compared with that of the isostructural compounds Lu2Co17 and Lu2Ni17. The Th2Ni17-type hexagonal crystal structure is preserved with no measurable discontinuous volume collapses up to the highest achieved pressure, p = 43 GPa. For Np2Co17, fits to the Birch-Murnaghan and Vinet equations of state give values of the isothermal bulk modulus and its pressure derivative of B-0 = 286 GPa and B-0' = 3, revealing that this Np compound is a highly incompressible solid with stiffness comparable to that of superhard covalently bonded materials. For the Lu2T17 (T = Co, Ni) compounds, the measured bulk modulus changes from B-0 = 137 GPa for T = Co to B-0 = 257 GPa for T = Ni. The isothermal equation of state for the studied compounds are in excellent agreement with the results of ab initio fully relativistic, full-potential local spin-density functional calculations. Theoretical estimates of the bulk modulus are given also for Np2Ni17, for which B-0 is predicted to assume values intermediate between those measured for Lu2Ni17 and Np2Co17.

Sorption and changes in bulk modulus of coal — experimental evidence and governing mechanisms for CBM and ECBM applications

Recent studies report the stiffness of coal changes, when exposed to sorbing gases such as CH4 and CO2. Although this effect might be potentially important for predicting the in situ mechanical behavior of coal seams during CH4 production or CO2 sequestration, very little understanding exists on the underlying mechanisms. In this paper, we report a single, long-duration mechanical test on a large, cube-shaped coal sample (Ruhr Basin, Germany). The sample was subjected to isostatic loading and unloading; first in the evacuated state (as received), and then each time after exposing it to pressurized, non-adsorbing He, or sorbing N2, CH4, and CO2. We find that exposure to sorbing gases led to swelling, which introduced a hysteresis in the stress–strain trajectory followed during mechanical loading. This hysteresis was almost absent in the evacuated state, and its magnitude depended strongly on the amount of adsorption-induced swelling exhibited by the sample. The apparent bulk modulus determined here for the CO2-equilibrated state was approximately 25% lower compared to the evacuated state. We qualitatively consider mechanisms that affect the elastic behavior of coal at the matrix and bulk scale, and argue that the observed effects are a combined effect of 1) changes in surface roughness at cleat interfaces and microfractures, and 2) a thermodynamic coupling between stress state, sorption capacity and swelling strain. The changes in stiffness relate to fluid–rock interaction effects, as well as to the presence of fractures, and hence not to the inherent elastic properties of the solid phase itself. We discuss the characteristics of each mechanism and the connection of the proposed mechanisms with formation-scale geomechanical effects of coal layers under conditions relevant to CBM/ECBM.

2D22 Experimental investigation of effective bulk modulus of oil with entrained air bubbles(The 12th International Conference on Motion and Vibration Control)

Although hydraulic systems are compact and have high output power, the demand for further downsized systems with increased output power has been on the rise in recent years. The operating pressures of hydraulic systems have recently been increasing, and condition monitoring of the properties of hydraulic fluid has been one of the most important technical issues. Bulk modulus is a property that indicates the compressibility of a hydraulic fluid. Hydraulic fluids typically become aerated during use, and a certain amount of air is always present in a hydraulic fluid. Aeration strongly influences the bulk modulus of hydraulic fluid because air is significantly more compressible than oil. Entrained air in the form of bubbles reduces the effective bulk modulus. Furthermore, air bubbles entrained in hydraulic fluids cause numerous problems in hydraulic systems. Active bubble elimination devices that use swirl flow capable of eliminating air bubbles from hydraulic fluid have been proposed and developed by the authors. We focus on the relationship between the change in bulk modulus and the elimination of air bubbles from hydraulic fluid. Hydraulic fluid from which bubbles have been eliminated is sampled in a vessel and experimentally pressurized by a servo piston. The volume and pressure change of the sampled oil is measured, and bulk modulus change is calculated to evaluate the bubble elimination. We conclude that the change in bulk modulus of the bubble-eliminated oil influences system performance with respect to positioning, power loss, response time, and stability in hydraulic systems.

Experimental investigation of change in sheet resistance and Debye temperatures in metallic thin films due to low-energy ion beam irradiation

We present a systematic experimental investigation of low-energy (0–1 kV) ion irradiation induced changes in sheet resistivity and Debye temperatures in metallic nano-films of Ag, Cu and Al of thickness d/λo ∼ 2–5, where d is the film thickness and λo is the bulk mean free path, as a function of ion beam induced defects and impurities in a controlled manner. Ions of both atomic (Ne, Ar and Kr) and molecular (H2, N2) gases are employed in the investigation and the number of defects and impurities in the nano-film can be varied in a controlled manner by varying the ionic mass number (1–84) and beam fluence (8.7 × 1015–1.4 × 1016 ions cm−2). Low-temperature measurements are carried out for pristine and irradiated films to obtain the residual sheet resistance (RRS). An empirical formula relating the variation of RRS with beam fluence and ionic mass number is proposed for the first time. The change in RRS is due to the large diffusion of the impurities inside the nano-films as confirmed from energy dispersive x-ray spectroscopy. The Debye temperature (ΘD) is determined from Bloch–Grüneisen fitting of the temperature variation of sheet resistance data and it is found that ΘD decreases with increase in both fluence and ionic mass number arising primarily from the change in bulk modulus of the nano-film.

Histology-Based Simulations of Ultrasound Imaging: Methodology

Simulations of ultrasound (US) images based on histology may shed light on the process by which microscopic tissue features translate to a US image and may enable predictions of feature detectability as a function of US system parameters. This technical note describes how whole-slide hematoxylin and eosin-stained histology images can be used to generate maps of fractional change in bulk modulus, whose convolution with the impulse response of the US system yields simulated US images. The method is illustrated by two canine mastocytoma histology images, one with and the other without signs of intra-operative hemorrhaging. Quantitative comparisons of the envelope statistics with corresponding clinical US images provide preliminary validation of the method.

The Effects of Temperature and Pressure on the Porosity Evolution of Flechtinger Sandstone

A porosity change influences the transport properties and the elastic moduli of rock while circulating water in a geothermal reservoir. The static and dynamic elastic moduli can be derived from the slope of stress–strain curves and velocity measurements, respectively. Consequently, the acoustic velocities were measured while performing hydrostatic drained tests. The effect of temperature on static and dynamic elastic moduli and porosity variations of Flechtinger sandstone was investigated in a wide range of confining pressure from 2 to 55 MPa. The experiments were carried out in a conventional triaxial system whereas the pore pressure remained constant, confining pressure was cycled, and temperature was increased step wise (25, 60, 90, 120, and 140 °C). The porosity variation was calculated by employing two different theories: poroelasticity and crack closure. The porosity variation and crack porosity were determined by the first derivative of stress–strain curves and the integral of the second derivative of stress–strain curves, respectively. The crack porosity analysis confirms the creation of new cracks at high temperatures. The porosity variation was increasing with an increase in temperature at low effective pressures and was decreasing with a rise in temperature at high effective pressures. Both compressional and shear wave velocities were increasing with increasing pressure due to progressive crack closure. Furthermore, the thermomechanical behavior of Flechtinger sandstone was characterized by an inversion effect where the sign of the temperature derivative of the drained bulk modulus changes.

S111025 油中気泡の除去が油の特性変化におよぼす影響([S111-02]第19回卒業研究コンテスト(2))

Although hydraulic systems are compact and have high output power, there have been demands for further downsizing and higher output power in recent year. The operating pressure of hydraulic systems has been increasing, and thermal load and cavitation have occurred significantly as pressure has increased. Bubbles generated by cavitation remain submerged in hydraulic oil. The bubbles have a significant effect on bulk modulus because air is much more compressible than oil. The entrained air in the form of bubbles reduces the effective bulk modulus. Furthermore, air bubbles entrained in hydraulic fluids cause many problems in hydraulic systems. Active bubble elimination device using swirl flow capable of eliminating air bubbles from hydraulic fluid has been proposed and developed by our smart & clean hydraulic project. In this paper, we focus on the relation between the bulk modulus change and the bubble elimination from hydraulic fluid. Hydraulic fluid eliminated bubbles are sampled in a vessel and experimentally pressurized by a servo-piston. The volume and pressure change of the sampled oil is measured and bulk modulus change is calculated to evaluate the bubble elimination. We can conclude that the bulk modulus change of oil with bubble elimination affects system performance in relation to positioning, power loss, response time, and stability in hydraulic systems.