Low Compressibility Material Research Articles

Influence of Anisotropic Consolidation on the Instability of Loose Granular Soils Under Undrained and Drained Loading

Previous studies, mostly experimental, have reported conflicting observations on the effect of the initial anisotropic consolidation stress ratio (η<sub>0</sub>) on the stress ratio at the onset of instability (η<sub>f</sub>) for drained and undrained loading that involve static liquefaction. They indicate that as η<sub>0</sub> increases, η<sub>f</sub> could decrease, increase, or remain invariant, albeit without providing potential mechanistic factors. In this study, the anisotropic critical state theory (ACST) is used to investigate potential factors, including compressibility, state, and fabric anisotropy, that can explain the influence of η<sub>0</sub> on η<sub>f</sub> under undrained and drained loading. The assessments consider numerical simulations with the ACST-based SANISAND-F model, insights from SANISAND-F based instability criteria, the instability surface concept, and available experimental observations. Our findings show that compressibility and fabric anisotropy (and its evolution) are key factors in explaining the influence of η<sub>0</sub> on η<sub>f</sub>. In particular, the results show that if fabric evolution is not substantial, an increase in η<sub>0</sub> decreases η<sub>f</sub> for materials with significant compressibility, whereas the effect of η<sub>0</sub> in low compressibility materials is minimal. On the other hand, for materials that promote fabric evolution, the results suggest that the effect of fabric changes counteract compressibility effects, potentially increasing η<sub>f</sub>.

Crystal structures and mechanical properties of tungsten monocarbide predicted by first-principles investigations

The crystal structure of tungsten monocarbide (WC) is researched from 0 to 650 GPa through first principles calculations. The results verify that the experimental structure (hP2-WC) with the space group P6¯m2 is the most stable phase in a wide range of pressure. Above 231 GPa, a new stable structure (space group P63/mmc, hP4-WC) is found to be the most stable phase, and it will transform to a CsCl-type phase (cF8-WC) around 582 GPa. Phonon calculations reveal that the hP4-WC phase is dynamically stable and may be a metastable structure at ambient conditions. The cF8-WC phase possesses dynamical stability above 20 GPa. The hP4-WC phase is a low compressible material with a large bulk modulus of 377 GPa at zero pressure. The hardness values of hP2-WC and hP4-WC at zero pressure are 32 and 21 GPa, respectively, while the cF8-WC phase possesses a hardness of 21 GPa at 20 GPa, implying that these phases are potential hard materials. The temperature–pressure phase boundary of WC is obtained by means of the quasi-harmonic approximation method. As the temperature increases, the transition pressure from hP2-WC to hP4-WC remained nearly unchanged. The transition pressure between hP4-WC and cF8-WC decreases with the increasing temperature.

The dependence of shale permeability on confining stress and pore pressure

We examined the permeability behavior of two Marcellus Shale samples and two Eagle Ford Shale samples using argon gas under multiple confining stresses (PC = 13.8–68.9 MPa) and pore pressures (PP = 1.6–28.2 MPa). We corrected our measured permeability values for the Klinkenberg effect and contoured permeability as a function of PP and PC to obtain the effective stress coefficient for permeability (nk), which scales the influence of PP on permeability relative to PC. We explored the underlying mechanisms controlling nk using two idealized models of a cylindrical capillary tube consisting of low and high compressibility material to model the unique pore structure present in our samples. Finally, we investigated the impact of PP reduction on permeability during production. We show that the permeability is stress-dependent and that nk is formation-dependent. Marcellus Shale samples, with predominantly organic matter hosted pores, have a Klinkenberg-corrected permeability of 11.0 to 1.9 nD (PC - PP = 5.3–33.8 MPa) and nk value of 1.11 and 1.60, respectively. In contrast, Eagle Ford Shale samples, with predominantly inter-particle pores, have Klinkenberg-corrected permeability of 33.6 to 2.0 nD (PC - PP = 13.3–40.8 MPa) and nk value of 0.96 and 0.84, respectively. We infer that the PP change produces considerable pore wall strain relative to the PC change in the Marcellus Shale organic matter pores resulting in nk > 1. In contrast, we infer a smaller pore wall strain for the same PP and PC changes in the Eagle Ford Shale inter-particle mineral pores giving in nk < 1. Our findings will inform models to predict production behavior of reservoirs and may be used to improve recovery efficiency by adopting the best production strategy in unconventional shale reservoirs.

Prediction of scandium tetraboride from first-principles calculations: Crystal structures, phase stability, mechanical properties, and hardness* *Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant Nos. 11704170 and 61705097) and the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR2016AP02 and ZR2016EMP01).

Using the evolutionary methodology for crystal structure prediction, we have predicted the orthorhombic Cmcm and Pnma phases for ScB4. The earlier proposed CrB4-, FeB4-, MnB4-, and ReP4-type structures for ScB4 are excluded. It is first discovered that the Cmcm phase transforms to the Pnma phase at about 18 GPa. Moreover, both phases are dynamically and mechanically stable. The large bulk modulus, shear modulus, and Young’s modulus of the two phases make it an optimistic low compressible material. Moreover, the strong covalent bonding nature of ScB4 is confirmed by the ELF analysis. The strong covalent bonding contributes greatly to its stability.

Low compressible β-BP3N6

Using first principles calculation, the structural and mechanical properties of β-BP3N6, which adopts an orthorhombic structure with space group Pna21 (no. 33), were determined at three different pressure values (0, 20, and 42.4 GPa). The nine independent elastic constants meet all necessary and sufficient conditions for mechanical stability criteria for an orthorhombic crystal. β-BP3N6 shows strong resistance to volume change and hence a potential low compressible material. The Vickers hardness of β-BP3N6 was found to range between 49 and 51 GPa for different external pressures imposed on the crystal. These high values of Vickers hardness imply that β-BP3N6 is a potential superhard material.

Crystal structure prediction of ReN at high pressure: a new incompressible phase

ABSTRACTBased on the swarm-intelligence-based CALYPSO method the NbO, R3m and NiAs phases for ReN are predicted. The R3m phase of ReN at high pressure is firstly found. The structural, mechanical and electronic properties of ReN with the three phases are studied systematically. Moreover, it is also firstly found that pressure stimulated ReN to undergo twice phase transitions, from NbO to R3m phase at 43.3 GPa and from R3m to NiAs phase at 53.6 GPa. The three phases of ReN are verified to be mechanically stable and a promising low-compressible material at ambient conditions. According to the electron density of states and electron localization functions we have found that their structural stability and high hardness is on account of the strong covalent bonding of Re-N and N-N.

Pressure and temperature induced phase transition in WB4: A first principles study

Using an unbiased structure search method based on particle-swarm optimization algorithms in combination with density functional theory calculations, we investigate the phase stability and electronic properties of WB4 under high pressures. Through structural searching as implemented in the CALYPSO code, we obtained the most state hexagonal phase (P63/mmc, named hp10) at ambient condition and a new monoclinic phase (C2/m structure, mp5) at high pressures for WB4. The P63/mmc structure transforms to the C2/m phase at about 71 GPa. Surprisingly, the two phases are both dynamically and mechanically stable at ambient conditions. The high bulk and shear modulus, low Poisson’s ratio for both phases in WB4, place WB4 as a promising low compressible material. Both phases with high hardness are stable due to the strong covalent bonding nature from electronic density of states and electron localization function analysis. To guide experimental finding of more metastable superhard materials, the high pressure high temperature phase diagram of WB4 is established within the quasi-harmonic approximation.

Determination of the consolidation coefficient of low compressibility materials: application to fresh cement based materials

Determination of the consolidation coefficient of low compressibility materials: application to fresh cement based materials

Determination of the consolidation coefficient of low compressibility materials: application to fresh cement-based materials

This paper focuses on the determination of the consolidation characteristics of mineral materials. The main objectives were to improve measurement accuracy and to reduce test duration. Consolidation characteristics govern fluid migration and the evolution of the properties; compressibility, permeability and consolidation coefficient are required to describe hydro-mechanical behaviour. In this paper, a method of consolidation coefficient determination is proposed. After the measurement of compressibility and permeability, the evolution of the consolidation coefficient as a function of void ratio was computed. The method was applied to two different mineral materials: a clay material (kaolin paste) and a fresh cement paste. The results obtained were compared with commonly used methods described in national standards; comparison showed that the developed procedure is quicker and provides more reliable results.

Structural Stability and Elastic and Electronic Properties of W2X (X = B, C, N): First-Principles Investigations

The structural stability, elastic property, and mechanical stability of W2X (X = B, C, N) are investigated using first-principles calculations with density functional theory. The calculations show that Re2N-type W2N is both thermodynamically and elastically stable. The calculated elastic properties indicate that W2X compounds are potential low-compressibility materials. The large elastic modulus, low Poisson’s ratios, small B/G ratios, and high Debye temperatures of thecompounds indicate that they are potential hard materials. The analysis of the density of states and electronic localization function provides further understanding of the elastic and chemical properties of these compounds.

The Fermi surface of a superconductor: OsB2

AbstractOsmium diboride has been known for some time as a low compressibility material and a superhard material. It is suitable for hard coating applications. It is also a superconductor below 2.1 K. Using first‐principles calculations, the author investigated the geometry of its Fermi surface (FS) and calculated the related physical quantities. The theoretical results are used to predict the frequencies of the Shubnikov–de Haas quantum oscillations. Comparison with recent measurements of the magneto‐resistance oscillations in osmium diboride is made.magnified imageThe picture shows the FS of OsB2 consisting of three sheets: a pair of two nested ellipsoidal surfaces and a corrugated tubular surface.(© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Density functional theory study of hexagonal carbon phases

It is reported frequently that the new carbon phases may be harder than diamond (Wanget al 2004 Proc. Natl Acad. Sci. 101 13699 and Mao et al 2003 Science 302 425). However,the mechanism is still unclear. In this paper we systematically investigate the structural,electronic, and mechanical properties of the diamond polytypes using first-principlesdensity functional calculations. The results show that the bulk modulus and shear modulusfor the hexagonal form of diamond approach those of diamond, suggesting they might behard and low compressibility materials. According to the semiempirical method forhardness based on the Mulliken overlap population, the hardnesses for hexagonal formshave been evaluated and compared to diamond. The results indicate that thesephases are superhard. More importantly, the bonds in some specific directions ofthe hexagonal phases are harder than those in diamond, which may lead to thenoticeable indentation marks on the diamond anvils observed in experiments.

Pressure-Induced Phase Transition of Ruthenium Diboride

Based on the first-principles calculations, we firstly predict that RuB2 undergoes a phase transition from the orthorhombic phase to the hexagonal phase with a volume collapse of 1% when the applied pressure is 15.7 GPa. The values of calculated elastic moduli indicate that RuB2 and RuN2 are low compressibility materials. Based on the calculated electronic density of states and valence charge density distribution, the bonding nature of RuB2 is examined to obtain a deeper insight into the physical origin of the mechanical properties. The metallicity and high elastic moduli of RuB2 and RuN2 suggest that they are potential hard conductors.

Evidence for a low-compressibility carbon nitride polymorph elaborated at ambient pressure and mild temperature

Superhard materials like diamond are essential for abrasive or cutting tool applications. In this way, carbon nitrides are of relevant interest because they are expected to exhibit exceptional mechanical properties, high values of bulk modulus being predicted. A smart and simple method was used to synthesize carbon nitrides and allowed elaborating a low-compressibility polymorph. The processing consists in the decomposition of commercial thiosemicarbazide (H 2NC(S)N 2H 3) powder at ambient pressure and 600 °C under nitrogen flow. Besides the presence of a graphitic C 3N 4 phase, a nanocrystalline material is obtained and is identified as a cubic carbon nitride with a cell parameter of 3.163 Å. Its impressive bulk modulus of 355 GPa propels it as a challenger for cubic boron nitride among low-compressibility materials. Thus, we prove that, in accordance with previous numerous theoretical predictions, crystalline carbon nitrides exhibit exceptional compressibility behaviour. Moreover, our synthesis strategy evidences that, despite usual admitted considerations, severe and expensive pressure and temperature conditions are not mandatory to elaborate low-compressibility covalent materials, which could give new insights for their development.

Elasticity properties of the low-compressible material ReB 2

By means of ab initio plane-wave pseudopotential density functional theory, the equilibrium structure parameters, the bulk module and shear module, and the elastic constants of ReB 2 have been investigated. Our results are consistent with the experimental and previous theoretical data. Comparing it with other hard materials, we conclude that ReB 2 is a sort of low-compressible material. The parameters of anisotropy are all larger than 1, which indicates that the hexagonal ReB 2 is anisotropic. The elastic constant c 33 is larger than c 11 at all pressure points, which shows that the compressibility of ReB 2 in the z direction is larger than that in the x and y directions.

Structural, Elastic, and Electronic Properties of ReB2: A First‐Principles Calculation

The structural, elastic, and electronic properties of the hard material ReB2 have been investigated by means of density functional theory. The calculated equilibrium structural parameters of ReB2 are in agreement with the experimental results. Our result of bulk modulus shows that it is a low compressible material. Furthermore, the elastic anisotropy is discussed by investigating the elastic stiffness constants. The charge density and the electronic properties indicate that the covalent bonding of Re‐B and B‐B plays an important role in formation of a hard material. The good metallicity and hardness of ReB2 might serve as hard conductors.

A new superhard material: Osmium diboride OsB 2

Superhard materials have many industrial applications, wherever resistance to abrasion and wear are important. The synthesis of new superhard materials is one of the great challenges to scientists. We re-examined the phase diagram of the binary osmium–boron system and confirmed the existence of two hexagonal phases, OsB 1.1, Os 2B 3, and an orthorhombic phase, OsB 2. Almost nothing is known about the physical properties of osmium borides. Microhardness measurements show that OsB 2 is extremely hard. Ab initio calculations show that this is due to formation of covalent bonds between boron atoms. OsB 2 is also a low compressibility material. It can be used as hard coating.

Experimental and Ab-initio Investigations of Osmium Diboride

AbstractMore than half a century after their discovery, almost nothing is known about the physical properties of osmium borides, thought their structures have been clearly identified in the early sixties. We re-examined the phase diagram of the binary system osmium-boron and confirm the existence of two hexagonal phases, OsB1.1, Os2B3 and an orthorhombic phase, OsB2. Our microhardness measurements show that the synthesized OsB2 is extremely hard. In addition, first-principles calculations have been conducted to investigate its physical properties. It is shown that OsB2 is also a low compressibility material. Most of the transition metal borides have already found applications as in protective armor, nuclear reactors, reinforcement, etc. OsB2 can be used in applications like hard coating.

Ab initiostudy of high-pressure behavior of a low compressibility metal and a hard material: Osmium and diamond

We performed Density-Functional electronic structure calculations in order to investigate the high pressure behavior of Os beyond what is tractable experimentally with a diamond-anvil cell. In addition to the room-temperature and pressure structure hcp, two hypothetical structures of Os have been considered: fcc and $\ensuremath{\omega}$ (hexagonal phase with three atoms by unit cell). Phase transitions are suggested by these calculations. For calculating the bulk modulus, the reciprocal of the compressibility, of Os and that of diamond, the computed total energies vs volume curves were fit to three different equations of state. Several volume ranges have been considered during the fitting procedure. First, it is shown that the claim of Cynn and co-workers [Phys. Rev. Lett. 88, 135701 (2002)] is confirmed at weak compression. Osmium is less compressible than diamond which is known as the hardest and the least compressible material. However, with increasing pressure osmium becomes more compressible than diamond. At strong compression, osmium transforms to the $\ensuremath{\omega}$ phase. It is also shown that the reconstructive phase transition $\mathrm{hcp}\ensuremath{\rightarrow}\mathrm{fcc}$ could be induced by cooling in this low compressibility material.

A New Class of Low Compressibility Materials: Clathrates of Silicon and Related Materials

We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.