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This study proposes a simple yet effective dynamic method that can nondestructively evaluate the elastic properties of homogeneous isotropic solid materials. Like some dynamic methods, such as resonance ultrasound spectrometry and impulse excitation technique, the proposed method consists of two steps: experimentally acquiring the specimen's natural frequencies and numerically calculating the elastic properties. Compared with the existing methods, the proposed method has much lower requirements on all four aspects of experimental operations: specimen preparation, specimen positioning, vibration excitation, and vibration detection. An inverse method based on finite element modal analysis is proposed to calculate the specimen's elastic properties, and it can deliver optimal estimations with high precision and accuracy. The performance of the proposed method was assessed using the well-established sound speed-based dynamic method, i.e., ultrasound pulse-echo testing. Taking a square aluminum specimen as an example, the differences in the measurements of Young's modulus and Poisson's ratio between these two methods are 2.25% and −2.07%, respectively; the differences in the measurements of shear modulus and bulk modulus are 0.01% and −1.46%, respectively. In summary, the proposed method provides a cheaper and experimentally simpler approach to determining the elastic properties of solid materials while maintaining accuracy and reliability similar to the established methods, which typically require sophisticated, costly equipment. [ABSTRACT FROM AUTHOR]

Multi-principal component transition metal (TM) diborides represent a class of high-entropy ceramics (HECs) that have received considerable interest in recent years owing to their promising properties for extreme environment applications that include thermal/ environmental barriers, hypersonic vehicles, turbine engines, and next-generation nuclear reactors. While the addition of chemical disorder through the random distribution of TM elements on the cation sublattice has offered opportunities to tailor elastic stiffness and hardness, the effects of irradiation-induced structural damage on the physical properties of these complex materials have remained largely unexplored. To this end, changes in the hardness and elastic moduli of a high-entropy TM diboride (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 and three of its quaternary subsets following irradiation with 10 MeV gold (Au) ions to fluences of up to 6 × 1015 Au cm−2 are investigated at the micrometer and sub-micrometer length-scales via the dispersion of laser-generated surface acoustic waves (SAW) and nanoindentation, respectively. The nanoindentation measurements show that the TM diborides exhibit an initial increase in hardness following irradiation with energetic Au ions, with a subsequent decrease in hardness following further irradiation. One quaternary composition, (Hf1/3Ta1/3Ti1/3)B2, exhibits a notable exception to the trend and continues to exhibit an increase in hardness with ion irradiation fluence. Although differences in the absolute values of the effective elastic moduli obtained from the measured SAW dispersion and nanoindentation are observed (and attributed to microstructural variations at the measurement length-scale), both techniques yield similar trends in the form of an initial reduction and subsequent saturation in the elastic modulus with increasing ion irradiation fluence. The quaternary TM diboride (Hf1/3Ta1/3Ti1/3)B2 again exhibits a departure from this trend. The high-entropy TM diboride (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 exhibits the greatest recovery in hardness and modulus when irradiated to high ion fluences following initial changes at low fluence, indicating superior resistance to radiation-induced damage over its quaternary counterparts. Opportunities for designing HECs with superior hardness and modulus for enhanced radiation resistance (compared to their single constituent counterparts) by tailoring chemical disorder and bond character in the lattice are discussed. [ABSTRACT FROM AUTHOR]

Ceramic materials are widely used in armor or protective structures, providing weight saving at equivalent performance in comparison to their steel counterparts. Plate-impact experiments are commonly used to investigate the dynamic behavior of ceramics under compressive loading. Using the particle velocity measured at the back of the target, some mechanical properties such as the Hugoniot elastic limit (HEL) as well as the Hugoniot curve of the material can be deduced. Nevertheless, these tests do not provide a direct measurement of the plastic hardening (post-HEL) behavior of the target. In the present work, an experimental shockless plate-impact configuration was developed and implemented to conduct a Lagrangian analysis. This configuration relies on the use of a wavy-machined flyer plate impacting a target made of a buffer, two ceramic plates of different thicknesses, and two window plates as backing. First, the use of wavy flyer plates to generate a loading ramp was validated by considering the impact of the wavy-machined flyer plate against a target, both made of 316L steel. A numerical analysis of this test was developed to confirm the pulse-shaping effect observed experimentally. Next, a ceramic, F99.7 alumina was subjected to the shockless plate impact test in Lagrangian configuration considering the same steel as a buffer and flyer plate material. These tests coupled with Lagrangian analysis enable the curve of axial-stress vs axial-strain beyond the isentropic elastic limit (IEL) to be deduced. The experimental data allow identifying the parameters of an elastoplastic with strain-hardening model to describe the behavior of the tested alumina. [ABSTRACT FROM AUTHOR]

At the line of triple contact of an elastic body with two immiscible fluids, the body is subjected to a force concentrated on this line, the fluid–fluid surface tension. In the simple case of a semi-infinite body, limited by a plane, a straight contact line on this plane, and a fluid–fluid surface tension normal to the plane, the classical elastic solution leads to an infinite displacement at the contact line and an infinite elastic energy. By taking into account the body–fluid surface tension (i.e., isotropic surface stress) and applying Kolosov's approach of plane strain elasticity, we present a new and simple expression of the solution concerning the semi-infinite body, which gives a finite displacement and a ridge at the contact line, and finite elastic energy. A detailed description of the displacements, strains, and stresses in the neighborhood of the contact line is given. This solution also shows that Green's formulae, in the volume and on the surfaces, are valid (these formulae play a central role in the theory). [ABSTRACT FROM AUTHOR]

The thermal transport and elastic properties of materials are often measured using the laser-induced transient grating spectroscopy (TGS) technique. The analysis of the TGS signal usually involves fitting well-known expressions, derived assuming the limiting cases of opaque or transparent materials, to the measured data. In this paper, the system of thermoelastic equations is analytically solved for an isotropic homogeneous material assuming finite laser penetration depth, which is an important consideration when the penetration depth is on the order of the acoustic wavelength. The need to use such a solution is discussed and compared to the expression for opaque material. The solution is benchmarked against TGS signal measured on single-crystal silicon with {100} surface orientation and is found to significantly improve the accuracy of the calculated thermal diffusivity as compared to using the expression for opaque material. [ABSTRACT FROM AUTHOR]

Constitutive models are essential for describing the mechanical behavior of materials under high temperatures and pressures, among which the Steinberg–Guinan (SG) model is widely adopted. Recent work has discovered a peculiar dual anomaly of compression-induced softening and heating-induced hardening in the elasticity of compressed vanadium [Phys. Rev. B 104, 134102 (2021)], which is beyond the capability of the SG model to describe. In this work, a modified SG elasticity constitutive model is proposed to embody such an anomalous behavior. Elemental vanadium is considered as an example to demonstrate the effectiveness of this improved model in describing the dual anomalies of elasticity. This new SG elasticity model can also be applied to other materials that present an irregular variation in the mechanical elasticity and are important to faithfully model and simulate the mechanical response of materials under extreme conditions. [ABSTRACT FROM AUTHOR]

We present results of resonant ultrasound spectroscopy (RUS) measurements applied to granular high explosive materials at different bulk pressing densities and degree of thermal conditioning. The material chosen in this study is a ubiquitously used explosive material known as pentaerythritol tetranitrate (PETN), which is used commercially in civil and defense applications both as a binderized plastic bonded explosive material and an unbinderized neat material. However, changes in granular PETN bulk elastic properties due to thermal conditioning, which could have implications for better understanding environmental aging-related effects, have not been well studied even though it is believed that elasticity may play an important role in explosive material initiation mechanisms. Furthermore, monitoring elastic property changes in granular explosive pressings has not yet been demonstrated using RUS, which is an appealing non-destructive characterization tool that requires only dry point contact with the explosive material. To this end, we report the first study using RUS to quantify the elastic properties of binderized and neat PETN pressings as well as to quantify changes in elastic properties as a function of both thermal conditioning and bulk pressing density. Elastic stiffness coefficients, sometimes more commonly referred to as elastic constants, calculated from the RUS measurements on the different PETN-based materials show a significant increase for the post-conditioned samples compared to the pre-conditioned samples. This trend of increasing elastic properties with thermal conditioning was consistent for different density pressings, different thermal exposure conditions, and even different neat PETN pressings of differing average crystal sizes and/or specific surface areas. [ABSTRACT FROM AUTHOR]

Owing to magnetoelastic coupling, surface acoustic waves (SAWs) may be scattered resonantly by magnetic elements, such as nickel stripes. The scattering may be further enhanced via the Borrmann effect when the elements are organized into an array that matches the acoustic wavelength. We use finite-element modeling to consider single- and double-layer stripes patterned on top of a lithium niobate surface that carries Love surface waves. We do observe enhancement in the coupling for single-layer stripes, but only for Gilbert damping below its realistic value. For double-layered stripes, a weak yet clear and distinct signature of Bragg reflection is identified far away from the acoustic band edge, even for a realistic damping value. Double-layered stripes also offer better magnetic tunability when their magnetic period is different from the periodicity of elastic properties of the structure because of staggered magnetization patterns. The results pave the way for the design of magnetoacoustic metamaterials with an enhanced coupling between propagating SAWs and local magnetic resonances and for the development of reconfigurable SAW-based circuitry. [ABSTRACT FROM AUTHOR]

A review of the structural, elastic, and thermodynamic properties of cubic and hexagonal ScxAl1−xN crystals over the range of possible random alloys is provided. Based on measured and simulated lattice and internal cell parameters of NaCl (B1), CsCl (B2), and α-ZnS (B3) type cubic ScxAl1−xN lattices as well as of β-ZnS (B4), lh-MgO (Bk), and NiAs (B81) type hexagonal ScxAl1−xN crystals, their atomic positions, distances to nearest neighbor atoms, geometric dimensions of crystal cells, mass density, as well as their average bond length and bond angles are presented in dependence on the alloy composition. The understanding gained about the crystal lattices is used to provide a model for the transitions from the β-ZnS to the lh-MgO or NaCl lattice induced by the alloying of AlN with ScN. Based on published data sets of stiffness coefficients, the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and the sound velocities are presented in relation to the orientation of representative crystal planes and axes for rock salt, layered hexagonal, and wurtzite ScxAl1−xN crystals. Particular attention is paid to the directional anisotropies of elastic properties of the different crystal lattices if Sc atoms substitute an increasing number of Al atoms. Based on sound velocities determined, an overview of the fundamental thermodynamic properties of cubic and hexagonal ScxAl1−xN alloys is provided, such as the Debye temperature, heat capacity, minimum heat conduction, and melting temperature. [ABSTRACT FROM AUTHOR]

This paper presents results of a comprehensive study from first principles into the properties of Ni, Pd, Rh, and Ir crystals under pressure. We calculated elastic constants, phonon spectra, isotherms, Hugoniots, sound velocities, relative structural stability, and phase diagrams. It is shown that in nickel and palladium under high pressures (>0.14 TPa) and temperatures (>4 kK), the body-centered cubic structure is thermodynamically most stable than of the face-centered cubic one. Calculated results suggest that nickel under Earth-core conditions (P ∼ 0.3 TPa, T ∼ 6 kK) have a bcc structure. No structural changes were found to occur in Rh and Ir under pressures to 1 TPa at least. This paper also provides estimations for the pressure and temperature at which the metals of interest begin to melt under shock compression. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of a graded piezoelectric composite consisting of an infinitely long graded radially polarized piezoelectric cylinder embedded in an isotropic elastic non-piezoelectric matrix, under an external strain field. The physical properties of the graded cylindrical inclusion have a power-law profile with respect to the cylindrical radial variable. Using the variable separation method, closed-form solutions for the elastic displacement and electrical field in the entire composite regions are derived from the governing equation. The effective elastic and piezoelectric properties of the graded piezoelectric composite are formulated and discussed. The study reveals a vanishing mechanism of effective piezoelectric response in the graded radially polarized cylindrical piezoelectric composite. In addition, the paper derives the effective elastic formulas of the graded cylindrical elastic composites for the purely elastic problem and discusses the effects of graded property parameters on the effective elastic properties. [ABSTRACT FROM AUTHOR]

MXenes' tunable properties make them excellent candidates for many applications in future nanoelectronics. In this work, we explore the suitability of Sc 2 CX (X=N 2 , ON, O 2) MXenes to act as the active anode materials in Na-ion based batteries (NIBs) by means of ab initio simulations. After analyzing the structural and elastic properties of all the possible models to evaluate the energetically favorable N and O functionalization sites, our calculations show that both Sc 2 CON and Sc 2 CN 2 present a clear metallic character, making them potential candidates as anode materials. The investigation of the most relevant features for anode performance, such as the adsorption and diffusion of Na atoms, the intrinsic capacity, the open circuit voltage, and the storage capacity, shows that both systems are serious alternatives to the most common 2D materials currently employed in alkali metal batteries. In particular, Sc 2 CN 2 presents better diffusion behavior thanks to the absence of Na clustering on its surface, with optimal diffusion barriers comparable to other 2D materials, such as MoN 2 , while the values of diffusion barriers for Sc 2 CON are at least three times smaller than those found for other anode candidates. Similarly, while the capacity of Sc 2 CON is close to the one reported for 2D Sc 2 C, Sc 2 CN 2 possesses a power density more than twice higher than the ones of 2D materials, such as Sc 2 C, graphite, and MoS 2. Our results, thus, confirm the urge for further experimental exploration of the MXene Sc 2 CX (X=N 2 , ON, O 2) family as anode material in NIBs. [ABSTRACT FROM AUTHOR]

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the crystal structure and site preference, magnetic and elastic properties, and martensitic transformation (MT) are systematically investigated with the three groups of Heusler alloys: (Co 2 − x M x)VGa (M1 x), Co 2 (V 1 − x M x)Ga (M2 x), and Co 2 V(Ga 1 − x M x) (M3 x , M = Ni and Fe, 0 ≤ x ≤ 1.0). It is shown that instead of the L 2 1 and X A structures, the fcc one is energetically preferred in the cubic M3x (x ≥ 0.8) alloys. In L 2 1 -Ni2x (x ≤ 0.6) and fcc-Ni3x (x = 0.8), Ni atoms even prefer the Ga and Co anti-sites, respectively, and the replaced atoms move to the sublattices of the deficient ones. Their total magnetic moment is dominated by the magnetic exchange interactions corresponding to the pairs of two Co atoms on the different sublattices in M = Ni and Fe1x, Co and Fe in Fe2x and Fe3x (x < 0.8), and Fe and Fe atoms in Fe3x (x ≥ 0.8) alloys, respectively. These Ni1x, Ni2x, and Fe3x with x ≥ 0.4 as well as Ni3x with x ≥ 0.2 alloys are predicted having the MT behavior and also the better mechanical property relative to Co 2 VGa. A lower shear modulus (C ′ = (C 11 − C 12) / 2) generally corresponds to a higher MT temperature, and these alloys, which can undergo the MT are further evaluated with C ′ < 36.50 GPa. Both considerable magnetocaloric and magnetovolume effects can be also expected during the MT of these Fe3x alloys (x = 0.4 and 0.6). In the remaining Fe1x and Fe2x alloys, the Fe doping disfavors the MT and also improves their brittleness. The structural preference of these cubic alloys and also their stability relative to the tetragonal martensite can be mainly attributed to the number of their minority density of states at the Fermi level: the smaller they are, the more stable their system tends to be. [ABSTRACT FROM AUTHOR]

In the solid state, the thermal properties of SCO materials give rise to a rich variety of behaviors, ranging from (i) simple continuous gradual spin transitions, corresponding to a Boltzmann population of two degenerate states to (ii) sharp first-order hysteretic[11] transitions, including (iii) incomplete transitions and (iv) two-step or multi-step spin transitions,[12] characterized by the presence of a macroscopic intermediate state in the course of the transition between the LS and the HS states. Ndiaye I et al i .[33] establish the existence of an isomorphism between the electro-elastic models developed for the spin transition and Ising-like models including competing interactions, which confirms the relevance of the spin models in describing the multi-step spin transitions. Indeed, due to the volume change accompanying the spin transition between the LS and the HS states, crystallography appears as a direct probe of the spin transition at several scales, giving information about the deformation of the molecular structure and its consequence on the expansion/contraction of the lattice along the spin transformation. Later on, new interesting initiatives emerge through the introduction of spin-phonon models and elastic models in which the spin states were coupled to the atomic displacements of the SCO lattice, renormalizing the ligand field to which an elastic contribution arising from the lattice is added. [Extracted from the article]

The structural, elastic, and basic thermodynamic properties of hexagonal ScxAl1−xN crystals are calculated and discussed over the whole range of possible random alloys, including the transition from wurtzite to the layered hexagonal structure. Based on a review of lattice and internal parameters in combination with complete datasets of stiffness coefficients published in the literature, differing in the considered alloying intervals and the predicted structural transitions, changes in the crystal lattices caused by the substitution of aluminum by scandium atoms are discussed and illustrated. Crystal properties like the mass densities, average bond angles, and bond lengths are calculated, and the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and sound velocities are determined depending on the alloy composition and in relation to the orientation of crystal planes and axes. Particular attention is paid to the occurring directional anisotropies and the changes in structural and elastic properties in the alloy region of the structural transition between wurtzite and layered hexagonal ScxAl1−xN crystals. The acoustic velocities determined are used to calculate basic thermodynamic properties such as the Debye temperature, heat capacity, and minimum heat conduction, as well as to evaluate both the influence of the alloying and the structural transition on these properties. [ABSTRACT FROM AUTHOR]

The elastic properties and solid solution strengthening of several Cu alloys that may be promising for high gradient applications were studied using ab initio calculations based on density functional theory. Specifically, the temperature and solute concentration dependence of elastic properties including bulk and shear moduli, thermal expansion coefficient, and heat capacity of these alloys were calculated. We found that the bulk and shear moduli are linearly dependent on the solute concentration in the dilute regime and change significantly for different Cu alloys. The thermal expansion coefficient and heat capacity are comparatively less sensitive to solute concentrations. Solid solution strengthening is observed to be linearly correlated with the change of lattice parameter of Cu. This work provides an in-depth understanding of the elastic properties of Cu alloys, which is key for predicting their performance at high gradient in normal conducting accelerating structures. [ABSTRACT FROM AUTHOR]

Here, we report time-resolved broadband transient reflectivity measurements performed in a single crystal of SnS2. We made use of time-domain Brillouin scattering and a broadband probe to measure the out-of-plane longitudinal sound velocity, υ L = (2950 ± 100) m s – 1 , in this semiconducting two-dimensional metal dichalcogenide. Our study illustrates the potential of this non-invasive all-optical pump–probe technique for the study of the elastic properties of transparent brittle materials and provides the value of the elastic constant c 33 = (39 ± 3) GPa. [ABSTRACT FROM AUTHOR]

The elastic moduli of most materials in nature are commonly assumed to be identical (symmetric) under compressive and tensile loading. Here, we report an obviously asymmetric elastic property of alkylthiol-capped gold nanocrystal superlattices (NCSLs) in compression and tension computed from fully atomistic molecular dynamics simulations. Elastic asymmetry exhibits a clear trend of increasing with the increasing strain, and we attribute the strain-dependent elastic asymmetry to the variations of interaction between flexible ligand molecules during elastic deformations. In compression, ligand molecules sterically interact more with each other to continuously stiffen the NCSL, while in tension, they interact less and cause less stiffness. Unlike hybrid molecular materials, we find that the terminal groups of ligand molecules in the superstructure play only a minor role in determining the elastic asymmetry of gold NCSLs. In addition, the elastic asymmetry is observed to be essentially independent of ligand length and core size. These findings are expected to deepen our understanding of underlying asymmetric elastic properties of NCSL materials and may find technological applications in device technologies. [ABSTRACT FROM AUTHOR]

We measured single crystal elasticity of Ta under high pressures up to 54 GPa at room temperature using inelastic x-ray scattering at room temperature. Simultaneously, we measured the density of Ta using x-ray diffraction. Combining the bulk modulus and density, we obtain an equation of state of Ta as a primary scale. The Vinet equation was fitted to the pressure–volume data and we found consistency with previous work including experimental static and shock compressions and theoretical calculation. We proposed a parameter set for the Vinet equation [K0 = 191.1(3) GPa, K′0 = 4.006(2)] which is consistent with the pressure based on extrapolated velocities within 2% up to ∼80 GPa. Furthermore, we found the present scale to be consistent with a recent ruby scale (Ruby2020) up to ∼50 GPa. [ABSTRACT FROM AUTHOR]

Balancing the piezoelectric stress coefficient (e33) and the elastic constant (C33) of AlN-based materials is challenging but crucial for its application in bulk acoustic wave resonators. In this work, via first-principles calculations, we demonstrate that e33 and C33 can be simultaneously enhanced by adding boron (B) in the ScxAl1−xN system. Compared with ScxAl1−xN, the large C33 in B0.125Scx−0.125Al1−xN is caused by the shorter and stiffer B–N bonds, and the enhancement of e33 mainly comes from a larger sensitivity of atomic coordinates with respect to the strain (| d u / d ε |). Further investigation shows that the introduction of B in ScxAl1−xN significantly decreases the ratio of lattice parameter c over a due to the planar coordination preference of bulk BN, which is accompanied by an increased average | d u / d ε | and e33. Such a negative correlation can be attributed to the fact that | d u / d ε | of N is proportional to the asymmetry of transversal bond strengths but inversely proportional to the overall average bond strengths around N atoms. Such a bonding character observed in this work could be beneficial to the design of wurtzite materials with large piezoelectric coefficients and high elastic constants. [ABSTRACT FROM AUTHOR]

Resonant ultrasound spectroscopy (RUS) is a mature and robust technique for the nondestructive characterization of the elastic properties of solids capable of providing the elastic constants of anisotropic crystalline solids. The traditional method is based on assuming that the solid is linear elastic and, therefore, obeys a linearized Hookean constitutive relationship (Hooke's law). In this article, an alternative constitutive law is provided that allows for an initial strain or prestrain to be present stemming from residual stress. Then, the constitutive relationship is integrated into the RUS framework. The model is demonstrated using a realistic prestrain field obtained by simulating shot-peening processing of a polycrystalline Cu sample. The sensitivity of the resonances to the developed prestrain is established and discussed. This work allows researchers to consider the influence of initial strain or residual stress in their samples and the potential influence on accurate elastic constant estimates. The model also supports the potential of RUS for the nondestructive characterization of prestrain in materials. [ABSTRACT FROM AUTHOR]

We report Brillouin light scattering measurements of monoclinic CdPS 3 , a 2D layered cadmium chalcogenophosphate. By measurement of over 400 spectra in different orientations and scattering geometries, acoustic phonons are measured to determine the 13 elastic stiffness coefficients, along with longitudinal and transverse sound velocities from Brillouin frequency shifts. Because the sample was polycrystalline with a high density of planar defects, it was not possible to assign a crystal orientation to each spectrum. Instead, we determined the anisotropy in the material properties through statistical analysis, treating each spectrum as coming from a randomly sampled crystal orientation. Values of the Voigt–Reuss averages for the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are calculated from measured stiffnesses. This work demonstrates analysis of elastic properties of a polycrystalline, monoclinic 2D layered material through statistical analysis of a significant number of spectra. [ABSTRACT FROM AUTHOR]

We report Brillouin light scattering measurements of monoclinic CdPS 3 , a 2D layered cadmium chalcogenophosphate. By measurement of over 400 spectra in different orientations and scattering geometries, acoustic phonons are measured to determine the 13 elastic stiffness coefficients, along with longitudinal and transverse sound velocities from Brillouin frequency shifts. Because the sample was polycrystalline with a high density of planar defects, it was not possible to assign a crystal orientation to each spectrum. Instead, we determined the anisotropy in the material properties through statistical analysis, treating each spectrum as coming from a randomly sampled crystal orientation. Values of the Voigt–Reuss averages for the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are calculated from measured stiffnesses. This work demonstrates analysis of elastic properties of a polycrystalline, monoclinic 2D layered material through statistical analysis of a significant number of spectra. [ABSTRACT FROM AUTHOR]

The Foreign Object Damage problem is considered as the damage tolerance statement for consecutive loading tests, which include the shock-wave loading (by explosive generator) of massive planar targets (aluminum alloy AlMg6) to provide a billet for the specimen machining with controlled damage that is the analogous material of the fan blades subjected to high-speed collision with solid particles. These samples were used to perform high cycle fatigue and very high cycle fatigue tests with the ultrasonic testing machine, which allows fatigue loading for 108–1010 cycles with an amplitude of up to several tens of micrometers and a frequency of 20 kHz. It is shown that the fatigue strength of AlMg6 alloy specimens pre-loaded by shock in the 109 cycle regime reduces by 24%. The fatigue damage-failure transition and crack initiation were studied by the amplitude–frequency analysis of higher harmonics associated with the influence of defects on the effective elastic properties. The structural study of the fracture surface for the specimens after consecutive loading was conducted using the profilometry data to identify the roughness scale invariants induced by defects for corresponding areas responsible for the staging of fatigue damage-failure transition. The scale invariants and corresponding lengths were used for the formulation of the generalized Paris law for the crack advance in the damaged material. [ABSTRACT FROM AUTHOR]

Carbon aerogels (CAs) are emerging carbon-based cellular materials with high porosity, low density, and a variety of functions. The combination of all these unique properties contributes to their wide applications in flexible sensors, energy devices, acoustic devices, and environmental applications. However, their wide applications are strictly limited by poor mechanical robustness. The existing conflicts between mechanical robustness and the sparse network of porous materials have never received due attention. Good robustness could ensure structural integrity and performance stability for practical applications of aerogels. Here, we discuss recently emerged strategies for optimizing mechanical robustness, including cell-wall strengthening, cell-wall orientation, pore topology control, and joint reinforcement. Particularly, we conclude advanced design principles to achieve stretching elasticity of CAs without introducing intrinsically stretchable elastomers. In addition, we briefly overview the recent applications of robust CAs and provide an outlook on the open questions for obtaining more mechanically robust CAs. [ABSTRACT FROM AUTHOR]

The mechanical properties of the cell membrane play an important role in electroporation. This paper studied the influence of the mechanical properties of the cell membrane on the transition energy of electroporation through both modeling and experiments. An electromechanical coupling model of a single pore on the cell membrane was established in COMSOL, and the effect of elastic strain energy on the formation of pores was analyzed. Additionally, to compare the transition energy barrier of pores for different elastic properties of the cell membrane, electroporation experiments were carried out at different temperatures. The simulation showed that the elastic strain energy of the cell membrane increased the transition energy barrier of the pores. The experiments also showed that the transition energy barrier was larger when the elasticity of the cell membrane is intact, which was in good agreement quantitatively with the simulation results. We demonstrated that the mechanical properties of the cell membrane hinder the pore formation, which may be due to the increase of the transition energy barrier. We analyzed the possible mechanism of the effect of cell membrane mechanical properties on electroporation and found the contribution of cell membrane mechanical properties to electroporation during the delivery of exogenous substances, which can provide guidance for improving therapies in electrochemotherapy. [ABSTRACT FROM AUTHOR]

Four new boron nitride polymorphs hP24 BN, hP18-I BN, mP36 BN, and hP18-II BN with sp2 hybridization are investigated in this study by first-principles calculations, including the structural properties, stability, elastic properties, anisotropy, and electronic properties. Predicted by the electronic band structure, all the BN polymorphs in hP24, hP18-I, mP36, and hP18-II phase are wide bandgap semiconductor materials with a bandgap of 2.97–4.72 eV. Meanwhile, the bandgap of hP24 BN is larger than that of ZnO, and the bandgaps of hP18-I BN, mP36 BN, and hP18-II BN are larger than those of GaN and SiC. The new boron nitride polymorphs have mechanical stability, dynamic stability, and thermodynamic stability by analyzing the elastic constants, phonon spectra, and related enthalpies. The values of B/G of hP24 BN, hP18-I BN, mP36 BN, and hP18-II BN are all larger than 1.75, which confirms that they are ductile materials. Their densities are around 2.100 g/cm3, which are smaller than that of the c-BN (3.466 g/cm3). BN polymorphs in this study show different degrees of anisotropy in Young's modulus, and hP24 BN has the largest anisotropy in Young's modulus, while mP36 BN displays the smallest Young's modulus anisotropy. [ABSTRACT FROM AUTHOR]

The first-principles calculations were used to comprehensively assess the structural, electronic, magnetic, and elastic properties of Fe23−xCrxC6 (x = 0–23). The absolute temperature stability follows the sequence of Fe1Cr22C6 (Fe: 4a) > Fe3Cr20C6 (Fe: 4a, 8c) > Fe15Cr8C6 (Fe: 4a, 8c, 48h) > Fe23C6 (Fe: 4a, 8c, 32f, 48h). There is a coexistence of covalent, ionic, and metallic bonds in Fe23C6, Fe15Cr8C6, Fe3Cr20C6, Fe1Cr22C6, and Cr23C6 according to the electronic analysis. In addition, the iron content of 0.4 triggers the magnetic transition, suggesting that a critical point exists between the paramagnetic nature and ferromagnetism. Around the concentration of x = 0.5, the longer nearest neighbor length of Fe–C corresponds to the higher value of magnetic moment. Up to the iron content of 1.0, Fe23C6 carbides give rise to an extraordinary magnetic property. The composition and Wyckoff position collectively determines the mechanical properties. Except for the hardness, the mechanical property improves with increasing chromium concentrations. Furthermore, the compounds Fe23−xCrxC6 (x = 0, 9, 10, 11) are brittle. The present work enriches the pool of information that is necessary for the design and property control of Fe-based materials. [ABSTRACT FROM AUTHOR]

The first-principles calculations were used to comprehensively assess the structural, electronic, magnetic, and elastic properties of Fe23−xCrxC6 (x = 0–23). The absolute temperature stability follows the sequence of Fe1Cr22C6 (Fe: 4a) > Fe3Cr20C6 (Fe: 4a, 8c) > Fe15Cr8C6 (Fe: 4a, 8c, 48h) > Fe23C6 (Fe: 4a, 8c, 32f, 48h). There is a coexistence of covalent, ionic, and metallic bonds in Fe23C6, Fe15Cr8C6, Fe3Cr20C6, Fe1Cr22C6, and Cr23C6 according to the electronic analysis. In addition, the iron content of 0.4 triggers the magnetic transition, suggesting that a critical point exists between the paramagnetic nature and ferromagnetism. Around the concentration of x = 0.5, the longer nearest neighbor length of Fe–C corresponds to the higher value of magnetic moment. Up to the iron content of 1.0, Fe23C6 carbides give rise to an extraordinary magnetic property. The composition and Wyckoff position collectively determines the mechanical properties. Except for the hardness, the mechanical property improves with increasing chromium concentrations. Furthermore, the compounds Fe23−xCrxC6 (x = 0, 9, 10, 11) are brittle. The present work enriches the pool of information that is necessary for the design and property control of Fe-based materials. [ABSTRACT FROM AUTHOR]

Owing to their atomic thickness and low bending rigidity, suspended two-dimensional (2D) materials are prone to wrinkle formation. Here, we use molecular dynamics (MD) simulations to probe the effect of these wrinkles on the nonlinear elasticity of atomically thin graphene membranes. We observe a stress–strain response that consists of two linear regions that are separated by a transition. It is found that this transition is sharp in membranes where wrinkles are formed by uneven stresses at the boundaries. However, when wrinkles are formed by crystal defects, this nonlinear transition is seen to be more gradual. To capture these effects, we use a phenomenological model based on experimentally measurable quantities. We demonstrate the model's fidelity by fitting it to the MD simulated nonlinear response of many graphene membranes providing evidence that the sharpness of the transition between the linear regions in the stress–strain response is a measure of the type of wrinkles and can be quantified by our model. [ABSTRACT FROM AUTHOR]