Low Shear Modulus Research Articles

High bulk modulus pentamodes: the three-dimensional metal water

Despite significant advances in the field of phononic crystals, the development of acoustic metafluids that replicate the behaviour of liquids in three dimensions remains elusive. For instance, water – the quintessential pentamode (PM) material – has a bulk modulus two orders of magnitude higher than current state-of-the-art PMs. The need for a low shear modulus inherently conflicts with the desire of high bulk modulus and density. In this letter, we shed light on the limitations of existing PM geometries and propose an innovative shape for the links that constitute the network. Inspired by the kinematics of ropes, these links are constructed from thin fibres and demonstrate the potential to create PMs with properties akin to those of liquids. As a prime example, we propose the design of the first metamaterial that fully deserves the name 3D metal water, since its acoustic properties in the low frequency regime are indistinguishable from water. Additionally, we highlight a shear band gap in the lattice dispersion diagram, and illustrate the influence of geometric parameters on the dynamic properties at higher frequencies. This novel design of metafluids holds promise for applications requiring anisotropic materials such as acoustic lenses, waveguides, and cloaks.

Effect of layering and pre-loading on the dynamic properties of sand-rubber specimens in resonant column tests

AbstractSeveral studies show that scrap tyre rubber mixed with sand is an effective and sustainable method for mitigating vibrations. The dynamic and cyclic response of this composite soil has already been investigated. However, layered sand-rubber configurations have not been considered yet. This study reports findings of resonant column tests on three types of specimen: (a) sand-only or rubber-only, (b) layered sand-rubber, and (c) sand-rubber mixtures. The analysis allowed for an evaluation of the maximum shear modulus and its degradation with strain over a wide range of confining stress and shear strain. The evolution of the damping ratio with strain was determined analogously. Effects of pre-loading and pre-straining were also considered. The results show that the behaviour of layered specimens is much more similar to that of pure rubber than to sand-rubber mixtures, with very low shear modulus values, smaller degradation of stiffness with strain and pre-loading, and higher damping. For example, at the confining stress of 100 kPa and rubber content of 0/33.3/50/67.7/100% by volume, the small strain shear moduli for sand-rubber mixtures are equal to 98.3/30.4/15.4/7.1/1.3 MPa and 98.3/3.6-4.2/2.4-2.8/2.1/1.3 MPa for sand-rubber layered specimens, depending on the arrangement of layers. A shear beam model is shown to be adequate for calculating the response of the layered specimens comprising layers of large stiffness contrast.

Structural features of bimetallic composites of the Me-Al type (Cu, Ni, Nb), obtained by ball milling of powder mixtures and consolidation by torsion under pressure

A comparative study of the features of the microstructure of bimetallic composites of the Me-Al (Cu, Ni, Nb) type, obtained by ball milling of powder mixtures and consolidation by torsion under pressure in Bridgman anvils, was carried out. In all systems studied in this work, the formation of a nanoband structural state is observed, the elements of which are elongated predominantly along the direction parallel to the anvil plane. It has been established that in local areas characterized by the absence of the aluminum component, an SMC state without a nanolaminate structure is formed. An analysis of the features of structure formation was carried out taking into account the comparison of the characteristics of powder systems components (melting point, shear modulus and stacking-fault energy). It was shown that low shear modulus of aluminum, compared to other components, in combination with a higher homologous temperature, provides it high accommodative ability. It has been suggested that under conditions of torsion under pressure, the aluminum component, being a kind of solid lubricant, ensures slipping and flattening of stronger layers of the second component, which contributes to the formation of a nanolaminate structure in the metal‑aluminum systems under consideration.

Molybdenum gallium carbide coated D-shape fiber for nanosecond dark pulse generation in erbium-doped fiber laser

Molybdenum gallium carbide (Mo2Ga2C), a material belongs to MAX phase group, has garnered significant interest in a wide range of scientific field, including material science, engineering, and laser physics. It is chemically and structurally promising since it exhibits a low shear modulus, superconducting behaviour, and high mechanical stability. Here, we prepared a saturable absorber (SA) based on Mo2Ga2C coated D-shape fiber using solution casting technique. It exhibits outstanding saturable absorption of 7.2%, allowing it to generate dark pulse laser in an erbium-doped fiber laser cavity. We analyzed the laser’s performance and obtained a dark pulse with a pulse energy, peak power, and average output power of 3.9 nJ, 27.5 mW, and 7.3 mW, respectively. This foundational work may introduce a new material as an alternative SA device in fiber laser cavity.

Measurements of Shear Wave Velocity for Collapsible Soil

This paper examines the effects of collapsible soil structure on shear wave velocity. The study attempts to simulate hydraulic fill sand deposits, which represent a natural soil deposition process that can result in a collapsible soil structure. A series of resonant column tests and bender element tests on Ottawa sand was conducted on sand specimens and prepared by dry pluviation and simulated hydraulic fill methods subjected to various confining pressures. Shear wave velocities measured from both methods of deposition are compared and discussed. Results from this study show that for soil specimens with the same void ratio, samples prepared by simulated hydraulic fill have a lower shear modulus and shear wave velocity than the specimens prepared by dry pluviation, and the differences are more pronounced at higher confining pressures. The resonant column test results performed in this study were consistent with results from the discrete element analysis, full-scale testing, and centrifuge testing. The discrete element analysis suggests that soil fabric and number of particle contacts are the key factors affecting the shear wave velocity. These factors are dependent on the methods of deposition. Results from this study examining hydraulic fill collapsible structure shear wave velocity provide a step forward toward a better correlation between soil dynamic properties measured in field and laboratory tests.

High friction stress and weak grain-refinement strengthening effect induced by severe lattice distortion in ZrTiNb medium entropy alloys

In this work, we have studied the grain-refinement strengthening effect of body-centered cubic Zr50Ti35Nb15 medium entropy alloy. The results suggest that the yield strength increases as grain size decreases from 530 μm to 0.51 μm, reaching the maximum value of 651 MPa, and still having decent ductility. Moreover, it is found that the alloys exhibit a high Hall–Petch intercept of 564 MPa and a low Hall–Petch slope, which means strong lattice friction stress and weak grain-refinement strengthening. The high lattice friction stress originates from the obstruction of dislocation motion caused by atomic size and modulus misfit. Dislocation interaction and multiplication in grain interior is difficult due to the high dislocation slip resistance, leading to a weak dislocation pile-up capability at grain boundary. Instead, dislocations nucleation and emission become the dominant deformation process since low shear modulus promotes dislocation source activation.

Elasticity and rheology of auxetic granular metamaterials

The flowing, jamming, and avalanche behavior of granular materials is satisfyingly universal and vexingly hard to tune: A granular flow is typically intermittent and will irremediably jam if too confined. Here, we show that granular metamaterials made from particles with a negative Poisson's ratio yield more easily and flow more smoothly than ordinary granular materials. We first create a collection of auxetic grains based on a re-entrant mechanism and show that each grain exhibits a negative Poisson's ratio regardless of the direction of compression. Interestingly, we find that the elastic and yielding properties are governed by the high compressibility of granular metamaterials: At a given confinement, they exhibit lower shear modulus, lower yield stress, and more frequent, smaller avalanches than materials made from ordinary grains. We further demonstrate that granular metamaterials promote flow in more complex confined geometries, such as intruder and hopper geometries, even when the packing contains only a fraction of auxetic grains. Moreover, auxetic granular metamaterials exhibit enhanced impact absorption. Our findings blur the boundary between complex fluids and metamaterials and could help in scenarios that involve process, transport, and reconfiguration of granular materials.

Rubber-sand infilled soilbags as seismic isolation cushions: experimental validation

This study proposes the use of soil bags filled with a rubber sand mixture (SFRSM) to address the issue of weak stability associated with rubber-sand layers for seismic isolation. To evaluate the dynamic characteristics of the SFRSM, large-scale cyclic simple shear tests were conducted to investigate the effects of rubber content, vertical pressure, shear displacement amplitude, fill percentage, and laying scheme. Furthermore, shaking table tests were carried out to evaluate the impact of vibration intensity and frequency on the seismic isolation of SFRSM layers. The results indicate that (1) Compared to the rubber-sand layer, the SFRSM exhibits a lower shear modulus and higher damping, indicating its potential for greater seismic isolation and energy dissipation. (2) The dynamic characteristics of the SFRSM were significantly influenced by the fill percentage and laying scheme, suggesting that an effective isolator capable of withstanding various external conditions could be developed. (3) The isolating effect of the SFRSM layer is attributed to its ability to dampen high-frequency vibration components effectively. Additionally, the threshold frequency required to trigger attenuation decreases with an increasing number of SFRSM layers. In summary, these experimental results provide evidence that the proposed innovative strategy enhances the strength and vertical stiffness of the original rubber-sand layer, making it well-suited for seismic design applications in low-rise buildings in less-developed regions. Highlights 1. A novel seismic isolation strategy using the soil bags filled with rubber-sand mixture (SFRSM) was proposed. 2. Large-scale cyclic simple shear tests were conducted to evaluate the dynamic properties of SFRSM. 3. The influence of key parameters on the dynamic shear modulus and damping ratio of SFRSM was analysed. 4. The proposed strategy is well suited for the seismic design of low-rise buildings in less-developed regions.

Origin of low lattice thermal conductivity in promising ternary PbmBi2S3+m (m = 1–10) thermoelectric materials

Ternary Pb-Bi-S compounds emerge as potential thermoelectric materials owing to low thermal conductivity, but the origin of their intrinsic low lattice thermal conductivities lacks further investigation. Herein, a series of ternary PbmBi2S3+m (m = 1–10) compounds are synthesized and their crystal structure evolutions with increasing m values are clearly unclosed. The room-temperature lattice thermal conductivities in PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9 can reach at 0.57, 0.56 and 0.80 W m−1 K−1, respectively, outperforming other ternary sulfur-based compounds. Theoretical calculations show that the low lattice thermal conductivities in PbmBi2S3+m (m = 1–10) mainly originate from soft phonon dispersion caused by strong lattice anharmonicity, and both asymmetric chemical bond and lone pair electrons (Pb 6s2 and Bi 6s2) can favorably block phonon propagation. Furthermore, the elastic measurements also confirm relatively low sound velocities and shear modulus, and the Grüneisen parameter (γ) calculated by sound velocities can reach at 1.67, 1.85 and 1.94 in PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9, respectively. Finally, the intrinsic low lattice thermal conductivities in PbmBi2S3+m (m = 1–10) contribute to promising thermoelectric performance, and the maximum ZT values of 0.47, 0.38 and 0.45 can be achieved in undoped PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9, respectively.

Exploring novel transition metal ceramics [formula omitted][formula omitted] via ab-initio calculations

The heavy transition metal borides, carbides, and nitrides are still difficult to synthesize, and certain compositions are not even possible to stabilize. With the help of existing materials databases, we assemble 240 materials of chemical formula M2X, that we intend to investigate via density-functional theory (DFT). Our calculations demonstrate the stability of several novel compounds, which are highly likely to be synthesized in experiment, widening the potential applications as structural ceramics. The X site plays the primary role in determining the structural stability, with boron leading to many more stable ceramics than carbon and nitrogen. The chemical bonding is found to arise from a mixture of covalent bonding (M-X) and weak metallic bonding (M-M), which ensures varied elastic properties. Among the newly predicted materials, Tc2B,Os2B, and Os2C are shown to be ultra-incompressible. A low shear modulus makes these systems prone to plasticity, which leads to an interesting coexistence of hardness and ductility for novel Os2B and Os2C, as well as existing Mo2B and Mo2C. Chemically, replacing 4d with 5d elements is shown to enhance bulk and shear moduli, which could be used for hardness engineering by selective doping. This report lays the foundations for further experimental research on the mechanical merits of the late transition metal borides, carbides, and nitrides of chemical formula M2X.

Full-scale seismic response test on a shallow foundation embedded in tire-derived aggregate for geotechnical seismic isolation

This paper presents results from full-scale tests aimed at characterizing the seismic response of shallow foundations embedded in tire derived aggregate (TDA) with large particle size. The high shear strength, low shear modulus, and high damping ratio of TDA with large particle sizes make it ideally suited for low-cost Geotechnical Seismic Isolation (GSI) systems. Unidirectional shake table tests were performed on a single-degree-of-freedom superstructure connected to a 0.46 m-deep concrete strip footing embedded within a 1.89 m-thick TDA layer inside a laminar box. The TDA-footing system was subjected to a series of sine sweep motions with varying amplitudes and frequencies between 0.4 and 10 Hz. Substantial nonlinearity was observed in the moment-rocking response of the footing, where the specimen experienced rocking stiffness softening at moment demands slightly below its moment capacity. While the footing exhibited moderate transient settlement and uplift during dynamic oscillation, it demonstrated low residual settlement. The TDA layer offered the footing an effective recentering system with an average residual recentering ratio of 0.991. In addition to being low-cost, abundant, and recycled, the TDA layer had both favorable energy dissipation and recentering, with better seismic resilience than structural hinging and conventional foundation rocking systems in soil.

Unveiling the interface between second phases and matrix on thermal conductivity of Mg alloys

Solute atoms and second phases with low thermal conductivity are habitually regarded as the factors to the thermal conductivity of alloys. Nevertheless, the interface that is usually neglected can also be a noteworthy factor influencing the thermal conductivity of alloys due to its inherent nature of defects. The effect of interface on the thermal conductivity of alloys was quantitatively scrutinized in the binary Mg–La, Mg–Ce, Mg–Sm, Mg–Al, Mg–Zn, and Mg–Si alloys with concentration gradients. The effect of diverse excess second phases on the deterioration of thermal conductivity for Mg alloys followed this order: Mg2Si＞Mg17Al12＞Mg17La2＞Mg12Ce＞Mg41Sm5＞MgZn2. The quantitative total interfacial thermal resistance model for alloys was proposed, which was quantitatively understood by R=AGsρs3+BGsρs+CGs3ρs. The sequence of experimental data was conformed to that of the theoretical data acquired by this model. Alloying elements which second phases possess low shear modulus (G) and high density (ρ) were beneficial for the development of the low-thermal-resistance alloys. This rule can reinforce the theoretical basis for the thermal conduction of alloys. The data of the total interfacial thermal resistance was established preliminarily to instruct the design of low-thermal-resistance and high-thermal-conductivity Mg alloys.

Modified third order shear-deformation model for anisotropic glulam beams via three-field mixed finite-element formulation

ABSTRACT Glulam timber structural linear elements often show low span-to-depth ratios. Moreover, timber is intrinsically orthotropic with very low shear moduli. These two circumstances justify the substantial contribution of shear strain to the overall deformation of linear elements. Since design specifications for timber beams commonly adopt 1D models, two such elastic models are proposed in this paper for static plane behavior, where, instead of fully orthotropic, glulam is assumed to be transversely isotropic. These models provide a good compromise between accuracy and simplicity for design proposes. A 3-field mixed formulation is generalized in order to produce two new 1D finite elements suitable for modeling transversely isotropic elastic glulam beams. To assess the accuracy of these new finite elements the results they produce are compared with those determined with a plane stress transversely isotropic 2D finite element. The included examples show that the proposed combination of transverse isotropy with a third order shear deformation model provides a suitable background to the 1D modeling of glulam beams with improved accuracy when compared to the models conventionally used in design. The paper is concluded with a parametric analysis which identifies the cases where the improved models should be used instead of simpler ones.

Experimental investigation on dynamic shear modulus of undisturbed marine soils in the east coast of China

The dynamic shear modulus G is one of the vital parameters for the dynamic properties of marine soils and is crucial for marine geotechnical engineering design. In order to investigate the G characteristics of various marine soils, a series of resonant column tests were performed on undisturbed marine soils with various depths taken from Bohai Bay, Yangtze River estuary, and Jintang Strait, respectively. In addition, the maximum dynamic shear modulus Gmax and strain-compatible G of the tested marine soils were compared with the marine and terrestrial soils from the published literature. A remarkable finding is that, compared with terrestrial soils, the marine soils in different sea area present the stronger nonlinear behavior with lower shear modulus due to the special depositional environment. With the increasing of H, G in each strain range increase, and the dynamic characteristics of the marine soils gradually transition from nonlinear to linear, the Gmax and reference shear strain γ0 value of marine soils in different sea areas increases linearly with the increasing H, but the Gmax and γ0 growth rate varied with the sea environment and soil type. Based on the quantitative prediction equation of the Gmax and G attenuation relationship (G/Gmax ∼ γ) of various marine soils, a new prediction equation can be also established to predict G value in different depth and strain levels of various marine soils. The proposed equation are validated by independent experimental data of marine and terrestrial soils from the literature. In this regard, the proposed procedure provides a significant advantage in the evaluation of dynamic properties of marine soils in practice.

Effect of Matrix Stiffness and Hepatocyte Growth Factor on Small Cell Lung Cancer Cells in Decellularized Extracellular Matrix-Based Hydrogels.

Small cell lung cancer (SCLC) is one of lethal cancers resulting in very low 5-year-survival rate. Although its clinical treatment largely relies on chemotherapy, SCLC cell physiology in three-dimenstional (3D) matrix has been less explored. In this work, the tumor microenvironment is reconstructed with decellularized porcine pulmonary extracellular matrix (dECM) with hyaluronic acid. To modulate matrix stiffness, the methacrylate groups are introduced into both dECM and hyaluronic acid, followed by photocrosslinking with photoinitiator. The stiffness of the resulting dECM-based hydrogel covers the stiffness of normal or cancerous tissue with varying dECM content. The proliferation and cancer stem cell marker expression of encapsulated SCLC cells are promoted in a compliant hydrogel matrix, which has a low shear modulus similar to that of the normal tissue. The hepatocyte growth factor (HGF) that induces SCLC cell invasion and chemoresistance markedly increases invasiveness and gene expression levels of CD44 and Sox2 in the hydrogel matrix. In addition, HGF treatment causes higher resistance against anticancer drugs (cisplatin and paclitaxel) in the 3D microenvironment. These findings indicate that malignant SCLC can be recapitulated in a pulmonary dECM-based matrix.

Effect of tissue viscoelasticity and adjacent phase-changed microbubbles on vaporization process and direct growth threshold of nanodroplet in an ultrasonic field

Understanding the behavior of nanodroplets converted into microbubbles with applied ultrasound is an important problem in tumor therapeutical and diagnostic applications. In this study, a comprehensive model is proposed to investigate the vaporization process and the direct growth threshold of the nanodroplet by following the vapor bubble growth, especially attention devoted to the effect of tissue viscoelasticity and adjacent phase-changed microbubbles (PCMBs). It is shown that the ultrasonic energy must be sufficiently strong to counterbalance the natural condensation of the vapor bubble and the tissue stiffness-inhibitory effect. The softer tissue with a lower shear modulus favors the vaporization process, and the nanodroplet has a lower direct growth threshold in the softer tissue. Moreover, the adjacent PCMBs show a suppression effect on the vaporization process due to the negative value of the secondary Bjerknes force, implying an attractive force, preventing the nanodroplet from escaping from the constraint of the adjacent PCMBs. However, according to the linear scattering theory, the attractive force signifies that the constraint is weak, causing the direct growth threshold to increase in the range of 0.09–0.24 MPa. The weak increase in threshold demonstrates that the direct growth threshold is relatively unaffected by the adjacent PCMBs. The prediction results of our model are in good agreement with the experiment results obtained by the echo enhancement method, in which the threshold is relatively independent of the intermediate concentration. The findings presented here provide physical insight that will be further helpful in understanding the complex behavior of the nanodroplet responses to ultrasound in practical medical applications.

A material model for thick, rate‐dependent adhesives with delocalized softening

AbstractThis contribution is dedicated to the development and implementation of a material model to describe the deformation behaviour of assembly adhesives. These assembly adhesives are usually used with thicknesses of several millimetres up to centimetres in order to compensate for large relative displacements of joining parts. These large displacements can be resisted by assembly adhesives, since they have a low shear modulus and thus a high strain until failure above their glass transition temperature. As a basis, the isothermal and isotropic hyperelasticity theory is used to describe the elastic deformation behaviour up to the postcritical range by using an isochoric–volumetric decomposition of the deformation gradient. The Arruda–Boyce and Ogden models are employed here for the isochoric‐elastic and volumetric‐elastic description. The modelling of the rate‐dependence concerning shear and bulk viscosity succeeds by extending the hyperelasticity theory to the theory of finite viscoelasticity with the generalized Maxwell model in each case. In order to model the postcritical deformation behaviour, an isotropic damage model is developed based on the energy limiting method and used to define an isochoric and a volumetric damage variable, so that the mapping of softening due to change of shape, as well as cavitation, succeeds. Furthermore, the damage variables are delocalized to prevent pathological mesh dependence by using the integral regularization method. Finally, the material parameters are determined and validated by means of measurement data due to tests at the assembly adhesive Betaforce 2850L. The results demonstrate a high prediction quality.

Stress redistribution in a multilayer chamber for compressed air energy storage in abandoned coalmine: Elastic analytical insights and material choice

AbstractCompressed air energy storage (CAES) is attracting attention as one of large‐scale renewable energy storage systems. Its gas storage chamber is one of key components for its success. A successful utilization of an abandoned coalmine roadway depends on the stability of the gas storage chamber. The chamber is a multilayer structure and the redistribution of the stress and displacement in each layer is critical to the chamber stability. So far, this redistribution mechanism under any lateral pressure coefficient and internal air pressure has been unclear and thus a quick and easy evaluation on the CAES chamber stability becomes difficult. In this study, the redistributions of stress and displacement in each layer are analytically solved based on complex variable function theory. First, the stress and displacement in three CAES multilayer structures are obtained under any lateral pressure coefficient and internal air pressure. Then, a comprehensive parameter b1 is obtained to describe the redistribution of stress and displacement in rock mass, lining layer, and grout layer. Its linkage with lateral pressure coefficient, internal air pressure, and material properties is analytically expressed. Thirdly, an analytical expression is obtained for the influence range of internal air pressure on chamber stress. Finally, the role and selection of lining and grouting layers are explored at different lateral pressure coefficient and internal air pressure. It is found that the CAES chamber stability can be effectively and quickly evaluated by these analytical solutions and comprehensive parameters and enhanced by a material with low bulk modulus but high shear modulus.

Investigation of stability, electronic, optical and mechanical properties of honeycomb BeN2 monolayer: A DFT study

In this work, from the DFT calculations, we investigate the physical properties of the 2D BeN2 monolayer with a honeycomb lattice. The dynamic stability of the BeN2 monolayer is demonstrated by the presence of real modes in its phonon spectrum. The theoretical electronic band structure and density of states reveal the semiconductor nature of the BeN2 sheet. The semi-local PBE results show a bandgap of 1.32 eV, while HSE hybrid functional computation yields a higher bandgap of 3.16 eV. Our results suggest that HSE approximation employing ultrasoft pseudopotentials can accurately predict the most important electronic property of BeN2 structure that is not only in excellent agreement with the most accurate GW predictions but also better than those reported before with the same functional. The wide-bandgap semiconductor properties make BeN2 nanostructure a highly promising 2D material for innovative applications in nanoelectronic devices. The optical analysis obtained from HSE calculations reveals that the BeN2 nanostructure has optical absorption in the violet range of visible light with a low static dielectric constant of 2.55. Further, our results indicate that this material presents low bulk and shear moduli of 61.3 and 12.0 N/m, respectively.

Effect of Ag content on friction and wear properties of TiCN/Ag films in different service environments

Thin-film materials require improved performance to withstand complex and harsh environments as the modern industry evolves. In this study, a series of TiCN/Ag films were fabricated to enhance the frictional properties of the films and extend the lifetime of friction sliding components. The microstructure, mechanical properties, friction, and wear properties of the films were investigated in different service environments. The results showed that the film comprised fcc-TiN, fcc-Ag, amorphous carbon, and amorphous carbon nitride. As the Ag content increased, the hardness of the film first increased, then decreased rapidly, after which the decreasing trend became stable. When the Ag content was 1.8 at%, the optimal hardness and elastic modulus of the films were 29.7 GPa and 228.09 GPa, respectively. Under oil lubrication conditions, Ag atoms can catalyze the formation of a highly graphitized carbon-based friction film on the TiCN/Ag worn surface, thereby enhancing the friction and wear properties of the films. In the air friction, the soft-phase Ag with a low shear modulus acts as a lubricant, and the friction coefficient decreases with an increase in Ag content; however, the consumption of Ag during friction increases the wear rate. In the 3.5 wt% NaCl solution, as the Ag content increased, the surface roughness and corrosion current of the film increased, while the corrosion potential and resistance of the film decreased, resulting in an increase in the friction coefficient and wear rate.