Increase In Shear Modulus Research Articles

Exploration of the structure, properties, and anisotropy of (r, h)-TiAl2 under high pressure

In this study, we use the first principles calculation based on the density functional theory (DFT) to investigate the effects of high pressure on the structural, anisotropic, mechanical, and thermal properties and the phase stability of r-TiAl2 (HfGa2 type) and h-TiAl2 (ZrGa2 type). The calculation results of the formation enthalpy indicate that r-TiAl2 and h-TiAl2 remain stable under the 0–40 GPa. There is no phase transition, and the two phase structures are mechanically stable under the applied pressure. The Bulk modulus (B), Shear modulus (G), and Young's modulus (E) increase with increasing pressure from 0 to 40 GPa. The 3D surface structure of the elastic modulus and the universal elastic anisotropy index (AU) indicate that the elastic anisotropy of h-TiAl2 is higher than that of r-TiAl2. In addition, Sound velocity and Debye temperature are investigated from analysis of the elastic constants and moduli. Finally, the density of states and charge density difference are also discussed.

Determination of Scale Effects on Mechanical Properties of Berea Sandstone

The key rock mechanical parameters are strength, elastic modulus, Poisson’s ratio, etc., which are important in reservoir development. The accurate determination of reservoir’s mechanical properties is critical to reduce drilling risk and maximize well productivity. Precisely estimating rock mechanical properties is important in drilling and well completion design, as well as crucial for hydraulic fracturing. Rocks are heterogeneous and anisotropic materials. The mechanical properties vary not only with rock types but also with measurement methods, sample geometric dimensions (sample length to diameter ratio and size), and other factors. To investigate sample scale effects on rock mechanical behaviors, unconfined compression tests were conducted on 41 different geometric dimensions of Berea sandstones; unconfined compressive strength (UCS), Young’s modulus ( E ), Poisson’s ratio ( υ ), bulk modulus ( K ), and shear modulus ( G ) were obtained and compared. The results indicate that sample geometry can significantly affect rock mechanical properties: (1) UCS decreases with the increase of length to diameter ratio (LDR), and the UCS standardize factor is between 0.71 and 1.17, which means -30% to +20% variation of UCS with LDR changing from 1 to 6.7. The test results show UCS exhibits positive relationship with sample size. (2) Young’s modulus slightly increases with LDR increases, while Poisson’s ratio decreases with the increase of LDR. For the tested Berea sandstones, Poisson’s ratio standardizing factor is between 0.57 and 1.11. (3) Bulk modulus of Berea sandstone samples decreases with the increase of LDR, while shear modulus increases with LDR increases. Both bulk modulus and shear modulus increase with the increase of sample size. (4) The principal failure modes were analyzed. The failure modes of the tested Berea sandstones are axial splitting and shear failure. Stocky samples ( LDR < 2 ) tend to go axial splitting, while slender samples ( LDR > 2 ) tend to show shear failure.

Preparation and rheological properties of hydrogels based on N-succinyl chitosan and hyaluronic acid dialdehyde

Hydrogels based on both synthetic and natural polymers are currently used in agriculture, pharmaceuticals, medicine and other industries. The aim of this work was to determine the conditions for preparing chemically cross-linked hydrogels based on modified biopolymers – N-succinyl chitosan (NSCTS) and hyaluronic acid dialdehyde (HAD) with tunable rheological properties. The hydrogel systems have a yield point, the value of which increases with an increasing concentration of NSCTS. We have obtained the dependences of storage elastic modulus and loss modulus on the load exposure frequency at constant stress. The obtained values of the complex shear modulus increase with the growth of NSCTS molecular mass and concentration. Network parameters of hydrogels were evaluated by using rheology-based methods. We have identified the possibility of varying the ability of the obtained hydrogels to large reversible deformations, which makes it possible to use apply them in various situations.

Simultaneously improved mechanical and electromagnetic interference shielding properties of carbon fiber fabrics/epoxy composites via interface engineering

Carbon fiber reinforced composites (CFRC) are in huge demand in aviation industry for reducing the fuel consumption, despite the unfavorable electromagnetic interference (EMI) shielding property. In this work, carbon fiber fabrics (CF) were coated by a thin layer of nickel (Ni) using electroless plating to increase the electrical conductivity of the composites. Dopamine was then self-polymerized on Ni coated CF (CF-Ni) surfaces to enhance the interfacial interactions between fibers and epoxy matrix. The results showed that the introduction of 0.39 wt% of polydopamine (PDA) content leads to a significant increase of interlaminar shear strength (ILSS), tensile strength and modulus by 70.7%, 22.7% and 15.3%, respectively, compared with CF-Ni/epoxy composites with free of PDA. The dominant facture mechanisms changed from fiber pulling-out and/or debonding to fiber breakage after the introduction of PDA. Compared with CF/epoxy composites, the EMI shielding effectiveness (SE) of CF-Ni/epoxy composites increased by 77.2% and slightly decreased with the increase of the PDA content. In order to further optimize the overall performances of the composites, the laminates structures were specially designed by replacing 2 plies of CF-Ni-PDA with CF-PDA in the middle according to EMI shielding mechanisms. The composites with special laminate stacking exhibited outstanding ILSS (61.2 MPa) and EMI SE (31.0 dB), which are dominant over most reported structural composites. The effects of humidity on the mechanical and EMI shielding properties were evaluated as well, indicating that the composites played a huge application potential in aircraft.

Effect of freeze-thaw cycles on engineering properties of biocemented sand under different treatment conditions

The recently developed microbially induced calcite precipitation (MICP) method is a potentially effective and environmentally friendly technique to improve the unfavorable soil conditions. However, the durability of biotreated sand under freeze-thaw cycles has not been investigated. This study investigates the effects of freeze-thaw (FT) cycles on shear strength and shear modulus of Narmada river sand (a poorly graded liquefiable sand) treated with MICP under different conditions. The bacterial growth and biotreatment were conducted under non-sterile and environmentally uncontrolled conditions that are typically encountered in the field conditions. First, the effects of main control variables involved in the MICP treatment, specifically two bacteria strains i.e., Sporosarcina pasteurii ( S. pasteurii ) and Bacillus sphaericus ( B. sphaericus ), two treatment cycles viz. 12 h and 24 h, and different pore volumes (1 PV, 0.75 PV, and 0.5 PV) of cementation solution injection, were investigated. After 18 days of continuous treatment, the biocemented specimens were tested for unconfined compressive strength (UCS), split tensile strength (STS), hydraulic conductivity, ultrasonic pulse velocity (UPV), and shear modulus after 0, 5, 10, 15 and 20 freeze-thaw (FT) cycles. The calcite content distribution in all of the biotreated samples was also analyzed. The results demonstrated that the maximum UCS, STS, UPV, shear modulus, and reduction in hydraulic conductivity were 2333.2 kPa, 437.7 kPa, 2670 m/s, 13 GPa, and 96.6%, respectively, at 12% calcite content using S. pasteurii , 12 h treatment cycle, and injection of 1 PV cementation solution in every cycle up to 18 days. The biocemented specimens maintained almost 90% shear strength and 77% shear modulus after 10 FT cycles in 9–12% calcite precipitated samples augmented with S. pasteurii. The similar biocemented samples resulted in 14–17% and 31–35% decrease in shear strength, and 41–44% and 54–57% decrease in shear modulus after 15 and 20 FT cycles, respectively. • Non-sterile cultivation of bacteria was explored to optimize time, energy, and cost. • Bioaugmentation with two bacteria was investigated in uncontrolled environment. • Strength and shear modulus increase with the increase in calcite content. • Ultrasonic pulse velocity results showed rock-like behavior of biocemented sand. • Biocemented sand was found durable even after 20 freeze-thaw cycles.

Mechanics of deformation of malaria-infected red blood cells

Plasmodium Falciparum (pf) Malaria is one of the life-threatening infections for human red blood cells (RBCs), which deteriorates the topology of the corresponding bi-layer membranes and causes a 10-fold increase in their respective shear modulus during the well-distinguished Ring, Trophozoite and Schizont stages of infection progression. Previous efforts to characterize the bulk shear stiffness of pf-iRBC membranes include both in-vitro stretching tests and few simulations that enabled partial description of the membrane elasticity while assuming a uniform shear modulus. Although these results provided good insights into the axial-deformation of pf-iRBCs, the computed transverse diameter did not show similar agreement with the experimental values. The aim of the present work is to build a computational model that simulates the stretching tests of healthy and infected RBCs to better understand the mechanics of disease progression and its influence on the elastic properties of RBC membranes. For this purpose, a new patching technique is developed to mimic the infection progression through the decomposition of the cell membrane into infected pair patches and quasi-normal membrane segments. The incompressible membranes are modeled using the non-linear hyper-elastic Skalak constitutive model implemented through a VUMAT subroutine within the framework of a 3-D ABAQUS/Explicit finite-element model. In the advanced Schizont stage, a spheroidal-like geometry with uniform shear modulus is assumed, whereas in the other two stages, sizable circular patches of 2.4 and 4 µm in diameters, respectively, with adaptive shear moduli are implemented to replicate the stiffer pair-patches. The Skalak model indicates an 8-fold increase in the bulk shear modulus of the Schizont-cell beside showing better agreement with the published experimental results. Interestingly, for all other intermediate stages of infection, the bulk shear modulus is found to increase linearly with the percent area-infection, whereas nearly-constant shear modulus in the range of 14 µm is obtained for the quasi-normal membrane segments.

Effect of Crosslinker Amount on Properties of Poly Phenylacrylamide Gels

The monomer phenyl acrylamide was synthesized by reacting acrylamide with chloro benzene in the presence of pyridine. Fourier transform infrared spectroscopy (FT-IR) was used to characterize the resulting monomer. High conversion poly phenyl acrylamide (PPAM) containing 0, 0.5, 1, 1.5 and 2 wt % (in conversion to mass of PPAA) of N,N'-methylenebisacrylamide (MBAA) as crosslinker have been successfully synthesized. The effect of MBAA percentage on swelling parameters, clarity, mechanical and thermal properties of the prepared xerogels and hydrogels were studied. 1.5 wt % of MBAA is required to obtain clear xerogels and hydrogels. The water content (EWC), volume fraction of polymer (φ2) and weight loss during swelling decrease with increasing MBAA content. Young’s and shear modulus (E and G) increase as MBAA content increases, the values of E and G are 0.661–3.878 MPa and 0.423–2.588 MPa, respectively. The hydrogels were characterized in terms of modulus crosslinking density (ve and vt) and polymer-solvent interaction parameters (χ). The results are 0.252–0.661 mol/dm3 for ve, 0.211–0.541 mol/dm3 for vt, and 0.813–0.987 for χ. Thermal properties of polymers enhance (Tg increase) by adding MBAA. These types of polymers and their hydrogels possess new properties with potential uses in different medical applications.

Dynamic analysis of bubble in liquid cavity wrapped by viscoelastic medium

Ultrasonic wave with higher intensity will directly cavitate in soft tissue. It is an important issue in ultrasonic therapy that the cavitation bubbles in soft tissues are driven in the ultrasonic field. It is assumed that the medium inside the bubble is gas, the cavity is filled with the incompressible viscous liquid, and the medium surrounding the cavity is viscoelastic solid. To introduce the effect of the surrounding tissue, it is assumed that the tissue is incompressible, linear and Voigt viscoelastic solid. The motion of a cavitation bubble can be affected by many factors, such as acoustic pressure, acoustic frequency, tissue elasticity and cavity size. Numerical simulation shows that the resonance frequency and amplitude of the bubbles decrease with cavity radius decreasing. It is also shown that the amplitude of the radial motion for bubbles decreases with the increase of the tissue shear modulus and the frequency, when the ratio of bubble radius to the cavity radius is constant. The effect of the elasticity is very obvious, which reduces the amplitude greatly. The effect of elasticity will be less when the driving pressure is strong. It is found that the inertial cavitation threshold of bubble is relatively low in a range of 1–5 μm. The inertial cavitation threshold of bubble increases with the increase of shear modulus and driving frequency. The smaller the cavity radius, the higher the inertial cavitation threshold of the bubble is. This report aims to provide a firm theoretical basis for the future study of bubbles in a liquid-filled cavity surrounded by a viscoelasticity tissue.

Evolution of defect concentration in Zr<sub>50–</sub><i><sub>x</sub></i>Cu<sub>34</sub>Ag<sub>8</sub>Al<sub>8</sub>Pd<i><sub>x</sub></i> (<i>x</i> = 0, 2) amorphous alloys derived using shear modulus and calorimetric data

Amorphous alloys exhibit unique physical and mechanical properties, which are closely connected with their microstructural heterogeneity. The correlation between structural heterogeneity and mechanical properties is one of the important issues of amorphous alloys. Micro-alloying is an effective way to tune the mechanical and physical properties of amorphous alloys. In the present study, Zr<sub>50–</sub><i><sub>x</sub></i>Cu<sub>34</sub>Ag<sub>8</sub>Al<sub>8</sub>Pd<i><sub>x</sub></i> (<i>x</i> = 0 and 2) amorphous alloys with ability to form excellent glass are chosen as model alloys. The evolutions of heat flow and shear modulus in different states (as-cast, relaxed and crystalline) with temperature of Zr<sub>50–</sub><i><sub>x</sub></i>Cu<sub>34</sub>Ag<sub>8</sub>Al<sub>8</sub>Pd<i><sub>x</sub></i> (<i>x</i> = 0 and 2) glass system are studied by differential scanning calorimetry (DSC) and electromagnetic-acoustic transformation (EMAT) technique, respectively. The experiment demonstrates that a decrease of the shear modulus is accompanied by the endothermic heat flow and vice versa. The correlation between the heat flow and shear modulus is investigated according to the interstitialcy theory. The calculations of the interstitialcy defect concentration and activation energy spectra suggest that the microstructure remains stable at relatively low temperatures. When temperature increases, the interstitialcy defect structure is activated. Compared with that in the as-cast state, the interstitialcy defect concentration in the relaxed state is reduced by structural relaxation, indicating that temperature-dependent shear modulus softening is inhibited. At temperatures above glass transition temperature, a rapid growth of interstitialcy defect concentration results in the accelerated shear softening, which is accompanied by significant endothermic heat flow. It is noted that the minor addition of palladium reduces the interstitialcy defect concentration in the Zr<sub>50–</sub><i><sub>x</sub></i>Cu<sub>34</sub>Ag<sub>8</sub>Al<sub>8</sub>Pd<i><sub>x</sub></i> (<i>x</i> = 0 and 2) metallic glass systems. It is suggested that the introduction of Pd reduces the atomic mobility and increases the characteristic relaxation time. In parallel, the change of shear modulus as a function of the aging time (below the glass transition temperature) is studied by using EMAT equipment. The results indicate that the interstitialcy defect concentration decreases in the physical aging process, which is accompanied by an increase of shear modulus. The interstitialcy defect concentration and shear modulus change towards the quasi-equilibrium state with aging time increasing. A reduction of the interstitialcy defect concentration leads to a decrease of the shear modulus change upon microalloying by Pd into Zr<sub>50–</sub><i><sub>x</sub></i> Cu<sub>34</sub>Ag<sub>8</sub>Al<sub>8</sub>Pd<i><sub>x</sub></i> (<i>x</i> = 0 and 2) metallic glass system.

Cavitation Nucleation and Its Ductile-to-Brittle Shape Transition in Soft Gels Under Translational Mechanical Impact

Cavitation bubbles in the human body, when subjected to impact, are being increasingly considered as a possible brain injury mechanism. However, the onset of cavitation and its complex dynamics in biological materials remain unclear. Our experimental results using soft gels as a tissue simulant shows that the critical acceleration (acr) at cavitation nucleation monotonically increases with increasing stiffness of gelatin A/B, while acr for agarose and agar initially increases but followed by a plateau or even decrease after stiffness reach to ~100 kPa. Our image analyses of cavitation bubbles and theoretical work reveal that the observed trends in acr are directly linked to how bubbles grow in each gel. Gelatin A/B, regardless of their stiffness, form a localized damaged zone (tens of nanometers) at the gel-bubble interface during bubble growth. In contrary, the damaged zone in agar/agarose becomes significantly larger (> 100 times) with increasing shear modulus, which triggers the transition from formation of a small, damaged zone to activation of crack propagation.

Experimental Study on the Dynamic Modulus and Damping Ratio of Compacted Loess under Circular Dynamic Stress Paths

Dynamic loads such as earthquakes and traffic will simultaneously generate vertical dynamic stress and horizontal shear stress in the foundation soil. When the vertical dynamic stress amplitude is twice the horizontal shear dynamic stress amplitude, and the phase difference between them is 90°, a circular dynamic stress path is formed in the τzθd ~ (σzd − σθd)/2 stress coordinate system. To simulate the stress state of soil in the area of the circular dynamic stress path caused by bidirectional dynamic stress coupling, a series of tests of compacted loess under the action of a circular dynamic stress path were carried out using a hollow cylindrical torsion shear apparatus. The effects of the mean principal stress, dry density, and deviatoric stress ratio (the ratio of deviator stress to average principal stress) on the dynamic modulus and damping ratio of compacted loess were mainly studied. The test results show that, under the action of the circular dynamic stress path, the larger the mean principal stress is, the larger the dynamic compression modulus and dynamic shear modulus are. The dynamic compression modulus increases obviously with increasing dry density, but the dynamic shear modulus increases only slightly. When the deviator stress ratio increases from 0 to 0.4, the dynamic compression modulus and dynamic shear modulus increase to a certain extent. In addition, the greater the dry density and deviatoric stress ratio are, the greater the initial dynamic compression modulus and initial dynamic shear modulus of the compacted loess. The dynamic compression damping ratio of compacted loess increases with increasing mean principal stress, but the dynamic shear damping ratio decreases with increasing mean principal stress. Dry density basically has no effect on the dynamic compression damping ratio and dynamic shear damping ratio of compacted loess. When the dynamic strain exceeds 1%, the greater the deviatoric stress ratio is, the smaller the dynamic compression damping ratio and the dynamic shear damping ratio are. The research results can provide reference for the study of dynamic modulus and damping ratio of loess under special stress paths.

Elastic properties of a reservoir sandstone: a broadband inter‐laboratory benchmarking exercise

ABSTRACTLow‐frequency forced‐oscillation methods applied to a reservoir sandstone allowed determination of the Young's modulus and Poisson's ratio (from axial loading), bulk modulus (by oscillation of the confining pressure) and shear modulus (from torsional‐forced oscillations) for comparison with conventional ultrasonic data. All tests were performed on a common sandstone core sample from an oil reservoir offshore West Africa. The results show a steady increase in ultrasonic velocities and shear modulus of the dry specimen as functions of pressure, which suggests a progressive closure of the inter‐granular contacts. An increase of bulk and Young's moduli and Poisson's ratio is observed on decane saturation of the sample when tested with a sufficiently small dead volume. This observation, consistent with Gassmann's theory, suggests that such measurements probe undrained (saturated isobaric) conditions. Diminution or absence of such fluid‐related stiffening for low‐frequency measurements with dead volumes comparable with the pore volume of the specimen indicates partially drained conditions and highlights the critical role of experimental boundary conditions. Directly measured bulk and shear moduli are consistent with those derived from Young's modulus and Poisson's ratio. These results of the inter‐laboratory testing using different measurement devices are consistent in terms of the effect of frequency and fluid saturation for the reservoir sandstone specimen. Such broad consistency illustrates the validity of forced‐oscillation techniques and constitutes an important benchmarking of laboratory testing of the elastic properties of a porous medium.

Dynamic Properties of Human Hair Fiber–Reinforced Yamuna Sand

Abstract A series of drained cyclic triaxial tests was conducted to examine the behavior of sand reinforced with human hair fiber of random lengths subjected to cyclic loading. Experiments were conducted at two different relative densities (i.e., 50 and 80 %) with varying fiber content (0.25 to 1.0 %). Factors affecting the cyclic behavior, such as relative density, fiber content, load cycles, and shear strain amplitude, were examined and discussed in this article. Shear modulus and damping ratio evaluated for all the tests indicate that the maximum increase in shear modulus of reinforced sand is observed under medium shear strains and at 0.5 % fiber inclusion for 80 % relative density. However, the fiber inclusion seems ineffective with the sand at 50 % relative density. The damping ratio of reinforced and unreinforced sand did not show a marked variation except for fiber content more than optimum.

Prediction of Elastic Properties of Short Fibers Reinforced Composites (Dept.T)

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Development of environmentally friendly epoxy and composite adhesives and applications in single and mixed-modulus joints

Epoxy adhesives are common and useful materials in several fields, especially in making joints for the aerospace industry. Lately, there is a growing demand for this kind of adhesives to become more environmentally friendly. In this work, an environmentally friendly epoxy adhesive is developed using commercially available materials, exhibiting a 12% increase in green carbon content and 22% increase in shear strength. The commercial eco-friendly epoxy system is then reinforced with dry olive pit powder in order to produce an eco-friendly composite adhesive, giving a 20% shear modulus increase, for the 2.5% filler content, compared to the pure matrix. The behavior of these two materials is investigated, when these are used as adhesives in lap joints, and their main shear properties are determined. In order to manufacture adhesively bonded joints using a thick layer of liquid resin without any pre-curing step, therefore achieving improved properties, two casting-like designs of the overlap area are made and tested, one in a single-modulus configuration and a second one in a mixed-modulus mode. When an eco-friendly epoxy adhesive is applied on each edge of the mixed modulus mode instead of a fossil-based epoxy adhesive, a 30% increase in shear strength is observed. Finally, the Property Predictive Model, a modification and extension of the Modulus Predictive Model, is proposed, allowing the accurate prediction of several properties of virtually any series of particulate composite materials. When the model is applied to the aforementioned composites, it proves to be capable of accurately predicting their main shear properties.

Quantum confinement and torsional responses of single-wall carbon nanotubes filled with hydrogen molecules

Molecular dynamics simulations are performed to investigate the torsional buckling behavior of single-walled carbon nanotubes (SWCNTs) filled with hydrogen gas. The considered key factors that affect the torsional responses of the SWCNTs are the pore radius and the hydrogen storage density. Our simulated results show that there presents strap-like morphology of the tube without filled particles and strand-like morphology is observed for the tube filled in H2 particle. The results further reveal that for SWCNTs with smaller pore size, the shear modulus of the filled nanotube is much greater than pristine one; however, the shear modulus increase moderately with the filled molecules. On the other hand, for SWCNTs with larger pore size, the shear modulus falls in a narrow band of variation. Finally, it is shown that the elastic coefficient, which reflects material property, is aspect ratio dependent.

A novel sandwich panel made of prepreg flax skins and bamboo core

This work describes the bending and shear mechanical properties of a novel concept of sustainable sandwich panel made from unidirectional prepreg flaxtape skins and bamboo rings as a circular core material. A Design of Experiment (DoE) is used to determine the influence of the bamboo diameter and the type of adhesive bonding between core and skins on the equivalent density, flexural and shear properties of these panels. Numerical analysis are also performed using cohesive surface contacts between skins and bamboo rings to investigate the structural behaviour and failure mechanisms of the sandwich panels. The equivalent density is affected by both factors, with an overall decrease when larger bamboo rings and lower density adhesive are used. Although sandwich panels with the larger bamboo rings as core show superior flexural properties and skin stress, smaller bamboo rings cores shows an increase in the core transverse shear modulus. The physical and mechanical characteristics of the adhesives directly affect the failure mode and the overall structural integrity of the panels.

Electronic, elastic, vibrational and superconducting properties of a ternary superconductors LaIrP (P = P, As): Insights from DFT

We have investigated the structural, mechanical, electronic, thermodynamics, and superconducting properties of new ternary equiatomic pnictides LaIrP and LaIrAs superconductors using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vicker's hardness and chemical bonding have also been estimated for these compounds. All the investigated results are compared with available experimental data. The evaluated structural parameters are found to be in good agreement with the experimental data. The single and polycrystalline elastic moduli have been calculated and the mechanical stabilities of LaIrP and LaIrAs have been theoretically confirmed. The ductility nature appears from the values of the Pugh ratio and Poisson's ratio. The shear modulus and Young's modulus increase in the case of As substitution by P in LaIrAs. The bulk modulus increases when P substitution by As in LaIrP. The evaluated elastic moduli show that both superconductors are anisotropic material. The valence band and conduction band are overlapped in the band structure and the electronic band structure shows that both materials behave metallic nature. The most effective contribution to the density of states comes from Ir-5d states at the Fermi level. The chemical bonding of LaIrP and LaIrAs denotes the excessively anisotropic combination between ionic, covalent, and metallic interactions. The Fermi surface created with hole-type and electron-type sheets. The theoretical Vicker's hardness shows that the LaIrP material is harder than LaIrAs. The Debye temperature 227.92 K (LaIrP) and 210.56 K (LaIrAs) are calculated by using present elastic constants data. The calculated theoretical superconducting transition temperatures are 6.43 K and 5.75 K for LaIrP and LaIrAs superconductors. All superconducting phenomena indicate the phonon-mediated medium couple BCS superconductor.

Fiber Reinforced Cementitious Matrix (FRCM) for strengthening historical stone masonry structures: Experiments and computations

Seismic events highlight the inherent fragility and vulnerability of stone masonry buildings, which represent a large part of the existing historical and artistic heritage. In order to preserve these structures, numerous reinforcement techniques are typically used on masonry walls, including mortar injections, reinforced drilling, and reinforced concrete plaster. Nowadays new and less invasive strengthening techniques are preferred; among them Fiber Reinforced Cementitious Matrix (FRCM) system with lime-based mortar, which is considered to be more compatible with the intrinsic properties of these ancient structures as compared to cement-based mortar. This work aims to investigate experimentally and computationally FRCM applied as reinforcement to ancient stone masonry. In particular, the paper presents results from diagonal compression tests carried out at the University of L’Aquila (Italy) on stone masonry specimens strengthened with layers of Glass-FRCM (GFRCM). In comparison with unreinforced panels, those strengthened by the GFRCM exhibited a significant increase in shear modulus and shear strength. A computational framework based on the Lattice Discrete Particle Model (LDPM) was then used to reproduce the experimental results. The fracture behavior and the damage evolution in masonry panels were investigated under different assumptions on the GFRCM system features (bond behavior, mortar thickness, fiber anchors and fiber grid). The good agreement between experimental results and the LDPM simulations show that this approach predicts well the mechanical behavior and the damage evolution in stone masonry under quasi-static loading conditions. Moreover, it can be considered a viable tool for engineers in developing effective reinforcement techniques.

Coarse-grained modeling of nanocellulose network towards understanding the mechanical performance

Owing to the impressive mechanical properties and renewability, nanocellulose has been increasingly used for the development of lightweight materials in various applications. Here, we present a coarse-grained (CG) modeling study for investigations of mechanical performance of cellulose-based bulk material consisting of disordered cellulose nanocrystals (CNCs), forming a porous network microstructure. The simulation results reveal that increasing density and cohesive interaction between CNCs leads to an increase in shear modulus and yield stress of bulk system, which strongly depends on the cohesive energy density of the system. Notably, by evaluating the local “molecular” stiffness, the bulk CNCs system tends to become more dynamically heterogeneous with increasing density and cohesive interaction, which is similar to glass-forming liquids such as polymers. Such influence on shear modulus and dynamical heterogeneity of bulk CNCs is found to be more pronounced with variation of density, which is likely due to the high rigidity of CNC and high porosity of network microstructure. Our study provides fundamental insights into the mechanical behavior of bulk nanocellulose under the influences of key microstructural and interfacial features, which is crucial to develop an extension of structure–property relationships as established for engineering materials.