Variation Of Elastic Modulus Research Articles

Mechanical characteristics and pore evolution of red sandstone under ultrasonic high-frequency vibration excitation

Ultrasonic vibration rock breaking is a new type of rock breaking technology. By studying the mechanical properties of red sandstone under ultrasonic vibration, the mechanical behavior and damage mechanism of rock under the impact of high-frequency vibration can be revealed more comprehensively from macro- and microscopic standpoints. In this paper, the cylindrical red sandstone specimen is used as the study object subjected to vibration excitation via the ultrasonic vibration device. The change in the mechanical parameters of red sandstone specimens is analyzed via a single-axial compression test. The red sandstone specimens are vibrated to study the effects of high-frequency vibration on their natural frequency. The latter’s natural frequency is measured using the knocking method, while the micro-disruption characteristics of the red sandstone are observed via electron microscopy. The T2 spectrum, aperture distribution, porosity, and nuclear magnetic resonance image (MRI) evolution characteristics of red sandstone specimens are obtained via nuclear magnetic resonance technology. The results show that ultrasonic vibration deteriorates the red sandstone compressive strength and elastic modulus by 55.3% and 26.9%, respectively, after 120 s of excitation. Under ultrasonic vibration excitation, the rock specimen’s natural frequency is reduced by 2.4% due to its mass and elastic modulus variation. Many transgranular cracks are generated in the sandstone, splitting the crystal nucleus into smaller blocks. The generation of new micropores is observed in the T2 spectrum, and the maximum increase in the dimensions of micropores and mesopores at the two peaks is 58.7% and 4.67%, respectively. The variation trend of rock specimen porosity is completely consistent with the variation in micropores’ content. MRI images indicate that the microcrack aggregation occurs in the edge area of the contact surface between the exciter and rock.

Experimental Investigation and Numerical Modeling of Elastic Modulus Variation with Stress during Hydration and Expansion Process of Static Cracking Agent

Based on the “axial-output method”, the time histories of radial and axial expansive pressures during the hydration process of static cracking agent (SCA) in a cylinder with various diameters were obtained by experiments. With the load input taken as the product of the normalized axial expansive pressure and the amplitude coefficient, a finite element model was established to simulate the experimental chemical expansion process of SCA. The relationships between elastic modulus, radial and axial expansive pressures were then obtained. The results indicate that the elastic modulus increases with increasing radial and axial expansive pressures, and then tends to be constant. The effect of Poisson’s ratio was discussed with the elastic modulus unchanged. It is shown that the Poisson’s ratio is inversely proportional to the amplitude coefficient, and has no effect on the ratio between the axial and radial expansive pressures. Finally, a mechanical model for the variation of elastic modulus with stress during the hydration process of static cracking agent was established in terms of the major principal stress. The model was verified by the experimental results, which can be extended for numerical simulation of SCA expansion under other compressive loading conditions, and then provide practical mechanical parameters for engineering application of SCA.

Variation of elastic modulus of high strength 21-6-9 tube and its influences on forming quality in numerical control rotary draw bending

Elastic modulus is one of the most crucial mechanical property parameters that affects the plastic forming quality of bent parts, especially for springback. Elastic modulus practically varies with plastic deformation, and its precise description is necessary to enhance simulation precision for tube bending and gain steady, high-precision bent components by actual bending. Using repeated loading-unloading tensile tests (RLUTTs), the variation of elastic modulus of high strength 21-6-9 stainless steel tube (21-6-9-HS tube) in terms of plastic strain has been obtained, which its decreases rapidly at the beginning, then decreases tardily and tends to be stable in the end with increasing the plastic strain. The variation can be expressed as a first order exponential decay function. By embedding the variation of elastic modulus with the plastic strain into ABAQUS software to simulate numerical control (NC) rotary draw bending of the 21-6-9-HS tube, the prediction precision for the springback angle, springback radius, maximum cross section distortion ratio and maximum wall thinning ratio can be improved by 11.98%, 7.62%, 35.53% and 11.55%, respectively.

Nanoporous gold-polypyrrole hybrid electrochemical actuators with tunable elasticity

This study explores the effective elastic response of hybrid electrochemical actuators based on nanoporous gold – decorated with a thin film of an electrosynthesized polypyrrole – during charging in an aqueous electrolyte. We found a new and yet unrevealed phenomenon in the hybrids – a reversible change of the material’s elasticity with alternating stiffening and softening behavior. Remarkably, the stiffness variations are larger and of opposite sign as compared to a non-coated nanoporous gold. The amplitude of the elastic modulus variation increases with the thickness of the polypyrrole layer, pointing to a dominant role of processes in the polymer bulk upon its doping or undoping. We propose that the reversible stiffness of the hybrid material is governed by the competition between the increased intermolecular bonding as consequence of interactions between the charged chains and dopant anions in the polymer and its plasticization due to solvent intake.

Study of structural, vibrational, elastic and magnetic properties of uniaxial anisotropic Ni-Zn nanoferrites in the context of cation distribution and magnetocrystalline anisotropy

Co-precipitation method was adopted to obtain zinc ferrite nanoparticles substituted with nickel (0.5 ≤ x ≤ 0.7) followed by sintering at 500 °C for 2 h. The formation of spinel ferrite phase in the present ferrite compositions was confirmed from the X-ray diffractograms. The experimental lattice parameter (a) and average crystallite size (<DXRD>) are in between 8.359 - 8.348 Å and 12.8 – 14.9 nm. As doping level of Ni2+ increases, an interesting relation was existed in between a and<DXRD>, such that the first one is decreasing and the later one is increasing. The variation of average particle size (<DFE-SEM>) from FE-SEM is different from the variation of<DXRD>. The present spinel ferrite Ni0.6Zn0.4Fe2O4 possessed smaller particle size of 17.6 nm. The existence of higher and lower vibrational frequencies in between 579–587 cm−1 and 380–386 cm−1, satisfied the Waldron proposals for the ferrite phase. The variations of elastic moduli are very interesting and tricky when compared to the reported literature. The consistency of Poisson’s ratio for these ferrite compositions, revealed the isotropic behavior of present ferrite systems. The saturation magnetization (MS) at room temperature (RT) has uneven variation and a highest value of 43.2 emu/g was noticed for the composition x = 0.6. The coercivity (HC) at RT is gradually increasing with the doping level of Ni2+ ion incorporation. As temperature is decreasing below the room temperature both the MS and HC are increasing for a particular composition. The blocking temperature (TB) lies in the range of 80–125 K and is increasing with the increase of Ni2+ ion concentration. The findings of the present study were discussed in terms of cation distribution and magnetocrystalline anisotropy presuming core-shell morphology.

Повышение работоспособности древесно-металлических подшипников скольжения лесопромышленных машин

The performance of slide bearings in forestry machines and equipment is largely determined by the load-carrying capacity and antifriction qualities that depend on the bearing capacity of the sleeve (insert) material, the design rigidity and the nature of the forces during operation. As a result, the bearing materials undergo cyclic changes in the state of the sleeve material, as well as the elements that provide reinforcing, heat-conducting and anti-wear functions. The paper shows the results of research on the stress-strain behavior of anisotropic composite materials in the structures of wood-metal slide bearings. A method for ensuring vibration stability is proposed. It is based on maintaining the damping properties of the support that change in the course of wearing. The functionality of the developed program, which is used to solve the contact and thermal issues in the design of slide bearings, is described. A wood-metal material for making bearing sleeves and inserts from laminated compositions was created and studied. The compositions include a vibration-absorbing and fine-fractional component in a vibration-weighted state and a layered structure heterogeneous in thickness of the sleeve, characterized by a variable elastic modulus, that provides damping properties. The proposed design of a slide bearing using this material is focused on its use mainly in the conditions of shock-cyclic loading, which is typical for operation of most forestry machines and equipment.

Effect of process parameters on wall thinning of high strength 21-6-9 stainless steel tube in numerical control bending

Wall thinning, as one of the key defects determined directly the usability of the bent tube, should be strictly controlled. Elastic modulus changes with the plastic deformation and its influence the plastic forming quality of tube bending. To precisely predict the wall thinning of tube bending, a finite element (FE) model for numerical control (NC) bending of high strength 21-6-9 stainless steel tube (21-6-9-HS tube) was established considering the variation of elastic modulus. Using the model, the effects of process parameters on wall thinning of the 21-6-9-HS tube in NC bending were investigated. The results show that the variation of elastic modulus has no obvious effect on the change tendency of the wall thinning degree, but only increases the value of the wall thinning degree. The wall thinning degree enhances sharply at first, then occurs a platform deforming characteristics, and finally reduces abruptly from the bending section to the initial bending section, and it increases with the increase of the clearance of tube-bending die, the friction coefficient of tube-bending die and the friction coefficient of tube-wiper die or with the decrease of the clearance of tube-wiper die, but the increased degree is not significant in all conditions.

Influence of La+3 doped nano spinel ferrites on infrared spectroscopy in elastic properties via O/W micro emulsion method

The elastic moduli of La+3 substituted Ni–Co–Zn nano ferrites synthesized by O/W micro emulsion method have been determined through X-ray diffraction pattern and IR spectral analysis. The analysis of IR spectra indicates the presence of splitting in the absorption band due to the presence of small amounts of Fe2+ ions in the ferrite system. The variation of elastic moduli with composition has been interpreted in terms of binding forces between the atoms of spinal lattice. The elastic moduli values for the compositions are found larger as compared to conventional commercially prepared compositions.

A simplified dynamic constitutive model for BFRCAC under confining pressure considering the coupling effect of fibre reinforcement and mechanical damage

To effectively characterise the dynamic mechanical properties of basalt fibre-reinforced coral aggregate concrete (BFRCAC) under confining pressure, a dynamic constitutive model of BFRCAC is presented through characterising the basalt fibre reinforcement by measuring the variation in elastic modulus and the mechanical damage by measuring the fracture probability of micro-crack propagation. The dynamic mechanical properties of BFRCAC under different confining pressures were investigated using a split Hopkinson pressure bar device with active confining pressure. A comparison of the theoretical results and experimental results indicates the good validity of the dynamic constitutive model. Analysis of damage development reveals that both strain rate and confining pressure have delayed effects on damage development. The addition of basalt fibre at an appropriate content reinforces the BFRCAC; consequently, the total damage is less than the mechanical damage in the early stage of deformation. As the deformation progresses, basalt fibre is gradually destroyed and its reinforcement effect gradually disappears, causing the total damage to gradually approach the mechanical damage. The bridging effect of basalt fibre helps restrain crack propagation; this not only slows the rate of damage in BFRCAC but also improves the confining pressure effect and strain rate effect of damage development.

Influence of surface morphology and internal structure on the mechanical properties and tribological response of Boa Red Tail and Python Regius snake skin

The understanding of the tribological behavior of natural structures has been used as inspiration to design and optimize surfaces for diverse applications in engineering. In the present work, morphological, microstructural, mechanical and tribological characterization of the shed skin of two snake species, namely Boa Red Tail and Python Regius was carried out. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analyses showed the existence of deterministic patterns, i.e., ordered arrays of geometrical features at the surface, while Transmission Electron Microscopy (TEM) allowed studying the internal structure and chemical composition of the skin sheds. Nanoindentation measurements showed significant variations in hardness and elastic modulus from the surface to the inner layers of the skin, and pin-on-disc tests revealed anisotropic behavior of the friction coefficient (COF) as a function of the sliding direction against balsa wood in dry conditions. Correlations between the friction data, nano-indentation mechanical properties and subsurface skin structure were established for both species taking into account the ways in which the skins’ deterministic patterns influence the tribological performance.

A waveform modification method for testing dynamic properties of rock under high temperature

In this study, a waveform modification method was proposed using a self-designed heating device combined with the split Hopkinson pressure bar (SHPB) technique for determination of dynamic behaviors of rock at high temperature. Firstly, the temperature gradient distribution on the incident bar was measured according to the variation of elastic modulus of the bar with temperature, and the relationship between the longitudinal wave velocity and temperature of the bar was obtained based on one-dimensional stress wave theory. The incident bar with a temperature gradient was divided into a series of microelements, and then the transmission coefficient of the whole incident bar was obtained. Finally, the stress wave was modified by the transmission coefficient from 25 °C to 600 °C. This method was used to study the dynamic properties of rock at high temperature, which not only preserves a classical SHPB device, but also effectively ensures the accuracy of the experimental results. A dynamic Brazilian disc experiment was carried out to explore the influences of loading rate and temperature on dynamic tensile strength of sandstone at high temperature using the proposed waveform modification method.

Porosity dependence of elastic moduli of snow and firn

AbstractMeasurements of elastic wave velocities enable non-destructive estimation of the mechanical properties, elastic moduli and density of snow and firn. The variation of elastic moduli with porosity in dry snow and firn is modeled using a differential effective medium scheme modified to account for the critical porosity above which the bulk and shear moduli of the ice frame vanish. A comparison of predicted and measured elastic moduli indicates that the shear modulus of ice in snow is lower than that computed from single crystal elastic stiffnesses of ice. This may indicate that the bonds between snow particles are more deformable under shear than under compression. A partial alignment of ice crystals also may contribute. Good agreement between elastic stiffnesses of the ice frame obtained from elastic wave velocity measurements and the predictions of the theory is observed. The approach is simple and compact, and does not require the use of empirical fits to the data. Owing to its simplicity, this model may prove useful in a variety of potential applications such as construction on snow, interpretation of seismic measurements to monitor and locate avalanches and estimation of density within compacting snow deposited on glaciers and ice sheets.

Modulating Nanoinhomogeneity at Electrode–Solid Electrolyte Interfaces for Dendrite‐Proof Solid‐State Batteries and Long‐Life Memristors

AbstractDendrite penetration in ceramic lithium conductors severely constrains the development of solid‐state batteries (SSBs) while its nanoscale origin remains unelucidated. An in situ nanoscopic electrochemical characterization technique is developed based on conductive‐atomic force microscopy (c‐AFM) to reveal the local dendrite growth kinetics. Using Li7La3Zr2O12 (LLZO) as a model system, significant local inhomogeneity is observed with a hundredfold decrease in the dendrite triggering bias at grain boundaries compared with that at grain interiors. The origin of the local weakening is assigned to the nanoscale variation of elastic modulus and lithium flux detouring. An ionic‐conductive polymeric homogenizing layer is designed which achieves a high critical current density of 1.8 mA cm–2 and a low interfacial resistance of 14 Ω cm2. Practical SSBs based on LiFePO4 cathodes can be stably cycled over 300 times. Beyond this, highly reversible electrochemical dendrite healing in LLZO is discovered using the c‐AFM electrode, based on which a model memristor with a high on/off ratio of ≈105 is demonstrated for &gt;200 cycles. This work not only provides a novel tool to investigate and design interfaces in SSBs but also offers opportunities for solid electrolytes beyond energy applications.

A comparative study of the experimental and the theoretical elastic data of silver oxide incorporated zinc tellurite glass system doped with Sm3+ Nps ions

The melt-quenching technique was used to fabricate a series of silver oxide incorporated zinc tellurite glass system doped Sm3+ NPs ions with chemical composition of [{(TeO2)0.7 (ZnO) 0.3}0.99 (Sm2O3 NPs) 0.01]1-y (Ag2O) y, y = 0.005, 0.01, 0.015, 0.02 and 0.025 M fraction. The samples were then characterized using densimeter, FTIR, XRD and ultrasonic method. Variations in density, molar volume, ultrasonic velocity, elastic moduli and Poisson’s ratio were discussed and correlated with the composition of the glass samples and the FTIR spectrum. The presence of Sm2O3 NPs was confirmed using high-resolution transmission electron microscopy (HR-TEM) with particles size of 72.43 nm. Ag2O incorporation encouraged bridging and non-bridging oxygen formation in the tellurite network. Additionally, elastic moduli and Poisson’s ratio were compared with the theoretically measured data using Makishima and Mackenzie, Rocherulle and Bond compression models.

Valence Electron Ratio for Design of Shape Memory Alloys with Desired Phase Transformation Temperatures

Dependence of phase transformation temperatures of TiPd- and TiPt-based shape memory alloys on valence electron ratio (VER), number (ev/a), and average atomic number of the alloys (Z) are investigated. The alloys have medium numbers of valence electrons (6.6 ≤ ev/a ≤ 7.3) that are near 7 and a wide range of the average atomic number (Z = 25–54). The forward and reverse phase transformation temperatures, Ms and (As), increase with average atomic number of the alloys, respectively. Clear correlations between transformation temperatures and VER are found. Ms and (As) both decrease from around 1184 °C (1175 °C) to as low as 20 °C (32 °C), respectively, with increasing VER from 0.134 to 0.270. Temperature hysteresis of the thermoelastic transformation in these alloys tends to decrease with increasing VER. Dependence of transformation temperatures and temperature hysteresis of these shape memory alloys on VER is discussed based on the variations of elastic moduli and atomic bonding due to composition change.

Measurement of Suction Stress and Soil Deformation at High Suction Range

Abstract Suction stress is the effective stress independent of mechanical boundary conditions but is due to water content variation. It occurs on or near particle contacts and does not directly transfer through the soil skeleton and hence can only be and has been measured indirectly and deduced from soil’s strength or deformation. In this work, a new technology to measure the soil-water retention curve, soil shrinkage curve, and suction stress characteristic curve in a high suction environment is established. A humidity-controlled device to measure suction stress was developed based on a previously established drying cake method. Nitrogen gas and molecular sieves were introduced as desiccant in addition to saturated salt solutions to generate an extreme dry environment up to 850 MPa of matric suction for the first time. A focus on the effect of adsorptive soil-water interaction on hydromechanical properties of expansive soils provides enriched information on elastic modulus variation, soil deformation evolution, and matric suction development of soil in very low water contents, making the suction stress measurement possible for matric suction as high as 850 MPa.

Relative variations of nonlinear elastic moduli in polystyrene-based nanocomposites

In this paper we apply the methodology based on the analysis of changes in acoustic wave velocities under static stress for measurements of the third-order elastic moduli in three polystyrene-based nanocomposites with different fillers: SiO2 particles, halloysite natural tubules, and carbon black particles. The samples were fabricated by the same technology and our data provide information on relative changes of nonlinear properties of the composites caused by addition of the fillers. The data obtained for composites are compared with that for commercial grade polystyrene. The substantial variations of the nonlinear elastic moduli for composites with different types of fillers are demonstrated and analyzed. The results are in a qualitative agreement with theoretical predictions.

Mechanical properties of additively manufactured variable lattice structures of Ti6Al4V.

Engineered micro- and macro-structures via additive manufacturing (AM) or 3D-Printing can create structurally varying properties in part, which is difficult via traditional manufacturing methods. Herein we have utilized powder bed fusion-based selective laser melting (SLM) to fabricate variable lattice structures of Ti6Al4V with uniquely designed unit cell configurations to alter the mechanical performance. Five different configurations were designed based on two natural crystal structures - hexagonal closed packed (HCP) and body-centered cubic (BCC). Under compressive loading, as much as 74% difference was observed in compressive strength and 71% variation in elastic modulus, with all samples having porosities in a similar range of 53 to 65%, indicating the influence of macro-lattice designs alone on mechanical properties. Failure analysis of the fracture surfaces helped with the overall understanding of how configurational effects and unit cell design influence these samples' mechanical properties. Our work highlights the ability to leverage advanced manufacturing techniques to tailor the structural performance of multifunctional components.

Effective estimation of flexural damage and strength of double-layer laminated composite beam

Layer structure like laminated composite beam (LCB) is widely used in engineering, and its mechanical properties always play an important role in application. Actually, its stress, strain and bending resistance will change with the variation of elastic modulus, layer thickness and damage parameter. In this paper, several significant variables, namely height, elastic modulus and damage modulus are considered comprehensively to estimate flexural damage and strength of double-layer LCB. Based on the definition and development prediction of damage, the position of the neutral axis when the beam fails is analyzed first, and then the estimation of its flexural strength is given. In addition, a reliable prediction of damage failure for LCB is carried out, and the change law of the neutral axis position and flexural strength of LCB under different variables is discussed accordingly. This will facilitate a more reasonable design of the laminated composite structure in engineering practice.

The impact of matrix texture and whisker orientation on property anisotropy in titanium matrix composites: Experimental and computational evaluation

In order to understand the relationship between microstructure and mechanical property as well as provide new guidance for composites design, the impacts of matrix texture and TiB whisker orientation on anisotropy of mechanical properties in hot-rolled titanium matrix composites (TMCs) were investigated by experimental and computational methods. The results show that the matrix contains a strong transverse type (T-type) texture due to the superposition of deformation texture and transformation texture. TiB whiskers aligned along the rolling direction (RD) enhance the intensity of the 112‾0 fiber texture in the matrix due to their special orientation relationship with matrix alloy ([112‾0]α−Ti∥[020]TiB). Significant variations in elastic modulus, yield strength and ductility are all noted, depending on the orientation of the tensile axis with respect to the basal of matrix texture and whisker axis. These property anisotropies were further quantified and corroborated numerical models as a function of matrix texture and whisker orientation. Specifically, T-type matrix texture results in a lower modulus and yield strength but a higher ductility in RD. However, the aligned whiskers lead to higher modulus, yield strength and ductility in RD. The strengthening contribution from aligned TiB whiskers decreases rapidly with cos4α with increasing off-axis angle (α). Moreover, the modeling results predict that the TiB whiskers would undergo fracture if the aspect ratio exceeds ARc/cos2α; otherwise, the interfacial debonding would occur.