Uniform Compression Research Articles

Some Aspects of Buckling Behavior of Channel Section Members Under Eccentric Compression

The buckling behavior of short length thin-walled cold-formed steel (TWCFS) columns of lipped channel cross-section is considered in the paper. The problem of buckling loads and the load carrying capacity of TWCFS members subjected to simple loading systems (pure bending or uniform compression) has been with satisfactory accuracy solved within the theory of thin-walled structures, as well as in design code specifications. However, the same problem concerning members subjected to combined loadings (compression and bending, eccentric compression) is still an open question [3]. The Eurocode [1] gives accurate predictions of the buckling load and ultimate strength of TWCFS members under concentric axial compression , but is less accurate in the examination of eccentrically compressed columns. TWCFS short length members are usually members of Class 4 sections [1]. Since these sections are prematurely prone to local or distortional buckling and they do not have a real post-elastic capacity, a failure of such members is initialized by the local-global interactive buckling of plastic-elastic type [2]. Thus, examination of buckling behavior of such members is of substantial importance in the case of eccentric compression, which has not been entirely recognized so far.

In-Plane Liquid Electrolyte Permeability of Porous Electrode in Vanadium Redox Flow Battery

Vanadium redox flow batteries (VRFBs) have received broad recognition due to their attractive characteristics, i.e., flexibility and scalability, high coulombic efficiency, and long cycle life. However, rapid market penetration of this technology is still restrained by high system capital cost and relatively low energy and power density compared to other energy storage technologies. At the cell level, mass transport contributes significantly to performance losses, limiting VRFB performance, especially for cells operating at high power densities [1]. Improving mass transport in the VRFB electrodes can lower system cost by enabling higher power densities and larger depth of discharge windows. In these systems, convective mass transport in the electrode is directly proportional to the electrochemical performance of the cell [2]. Permeability and diffusivity of the vanadium active species are also significant mass transport parameters affecting electrochemical performance [3]. In this study, the in-plane electrolyte permeability of the porous electrode is investigated computationally and experimentally as a function of electrode compression.Lattice Boltzmann models (LBMs) are a class of numerical methods which can be used to simulate fluid flows, mass transfer, heat transfer and many relevant physical phenomena which occur in these fields. The implementation of boundary conditions combined with the ease of parallelization make LBMs attractive for modeling mass transfer in geometrically complex domains such as porous media. A three-dimensional single-relaxation-time (SRT) LBM is employed (utilizing the Palabos library written in C++) to simulate the liquid electrolyte in the porous electrode [4]. Pressure-driven flow in porous media is achieved by imposing a constant pressure at the inlet and a constant lower pressure at the outlet. A computational domain (100 x 100 x 100 lattice unit) created within Python (Porespy module) [5] consists of randomly-generated fibers, having uniform diameter to simulate the carbon paper electrode pore structure as seen in Figure 1. Porosity of the unit structure is achieved by controlling the number of fibers in the domain. Permeability parameters are calculated for generated pore structures as functions of the electrode porosity.The in-plane electrolyte permeability of porous electrodes was measured to compare with computational predictions. The sample electrode was placed between two plates as shown in Figure 2. Various electrode thicknesses were tested using an incompressible PTFE gasket. The end plates were secured by eight bolts to a torque of 10 N m each to ensure uniform compression and tight sealing. The electrode thickness during compression was converted to porosity to compare experimental measurements with mathematical model predictions [6]. The inlet pressure was measured via pressure transducer (Omega Engineering Inc, 0-50 psi, 0.25% accuracy, Norwalk, CT, USA) for a range of flow rates from 10 mL min-1 up to 50 mL min-1 at each electrode thickness. The permeability was then calculated using Darcy’s law for incompressible fluid flow.Good agreement was achieved between experimental measurements and computational predictions. The result of this study will provide useful data for three-dimensional multi-physics VRFB models. References Ertugrul, T. Y., Clement, J. T., Gandomi, Y. A., Aaron, D. S., and Mench, M. M. “In-Situ Current Distribution and Mass Transport Analysis via Strip Cell Architecture for a Vanadium Redox Flow Battery” Journal of Power Sources 437, (2019): 226920. doi:10.1016/j.jpowsour.2019.226920Ertugrul, T. Y., Daugherty, M. C., Houser, J. R., Aaron, D. S., and Mench, M. M. “Computational and Experimental Study of Convection in a Vanadium Redox Flow Battery Strip Cell Architecture” Energies 13, no. 18 (2020): 4767. doi:10.3390/en13184767Ertugrul, T. Y., Daugherty, M., Aaron, D., and Mench, M. M. “Vanadium Flow Battery Electrochemistry and Fluid Dynamics Model with In-Situ Current Distribution Validation” ECS Meeting s MA2020-01, no. 3 (2020): 473–473. doi:10.1149/ma2020-013473mtgabsChopard, J. L. and O. M. and D. K. and A. P. and D. L. and F. B. and M. B. B. and Y. T. and S. L. and S. L. and F. M. and J. L. and C. K. “Palabos: Parallel Lattice Boltzmann Solver” Computers & Mathematics with Applications no. 0898–1221 (2020): doi:https://doi.org/10.1016/j.camwa.2020.03.022Gostick J, Khan ZA, Tranter TG, Kok MDR, Agnaou M, Sadeghi MA, J. R. “A Python Toolkit for Quantitative Analysis of Porous Media Images. Journal of Open Source Software” (2019): doi:10.5281/zenodo.2633284Mench, M. M. “Fuel Cell Engines” Fuel Cell Engines (2008): doi:10.1002/9780470209769 Figure 1

Semi-Analytical Model to Predict the Elastic Post-Buckling Response of Axially Compressed Cylindrical Shells With Tailored Distributed Stiffness

Abstract This study introduces an approximate analytical model to predict the post-buckling response of cylinders with tailored non-uniform distributed stiffness. The shell's wall thickness, and thus its stiffness, is tailored so as to obtain multiple controlled elastic local buckling events when the cylinder is subjected to uniform axial compression. The proposed model treats cylinder segments of different stiffness as individual panels and combines their response by considering them as connected linear or nonlinear springs. The governing equations for the panels are formulated using von Karman's theory and solved by Galerkin's approximate method for a predefined radial deformation. Radial deformation functions are used to improve the model's accuracy, and results show that the model's accuracy increases significantly with the number of considered radial functions. The model's predicted axial response for different cylinders is compared with results from experiments on three-dimensional printed samples. Results indicate that this model accurately predicts the order of the buckling events, while the buckling forces from the model are higher than those measured experimentally.

Mathematical simulation of elastoplastic deformation in cubic materials with an account of anisotropic bulk compressibility

It was shown for the first time that when modelling the deformation of materials with cubic symmetry (at full stress), the rotation of the computational axes leads to the identification of anisotropic volumetric compressibility. Loading of the materials with cubic symmetry of properties in the directions not coincided with the main directions (for example, 011) allows one to detect 75% cases of the auxetic single crystals (i.e. with negative Poisson’s ratio). In these cases, the negative volumetric compressibility has anisotropy, in contrast to the volumetric compressibility calculated along the crystallographic axes for cubic materials. Anisotropy of the volumetric compressibility leads to anisotropy of velocities of propagation of body waves. This paper considers several elastoplastic problems for a cubic material with different orientations of a coordinate system about its crystallographic axes. The behaviour of such a material under dynamic loads is modelled with an account of anisotropic bulk compressibility to provide the same anisotropy of bulk wave velocities in the elastic and plastic ranges and a uniform pressure function at the elastic-to-plastic strain transition. For each orientation of the coordinate system and respective planes, different values at the indicatrices of elastic constants are specified, and this specifies different deformation processes in cubic materials. Such an effect is demonstrated by solving three problems in three-dimensional (3D) statements approximating the following processes: (1) one-dimensional elastoplastic deformation in a thin target impacted by a thin plate; (2) uniform compression in a spherical body under pulsed hydrostatic pressure; and (3) 3D elastoplastic deformation in a cylindrical body striking a rigid target in view of anisotropic bulk compressibility. The problems were solved numerically using original programs based on the finite element method modified by GR Johnson for impact problems. Solving problems in a 3D formulation makes it possible to take into account the dependences of the direction of the elastic and plastic characteristics of the material, as well as the velocities of propagation of elastic and plastic waves from that direction. The simulation results suggest that for cubic materials, changing the orientation of two coordinate axes in a plane changes the strains along all three axes, including those perpendicular to this plane. It is concluded that anisotropic bulk compressibility in cubic materials should be allowed for by mathematical models of their elastic and plastic deformation. We demonstrate that the orientation of a computational coordinate system for cubic materials should be in those directions in which their deformation is analysed in each particular case.

Residual Ultimate Strength of Steel Plates with Longitudinal Crack and Pitting Corrosion under Axial compression: Nonlinear Finite Element Method Investigations

The main aim of present study was to determine the ultimate strength of cracked and corroded plates under uniform in-plane compression. Corrosion is considered as pitting-type corrosion at one side of the plate with a central longitudinal crack. Nonlinear finite element analysis using commercial computer code, ANSYS, is used to determine the ultimate strength of deteriorated plates. Different geometrical parameters, including the aspect ratio (AR) and thickness of the plate, number of pits, pit depth-to-thickness ratio, and crack length, are considered. It is found that the AR of plates have great influence on the ultimate strength of cracked-pitted plates. Because of the position and orientation of the crack, the length of central longitudinal crack has no influence on ultimate strength reduction of cracked and cracked-pitted plates. The results show that regardless of the number of pits and crack length, in thin plates where buckling controls failure modes at ultimate strength, the number of pits has less influence on reduction of the ultimate strength than thick plates where yielding controls failure mode. Also it is concluded that in rectangular plates, arrangements of pits has more effect on reduction of the ultimate strength of cracked-pitted plates than the number of pits.

The stress-strain state of the spherical body under uniform compression taking into account the radial non-monotonic distribution of the material elastic characteristics

The mathematical model describing the centrally symmetric stress-strain state of an inhomogeneous elastic spherical body under the action of uniform all-sided compression is constructed. Approximate analytical solutions are found. The inhomogeneity of the elastic characteristics of the material is modeled by a radial non-monotonic elastic modulus at a constant Poisson’s ratio. Based on experimental data, the components of the stress-strain state are numerically calculated for the problem under consideration, and characteristic effects are revealed.

Influence of uniform compression on fluctuation paraconductivity of single crystals Y0.77Pr0.23 Ba2Cu3O7−δ

The work investigated the effect of high hydrostatic pressure up to 12 kbar on the fluctuation conductivity of medium-doped praseodymium (x≈0.23) single-crystal Y1−xPrxBa2Cu3O7−δ samples. It was found that in contrast to the pure YBa2Cu3O7−δ samples and the Y0.95Pr0.05Ba2Cu3O7−δ samples lightly doped with praseodymium, the application of high pressure leads to a significant decrease in the transverse coherence length ξc and an increase in the baric derivative dTc/dP. Possible mechanisms of the effect of high pressure on the critical temperature and coherence length in the bulk of the experimental sample are discussed.

ВЛИЯНИЕ ДАВЛЕНИЯ НА ХАРАКТЕРИСТИКИ ДИОДОВ ШОТТКИ ИЗ ПЕРЕКОМПЕНСИРОВАННОГО ПОЛУПРОВОДНИКА

The effect of uniform compression on the properties of n-Si <Au> Schottky diode based on overcompensate semiconductor has been studied. It was shown that overcompensation is a result of structure defects generation in the thermo treatment of the starting silicon wafer

2D Model Graphene Nanoribbons in a Polymer Matrix

A 2D model of a graphene nanoribbon in a polymer matrix (in a crystal of polyethylene macromolecules) is proposed, which makes it possible to consider large polymer samples with inclusions of single- and multilayer nanoribbons. The model is used to show that it is energetically more favorable for nanoribbons to be inside the polymer matrix than on its surface, and it is advantageous for multilayer nanoribbons inside to separate into individual layers. Compression of nanoribbons inside and on the surface of the matrix is carried out. It is shown that, regardless of the number of layers of a nanoribbon, its longitudinal compression, together with the matrix, can occur according to two scenarios: uniform compression of the entire nanoribbon + matrix system or nonuniform compression, for which localized bending occurs at the nanoribbon. The first scenario is achieved with weak compression, the second, with strong compression.

Interactive Plastic Local Buckling of Box-shaped Aluminium Members under Uniform Compression

A theoretical approach for predicting the ultimate resistance of aluminium alloy members subjected to local buckling under uniform compression is presented focusing the attention on box sections. Starting from the J2 deformation theory of plasticity, the theory of plastic buckling of plates is presented including, as an original contribution, also the variability of the Poisson’s ratio depending on the stress levels. The differential equation of the plates at the onset of buckling is developed and the corresponding solution is provided. Starting from the obtained closed-form solution, the interactive buckling either in the elastic or in the plastic range is analysed. The interaction between the plate elements constituting the member section is explicitly accounted for using a completely theoretical approach where the evaluation of the critical stress leading to local buckling in the plastic range is derived as the value corresponding to the existence of a non-trivial solution for which the determinant of the matrix of the equation system is equal to zero. The accuracy of the plastic buckling theory is pointed out by comparing the buckling resistance obtained by the theoretical approach with the values of the ultimate resistance provided by stub column tests.Finally, some advances concerning the use of the effective thickness approach, currently adopted by Eurocode 9, are also proposed and herein presented for the first time and compared with test results.

Strength, plasticity, thermal stability and strain rate sensitivity of nanograined nickel with amorphous ceramic grain boundaries

A large fraction of grain boundaries imparts high strength to nanocrystalline (NC) metals but causes the poor thermal stability of microstructures and a significant reduction of strength with increasing deformation temperature. Stabilizing the microstructure is thus desired. In this work, we self-patterned 1–2 nm thick amorphous ceramic SiOC as grain boundaries in NC Ni with grain size of 13 nm through co-sputtering 75 at.%-Ni and 25 at.%-SiOC, producing Ni-SiOC amorphous ceramic reinforced metals (Ni-SiOC ACRMs) with a core-shell structure. Microscopic characterizations of Ni-SiOC ACRMs before and after 400 °C annealing and after compression deformation confirmed the thermally and mechanically stable core-shell structure. Mechanical properties, such as stress-strain responses and strain rate sensitivity of Ni-SiOC ACRMs over a range of temperatures from room temperature (RT) to 400 °C were measured using in situ micropillar testing in a scanning electron microscope (SEM). We demonstrated that amorphous ceramic SiOC grain boundaries impart a high strength (2.5 GPa at RT and 1.6 GPa at 400 °C), large compressive plasticity (uniform compression strain greater than 35% without shear instability) and thermal stability to Ni-SiOC ACRMs. High strain rate sensitivity (0.015 at RT to 0.042 at 400 °C), small activation volume (about 13b3) and no obvious strain hardening/softening behavior suggest that plastic deformation is accommodated by dislocation slips in Ni grains. Amorphous ceramic grain boundaries act as strong barriers and sinks for impeding and trapping dislocations, strengthening the ACRMs and promoting plastic co-deformation between Ni nanograins and amorphous ceramic grain boundaries; the accumulated dislocations are smeared along the amorphous-crystal interfaces, preventing formation of localized shear bands across multiple nanograins.

Cell-induced confinement effects in soft tissue mechanics

The mechanical properties of tissues play a critical role in their normal and pathophysiological functions such as tissue development, aging, injury, and disease. Understanding tissue mechanics is important not only for designing realistic biomimetic materials for tissue engineering and drug testing but also for developing novel diagnostic techniques and medical interventions. Tissues are heterogeneous materials consisting of cells confined within extracellular matrices (ECMs), both of which derive their structural integrity, at least in part, from networks of biopolymers. However, the rheology of purified reconstituted biopolymer networks fails to explain many key aspects of tissue mechanics. Notably, purified networks typically soften under applied compression, whereas many soft tissues like liver, fat, and brain instead stiffen when compressed. While continuum models can readily capture this compression-stiffening behavior, the underlying mechanism is not fully understood. In this perspective paper, we discuss several recently proposed microscopic mechanisms that may explain compression stiffening of soft tissues. These mechanisms include (I) interactions between the ECM and volume-preserving inclusions that promote extension-dominated stiffening of fibrous ECMs when subject to uniform compression, (II) ECM interactions with rigid inclusions under non-uniform compression, (III) other internal physical constraints that cause compression stiffening of cells and ECMs, and (IV) propagation of compressive forces through jammed, compression-stiffening cells. We further identify a few of the many open problems in understanding the structure–function relationship of soft-tissue mechanics.

Uniaxial Compression Mechanical Analysis of Cylindrical Rock Specimens Based on Space Axisymmetric Problem

The common failure forms in the uniaxial compression test of standard cylindrical rock specimens are symmetric cone failure and splitting failure. In the past, two kinds of failure forms were explained from the plane problems of elasticity theory. However, there was a lack of research based on space problems. In this paper, based on spatial axisymmetric elastic mechanics theory, three-dimensional stress function is constructed for the cylindrical rock specimen under uniform axial compression by adopting the semi-inverse method. According to the stress function, the stress components and the principal stress are deduced when considering the end effect. The failure form is speculated, which can well explain the two common types of damage in uniaxial compression. This work may enrich the basic research of rock mechanics.

Tunable vacuum ultraviolet cross-luminescence from KMgF under high pressure as potential fast-response scintillator.

We report on the potential of the potassium magnesium fluoride (KMgF) crystal as a fast-response scintillator with tunable cross-luminescence (CL) emission wavelength through high-pressure applications. By performing first-principles density functional theory calculations using the Perdew-Burke-Ernzerhof (PBE) hybrid functional including exact exchange (PBE0) and Green's function and screened Coulomb interaction approximation as implemented in the Vienna Ab initio Simulation Package using plane-wave basis sets within the projector-augmented wave method, we identify the specific valence-to-core band transition that results in the experimentally observed CL emission at 148 nm (8.38 eV) and 170 nm (7.29 eV) wavelengths with intrinsically fast decay times of 290 ps and 210 ps, respectively. Uniform volume compression through hydrostatic high-pressure applications could decrease the energy gap between the valence and core bands, potentially shifting the CL emission wavelength to the ultraviolet (UV) region from 200 nm (6.2 eV) to 300 nm (4.1 eV). The ability to tune and shift the CL emission to UV wavelengths allows for the detection of the CL emission using UV-sensitive photodetectors in ambient atmosphere instead of highly specialized vacuum UV detectors operating in vacuum while maintaining the intrinsically fast CL decay times, thereby opening up new possibilities for KMgF as a fast-response scintillator.

Research on the post-buckling strength of screw composite thin plate with large deflection

The effect of membrane stress on axial strength of screw composite thin plate is addressed in this paper. In order to study the post-buckling behavior of the screw composite thin plate, the instability mechanism was analyzed theoretically based on the large deflection theory, experimental and numerical investigation were described in this paper. Considering the shear deformation and screw restraint, the calculation model of ultimate stress for the screw composite thin plate was established, and the analytical formula of the ultimate stress of the screw composite thin plate with four simply supported edges and two opposite sides under uniform compression was derived. The composite thin plate obtained from cold-formed steel back-to-back built-up short columns assembled by self-drilling screws, commonly used in practical projects, was used as the test models. Then, the experimental and numerical results were compared with theoretical results mentioned above to modify the proposed formula. According to the comparison, the modified coefficient φ was derived by nonlinear regression, and the modified ultimate stresses were in good agreement with the experimental and numerical results, the results were reasonable and reliable.

Ultimate resistance of longitudinally stiffened curved plates subjected to pure compression

Design guidelines are proposed for the calculation of the ultimate resistance of longitudinally stiffened, transversally curved plates subjected to uniform compression. They represent internal plated members of box-girders. The proposed method is in accordance with the Eurocode formalism and follows the effective width concept from EN 1993-1-5. The latter strongly underestimates the resistance of stiffened, curved plates. Therefore, the new method extends the scope of the current European standards from flat to curved plates. A general form of the buckling coefficient is derived for orthotropic shell buckling, which is consistent with the solution for orthotropic buckling of plates according to Annex A, EN 1993-1-5. The method presented combines the new equation with the existing design proposals for unstiffened curved panels from the literature and the current design rules for flat plated structures according to EN 1993-1-5. The method is compared with numerical results on simply supported, cylindrically curved panels stiffened with trapezoidal longitudinal stiffeners, where the longitudinal edges are unconstrained and loaded edges are constrained, and a good correlation is achieved.

Efficient Approximate Analytic Solution for the Problem of Stability of a Three-Layer Conic Shell Under Combined Loading

We propose a solution of the linear problem of behavior of an elastic three-layer conic shell under the combined action of several external force factors (uniform pressure, axial compression, and torque), which may lead to the loss of stability of the analyzed structure. The problem is reduced to the integration of the resolving singular sixth-order ordinary differential equation with variable coefficients. The solutions obtained by the methods of phase integrals (WKB method), hybrid WKB–Galerkin method, and finite-difference method are compared. We demonstrate the advantages of the asymptotic hybrid approach to the solution of the analyzed class of equations. The rational relationships between the thicknesses and elasticity moduli of layers of the shell required for attainment of the highest stability of the investigated structure under given external loads are analyzed. The problem of construction of the boundary surfaces separating the regions of stability and instability of the shell is discussed. The efficiency of three-layer shells as load-bearing elements aimed at improving stability is confirmed.

Study of the Elastic and Elastoplastic Properties of a Dispersed Composite Based on Computational Experiments

In the paper, the averaging method was used to determine the effective elastic moduli of dispersed B4C/2024Al composites and porous geomaterials using 2D and 3D X-ray images of their internal structure. A comparison of calculated values of Young’s modulus with experimental data showed that the use of 2D models of the real structure led to underestimated values of Young’s modulus, especially for porous materials. It was found that 3D models with model inclusions in the form of ellipsoids could be used to estimate the effective elastic moduli for composites with inclusion concentrations to 20%. Computational experiments on 3D models of the B4C/2024Al composite showed that the stress concentration in its inclusions and matrix was significantly higher when the real inclusions were considered instead of ellipsoidal ones. The dynamic behavior of the dispersed B4C/2024Al composite was studied using models with inclusions in the form of ellipsoids. Stress concentrations under dynamic loading were significantly higher than those in statics. The elastoplastic behavior of the real structure of the B4C/2024Al composite was investigated in computational experiments on uniform compression, pure shear, and a combination of pure shear and uniform compression. Calculations considering the real structure of inclusions showed that the pure shear diagram depended on the uniform compression, although such a dependence was absent for the matrix material.

Structure-property relationships of molecular shape and orientation with compression and expansion of xylitol.

Easy crystallization distinguishes xylitol from other sugars, which usually condense into a syrup from aqueous solution. Although two polymorphs, i.e. metastable monoclinic and high-density orthorhombic, have been reported for xylitol, only the latter is in practical use. Under high pressure, the same orthorhombic phase has been obtained by both isothermal and isochoric recrystallization. The stability of the orthorhombic xylitol phase to 5.0 GPa has been correlated with a uniform compression of all hydrogen bonds and some flexibility of the molecular conformation, which cushion the pressure-induced local strains. The anisotropic compressibility of xylitol and its thermal expansion are consistent with the rule of inverse effects of pressure and temperature. This inverse strain relationship has been correlated with the dimensions and orientation of xylitol molecules in the crystal structure.

In-plane failure mechanisms and strength design of circular steel tubular Vierendeel truss arches with rectangular section

This paper investigates the in-plane failure mechanisms and strength of circular steel tubular Vierendeel truss arches with a rectangular section by using the finite element models. Firstly, the analytical solution for the in-plane elastic buckling load of pin-ended circular steel tubular Vierendeel truss arches with a rectangular section under a uniform radial load is obtained. Then, limiting conditions of avoiding chord local buckling before the global elastic buckling of the arch are also derived. Lastly, the in-plane instability mechanisms and failure modes of the arch under a uniform radial load, a full-span uniform vertical load (FSUVL) and a half-span uniform vertical load (HSUVL) are investigated. It is found that the arch may undergo a global failure mode or three local failure modes under FSUVL and HSUVL. Based on the theoretical and finite element results, a design equation for the global strength of arches subjected to uniform compression is proposed. Strength design equations for global failure and local failure of arches subjected to FSUVL and HSUVL are also proposed. There is a good agreement between the prediction of the proposed design equations and the FE results.