Modulus Of Elasticity In Tension Research Articles

Studying the Structure and Properties of Epoxy Composites Modified by Original and Functionalized with Hexamethylenediamine by Electrochemically Synthesized Graphene Oxide.

In this study, we used multilayer graphene oxide (GO) obtained by anodic oxidation of graphite powder in 83% sulfuric acid. The modification of GO was carried out by its interaction with hexamethylenediamine (HMDA) according to the mechanism of nucleophilic substitution between the amino group of HMDA (HMDA) and the epoxy groups of GO, accompanied by partial reduction of multilayer GO and an increase in the deformation of the carbon layers. The structure and properties of modified HMDA-GO were characterized using research methods such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy and Raman spectroscopy. The conducted studies show the effectiveness of using HMDA-OG for modifying epoxy composites. Functionalizing treatment of GO particles helps reduce the free surface energy at the polymer-nanofiller interface and increase adhesion, which leads to the improvement in physical and mechanical characteristics of the composite material. The results demonstrate an increase in the strength and elastic modulus in bending by 48% and 102%, respectively, an increase in the impact strength by 122%, and an increase in the strength and elastic modulus in tension by 82% and 47%, respectively, as compared to the pristine epoxy composite which did not contain GO-HMDA. It has been found that the addition of GO-HMDA into the epoxy composition initiates the polymerization process due to the participation of reactive amino groups in the polymerization reaction, and also provides an increase in the thermal stability of epoxy nanocomposites.

The Thermal Stress Problem of Bimodular Curved Beams under the Action of End-Side Concentrated Shear Force.

A bimodular material is a kind of material that presents two elastic moduli in tension and compression. In classical thermoelasticity, however, the bimodular material is rarely considered due to its complexity in analysis. In fact, almost all materials will present, more or less, bimodular characteristics, and in some cases, the mechanical properties of materials cannot be fully utilized simply by ignoring the bimodular characteristics. In this study, the thermal stress problem of bimodular curved beams under the action of end-side concentrated shear force is analytically and numerically investigated, in which the temperature rise modes in a thermal environment are considered arbitrary. Using the stress function method based on compatibility conditions, a two-dimensional solution of thermoelasticity of the bimodular curved beam subjected to end-side concentrated shear force was obtained. The results show that the solution for a bimodular curved beam with a thermal effect can be reduced to that of a bimodular curved beam without a thermal effect. At the same time, the numerical simulation for the problem verifies the correctness of the theoretical solution. The results may serve as a theoretical reference for the refined analysis and optimization of curved beams in a thermal environment.

Investigation on cotton dust-reinforced epoxy composites

A partially biodegradable composite material with cotton dust as reinforcement in epoxy resin matrix has been developed. Composite laminas are prepared with various percentages of untreated and alkali treated cotton dust fiber and their strength and elastic modulus in tension and flexure are determined. Influence of alkali treatment of fibers on mechanical properties of the composite is studied. It is concluded that alkali treatment of fibres has pronounced effect on tensile and flexure properties of the composite.

Load-bearing characteristics of marine complex sandwich composites considering unequal elastic modulus in tension and compression

The panel and core materials of sandwich composite usually have the characteristics of unequal elastic modulus in tension and compression. However, in the numerical calculation of sandwich composite, it is usually considered as the material with the same tensile modulus or compression modulus, which often leads to larger calculation errors. The test results show that when the elastic modulus of tension and compression is about 10 times different, the maximum calculated stress and maximum deflection will be more than twice different. In view of the complexity of sandwich composite structure, based on the bi-modulus model of laminated plates, a simplified theoretical formula and numerical calculation method are proposed for bi-modulus sandwich composite structures in this paper. Furthermore, the accuracy of the proposed numerical calculation method of bi-module is verified by the experimental study of composite single-layer plate structure and sandwich composite cabin structure. The results show that the error between the improved numerical calculation method and the experimental measurement results is basically within 6%. Meanwhile, the numerical method based on field variables has wide application range and high convergence, and can be used to calculate complex marine composite structures.

A Bi-Modulus Material Model for Bending Test on NHL3.5 Lime Mortar

The research provides an innovative contribution to the interpretation of three-point and four-point bending tests on mortars by employing a bi-modulus material model, which assumes an asymmetric constitutive law, i.e., different elastic moduli in tension and in compression. To this aim, Euler-Bernoulli and Timoshenko bi-modulus beam models are defined, and the related displacement fields are reported for three-point loading, and provided for the first time for the four-point bending layout. A wide experimental campaign, including uni-axial tensile and compressive tests, three-point and four-point bending tests, and on notched specimens three-point tests for mode-I fracture energy, has been carried out on lime mortar specimens exploiting traditional contact (CE-DT) and contactless (DIC) measurement systems. Experimental results provided the values of tensile and compressive mechanical characteristics, which are employed to validate estimations of the analytical model. The tension-to-compression moduli ratio experimentally observed is on average 0.52. Experimental outcomes of the DIC analysis proved the bi-modulus behaviour during the four-point bending tests showing visible shifting of the neutral axis. The bi-modulus analytical model provides closer results to the experimental ones for the slender specimens subjected to four-point bending.

Contact Bending Problem for a Multilayer Composite Plate with Allowance for Different Moduli of Elasticity in Tension and Compression

Contact Bending Problem for a Multilayer Composite Plate with Allowance for Different Moduli of Elasticity in Tension and Compression

EVALUATION OF THE APPLICATION OF DOUBLE-EXPOSURE SPECKLE PHOTOGRAPHY WITH DIFFERENT APERTURES IN EXPERIMENTAL MECHANICS

The article presents an experimental evaluation of the use of double-exposure speckle photography with circular and annular apertures in experimental mechanics using the example of determining the modulus of elasticity in tension. The description of the process of registration of speckle photography and its subsequent processing is given. Based on the results of calculations of the finite element model of the sample, the areawhere the boundary conditions do not affect its tension is determined. A description is given of the procedure for processing speckle photographs to determine the modulus of elasticity and the error in its measurement with different apertures.

MECHANICAL PROPERTIES OF BAMBOO (BAMBUSA VULGARIS)

This research project investigated the tensile, bending and compressive strength of a species of bamboo called Bambusa vulgaris. The density of the B. vulgaris was found to be 500kg/m3 (oven dry). The tensile strength was 94.3MPa with nodes and 117.8MPa without nodes. The compressive strength was 49.9MPa with nodes and 56.7MPa without nodes, bending strength was 107.0MPa with nodes and 137.7MPa without nodes and Modulus of Elasticity in tension was 3002.2MPa with nodes and 3594.0MPa without nodes. Modulus of Elasticity in compression was 10,405.3MPa without nodes and 7,268.1MPa with nodes. The nodes were found to have a significant effect in lowering the tensile and bending strength of bamboo. The compressive strength was not affected by the presence or absence of nodes.

Experimental determination of the constitutive properties of a graphite anode layer in lithium-ion batteries using a bending test method

The stress-strain relationship of a dry lithium-ion graphite anode coating has been characterized by a bending test method. The method is based on U-shaped bending of single-side coated electrodes, which enables separate measurements of tensile and compressive properties of the electrode coating. The experiments reveal that the elastic modulus of the anode coating in compression is higher than the elastic modulus in tension and that the compressive stiffness increases with strain level. Contrary, the tensile modulus is approximately independent of strain. The quantitative results for compressive modulus, and in particular the stiffening effect with increasing strain, are believed to be new to the battery research community. The measured stiffness of the anode coating is compared to previously reported results for a cathode coating. It is found that the anode coating is stiffer in compression compared to the cathode coating despite a much larger particle stiffness of the cathode material in comparison to the anode. It is concluded that differences in porosity are the main reason for the observed behavior. The method also successfully captures the hysteresis effects, both in tension and compression, that are present due to the polymeric binder and the evolution of microstructural contacts. Relaxation experiments are as well conducted to characterize the time-dependent properties of the anode coating, and the response is modeled by a Prony series.

Experimental studies on mechanical and dielectric behavior of Glycerol filled Silicone rubber composites

In this study, Silicone rubber composites are prepared with Glycerol filler in three different volume fractions. The samples developed are subjected to mechanical and dielectric testing. The tensile strength increases first and later decreases with Glycerol loading whereas compression strength decreases with Glycerol loading. Modulus of elasticity in tension and compression both decreases with the increase of Glycerol loading. Dielectric permittivity, dissipation factor and conductivity are increases with the increase of Glycerol loading. The Silicone Rubber (SR) composite with 15% volume of Glycerol filler shown a maximum reduction in modulus of elasticity of 29% (in tension) and 16.8% (in compression), and maximum improvement in the dielectric permittivity of 112% compared to neat silicone rubber. The reduction in modulus of elasticity with an increase in dielectric permittivity with an increase in Glycerol loading suggests that this material is a potential candidate for materials to be used in soft dielectric sensors and actuator applications.

ВЛИЯНИЕ ЭКСПЛУАТАЦИОННЫХ ФАКТОРОВ НА ОСНОВНЫЕ ФИЗИКО-МЕХАНИЧЕСКИЕ СВОЙСТВА ИЗДЕЛИЯ ИЗ СТЕКЛОПЛАСТИКА ВПС-31

The results of the work performed at NRC «Kurchatov Institute» – VIAM in research on aspects of the influence of operational factors (high humidity and temperature) on the physic-mechanical properties of glass fiber composite VPS-31. The main physical and mechanical properties of samples obtained from the spar of the helicopter's main blade are presented (including the glass transition temperature, strength and modulus of elasticity in tension, elongation at break at various test temperatures in the initial state and after exposure to moisture). We studied the fragments of the spar, successfully passed thermocyclic tests («day/night»). The results of the research confirmed the possibility of exploitation of glass fiber composite VPS-31in a humid tropical climate.

Estimation of tensile strength and moduli of a tension compression bi modular rock

The Brazilian test has been widely used to determine the indirect tensile strength of rock, concrete and other brittle materials. The basic assumption for the calculation formula of Brazilian tensile strength is that the elastic moduli of rock are the same both in tension and compression. However, the fact is that the elastic moduli in tension and compression of most rocks are different. Thus, the formula of Brazilian tensile strength under the assumption of isotropy is unreasonable. In the present study, we conducted Brazilian tests on flat disk-shaped rock specimens and attached strain gauges at the center of the disc to measure the strains of rock. A tension-compression bi-modular model is proposed to interpret the data of the Brazilian test. The relations between the principal strains, principal stresses and the ratio of the compressive modulus to tensile modulus at the disc center are established. Thus, the tensile and compressive moduli as well as the correct tensile strength can be estimated simultaneously by the new formulas. It is found that the tensile and compressive moduli obtained using these formulas were in well agreement with the values obtained from the direct tension and compression tests. The formulas deduced from the Brazilian test based on the assumption of isotropy overestimated the tensile strength and tensile modulus and underestimated the compressive modulus. This work provides a new methodology to estimate tensile strength and moduli of rock simultaneously considering tension-compression bi-modularity.

Influence of the Cross-Sectional Shape of a Reinforced Bimodular Beam on the Stress-Strain State in a Transverse Impact

The paper considers the stress-strain state of a reinforced concrete beam, as a bimodular material, under the action of an impact. The behavior of bimodular concretes with different moduli of elasticity in tension and compression has not been studied enough. At the same time, taking into account the bimodularity of concrete makes it possible to design a more economical structure, especially for dynamic load. In this article, the impact is considered as an absolutely plastic impact of an absolutely rigid body on an elastic system. The stress state is investigated for beams of rectangular, T-section and I-sections, and is compared with and without the bimodularity of reinforced concrete. The analysis of the dependence of the stress state on the shape, cross-sectional dimensions, and the location of reinforcing bars in the compressed and tensioned zones was carried out for lightweight concrete (Et < Ec) and for heavy concrete (Et > Ec) under the action of shock load with and without regard to the mass of the beam. The numerical study shows that taking into account the mass of the beam upon impact significantly decreases the magnitude of the normal stresses in both the tensioned and compressed zones. Beams of rectangular cross-section have the highest load-bearing capacity when the cross-section height is equal for both light and heavy concrete. An increase in the size of the flange of the I-beam in the stretched zone leads to a sharp decrease in normal tensile stresses and a slight increase in normal compressive stresses. The proposed engineering method makes it possible to numerically study the effect on the stress-strain state of a beam under the action of a concentrated impact of various geometric characteristics of the cross-section, bimodularity of the material, size, number and location of reinforcement.

LIMIT STATE OF ARCHES OF VARIABLE STIFFNESS

Abstract. An algorithm is proposed for numerically solving the problem of finding the maximum load for flat bar systems having a rectangular section of variable height. The material is elastoplastic; its physical properties are described by the Prandtl diagram. It is assumed that the compressive and tensile strength of the material are different. The modulus of elasticity in tension and compression is the same. The limiting state of a rectangular cross section under the simultaneous action of a longitudinal force and a bending moment is described. Using the proposed algorithm, a program was developed for calculating rod systems by the limit equilibrium. The C++ programming language was used to create a program for the numerical determination of the ultimate load for rod systems. The finite element method was used as the most universal to write a module that performs static analysis of the bar system. Its use makes it easy to design rod systems of arbitrary configuration with arbitrary boundary conditions. As a test example, a hinged circular arch loaded with a uniformly distributed vertical load is considered. Analytical dependences are written, which allow to obtain the ultimate load for an arch of variable section. Examples of calculating the limiting state of the arch and comparing the ultimate loads with and without longitudinal force are considered. The analytical solution is compared with the numerical solution found by the author's program. Good convergence of analytical and numerical solutions is shown. The proposed algorithm for the numerical calculation of the limit states uses the so-called direct method for finding the ultimate load. This allows not only to obtain the value of the ultimate load, but also to establish the order of formation of plastic regions in the sections of the rod system. The calculation algorithm does not imply the use of iterative processes, which has a positive effect on the speed of calculations. Within the accepted assumptions, the calculation methodology is accurate.

Numerical Analysis of the Mechanical Behavior and Failure Mode of Jointed Rock under Uniaxial Tensile Loading

In the field of rock engineering, tensile failure is one of the most significant failure modes due to the presence of joints/fractures. However, due to the limitations of current laboratory testing, it is difficult to carry out direct tensile tests on jointed rock specimens in the laboratory. To study the effect of joints on the mechanical behavior and failure mode of jointed rock specimens, a three-point modeling method that can consider arbitrarily arranged rock joints is deduced and applied to discrete element simulation. The effects of different joint angles (the inclination angle α, rotation angle β, and superimposed angle γ of α and β, where γ is the angle between the joint and horizontal plane), the density (n), and the rate of cutting area (RCA) of the specimen loading surface (LSS) on the tensile strength (σt), elastic modulus in tension (Et), and failure mode of the specimens were analyzed. The results show that the joint angle (considering α, β, and γ) and RCA have a significant effect on the resulting σt and failure mode, while n has a significant effect on Et. The failure mode of the specimen changes from tensile failure along the joint to direct tensile failure of the specimen as γ increases, and the mechanical behavior transitions from unstable to stable. In addition, the main influence of γ on the mechanical behavior of specimens is revealed, and the change process of the failure mode after the cutting of the LSS is analyzed. The present research can be utilized for multiple purposes, including the joint development of surrounding rock and failure dominated by tensile failure in underground engineering, especially for tunnels, roadways, chambers, and so forth.

Створення низькотеплопровідних полімерних нанокомпозитів для внутрішніх газовідвідних стволів димових труб котелень

Methods and results of experimental studies of thermophysical, structural and mechanical properties of low-heat-conducting polymer nanocomposites, oriented to use for gas ducts and chimneys of boiler installations, as well as various other gas and water communications are presented. In this work, on the basis of the performed set of methodological studies regarding the analysis of the legitimacy of using different models of heat conductivity for predicting the heat-conducting properties of these composites, the possibility of using for this prediction a number of models of the theory of the effective medium and the theory of percolation is considered. The analysis of thermophysical properties, structural characteristics and Young's modulus of low-heat-conductivity polymer nanocomposites based on polyethylene and polypropylene is carried out. Using these nanocomposites as an example, the achievement of a significant increase in their Young's modulus in comparison with unfilled polymers with a relatively small increase in heat conductivity is demonstrated. To obtain nanocomposites, we used a method based on mixing the components in a polymer melt using an extruder and then shaping the composite into the required shape by hot pressing. The method of differential scanning calorimetry was used to determine Young's modulus. On the basis of the studies carried out, the possibility of obtaining low-heat-conducting polymer nanocomposites with improved mechanical characteristics has been shown. In particular, it was shown that for nanocomposites based on polyethylene or polypropylene filled with CNTs (carbon nanotubes) or nanodispersed aerosil particles, with a mass fraction of the latter up to 2%, the following takes place a relatively insignificant increase in heat conductivity coefficients and a significant increase in the modulus of elasticity in tension. The research data also made it possible to obtain for the developed nanocomposites the temperature dependences of their specific mass heat capacity and, on this basis, to analyze the regularities of changes in the structural characteristics of these materials.

Lengthwise Fracture Study of Transversely Inhomogeneous Rods

A lengthwise crack in a rod that exhibits smooth (continuous) material inhomogeneity in the transverse direction is studied. The rod has a circular cross-section. The lengthwise crack is located arbitrarily along the thickness of the rod. A solution to the strain energy release rate is derived assuming that the moduli of elasticity in tension and compression are distributed continuously in the transverse direction. The strain energy release rate is also analyzed by applying the compliance method for verification. The influences of various factors such as the crack location, material inhomogeneity and the different mechanical behavior of the material in tension and compression on the fracture are investigated and discussed in detail.

Characterization of the Constitutive Behavior of a Cathode Active Layer in Lithium-Ion Batteries Using a Bending Test Method

Presently used experimental techniques for the characterization of tensile and compressive behavior of active layers in lithium-ion batteries have limitations of different kinds. This is particularly true for measurements of compressive properties. Furthermore, the characterizations of time-dependent stress-strain behavior are largely missing. In order to characterize the stress-strain relationship for a dry cathode active layer in lithium-ion batteries, a mechanical testing method is presented that previously has been applied to the testing of optical fibers. The method is based on U-shaped bending of single-side coated aluminum foils, which enables separate measurements of tensile and compressive properties. In particular, the method has clear advantages for measurements of compressive properties in comparison to previously reported techniques. Relaxation experiments are also conducted in order to characterize the time-dependent properties of the dry active layer and to check if these effects could explain the measured hysteresis. It is found that the elastic modulus in compression is significantly larger than the elastic modulus in tension and that the compressive modulus increases with strain level. Contrary, the tensile modulus is approximately independent of strain. Furthermore, hysteresis effects are present at loading-unloading measurements, both for tension and compression. The low values of the measured elastic moduli show that the electrode properties are largely controlled by the binder and carbon additives. It is concluded that the development of particle-particle contacts most likely is the reason for the higher modulus in compression in comparison to tension. The time-dependent effects are significant, primarily for shorter time scales, which explains the relaxation behavior, but they cannot fully explain the hysteresis effects. Most likely non-linear micro-mechanisms do contribute as well.

ВЛИЯНИЕ КРИСТАЛЛИЧЕСКОЙ СТРУКТУРЫ SiO2 НА ТЕРМИЧЕСКОЕ ЦИКЛИРОВАНИЕ ПОЛИМЕРНЫХ КОМПОЗИТОВ

polymer composites are widely used in the space industry for the manufacture of spacecraft, satellite panels, antennas, thermostatically controlled coatings, etc. In space, they are subjected to harsh environmental conditions, such as ultraviolet, deep vacuum, atomic oxygen, charged particles, anthropogenic debris, micrometeoids, electromagnetic radiation and thermal cycles that cause severe degradation of the material. One of the most important environmental effects of materials based on polymers is the thermal cycle, in which the composite undergoes a large temperature difference from -170˚C to + 200˚C. The paper presents an assessment of the use of composites based on a polyalkane-rich matrix and a filler in the form of an SiO2 amorphous and crystalline structure under thermal cycling conditions. The data on the change in tensile strength, modulus of elasticity in tension and relative elongation in tension of materials after several cycles of a sharp differential temperature (from -190 to +200°C) are presented. The thermal cycle was repeated 5, 10 and 20 times. It is shown that the sample polyalkanimide has a large value of tensile strength and elastic modulus compared with highly filled composites.However, during thermal cycling there is a significant decrease in these parameters.For a highly filled composite sample with 65% crystalline SiO2 content, the decrease in tensile strength and elastic modulus after thermal cycling is insignificant and is within the measurement error. A composite with amorphous SiO2 is more susceptible to a change in mechanical properties after thermal cycling in comparison with a composite containing crystalline SiO2.

Effect of Titanium Diboride Content on Basic Mechanical Properties of Composites Sintered from TiH2 + TiB2 Powder Mixtures

The paper examines how the titanium diboride content of the starting TiH2–TiB2 powder mixture influences basic mechanical properties of the resultant sintered composites in tension and compression tests. The porosity of the compacts sintered at 1250°C increases with greater titanium diboride content of the starting mixture, which is associated with the Frenkel effect that occurs in the sintering process. Although the porosity somewhat increases, the strength, hardness, and elastic modulus in tension become higher when 5% TiB2 powder is introduced into the charge. These characteristics however decrease when the high-modulus component increases to 10% in the charge. The ductility of the sintered alloys monotonically reduces with higher boride content. The yield point and compressive strength monotonically increase with higher TiB2 content of the charge, despite greater porosity. This occurs because porosity has a significantly weaker effect on the strain resistance of the sintered Ti–TiB composites in compression than in tension.