Papers by Keyword: Poisson's Ratio

Abstract: The aim of this study was to determine the compressive mechanical properties and the energy absorption characteristics of a bio-composite material based on lime, wheat straw, and additives (protein and entraining agent). The selected samples with fiber to binder ratio of 30% were subjected to compression tests at different strain rates (1 mm/min, 10 mm/min, and 100 mm/min), in the perpendicular and parallel directions to fiber orientation. Image analysis supported with Digital Image Correlation (DIC) method is performed to follow longitudinal and lateral deformations, thus making it possible to evaluate elastic properties. The results show that the highest density and compressive strength in the parallel direction are ~349 kg/m³ and ~0.101 MPa, respectively. The perpendicular specimens at 100 mm/min of speed test showed the highest values of densification strain, stress plateau, energy efficiency, and absorbed-energy of 47.27%, 0.32 MPa, 16.98 %, and 13.84 kJ/m², respectively. The values of Young’s modulus identified with DIC are significantly different from those determined by the slope of the linear part of the stress-strain curve. A slight influence of strain rate on mechanical properties is observed.

Abstract: Currently, there is a steady increase in the production of reinforced concrete structures in factory and construction site conditions for various types of modern buildings with higher operational requirements for them. These structures are pre-calculated according to complex design schemes of loading which also leads to increased requirements for the materials used. One of the ways to solve a number of these problems is the use of fiber-reinforced concretes, but for this it is necessary to experimentally identify the deformation and strength characteristics of dispersed reinforced concretes and take it into account when calculating structures. A scientific team of the Institute of New Materials and Technologies of the Ural Federal University is engaged in solving of this research task, which will expand a number of construction opportunities while maintaining economic feasibility in the future.

Abstract: This paper presents the study results of the nonlinear stress-strain diagrams of concrete based on the local materials of Central Yakutia. The results of comparing the obtained data with the requirements of normative documents of the Russian Federation, European countries, India and China are presented. The calculation results for bending bearing elements with concrete nonlinear deformation taken into account obtained using the Ansys software are given. The reliability of the calculated data was verified using the proposed diagrams, using the example of the results of a survey of characteristic failures of bending concrete and reinforced concrete elements in the Republic of Sakha (Yakutia).

Abstract: This paper deals with an evaluation of long-term experimental work carried out in cooperation with concrete suppliers and a specific company (named Sobriety). The key part of this work is focused on the experimental determination of secant modulus of elasticity and Poisson's Ratio of special concrete (self-compacting concrete, steel fibre reinforced concrete, polymer fibre reinforced concrete, specific high-strength concrete). Two different real-time approaches were used to detect modulus of elasticity. In parallel, both approaches - the (European) standard approach and the DIC (2D DIC; 3D DIC with varying lengths in the vertical direction) - were applied.

Abstract: This paper presents the results of an experimental study on the strength and elasticity of concrete subjected to high temperatures up to 800C carried out to determine the effects of exposure temperature and the effects of mixture proportion of concrete. Cylinders made of 4 mixture of normal-weight concrete with the W/C of 50 and 60% and slump of 50 and 210mm were subjected to 13 phases of temperatures from 20 to 800C without seal at the age of 91 days. Exposure term was 91 days for exposure up to 300C, 60 days for 400C and 24 hours for higher temperatures above 500C. After temperature exposure, cylinders were tested for weight loss, compressive strength, dynamic and static moduli of elasticity and Poisson's ratio at room temperature.Weight loss increased with exposure temperature, indicating greater loss below 110C and smaller loss above 300C. Compressive strength did not decline monotonously with temperature rise between 20 and 110C, but showed 10 % reduction at 35 to 50C and recovery at 80 to 110C, indicating the minimal and maximum points. The minimal point was associated with intermediate weight loss of 4 to 5 %. At temperatures higher than 400C, residual compressive strength showed greater reduction with temperature rise for smaller weight loss.As for the effects of mixture proportion, concrete with higher W/C and higher water content showed greater weight loss and greater strength reduction below 300C, while those with higher cement content showed greater strength reduction above 500C.Both dynamic and static modulus of elasticity declined monotonously with temperature rise, indicating higher reduction rate than compressive strength. And the relationship between the two moduli of elasticity was in good correlation. Poisson's ratio did not show monotonous change with temperature, but showed discontinuity between elevated and high temperatures, indicating downward peaks at about 80C which associated with 2 to 5 % weight loss, and an upward peak at 200 to 300C, which was associated with about 7 % weight loss, and a rapid increase at higher temperature of 700 to 800C.

Abstract: An article is about mechanical effect of the physic-mechanical material properties on the radial pressure in the compression chamber during the compacting process of wood. Some general methods that describe the transformation process of axial pressure into the radial pressure are shown, As well as the mathematical or experimental methods specifying dependencies and physical conditions. Mathematical finite element method in this area is very useful, but rarely used. Common problems using FEM are the proper definition of the physical material properties in a particular stage of compaction. Material properties are greatly influenced by a number of factors such as moisture, fraction size, chemical composition, current temperature, radial macro structure, axial macrostructure, current pressure and others. The chamber material and the manufacturing processes or the state of wear has an impact on the physical conditions. In terms of tensile elastic deformations, these complex effects reflect and can be merged into several properties. The conversion of axial to radial pressure indicates that some properties of the compacted material have a major impact on the process, such as friction between material and chamber, elastic modulus and Poisson's ratio. The geometry of the pressing chamber also has a significant impact. This paper does not deal so much with the pressing chamber geometry but more so with the characteristics embodied in experimentally measurable quantities. The measurement of these properties in combination with the application of FEM methods proves to be a highly progressive method for understanding the compaction process and the engineering design of compaction machines for the production of briquettes and pellets. The article urges further examination and measurement of a wider range of material properties in the densification process.

Abstract: The broader knowledge about physical and mechanical properties of wood allows reliable timber structures design. Even little addressed in the literature, in several situations Poisson's ratios are required for the evaluation of stresses acting on structural elements. This study aimed to obtain values of Poisson's ratios (ν), plans Longitudinal-Radial (ν_LR) and Longitudinal-Tangential (ν_LT), for species Peroba Rosa (Aspidosperma polyneuron) and Jatobá (Hymenaea courbaril L.). For this purpose, forty samples Peroba Rosa and eight samples of Jatobá were prepared for testing in compression parallel to the grain, following the recommendations of ABNT NBR 7190 standard. The results of means confidence intervals, considered at the level of 5% significance, revealed that the Poisson's ratios ν_LR e ν_LT to Peroba Rosa are 0.27 and 0.42, respectively, and 0.25 and 0.43 to Jatobá.

Abstract: Conventional foam could be converted to auxetic foam under auxeticity process. A new and simple technique to fabricate auxetic foam and to further determine its Poisson’s ratio is described in this paper. It is evident that the present modified technique in fabricating auxetic foam could be adopted to produce desirable auxeticity characteristics. Moreover, the approach used for determination of Poisson’s ratio has considerably merit with great cost effectiveness. This method is, however, specific to auxetic foam sample under compression loading.

Abstract: Material research and development on piezoelectric ceramics, especially lead-free ceramics, was proposed from a viewpoint of relationships between piezoelectricity and elastic constants such as Young’s modulus and Poisson’s ratio. We developed a method to be convenient to measure acoustic wave velocities by an ultrasonic thickness gauge with high-frequency. From the change in longitudinal and transvers wave velocities before and after DC poling, it was found that the ceramic bulk density was important to improve the piezoelectricity in lead-free ceramics. As a result, the candidates of lead-free ceramic compositions with higher piezoelectricity were proposed. Furthermore, the ratio of transvers wave velocity to longitudinal wave velocity was clarified to estimate compositions with higher piezoelectricity. The measurement of sound velocities was an effective method for researching and developing piezoelectric materials, and it was possible to design the material compositions of lead-free piezoelectric ceramics as well as lead-containing ceramics by the novel measuring method.

Abstract: Anisotropic and isotropic Poisson’s ratios for cuprum oxide are studied basing on the known experimental values of rigidity constants of Cu₂O monocrystals within the temperature interval 4.2...873 K. The Poisson’s ratios of the given crystal are studied under the change of external conditions within the given intervals.