Diana Šimić Penava

The Analyses of Pure Shear Behaviour of E-Glass Woven Fabrics by Picture Frame Test

This paper describes an experimental study on the pure shear properties of E-Glass woven fabric by picture frame test. During shear deformation, the fabric yarns experience large angular change between warp and weft yarns. The picture frame test is one of the fundamental methods to characterize the in-plane shear behaviour of woven fabrics and can produce a quite uniform shear deformation state in the fabric sheet. Tests are conducted on two different size of EGlass specimens 40x40 mm and 80x80 mm. For a double increase the specimen size, the values of shear force and axial load are also almost double increase at the maximum displacement and shear angle.

The Impact of Lateral Restraint on Structural Stability of Thin-Walled C-Cross Section Column Subjected to Axial Force

The paper analyses the impact of lateral restraining by trapezoidal steel sheeting on the structural stability of thin-walled C-cross section columns subjected to axial forces. Firstly, mechanical properties of the column material (steel) and lateral stiffness of the rotational restraint are determined by testing standard specimens in a laboratory. Based on the obtained data, a stability analysis of unrestrained columns and of columns laterally restrained by trapezoidal steel sheeting has been carried out and critical forces have been determined analytically by using the theory of thin-walled beams, numerically by using the finite element method (FEM), and experimentally by testing the C-cross section columns in a laboratory. The analysis of critical forces and stability shows that the calculation according to the theory of thin-walled beams and the FEM calculation gives results similar to the results of the experimental tests. By comparing the results of the investigation into thin-walled C-cross section columns with and without lateral restraints a significant influence of lateral restraints on the stability of thin-walled C-cross sections subjected to axial forces has been proven: lateral restraint significantly affects final results of the level of the critical force, raising the possibility of optimizing the use of such structures in practice.

Experimental Analysis of the Tensile Properties of Painting Canvas

Abstract In this paper, the practical application of uniaxial testing of painting canvas for determining its mechanical properties is presented. Painting canvases have a complex composite structure whose mechanical properties are considerably improved in relation with the initial basic material. Painting canvas or coated fabrics are obtained by applying a certain number of coatings to raw fabrics. Experimental testing and determining mechanical properties of painting canvas under tensile force at different angles in relation to the weft direction are discussed in the paper. The fabrics were tested before coating, as well as after one, two and three coatings. The values of tensile force in relation to relative extension of coated textiles were measured, as well as breaking force values, elongation at break, contraction at break, work to rupture. Based on the experimentally obtained values, modulus of elasticity, Poisson’s ratio and the level of anisotropy of the coated textile materials were calculated. The experimental results demonstrate the applicability of theoretical formulae. The number of coated layers on the raw fabric exerts a significant impact on the Poisson’s ratio. The values of breaking force, elongation at break, work to rupture and modulus of elasticity increase with an increase in the number of coated layers, and at the same time coefficient of anisotropy decrease. It has been shown that by increasing the number of coated layers in a coated material, its anisotropic properties decrease, while isotropic properties increase. With an increase in the number of coatings, the differences between experimental and theoretical values of modulus of elasticity decrease.

Critical Force Analysis of Thin-Walled Symmetrical Open-Section Beams

This paper analyzes critical forces and stability of steel thin-walled C-cross-section beams without lateral restraints. Mechanical properties of the rods material are determined by testing standard specimens in a laboratory. Based on the obtained data, the stability analysis of rods is carried out and critical forces are determined: analytically by using the theory of thin-walled rods, numerically by using the finite element method (FEM), and experimentally by testing the C-cross-section beams. The analysis of critical forces and stability shows that the calculation according to the theory of thin-walled rods does not take the effect of local buckling into account, and that the resulting critical global forces do not correspond to the actual behaviour of the rod. The FEM analysis and experimental test show that the simplifications, which have been introduced into the theory of thin-walled rods with open cross-sections, significantly affect final results of the level of the critical force.

Influence of Coating on the Poisson's Ratio of Woven Fabrics

Coated fabrics have complex composite structure whose mechanical properties are considerably improved in relation with the initial basic material. They are obtained by applying a certain number of coatings to raw fabrics. In this paper the practical application of uniaxial testing of coated fabrics for determining its breaking properties and Poisson’s ratio is presented. Due to the anisotropy of woven and coated fabrics, Poissons ratio changes over the fabric sample stretching. Experimental testing were carried out on two samples of plain weave cotton fabrics. The fabrics were tested before coating, and after one, two and three coatings. Samples are stretched with tensile force in the weft and warp direction, and based on different measured values of fabric stretching, warp and weft Poissons ratio is calculated. The values of tensile force and relative extension of coated fabrics were measured, and breaking force values, elongation at break, contractions at break.

Impact of Anisotropy on the Elastic Modulus of Basic Woven Fabric Structure

Anisotropy is the characteristic which is typical for most materials, especially woven fabrics. Influence of direction of tensile force action on the properties of the fabric is big and frequently tested. The woven fabric can be defined as orthogonal elastomer. The values of elastic modulus of woven fabrics for different angles of extension direction were analyzed. Three types of fabric samples of different weaves (plain, twill, sateen) and the same raw material composition were tested under tensile forces in seven directions oriented with 15° increment with respect to the weft direction. Elastic modulus of woven fabrics was determined experimentally in the laboratory. Based on the experimentally obtained values, theoretically calculated elastic modulus for arbitrarily chosen fabric directions was calculated. A good agreement between experimental results and the calculated obtained values of the elastic modulus was shown, so the theoretical equations can be used with high accuracy to calculate the elastic modulus of the fabric in various directions. Therefore, the measurements need to be implemented when the tensile force acting on the fabric only in the warp (90°), weft (0°) and at angle of 45°.