Influence of the Scale Factor on the Young's Modulus of Steel Determined by the Tensile Strength of the Specimens

The modulus of elasticity is considered a fairly stable physicomechanical characteristic of materials, which is little dependent on their composition and structure. Among the factors influencing the modulus of elasticity, temperature and anisotropy are distinguished. Information about the influence of scale factor on the modulus of elasticity is quite limited and sometimes contradictory. The aim of this study is to investigate the influence of the scale factor on the elastic modulus of steel 45 determined by tension geometrically similar specimens with different initial diameters. The specimens were tested on an Instron 8801 universal testing machine at a deformation rate of 0.1 mm/min at room temperature. Elastic deformations during tension were measured using two methods-with the help of a strain gauge and the digital image correlation method. Both methods showed fairly close results when testing specimens of the same diameter. However, the digital image correlation method allowed for measurements of elastic deformations on specimens with small diameters, where it was not possible to attach a strain gauge. A decrease in the modulus of elasticity with an increase in the initial diameter of the specimen was established. Graphical dependences of the modulus of elasticity on the diameter of the specimen and the area of its cross section were obtained. Possible reasons for the decrease in the modulus of elasticity under the influence of the scale factor are outlined. A decrease in specific surface area and specific surface energy, an increase in the deformable volume, and a decrease in the deformation rate at a constant deformation speed are among the main reasons. The decrease in the modulus of elasticity under the influence of the scale factor should be taken into account in strength calculations and when assessing the residual life of parts and structures with relatively large cross sections and wall thicknesses.