Analytical Description of Neck Profile during Tensile Testing of Cylindrical Specimens

One of the problems of studying the rheological properties and plasticity of metals and alloys from the results of tensile tests of cylindrical specimens is the need to determine the stress triaxiality value, which depends on the shape and size of the neck formed. An analytical description of the neck profile makes it possible to increase the accuracy of experimental measurements of its dimensions, in particular, the radius of curvature in the smallest cross-section of specimen. This paper is devoted to searching a universal neck profile equation that allows calculating the radius of neck curvature regardless of the nature of the material hardening curve and the stage of strain localization. The exact surface equation is established and its accuracy is estimated for hardening and softening material.

Angular Rolling of the Hollow Flanges of Pipe Joints

The paper considers a three-stage technology for angular rolling of the pipe workpiece. This technology facilitates the expansion of the range of flange parts available by eliminating a number of drawbacks of the known methods of metal forming. In the presented paper, we analyze the results of numerical calculations and experiments, as well as the effective deformation values in blank material, using computer simulation in the DEFORM-3D software package. The results of the computer simulation were reached taking into account experimental studies of the rheological properties of copper alloy L68 in the form of a strain hardening curve using the Instron-8850 complex. The results of the ratio of basic geometric dimensions expanded the range of flange parts under investigation and allowed us to consider angular rolling technology with a variable angle of inclination of the rolling roll from a three-stage perspective, especially in small-scale production.

Modeling of the torsion test of a cylindrical specimen with the help of the inverse method

This article discusses the torsion problem of a continuous cylindrical specimen used to construct a hardening curve. A brief review of the methods for processing the results of the method of torsion of a cylindrical specimen is given. The possibility of using the inverse method to determine the material model in the case of the torsion of the continuous cylindrical specimen made of steel 20H is shown. By means of QFORM 9.0 software package virtual experiment connected with torsion of a cylindrical specimen is carried out. As a result of this research, the rheological model of steel 20His determined with a high degree of accuracy. The stress-strain state of the material was analyzed during the torsion of the specimen by means of the QFORM. The results of the virtual experiment are compared with the full-scale test.Anexceptionally good match of the results was obtained. The inverse method showed its efficiency and made it possibleto determine a rheological model of the material. The model accurately describes the experimental data. The resulting material model (for steel 20H) is valid in the following range of parameters: deformation temperature of 20°C, deformation rate of 0.5 s−1, the strain range of 0 to 2.5.

The development of the method for identifying the hardening curves of materials based on the results of torsion tests of notched specimens

The article is devoted to studying the rheological properties of metals and alloys in a cold state. The method is proposed to identify the hardening curve of a material based on torsion tests of round specimens with a notch. Determining the hardening curve is based on measuring the coordinates of points on the surface of the specimen after testing and determining the corresponding value of the torque. Based on these values the coefficients in an equation for the stress-strain dependence can be determined by minimizing the derived functional. The paper proposes the algorithm for the numerical implementation of the new identification method. The results of the computer simulation confirmed its effectiveness.

REGULARITIES OF MACROPLASTIC DEFORMATION OF NARROW-BAND SINGLE CRYSTALS OF CdxHg 1-xTe SOLID SOLUTIONS

The regularities of macroplastic deformation of narrow-band semiconductors of HgTe-CdTe solid solution crystals were studied by the uniaxial compression method on a Regel-Dubov relaxometer. The four-stage character of the strain hardening curve “stress-strain” is established. The influence of stoichiometry, load velocity and temperature on the nature of load curves is investigated. From the experiments on the relaxation of mechanical stresses, a thermoactivation analysis of the kinetics of microplastic deformation was performed. Thermoactivation parameters of dislocation motion are estimated. The criteria for performing the Pierrels mechanism of dislocation motion in these crystals are investigated. The influence of light on the macroplastic fluidity of CdxHg1-xTe crystals is described.

The Influence of Hardening Curve on the Shape and Size of the Neck of Specimen in Tensile Test

The article is devoted to the testing of samples for tensile, namely the formation of the neck. The objective of the study is to establish the qualitative level of influence of the nature of the hardening curve of the material on the shape and size of the neck. By using computer simulation, testing of samples of the two test materials, selected so as to provide the possibility of direct comparisons, forming the necks of the same diameter in the minimum section and the section near the neck, is worked over. It is found that the nature of the hardening curve determines the shape and size of the neck, including the radius of its curvature. This makes it possible to recover the hardening curve for large values of the strain. At the same time, it is established that the equation of the forming neck is invariant to the nature of the hardening curve of the material.

METHODS OF CONSTRUCTION OF THE GENERALIZED HARDENING CURVE

The development of new structural materials and increasing requirements for the efficiency and safety of operation of structures and at the same time, reducing their material consumption, tighten the requirements for the accuracy of the experimental and calculated parts of the study. The experimental implementation of the entire spectrum of stress-strain states of samples of structural elements requires the destruction of a large number of samples, the creation and maintenance of cost equipment. Therefore, the search for effective methods for calculating the predicted critical loads for structural elements and determining a realistic safety factor is an urgent task. Stresses and strains throughout the process of loading the material are monitored by deformation curves. In this study attention is paid to the area of hardening of the deformation curve, which reflects the plastic deformation of the material after reaching the yield strength. The stress strain curves in principal stresses and principal strains are primary for further processing and analysis. The aim of the work is to propose an universal method for obtaining a model of the hardening section of a generalized deformation curve for plastic metal materials, which would be better consistent with the experimental data for each specific material. To this end, equivalent stresses and strains are introduced, which are a generalization of the two “classical” approaches of von Mises and Tresca. The model contains a single parameter p, which is determined by the results of several simple experiments. To find the optimal value of p, statistical estimation of quality and errors is used. Application of the method for plastic materials will allow satisfactory accuracy to describe the generalized deformation curve and to predict the stress-strain state of the material at various ratios of principal stresses. In combination with the methods of taking into account the geometry of structures, the obtained generalized curve can be used to predict the values of real stresses arising by structural elements under load.