Problems Determining of the Mechanical Properties of Metallic Materials from the Tensile Test in the Aspect of Numerical Calculations of the Technological Processes

Abstract

The increase of requirements concerning the accuracy of numerical analysis of technological processes with nonlinear contact such as drawing, cutting, embossing, burnishing rolling, thread rolling and machine cutting involves the extension of accuracy in determining workability parameters: initial yield stress σY0, plastic hardening modulus ET and true failure strain φf. Currently, those parameters are often determined in uniaxial tensile testing. Determination of the strain and stress states after the exceedance of ultimate tensile strength of the material, in the moment of stability loss (creation of the neck) constitutes the basic issue. Appearance of characteristic necking disturbs uniform, uniaxial state of stress. In the smallest intersection of the specimen there additionally appear radial stress and circumferential stress - three-dimensional state of stress is obtained. Currently used methods: Birdgman, Davidenkov-Spiridonova or Siebel do not allow calculating the values of those stress precisely enough. The paper concerns the new hybrid method of evaluating stress and strain states in the cylindrical specimen during of tension with the use of Finite Element Method (FEM).