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).

Experimental Assessment of the Depth of the Deformed Layer in the Roller Burnishing Process

“…The roller burnishing (RB) process is used when the goal is to achieve a high-quality surface finish strengthened by the strain hardening phenomenon [1][2]. Many material forming technologies such as burnishing, thread rolling, spline rolling, knurling, drawing lead to both the deformation of the surface layer of the material and changes of its properties.…”

“…Many material forming technologies such as burnishing, thread rolling, spline rolling, knurling, drawing lead to both the deformation of the surface layer of the material and changes of its properties. This phenomenon of cold plastic deformation introduces the compressive stresses into the surface layer increasing its surface hardness, and both static and fatigue strength [1,2]. Under the pressure of rounded tool the small layer deformation occurs not only in plastic forming processes but also in turning, milling, grinding [3] or even laser surface treatment [4][5][6].…”

Influence of roller - burnishing on surface roughness parameters and roundness

“…Stoić at all [3] defined roller burnishing as a fine machining process that is used to improve certain physical and mechanical properties, such as surface roughness, corrosion resistance, friction coefficient, wear, and fatigue resistance. This process is used when the goal is to achieve a high quality surface finish strengthened by the strain hardening phenomenon [5,6]. In the RB process a cylindrical roller is pressed across the part being processed.…”

Mathematical Modelling Of Elastic Deflection Of A Tubular Cross-Section

“…The elastic strain energy accumulated in the ring is a sum of amounts of energy due to the bending moment and the compressive force [4,7]: (6) where:…”

“…In machinery construction area, are mainly considered issues dealing with design principles and strength analysis of steel structures [6], principles of FEM application and numerical analysis [2,5,6], however detail issues concerning elastic deformations of structural elements are lacking in them.…”