Rotational Compression of Cylindrical Specimen As a New Calibrating Test for Damage Criteria

Abstract

The subject-matter of the article is the ductile fracture of materials—A phenomenon occurring in numerous metal forming processes. In order to prognosticate the possibility of a fracture, damage criteria are employed. Their effectiveness, however, depends on the accurate determination of the critical values of damage. These values are obtained through calibrating tests, where the stress state has to be as similar to the actual process as possible. The currently employed calibrating tests do not enable one to determine the limit values of the damage function when the Mannesmann effect occurs. Therefore it was not possible to effectively prognosticate the material fracture in the processes of cross- and skew-rolling. A new calibrating test, based on rotational compression of a cylindrical sample, in which the fractures are caused by the Mannesmann effect, was developed at the Lublin University of Technology. This test was discussed in the article, with a particular focus on the stress and strain state in the sample. A practical use of the test was presented on the example of C45 grade steel, formed in the temperature equal 1150 °C. In the research ten material damage criteria were adopted.

Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

“…It is also important that the proposed CWR test be compared with previous calibration tests. To this end, one should use the plot made in the η - θ plane ( Figure 18 ) showing the stresses in the CWR test, rotary compression tests [ 17 , 18 ], and classical tests based on tension, compression and torsion [ 57 , 58 ]. The stress in the CWR test was measured with 25 virtual sensors located in the cylindrical section of the specimen.…”

“…However, their experiments were limited to the cold forming of steel. Other tests were developed by Pater et al and they were based on the rotary compression of either a disc-shaped specimen in tool cavity [ 17 ] or a cylindrical specimen between two flat plates [ 18 ]. Conducted under hot forming conditions, the tests showed that the critical damage depends greatly on temperature.…”

The study of central cracking mechanism and criterion in cross wedge rolling

“…10 This method is advantageous compared with the conventional ways such as uniaxial tensile or shear tests, because it simulates the actual stress states in CWR and central cracking behaviours, thus ensuring a higher degree of accuracy. The novelty of this method is supported by a recent study on the calibration of the critical damage value using rotary compression tests [44]. Meanwhile, compared with the method used in the previous study [22] which required a high number of CWR dies, only one pair of slopped/flat plates is required, raising one end of each plate to get different slopes for real applications.…”

Analysis of Wall Thickness Eccentricity in the Rotary Tube Piercing Process Using a Strain Correlated FE Model

“…One of the characteristics of the rotary tube piercing process is the generation of a crack in the axis of the billet due to Mannesmann effect [26]. Therefore, in order reproduce this crack, a cavity of 2 cm diameter has been incorporated in the mesh of the billet.…”