Rotary compression in tool cavity—a new ductile fracture calibration test

Abstract

Ductile fracture is one of the most common failure modes in hot metal forming. It can be predicted by means of so-called damage functions that describe the relation between stress, deformation and fracture initiation. A practical use of these functions requires the knowledge of the critical damage value of the material that is determined by calibration tests based on compression, tension and torsion. For the prediction to be correct, one must ensure that the modelled and real stresses are in agreement. Previous studies did not offer any effective test for determining critical values of damage under changing load conditions that occur in cross and skew rolling processes, among others. To compensate for this knowledge gap, researchers at the Lublin University of Technology have developed a new test consisting in rotary compression of a test-piece in a cavity between the tools, which is described in this paper. In the proposed test, a cylindrical test-piece is rolled over a cavity (impression) created by grooves on two mating tools. The cavity height is smaller than the test-piece diameter. At the critical value of the forming length, the state of stress induced thereby in the test-piece axis causes fracture. Knowing the critical forming length, it is possible to determine the critical value of damage by numerical modelling. The practical application of the proposed test is illustrated through the case of C45 grade steel subjected to forming in the temperature range 950-1150°C. The analysis makes use of the normalized Cockcroft-Latham (NCL) criterion of ductile fracture.

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.…”

Conception of a Three Roll Cross Rolling Process of Hollow Rail Axles

“…In order to determine the critical damage value rotary compression in a channel 25,26) was performed. During this test the stress state is very similar to the stress state occurring in the process of CR.…”

Numerical Simulation and Experimental Validation of the Cladding Material Distribution of Hybrid Semi-Finished Products Produced by Deposition Welding and Cross-Wedge Rolling

“…Before any experimental investigations of cross-wedge rolling were conducted, the process was first simulated, to save resources and time. As mentioned before, finite element analysis (FEA) can accurately depict the CWR process [33,34]. The simulations were calculated within the commercial FEA software Forge NxT 3.0, developed by TRANSVALOR S.A. (CS 40237 Biot, 06904 Sophia Antipolis cedex, France).…”