An Improved Experimental Method for Determining the Workability Diagram

Alexandrov, Sergei; Vilotić, Dragiša; Konjović, Zora; Vilotić, Marko

doi:10.1007/s11340-012-9676-3

Cited by 10 publications

(10 citation statements)

References 17 publications

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“…Compression tests under negative stress triaxialities are performed on cylindrical, ring, flanged and tapered test-pieces [21,22]. To reduce the impact of friction, Aleksandrov et al [23] recommend making a recess on the test-piece end and filling it with lubricant. It must be emphasized that if compression tests are performed in hot working conditions, it is difficult to determine fracture initiation.…”

Section: Introductionmentioning

confidence: 99%

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

Pater

Tomczak

Bulzak

et al. 2020

Int J Adv Manuf Technol

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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.

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Section: Introductionmentioning

confidence: 99%

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

Pater

Tomczak

Bulzak

et al. 2020

Int J Adv Manuf Technol

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“…Therefore, experimental data are usually combined with numerical simulation to find the function F using the empirical fracture criterion in Eq. (5). To this end, however, it is necessary to specify constitutive equations and, in many cases, frictional boundary conditions.…”

Section: Ductile Fracture Criterion Based On the Workability Diagrammentioning

confidence: 99%

“…The final result is presented in Table 6. Using these values along with the results of standard tests [5,10] …”

Section: Determination Of the Function Fmentioning

confidence: 99%

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A Study on Material Workability by Upsetting of Non-Axisymmetric Specimens by Flat Dies

et al. 2014

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Upsetting is a typical test for determining the workability diagram. In most cases axisymmetric samples are used for such tests. However, the shape of samples may have a significant effect on the ductile fracture initiation. Therefore, a greater variety of sample geometry should lead to a more accurate shape of the workability diagram. A difficulty here is that a theoretical treatment of samples in which threedimensional flow occurs is more difficult and time consuming as compared to axisymmetric samples under axisymmetric loading. This difficulty can be overcome in the case of the ductile fracture criterion based on the workability diagram and the average value of the triaxiality factor. In particular, if fracture occurs at free surfaces then it is sufficient to determine experimentally in-surface strains after several stages of the upsetting process, up to the initiation of ductile fracture. After that, the corresponding point of the workability diagram can be found by means of a simple analytical procedure and numerical integration. This approach is used in the present paper to correct the workability diagram using nonaxisymmetric upsetting of five different samples made of steel. Some previous results are combined with the new results to obtain the workability diagram over a wide range of the triaxiality factor.

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“…Therefore, the strain path should be determined to calculate eq . However, since the material is supposed to be incompressible, it is sufficient to find the dependence of 2 on 3 [16]. This dependence can be found using high speed photography.…”

Section: Free Surface Fracturementioning

confidence: 99%

An Efficient Approach for Identifying Constitutive Parameters of the Modified Oyane Ductile Fracture Criterion at High Temperature

Alexandrov

Mustafa

Yahya

2013

Mathematical Problems in Engineering

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The paper presents the theoretical part of a method for identifying constitutive parameters involved in the modified Oyane ductile fracture criterion at high temperature. Quite a general rigid viscoplastic model is adopted to describe material behavior. The ductile fracture criterion is in general path-dependent and involves stresses. Therefore, the identification of constitutive parameters of this criterion is a difficult task which usually includes experimental research and numerical simulation. The latter requires a precisely specified material model and boundary conditions. It is shown in the present paper that for a wide class of material models usually used to describe the behavior of materials at high temperatures, the criterion is significantly simplified when the site of fracture initiation is located on traction free surfaces. In particular, this reduced criterion does not involve stresses. Since there are well established experimental procedures to determine the input data for the reduced criterion, the result obtained can be considered as a theoretical basis for the efficient method for identifying constitutive parameters of the modified Oyane ductile fracture criterion at high temperature. The final expression can also be used in computational models to increase the accuracy of predictions.

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An Improved Experimental Method for Determining the Workability Diagram

Cited by 10 publications

References 17 publications

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

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

A Study on Material Workability by Upsetting of Non-Axisymmetric Specimens by Flat Dies

An Efficient Approach for Identifying Constitutive Parameters of the Modified Oyane Ductile Fracture Criterion at High Temperature

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