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Computational Methods of the Identification of Chaboche Isotropic-Kinematic Hardening Model Parameters Derived from the Cyclic Loading Tests

Wójcik Marta, Gontarz Andrzej, Skrzat Andrzej, Winiarski Grzegorz

Advances in Science and Technology. Research Journal

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2024

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Vol. 18, no 1

61--75

EN

The Chaboche-Lemaitre combined isotropic-kinematic hardening model (CKIH) gives an overall information about the material behaviour under cyclic loading. The identification of hardening parameters is a difficult and time-consuming problem. The procedure of the parameters identification using the experimental hysteresis curve obtained in a cyclic loading test under strain control is presented in details here for a S235JR construction steel. The last stabilized cycle extracted from the hysteresis curve is required for the identification of hardening parameters. The model with three backstresses is tested here. The optimization algorithm is also used for the improvement of the agreement between experimental and numerical data. In order to include some uncertainty of experiment and the identification procedure, the authorial algorithm written on the basis of the fuzzy logic soft-computing method is applied here. The results obtained show that the identification procedure presented in this paper ensures the good agreement between the experimental tests and numerical calculations. The correct selection of parameters associated with the hardening is essential for the right description of material behaviour subject to loading in different engineering problems, including in metal forming processes.

2

Crystal plasticity elastic-plastic rate-independent numerical analyses of pollycrystalline materials

Wójcik Marta, Skrzat Andrzej, Stachowicz Feliks, Spišák Emil

Advances in Mechanical and Materials Engineering

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2023

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Vol. 40, nr 1

63--78

EN

Macroscopic analyses of plastic forming processes give only the overall description of the problem without the consideration of mechanisms of plastic deformation and the microstructure evolution. For the consideration of these processes, numerical simulations within crystal plasticity include the change of texture, anisotropy, and strain hardening of the material are used. In this paper, a crystal plasticity rate-independent model proposed by Anand and Kothari is applied for numerical analyses of polycrystalline materials. The slip was considered as the main mechanism of the plastic deformation. Basic constitutive equations of crystal plasticity for large deformation theories are presented. The selected results of elastic-plastic problems obtained using both macro- and micro- scales software for the explicit and implicit integration are featured here. The heterogeneous distribution of strain and stress in different grains are obtained, which is associated with the various crystal orientation. The crystal plasticity modelling of materials subject to plastic deformation involves not only the information about the change of a material’s shape in a macro-scale, but also describes the phenomena occurring in material in a micro-scale.

PL

Analizy makroskopowe procesów przeróbki plastycznej prezentują jedynie ogólny zarys rozważanego problemu, bez uwzględnienia mechanizmów odkształcenia plastycznego oraz ewolucji mikrostruktury. W celu rozważania procesów przeróbki plastycznej stosowane są symulacje numeryczne w ramach teorii plastyczności kryształów uwzgledniające zmianę tekstury, anizotropię oraz umocnienie odkształceniowe. W artykule zaprezentowano zastosowanie modelu Ananda i Kothari w ramach teorii plastyczności kryształów niezależnej od prędkości odkształcenia do rozwiązywania analiz numerycznych dla materiałów polikrystalicznych. W badaniach uwzględniono poślizg dyslokacyjny jako główny mechanizm odkształcenia plastycznego. Zaprezentowano wybrane rezultaty dla problemów sprężysto-plastycznych uzyskane zarówno w skali makro, jak i mikro- dla całkowania typu explicit i implicit. Uzyskano niejednorodny rozkład naprężenia i odkształcenia w poszczególnych ziarnach, związany z różną orientacją kryształów. Modelowanie numeryczne zzastosowaniem teorii plastyczności kryształów dla materiałów poddanych plastycznemu odkształceniu dostarcza nie tylko informacje o zmianie kształtu materiału w skali makro, ale także opisuje zjawiska zachodzące w materiale w skali mikro-.

3

Coupled Thermomechanical Eulerian-Lagrangian Analysis of the KOBO Extrusion Process

Wójcik Marta, Skrzat Andrzej

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 3

1185--1193

EN

Numerical simulations of the KOBO extrusion process are presented in this paper. The coupled thermomechanical Eulerian-Lagrangian approach was applied for the three-dimensional finite element model. The dynamic explicit Euler forward method was used in numerical calculations. The elastic-plastic Chaboche model assuming isotropic and kinematic hardening under variable temperature conditions was applied to describe the behaviour of the material under cyclic loading. In numerical computations Chaboche material model implemented in commercial software, as well as the proprietary one written as FORTRAN procedure were tested. The numerical results present the stress and strain distributions in the extruded material, as well as an increase of temperature due to the plastic work and friction. The shape of plastic strain zones was verified experimentally. The approach presented in the paper is a promising numerical tool to simulate the KOBO process.

4

An Elastic-Plastic Analysis of Polycrystalline Structure Using Crystal Plasticity Modelling – Theory and Benchmark Tests

Wójcik Marta, Skrzat Andrzej

Advances in Science and Technology. Research Journal

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2022

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Vol. 16, no 5

163--177

EN

Numerical simulations of tension and shear tests for a polycrystalline, anisotropic material were performed using crystal plasticity theory. The slip was considered here as the main mechanism of plastic deformation. Constitutive equations to describe the elastic-plastic deformation caused by the slip are presented. The generation and meshing of various shapes geometries (cubic and paddy shapes) with randomly-orientated grains by means of open source program NEPER program was shown. The Voronoi tessellation was used in order to include morphological properties of a crystalline material. The selected results of elastic-plastic analyses (stress, strain distributions and the macroscopic stress-strain resulting from homogenization) are presented here. The results obtained show the non-uniform distribution of stress and strain for different grains associated with their crystal orientation. The crystal plasticity finite element modelling of materials subjected to plastic deformation is important for microstructure-based mechanical predictions, as well as for the engineering design and to perform simulations involving not only the change of a material’s shape at a macro level but also the phenomena occurring in material in a micro-scale.

5

The Coupled Eulerian-Lagrangian Analysis of the KOBO Extrusion Process

Wójcik Marta, Skrzat Andrzej

Advances in Science and Technology. Research Journal

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2021

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Vol. 15, no 1

197--208

EN

The KOBO extrusion is an unconventional elastic-plastic deformation process in which the phenomenon of chang- ing a path of plastic deformation due to die cyclic oscillations by a given angle and with a given frequency is applied. As the result of the application of the oscillating rotary motion of the die, the reduction of the extrusion force was obtained. The numerical study of the KOBO extrusion of metallic materials was presented in this paper. The three-dimensional coupled Eulerian-Lagrangian (CEL) analysis was applied. The relationship between the extrusion force and the punch displacement during the KOBO process was achieved. The effective plastic strain distribution in the butt was found. The results of the numerical computations were compared with the experimen- tal data. The influence of the material hardening parameters on the cyclic loading phenomena (ratcheting, mean stress relaxation) in terms of the course of the KOBO extrusion was also examined. The proper determination of the material hardening parameters can help to optimize the KOBO process in terms of the reduction the extrusion force and the choice of the amount of die oscillations.

6

Numerical Modeling of Superplastic Punchless Deep Drawing Process of a TI-6AL-4V Titanium Alloy

Skrzat Andrzej, Wójcik Marta

Advances in Science and Technology. Research Journal

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2020

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Vol. 14, no 1

127--136

EN

The numerical results of superplastic punchless deep drawing of the Ti-6Al-4V titanium alloy were presented in this paper. The material behavior subjected to the forming process was characterized by deformation-microstructure constitutive equations including the grain growth. Superplastic stress-strain characteristics used in the numerical simulations were computed with the application of authorial program. The explicit integration scheme is used in solving differential equations. The numerical simulations of the super-elastic deep drawing were made with finite element method analysis. The von Mises stress distribution in the blow-forming process was obtained. The possible faults of extrusions caused by the improper load history as well as unsuitable pressure were also presented in this paper. The numerical simulations included in this research allow for the proper choice of material and drawing parameters which can help to optimize the superplastic forming process.