The self-similarity theory of high pressure torsion

By analyzing the problem of high pressure torsion (HPT) in the rigid plastic formulation, we show that the power hardening law of plastically deformed materials leads to self-similarity of HPT, admitting a simple mathematical description of the process. The analysis shows that the main parameters of HPT are proportional to β q , with β being the angle of the anvil rotation. The meaning of the parameter q is: q = 0 for velocity and strain rate, q = 1 for shear strain and von Mises strain, q = n for stress, pressure and torque (n is the exponent of a power hardening law). We conclude that if the hardening law is a power law in a rotation interval β, self-similar regimes can emerge in HPT if the friction with the lateral wall of the die is not too high. In these intervals a simple mathematical description can be applied based on self-similarity. Outside these ranges, the plasticity problem still has to be solved for each value of β. The results obtained have important practical implications for the proper design and analysis of HPT experiments.

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Hardening model of severe plastically deformed AA2024 by high-pressure torsion

International Journal of Structural Integrity ◽

10.1108/ijsi-10-2019-0102 ◽

2020 ◽

Vol 11 (4) ◽

pp. 591-603

Author(s):

Fauziana Lamin ◽

Ahmad Kamal Ariffin Mohd Ihsan ◽

Intan Fadhlina Mohamed ◽

Cheeranan Krutsuwan Nuphairode

Keyword(s):

High Pressure ◽

Simulation Model ◽

High Pressure Torsion ◽

Model Verification ◽

Von Mises Stress ◽

Rotational Axis ◽

Content Type ◽

Hardening Model ◽

Von Mises ◽

Stress Flow

PurposeThis paper aims to evaluate the validity of bilinear hardening model to represent the stress flow of high-pressure torsion (HPT)-strengthened lightweight material, AA2024.Design/methodology/approachFinite-element HPT simulation was performed by applying a simultaneous prescribed displacement on the axial and rotational axis that is equivalent to 4 GPa pressure and 30° torsion. The material behaviour incorporates plasticity attributes with a bilinear constitutive equation that consists of elastic and tangent modulus.FindingsAs a result, the von Mises stress generated from the simulation is in good agreement with the experiment, indicating that the assumptions of plasticity properties applied for the FEM simulation model are acceptable. The model verification confirms the anticipated plasticity parameters’ effect on the generated von Mises stress. The disc centre also evidenced an insignificant stress increment due to the limited shear straining.Research limitations/implicationsA reliable hardening model would assist in understanding the stress flow associated with mechanical properties enhancement.Practical implicationsThe bilinear hardening model exhibits a satisfactory stress estimation. It simplifies the ideal strain variable hardening procedures and lessens the total computation time that is valuable in solving severe plastic deformation problems.Originality/valueAn integration of well-defined input parameters, concerning the hardening behaviour and the plasticity properties, contributes to the establishment of a validated HPT simulation model, particularly for AA2024. This study also proved that perfectly plastic behaviour is inappropriate to represent hardening in the HPT-strengthened materials due to the remarkable stress deviation from the experimental data.

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Strengthening of Nickel Deformed by High Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.584-586.417 ◽

2008 ◽

Vol 584-586 ◽

pp. 417-421 ◽

Cited By ~ 3

Author(s):

Hong Wang Zhang ◽

X. Huang ◽

Niels Hansen ◽

Reinhard Pippan ◽

Michael Zehetbauer

Keyword(s):

High Pressure ◽

Cold Rolling ◽

High Pressure Torsion ◽

Structural Evolution ◽

Longitudinal Section ◽

High Angle ◽

Microstructural Parameters ◽

Transmission Electron ◽

Structure Relationship ◽

Von Mises

The strength of a deformed metal depends on the content of high angle boundaries, low angle dislocation boundaries and the dislocations between the boundaries. High angle boundaries contribute by Hall-Petch strengthening, whereas for the low angle dislocation boundaries and dislocations between boundaries the strengthening is proportional to the square root of the dislocation density. Based on an assumption of additivity of these contributions, the flow stresses of metals deformed by cold rolling have been calculated successfully. In the present investigation pure Ni (99.9%) has been deformed by high pressure torsion (HPT) to von Mises strains of 0.9, 1.7, 8.7 and 12. The strength of the HPT Ni has been determined by Vickers microhardness (HV) measurements and the microstructural parameters have been determined by transmission electron microscope (TEM) in the longitudinal section. HPT has been compared with deformation by cold rolling and torsion based on the structural evolution with strain and the stress-structure relationship. Based on an assumption of a linear additivity of boundary strengthening and dislocation strengthening, good agreement has been found between the calculated and the experimental flow stress.

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Mathematical modeling of materially nonlinear problems in structural analyses, Part I: Theoretical fundamentals

Facta universitatis - series Architecture and Civil Engineering ◽

10.2298/fuace1001067b ◽

2010 ◽

Vol 8 (1) ◽

pp. 67-78 ◽

Cited By ~ 1

Author(s):

Zoran Bonic ◽

Verka Prolovic ◽

Biljana Mladenovic

Keyword(s):

Nonlinear Problems ◽

Failure Surface ◽

Plasticity Theory ◽

Rigid Plastic ◽

Material Models ◽

Linear Elastic ◽

Hardening Law ◽

Plastic Yield ◽

Normality Condition ◽

Von Mises

Material models describe the way they behave when loaded. The paper presents the development of the model beginning with the simplest linear-elastic and rigid-plastic ones. The basic data in the plasticity theory have been defined, such as criterion and yield (failure) surface, hardening law, plastic yield law and normality condition. Yield criteria of Tresca, Von Mises, Mohr-Coulomb and Drucker-Prager were given separately.

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Finite Element Analysis of High Pressure Torsion Processing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.306-307.1317 ◽

2011 ◽

Vol 306-307 ◽

pp. 1317-1320 ◽

Cited By ~ 1

Author(s):

Qian Guan ◽

Chun Dong Zhu ◽

Tai Liang Dai

Keyword(s):

Finite Element Analysis ◽

Plastic Deformation ◽

Finite Element ◽

High Pressure ◽

Severe Plastic Deformation ◽

High Pressure Torsion ◽

Bulk Materials ◽

Rigid Plastic ◽

Element Analysis ◽

Plastic Deformation Behavior

Considerable interest has recently been developed in processing bulk materials through the application of severe plastic deformation (SPD). High pressure torsion(HPT) is one of severe plastic deformation methods. By this method, the material grain size can be refined to 20~200nm, which are nanometer level, and the micro-hardness and mechanical properties of materials can be improved. So the nanometer material can be got through this method. In this paper, the results of the rigid-plastic finite element analysis of the plastic deformation behavior of bulk materials during the HPT processing are presented. The torque and strain patterns of the sample as well as the relationship between the slippage time and pressure are also investigated.

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