Frictional effects on flow stress determination at high temperatures and strain rates

The deformation behavior of AZ31 magnesium alloy has been investigated by isothermal compression at temperatures between 573-723K and at constant strain rates ranging from 10-3 -1s-1. It is shown that the form of flow stress curves is very sensitive to temperature and strain rate. In the experimental domain studied, the flow stresses are modeled using a power law with an average activation energy of 145.16 kJ/mol, and dynamic recrystallization (DRX) occurs. The critical strain for DRX is determined by analysis of flow stress curves. The ratio of the critical strain to the peak strain falls in the range of 0.4-0.5. At low temperatures and high strai rates, the deformation become macroscopically inhomogeneous, and the fracture of the specimens is accompanied by shear banding. Grain refinement resulting from DRX is less effective at high temperatures due to rapid grain growth. It is also shown that there is no difference between peak stress and stable state stress at high temperatures and lower strain rates, presenting the feature of continuous dynamic recrystallization (CDRX).

Download Full-text

Numerical modeling of the dynamic strain aging in steels at high strain rates and high temperatures

EPJ Web of Conferences ◽

10.1051/epjconf/202125002023 ◽

2021 ◽

Vol 250 ◽

pp. 02023

Author(s):

R. A. Rubio ◽

M. Hokka

Keyword(s):

Flow Stress ◽

High Temperatures ◽

Dynamic Strain Aging ◽

Strain Aging ◽

High Strain ◽

Dynamic Strain ◽

Support Vector ◽

Strain Rates ◽

High Strain Rates ◽

Thermomechanical Behaviour

Carbon steels can be heat treated to produce different microstructural variations and mechanical properties. At high temperatures the material plasticity and strength can be influenced by diffusional effects like the Portevin-Le Chatelier effect, leading to a commonly observed increased strength at elevated temperatures. The diffusional effects are influenced by the chemical composition, but also the heat treatment history that affects the local composition and especially the concentrations of free solute atoms. In this work, a numerical approach was implemented to reproduce the thermomechanical behaviour of two different microstructural variants of steel grade C45. The experimental data used to calibrate the model includes information of the plastic behaviour of material subjected to dynamic compression loading at a wide range of temperatures. Special emphasis was focused to describe the effects of the dynamic strain aging (DSA) on the flow stress. A strategy based on machine learning was implemented to obtain a model that reproduces the strengthening of the material due to diffusional effects. Cubic Support Vector Machine models were trained for both microstructure variants of the steel and different surfaces were obtained to describe the topology of the flow stress as function of temperature and strain rate. The model predictions were compared to the behaviour described by the Johnson-Cook model to estimate the influence of the DSA effect on the strength of the material at high strain rates and temperatures. Furthermore, the model quantifies how the microstructure affects the strength of the material and the strength of the DSA-hardening.

Download Full-text

Alloys based on NiAl for High Temperature Applications

MRS Proceedings ◽

10.1557/proc-39-411 ◽

1984 ◽

Vol 39 ◽

Cited By ~ 15

Author(s):

K. Vedula ◽

V. Pathare ◽

I. Aslanidis ◽

R. H. Titran

Keyword(s):

Grain Size ◽

High Temperature ◽

Powder Metallurgy ◽

Flow Stress ◽

High Temperatures ◽

Strain Rates ◽

Dislocation Interaction ◽

Alloying Additions ◽

Ternary Alloying ◽

Temperature Applications

ABSTRACTThis paper presents some of the results obtained in an on-going study of NiAl alloys for potential high temperature applications. Alloys were prepared by powder metallurgy techniques. Flow stress values at slow strain rates and high temperatures were measured. Some promising ternary alloying additions (Hf, Ta and Nb) have been identified. The mechanism of strengthening in alloys containing these additions appears to be a form of particle dislocation interaction. Interesting effects of grain size and stoichiometry in binary alloys are also presented.

Download Full-text

Flow stress of lead-free solder alloys over a broad range of temperatures and strain rates

DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading ◽

10.1051/dymat/2009203 ◽

2009 ◽

Author(s):

T. Chen ◽

X. Y. Niu ◽

Z. G. Li ◽

X. F. Shu

Keyword(s):

Flow Stress ◽

Lead Free ◽

Strain Rates ◽

Lead Free Solder ◽

Solder Alloys ◽

Free Solder

Download Full-text

A Numerical and Experimental Study of Cavitation in a Hot Tensile Axisymmetric Testpiece

The Journal of Strain Analysis for Engineering Design ◽

10.1243/030932405x30768 ◽

2005 ◽

Vol 40 (6) ◽

pp. 571-586 ◽

Cited By ~ 9

Author(s):

Y Liu ◽

J Lin ◽

T. A Dean ◽

D. C. J Farrugia

Keyword(s):

Experimental Study ◽

Flow Stress ◽

Grain Boundary ◽

Thermal Gradient ◽

Tensile Testing ◽

Tensile Deformation ◽

Strain Rates ◽

Test Results ◽

Integrated Technique ◽

Hot Tensile Deformation

During axisymmetric hot tensile testing, necking normally takes place due to the thermal gradient and the accumulation of microdamage. This paper introduces an integrated technique to predict the damage and necking evolution behaviour. Firstly, a set of multiaxial mechanism-based unified viscoplastic-damage constitutive equations is presented. This equation set, which models the evolution of grain boundary (intragranular) and plasticity-induced (intergranular) damage, is determined for a free-cutting steel tested over a range of temperatures and strain rates on a Gleeble thermomechanical simulator. This model has been implemented using the CREEP subroutine of the commercial finite element (FE) solver ABAQUS. Numerical procedures to simulate axisymmetric hot tensile deformation are developed with consideration of the thermal gradient along the axis of the tensile testpiece. FE simulations are carried out to reproduce the necking phenomenon and the evolution of plasticity-induced and grain boundary damage. The simulated results have been validated with experimental tensile test results. The effects of necking and its associated stress state on flow stress and ductility are investigated. The flow stress and ductility data obtained from a Gleeble material simulator under various hot deformation conditions have also been numerically studied.

Download Full-text

Forging, textures, and deformation systems in a B2 FeAl alloy

Journal of Materials Research ◽

10.1557/jmr.1999.0097 ◽

1999 ◽

Vol 14 (3) ◽

pp. 715-728 ◽

Cited By ~ 3

Author(s):

P. Zhao ◽

D. G. Morris ◽

M. A. Morris Munoz

Keyword(s):

High Temperature ◽

Flow Stress ◽

Slip System ◽

High Temperatures ◽

Low Temperatures ◽

High Speed ◽

Deformation Texture ◽

Slip Systems ◽

Feal Alloy ◽

Very High

High-temperature forging experiments have been carried out by axial compression testing on a Fe–41Al–2Cr alloy in order to determine the deformation systems operating under such high-speed, high-temperature conditions, and to examine the textures produced by such deformation and during subsequent annealing to recrystallize. Deformation is deduced to take place by the operation of 〈111〉 {110} and 〈111〉{112} slip systems at low temperatures and by 〈100〉{001} and 〈100〉{011} slip systems at high temperatures, with the formation of the expected strong 〈111〉 textures. The examination of the weak 〈100〉 texture component is critical to distinguishing the operating slip system. Both texture and dislocation analyses are consistent with the operation of these deformation systems. Recrystallization takes place extremely quickly at high temperatures (above 800 °C), that is within seconds after deformation and also dynamically during deformation itself. Recrystallization changes the texture such that 〈100〉 textures superimpose on the deformation texture. The flow stress peak observed during forging is found at a very high temperature. Possible origins of the peak are examined in terms of the operating slip systems.

Download Full-text

A modified Arrhenius model for as-quenched Al-Mg-Si alloy considering the effect of cooling rate

Engineering Computations ◽

10.1108/ec-03-2020-0159 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Ruichao Guo ◽

Jianjun Wu ◽

Yinxiang Ren

Keyword(s):

Residual Stress ◽

Flow Stress ◽

Cooling Rate ◽

Flow Behavior ◽

Constitutive Behavior ◽

Strain Rates ◽

Arrhenius Model ◽

Content Type ◽

Stress Behavior ◽

Flow Stress Behavior

Purpose Accurate prediction of residual stress requires precise knowledge of the constitutive behavior of as-quenched material. This study aims to model the flow stress behavior for as-quenched Al-Mg-Si alloy. Design Methodology Approach In the present work, the flow behavior of as-quenched Al-Mg-Si alloy is studied by the hot compression tests at various temperatures (573–723 K), strain rates (0.1–1 s−1) and cooling rates (1–10 K/s). Flow stress behavior is then experimentally observed, and an Arrhenius model is used to predict the flow behavior. However, due to the fact that materials parameters and activation energy do not remain constant, the Arrhenius model has an unsatisfied prediction for the flow behavior. Considering the effects of temperatures, strain rates and cooling rates on constitutive behavior, a revised Arrhenius model is developed to describe the flow stress behavior. Findings The experimental results show that the flow stress increases by the increasing cooling rate, increasing strain state and decreasing temperature. In comparison to the experimental data, the revised Arrhenius model has an excellent prediction for as-quenched Al-Mg-Si alloy. Originality Value With the revised Arrhenius model, the flow behaviors at different quenching conditions can be obtained, which is an essential step to the residual stress prediction when the model is implemented in a finite element code, e.g. ABAQUS, in the future.

Download Full-text

Hot Deformation Behavior of a New Al–Mn–Sc Alloy

Materials ◽

10.3390/ma13010022 ◽

2019 ◽

Vol 13 (1) ◽

pp. 22

Author(s):

Weiqi Kang ◽

Yi Yang ◽

Sheng Cao ◽

Lei Li ◽

Shewei Xin ◽

...

Keyword(s):

Flow Stress ◽

Hot Deformation ◽

Deformation Behavior ◽

Material Model ◽

Strain Rates ◽

Hot Workability ◽

Hot Deformation Behavior ◽

Hollomon Parameter ◽

Dynamic Material Model ◽

Optimal Processing

The hot deformation behavior of a new Al–Mn–Sc alloy was investigated by hot compression conducted at temperatures from 330 to 490 °C and strain rates from 0.01 to 10 s−1. The hot deformation behavior and microstructure of the alloy were significantly affected by the deformation temperatures and strain rates. The peak flow stress decreased with increasing deformation temperatures and decreasing strain rates. According to the hot deformation behavior, the constitutive equation was established to describe the steady flow stress, and a hot processing map at 0.4 strain was obtained based on the dynamic material model and the Prasad instability standard, which can be used to evaluate the hot workability of the alloy. The developed hot processing diagram showed that the instability was more likely to occur in the higher Zener–Hollomon parameter region, and the optimal processing range was determined as 420–475 °C and 0.01–0.022 s−1, in which a stable flow and a higher power dissipation were achieved.

Download Full-text

Plastic Flow Stress and Constitutive Model for H96 Brass Alloy

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.782.130 ◽

2015 ◽

Vol 782 ◽

pp. 130-136 ◽

Cited By ~ 1

Author(s):

Ping Zhou ◽

Wei Guo Guo ◽

Hai Hui Wu

Keyword(s):

Flow Stress ◽

Constitutive Model ◽

Plastic Flow ◽

Split Hopkinson Pressure Bar ◽

Testing Machine ◽

Experimental Results ◽

Dynamic Strain ◽

Strain Rates ◽

Brass Alloy ◽

Plastic Flow Stress

To explore the thermo-mechanical response of H96 brass alloy, the quasi-static (universal-testing machine) and dynamic (the split Hopkinson pressure bar apparatus) uniaxial compression experiments have been performed under the temperatures from 293 K to 873 K and the strain rates from 0.001 s-1 to 6000 s-1, and the strains over 60% are obtained. Results show that, H96 brass alloy has strong strain hardening behavior, and it becomes weaker with the increasing temperature. In addition, this alloy is sensitive to strain rates; and, it has temperature sensitivity, the dynamic strain aging occurs at the temperature of 473 K and a quasi-static strain rate of 0.001 s-1. Based on the thermal activation dislocation mechanism, paralleled with the experimental results, a plastic flow constitutive model with the physical conception is developed. The model is suitable to predict the plastic flow stress at different temperatures and strain rates. According to comparing results, the model predictions are in good agreement with the experimental results.

Download Full-text