scholarly journals Avrami Kinetic-Based Constitutive Relationship for Armco-Type Pure Iron in Hot Deformation

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 365 ◽  
Author(s):  
Yan Zhang ◽  
Qichao Fan ◽  
Xiaofeng Zhang ◽  
Zhaohui Zhou ◽  
Zhihui Xia ◽  
...  
Keyword(s):  
Kinetic Equation ◽  
Strain Rate ◽  
Strain Hardening ◽  
Pure Iron ◽  
Constitutive Relationship ◽  
Structure Evolution ◽  
Wide Range ◽  
Z Parameter ◽  
Time Exponent ◽  
Fractional Softening

The work presents a full mathematical description of the stress-strain compression curves in a wide range of strain rates and deformation temperatures for Armco-type pure iron. The constructed models are based on a dislocation structure evolution equation (in the case of dynamic recovery (DRV)) and Avrami kinetic-based model (in the case of dynamic recrystallization (DRX)). The fractional softening model is modified as: X = ( σ 2 − σ r 2 ) / ( σ d s 2 − σ r 2 ) considering the strain hardening of un-recrystallized regions. The Avrami kinetic equation is modified and used to describe the DRX process considering the strain rate and temperature. The relations between the Avrami constant k ∗ , time exponent n ∗ , strain rate ε ˙ , temperature T and Z parameter are discussed. The yield stress σ y , saturation stress σ r s , steady stress σ d s and critical strain ε c are expressed as the functions of the Z parameter. A constitutive model is constructed based on the strain-hardening model, fractional softening model and modified Avrami kinetic equation. The DRV and DRX characters of Armco-type pure iron are clearly presented in these flow stress curves determined by the model.

Sensitivity Analysis of the Material Flow Stress in Machining

Manufacturing ◽  
2003 ◽  
Author(s):  
Ning Fang
Keyword(s):  
Sensitivity Analysis ◽  
Flow Stress ◽  
Aluminum Alloys ◽  
Strain Rate ◽  
Strain Hardening ◽  
Material Flow ◽  
Chemical Compositions ◽  
Wide Range ◽  
Strain Rate Hardening ◽  
Factor Governing

Among the effects of strain hardening, strain-rate hardening, and temperature softening, it has long been argued about which effect is predominant in governing the material flow stress in machining. This paper compares four material constitutive models commonly employed, including Johnson-Cook’s model, Oxley’s model, Zerilli-Armstrong’s model, and Maekawa et al.’s model. A new quantitative sensitivity analysis of the material flow stress is performed based on Johnson-Cook’s model covering a wide range of engineering materials, including plain carbon steels with different carbon contents, alloyed steels, aluminum alloys with different chemical compositions and heat treatment conditions, copper and copper alloys, iron, nickel, tungsten alloys, etc. It is demonstrated that the first predominant factor governing the material flow stress is either strain hardening or thermal softening, depending on the specific work material employed and the varying range of temperatures. Strain-rate hardening is the least important factor governing the material flow stress, especially when machining aluminum alloys.

scholarly journals Characterization of Hot Deformation Behavior and Dislocation Structure Evolution of an Advanced Nickel-Based Superalloy

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 920 ◽  
Author(s):  
Zhihao Yao ◽  
Hongying Wang ◽  
Jianxin Dong ◽  
Jinglin Wang ◽  
He Jiang ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Hot Deformation ◽  
Deformation Behavior ◽  
Deformation Temperature ◽  
Flow Instability ◽  
Processing Condition ◽  
Constitutive Relationship ◽  
Structure Evolution ◽  
Hot Deformation Behavior

The hot deformation behavior of an advanced nickel-based Haynes282 superalloy was systematically investigated employing isothermal compression tests in the sub-solvus and super-solvus temperature with various strain rates. The influence of deformation temperature and strain rate on the microstructure was studied by transmission electron microscope. The results reveal that the interaction between work hardening and dynamic softening did not reach equilibrium under lower deformation temperature and higher strain rate. The active energy of alloy is around 537.12 kJ/mol and its hot deformation constitutive relationship equation was expressed. According to the processing map and microstructure observations, two unsafe flow instability domains should be avoided. The optimum hot processing condition for homogeneous and fine dynamic recrystallization grains are obtained. TEM micrograph observations indicated that deformation temperature and strain rate affected recrystallization by affecting the evolution of dislocation substructures within the alloy. The nucleation and growth of DRX grains can be promoted by the relatively high deformation temperature and low strain rate. The main mechanism of dynamic recrystallization nucleation preferred to discontinuous dynamic recrystallization and the typical feature of discontinuous dynamic recrystallization showed grain boundary migration nucleation. The findings improve the understanding of hot deformation behavior and dislocation substructures evolution of the superalloy, which benefits the accurate control of microstructures of nickel-based superalloys, and tailors the properties of final components used in the land-based gas turbine.

scholarly journals Study on Constitutive Characteristic of As-Cast AA6061 Alloy under Plane Strain Compression Based on Orthogonal Analysis

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Fangcheng Qin ◽  
Huiping Qi ◽  
Yuehua Kang ◽  
Chongyu Liu
Keyword(s):  
Strain Rate ◽  
Plane Strain ◽  
Orthogonal Experiment ◽  
Constitutive Models ◽  
Plane Strain Compression ◽  
Constitutive Relationship ◽  
Aa6061 Alloy ◽  
Average Absolute Relative Error ◽  
Wide Range ◽  
Orthogonal Analysis

Constitutive relationship and microstructure evolution of as-cast AA6061 alloy were studied using plane strain compression (PSC) under the temperature of 300–450°C, the strain rate of 0.01–5 s−1, and the strain of 0.9. It is found that the flow stress decreases with increasing temperature and decreasing strain rate. The dynamic recovery (DRV) and recrystallization (DRX) are found to easily occur by optical microscopic (OM) techniques. The softening mechanisms are mainly due to DRV that is accompanied by a slight DRX. Based on orthogonal analysis, the strain should be taken into account to derive the constitutive model accurately, and the interaction effect between the strain rate and temperature on the stress can be neglected when compared with the individual effect of the strain rate and temperature. The strain-compensated constitutive models based on orthogonal experiment are established, and the activation energy Q is found to be 158.465 kJ/mol. The correlation coefficient and the average absolute relative error between the experimental and the predicted results are 0.9946 and 4.2656%, respectively. The developed models can be used to predict the stress precisely at a wide range of strains, strain rates, and temperatures.

scholarly journals Computational Analysis of Compressive Strain Hardening Exponents of Bimetal with Pearlitic Steel and Low Carbon Steel

2014 ◽  
Vol 553 ◽  
pp. 71-75 ◽  
Author(s):  
Xing Jian Gao ◽  
Zheng Yi Jiang ◽  
Dong Bin Wei ◽  
Si Hai Jiao ◽  
Jing Tao Han
Keyword(s):  
Carbon Steel ◽  
Strain Rate ◽  
Strain Hardening ◽  
Deformation Temperature ◽  
Computational Analysis ◽  
Compressive Strain ◽  
Low Carbon Steel ◽  
Pearlitic Steel ◽  
Low Carbon ◽  
Wide Range

The compressive strain hardening behaviour of a novel bimetal with pearlitic steel and low carbon steel was investigated by computational analysis based on the isothermal compression tests in a wide range of deformation temperature and strain rate. The Hollomon’s equation was employed to calculate the strain hardening exponent (SHE) with the assistance of mathematical manipulation. The result shows that the logarithmic relationship between the flow stress and plastic strain of the bimetal is highly non-linear, which results in the variation of the SHE of the bimetal. This variation reflects the dynamic competition between the strain hardening and softening mechanism by the varying value of the SHE in the range of 0.4 to-0.4. Furthermore, the influences of deformation temperature and strain rate on the SHE are significant. With decreasing temperature and increasing strain rate, the strain hardening of the bimetal was enhanced, while the dynamic recrystallisation was activated under the opposite conditions with the evidence of negative SHE value.

scholarly journals Development of an integrated approach combining artificial neural network material based on modeling with finite element analysis of forming processes

2005 ◽  
Author(s):  
◽  
Brian Scott Kessler
Keyword(s):  
Finite Element ◽  
Flow Stress ◽  
Strain Rate ◽  
Strain Hardening ◽  
Integrated Approach ◽  
Hot Forming ◽  
Energy Materials ◽  
Softening Mechanism ◽  
Wide Range ◽  
Early Strain

The use of a finite element model for design and analysis of a metal forming processes is limited by the incorporated material model's ability to predict deformation behavior over a wide range of operating conditions. Conventionally generated rheological models prove deficient in several respects due to the difficulty in establishing complicated relations between many parameters. More recently, artificial neural networks (ANN) have been suggested as an effective means to overcome these difficulties. To this end, a robust ANN with the ability to determine flow stresses based on strain, strain rate, and temperature is developed and linked with finite element based simulation model. Comparisons of this novel method with conventional means are carried out to demonstrate the advantages of this approach as applied to industrial applications. The flow stress curves generated using the developed ANN method for 6061 alumimum show the typical behavior of high stacking fault energy materials, where the controlling softening mechanism is dynamic recovery (early strain hardening followed by a smooth transition to a plateau of stress). In contrast, the flow stress behavior of nickel aluminide exhibits the typical behavior of low stacking fault energy materials, where the controlling softening mechanism in hot working is dynamic recrystallization (early strain hardening to a peak stress followed by drop and oscillation of the flow stress about a steady average value). A thermo-mechanical coupled finite element method (FEM) using the commercial code ABAQUS as a platform for development is introduced to simulate hot forming processes. The FEM model is integrated with the developed ANN material based model in order to account for the effects of strain, strain rate, and temperature variations within the material during hot-forming. An industrial case study involves hot forging of an aftermarket automotive wheel made out of 6061 aluminum is used to evaluate the effectiveness of the integrated approach. The load-displacement curves predicted by the developed virtual model are in good agreement with the experimental observations of an industrial forging process. The developed approach and knowledge gained from the present work, has a wide range of application in general, and is not limited to hot forming of the investigated materials. The new approach is applicable to all hot forming processes of different alloy systems.

Temperature and Rate-Dependent Constitutive Relationship for Vanadium Alloy V-5Cr-5Ti and Failure Modes

2010 ◽  
Vol 44-47 ◽  
pp. 2336-2340
Author(s):  
Xi Cheng Huang ◽  
Wen Jun Hu ◽  
Yi Xia Yan ◽  
Ruo Ze Xie ◽  
Fang Ju Zhang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Strain Rate ◽  
Yield Stress ◽  
Failure Modes ◽  
Constitutive Relationship ◽  
Strain Rates ◽  
Vanadium Alloy ◽  
Rate Dependent ◽  
Brittle Ductile Transition ◽  
Wide Range

In this work the static and dynamic properties of vanadium alloy V-5Cr-5Ti over a wide range of temperature from 20 to 1000 degree at strain rates ranged from 10-4/s~103/s were studied experimentally under uniaxial quasi-static tension with MTS universal testing machine, uniaxial dynamic compression and tension with split Hopkinson bar system with temperature control. The stress-strain curves of V-5Cr-5Ti at various temperatures and various strain rates were obtained. Experimental data show that V-5Cr-5Ti behaves strain-rate sensitive and temperature dependent, for instance the material parameters yield stress, tensile strength and failure strain. And fracture mode of the material is also dependent on strain-rate and temperature. Based on experimental data the temperature-rate-dependent constitutive relations were established in the form of Johnson-Cook and Cowper-Symonds models which are widely used in numerical simulation of dynamic processes of structures under impact loading. The material microstructures and failure modes were analyzed using optical microscope, TEM etc, and results shows that the yield stress and strength are increased with strain rate. The brittle-ductile transition strain-rate is from 101/s to102/s.

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