Dynamic Material Behavior Modeling Using Internal State Variable Plasticity and Its Application in Hard Machining Simulations

2005 ◽  
Vol 128 (3) ◽  
pp. 749-759 ◽  
Author(s):  
Y. B. Guo ◽  
Q. Wen ◽  
K. A. Woodbury
Keyword(s):  
Internal State ◽  
Kinematic Hardening ◽  
Material Behavior ◽  
Machining Process ◽  
Hard Machining ◽  
Internal State Variable ◽  
Strain Rates ◽  
Material Constants ◽  
State Variable ◽  
Jc Model

Work materials experience large strains, high strain rates, high temperatures, and complex loading histories in machining. The problem of how to accurately model dynamic material behavior, including the adiabatic effect is essential to understand a hard machining process. Several conventional constitutive models have often been used to approximate flow stress in machining analysis and simulations. The empirical or semiempirical conventional models lack mechanisms for incorporating isotropic/kinematic hardening, recovery, and loading history effects. In this study, the material constants of AISI 52100 steel (62 HRc) were determined for both the Internal State Variable (ISV) plasticity model and the conventional Johnson-Cook (JC) model. The material constants were obtained by fitting the ISV and JC models using nonlinear least square methods to same baseline test data at different strains, strain rates, and temperatures. Both models are capable of modeling strain hardening and thermal softening phenomena. However, the ISV model can also accommodate the adiabatic and recovery effects, while the JC model is isothermal. Based on the method of design of experiment, FEA simulations and corresponding cutting tests were performed using the cutting tool with a 20 deg chamfer angle. The predicted chip morphology using the ISV model is consistent with the measured chips, while the JC model is not. The predicted temperatures can be qualitatively verified by the subsurface microstructure. In addition, the ISV model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.

The Use of Internal State Variable Plasticity Model via a User Subroutine to Evaluate the Effect of Materials Testing Modes on Hard Machining Simulation

2007 ◽  
Author(s):  
S. Anurag ◽  
Y. B. Guo ◽  
M. F. Horstemeyer
Keyword(s):  
Internal State ◽  
Machining Process ◽  
Materials Testing ◽  
Hard Machining ◽  
Internal State Variable ◽  
Plasticity Model ◽  
True Nature ◽  
Material Constants ◽  
State Variable ◽  
Material Deformation

Hard machining involves large strain, high strain rate, high temperatures, strain rate/temperature coupling, and potential loading history effects. The accuracy of characterizing the dynamic mechanical behavior in hard machining using any constitutive models is strongly affected by materials testing data in which a constitutive model is fitted. Tension or compression tests have been widely used to approximate material properties in various manufacturing processes. However, it has been a critical question whether tension or compression test should be utilized for capturing the true nature of material deformations in a hard machining process. In this study, the influences of two material testing modes on mechanical behavior of AISI52100 steel (62 HRc) were investigated using the internal state variable (ISV) plasticity model. Twenty material constants have been found by nonlinear fitting the ISV plasticity model to the base line test data obtained from each deformation mode. To understand the true nature of hard turning mechanics, a numerical model that incorporate the internal state variable plasticity model via a material user subroutine has been developed with the material constants from the compression and tension tests. A global material failure/damage evolution model was implemented to simulate chip formation which solely depends on the material deformation state. Orthogonal hard turning experiments have been performed to validate the numerical model. It has shown that the material testing modes have profound effects on some materials constants of the ISV model. The stress sensitivity study to ISV model parameters has identified the critical material constants for reflecting the nature of material deformation. The different testing modes have significant influence on the material constants associated with isotropic hardening rather than kinematic hardening. The numerical and experimental results have shown that the material constants from the compression test capture the true nature of a hard machining process. The compression mode of material deformation prevails in hard machining.

A Physically Motivated Internal State Variable Plasticity/Damage Model Embedded With a Length Scale for Hazmat Tank Cars’ Structural Integrity Applications

2011 ◽  
Author(s):  
Fazle R. Ahad ◽  
Koffi Enakoutsa ◽  
Kiran N. Solanki ◽  
Yustianto Tjipowidjojo ◽  
Douglas J. Bammann
Keyword(s):  
Evolution Equation ◽  
Internal State ◽  
Damage Model ◽  
Mesh Size ◽  
Material Behavior ◽  
Length Scale ◽  
Internal State Variable ◽  
State Variable ◽  
Fe Simulations ◽  
The Impact

In this study, we use a physically-motivated internal state variable plasticity/damage model containing a mathematical length scale to represent the material behavior in finite element (FE) simulations of a large scale boundary value problem. This problem consists of a moving striker colliding against a stationary hazmat tank car. The motivations are (1) to reproduce with high fidelity finite deformation and temperature histories, damage, and high rate phenomena which arise during the impact and (2) to address the pathological mesh size dependence of the FE solution in the post-bifurcation regime. We introduce the mathematical length scale in the model by adopting a nonlocal evolution equation for the damage, as suggested by Pijaudier-Cabot and Bazant (1987) in the context of concrete. We implement this evolution equation into existing implicit and explicit versions of the FE subroutines of the plasticity/failure model. The results of the FE simulations, carried out with the aid of Abaqus/Explicit FE code, show that the material model, accounting for temperature histories and nonlocal damage effects, satisfactorily predicts the damage progression during the tank car impact accident and significantly reduces the pathological mesh size effects.

Adiabatic Shear Modeling and Its Influence on Machining Simulations: BCJ vs. JC Model

2005 ◽  
Author(s):  
Q. Wen ◽  
Y. B. Guo ◽  
K. A. Woodbury
Keyword(s):  
Mechanical Behavior ◽  
Orthogonal Cutting ◽  
Complex Loading ◽  
Least Square ◽  
Machining Process ◽  
Von Mises Stress ◽  
Large Strains ◽  
Strain Rates ◽  
Material Constants ◽  
Jc Model

The understanding of mechanical behavior in machining is critical to analyze and design a process. It is well known that work materials experience large strains, high strain rates, high temperatures, and complex loading histories. Adiabatic or quasi-adiabatic condition is an important feature of material deformations in machining ferrous alloys. The problem of how to accurately model the mechanical behavior including the adiabatic effect is essential to understand a machining process. Several constitutive equations such as the simple power law model, Johnson-Cook (JC) model, and other models have often been used to approximate flow stress in machining analysis and simulations. The JC and other empirical or semi-empirical models lack mechanisms in incorporating complex loading effects. The internal state variable plasticity Baumann-Chiesa-Johnson model (BCJ model) has been shown to incorporate loading histories as well as state variables. In this study, we have determined the material constants of AISI 52100 steel (62 HRc) for both the JC and BCJ models using the same baseline stress-strain data. The material constants were obtained by fitting the JC and BCJ models to these test data at different strains, strain rates, and temperatures using nonlinear least square methods. Both models are capable of modeling strain hardening and thermal softening phenomena. However, the BCJ model can also accommodate the adiabatic effect, while the JC model is basically isothermal. Orthogonal cutting tests and FEA simulations, based on the design-of-experiment method, were performed using the cutting tool with a 20° chamfer angle. The predicted saw-tooth chip morphology and dimensions using the BCJ model are consistent with the measured chips in the cutting tests, while the JC model yielded discontinuous chips. In addition, the BCJ model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.

Using Internal State Variable Plasticity to Determine Dynamic Loading History Effects in Manufacturing Processes

2004 ◽  
Author(s):  
Y. B. Guo ◽  
Q. Wen ◽  
M. F. Horstemeyer
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Internal State ◽  
Material Behavior ◽  
Temperature History ◽  
Loading Path ◽  
Internal State Variable ◽  
State Variable ◽  
History Effects ◽  
Deformation Processes

Worked materials in large deformation processes such as forming and machining experience a broad range of strain, strain rate, and temperatures, which in turn affect the flow stress. However, the flow stress also highly depends on many other factors such as strain path, strain rate and temperature history. Only a model that includes all of these pertinent factors is capable of predicting complex stress state in material deformation. In this paper, the commonly used phenomenological plasticity models (Johnson-Cook, Usui, etc.) to characterize material behavior in forming and machining were critically reviewed. Although these models are easy to apply and can describe the general response of material deformation, these models lack the mechanisms to reflect static and dynamic recovery and the effects of load path and strain rate history in large deformation processes. These effects are essential to understand process mechanisms, especially surface integrity of the manufactured products. As such a dislocation-based internal state variable (ISV) plasticity model was used, in which the evolution equations enable the prediction of strain rate history and temperature history effects. These effects can be quite large and cannot be modeled by the equation-of-state models that assume that stress is a unique function of the total strain, strain rate, and temperature, independent of the loading path. The temperature dependence of the hardening and recovery functions results in the prediction of thermal softening during adiabatic temperatures rises, which are common in metal forming and machining. The dynamic mechanical behaviors of three different benchmark work materials, titanium Ti-6Al-4V, AISI 52100 steel (62 HRc), and aluminum 6061-T6, were modeled using the ISV approach. The material constants were obtained by using a nonlinear regression fitting algorithm in which the stress-strain curves from the model were correlated to the experiments at different (extreme) temperatures. Then the capabilities of the determined material constants were examined by comparing the predicted material flow stress with the test data at different temperatures, strains, and strain rate history. The comparison demonstrates that the internal state plasticity model can successfully recover dynamic material behavior at various deformation states including the loading path effect. In addition, thermal softening due to adiabatic deformation was also captured by this approach.

Cutting Mechanics of High Speed Dry Machining of Magnesium-Calcium Biomedical Alloy Using Internal State Variable Plasticity Model

2011 ◽  
Author(s):  
M. Salahshoor ◽  
Y. B. Guo
Keyword(s):  
Mechanical Properties ◽  
Chip Formation ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Internal State ◽  
Material Behavior ◽  
Internal State Variable ◽  
Plasticity Model ◽  
Dry Cutting ◽  
State Variable

Magnesium-Calcium (MgCa) alloys have become attractive orthopedic biomaterials due to their biodegradability, biocompatibility, and congruent mechanical properties with bone tissues. However, process mechanics of machining biomedical MgCa alloys is poorly understood. Mechanical properties of the biomedical magnesium alloy at high strain rates and large strains are determined by using the split-Hopkinson pressure bar testing method. Internal state variable (ISV) plasticity model is implemented to understand the dynamic material behavior under cutting conditions. A finite element simulation model has been developed to study the chip formation during high speed dry cutting of MgCa0.8 (wt %) alloy. Continuous chip formation predicted by the FE simulation is verified by high speed dry face milling of MgCa0.8 using polycrystalline diamond (PCD) inserts. Chip ignition is known as the most hazardous aspect of machining Mg alloys. The predicted temperature distributions may well explain the reason for machining safety of high-speed dry cutting of MgCa0.8 alloy.

Analysis and Application of a Coupled Thermoviscoplasticity Theory

1990 ◽  
Vol 57 (4) ◽  
pp. 828-835 ◽  
Author(s):  
H. Ghoneim
Keyword(s):  
Cyclic Loading ◽  
Constitutive Equation ◽  
Internal State ◽  
Internal State Variable ◽  
Strain Rates ◽  
Finite Element Program ◽  
Coupled Equations ◽  
State Variable ◽  
Different Temperatures ◽  
Element Program

Coupled thermoviscoplasticity equations are developed based on the rational theory of thermodynamics. A power-form internal state variable constitutive equation is proposed. Limitation of the proposed constitutive equation is discussed and simulation results of cyclic loading of 1070 steel at different temperatures and strain rates are presented. The developed coupled equations and the proposed constitutive equation are implemented into a finite element program which is used to investigate the thermomechanical problem of cyclic loading of a constrained-ended cylinder.

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