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.

Viscoplastic Constitutive Equations for Copper With Strain Rate History and Temperature Effects

1978 ◽  
Vol 100 (4) ◽  
pp. 388-394 ◽  
Author(s):  
S. R. Bodner ◽  
A. Merzer
Keyword(s):  
Strain Rate ◽  
Constitutive Equations ◽  
Internal State ◽  
Rate Sensitivity ◽  
Experimental Program ◽  
Internal State Variable ◽  
Plastic Working ◽  
State Variable ◽  
History Effects ◽  
Good Agreement

Elastic-viscoplastic constitutive equations based on a single internal state variable which is a function of plastic work are used to calculate the response of copper to a six decade change of strain rate over a range of temperatures. Calculations were performed for the conditions of an experimental program on copper by Senseny, Duffy, and Hawley, namely, temperatures ranging from 77°K to 523°K and strain rate jumps from 2 × 10−4sec−1 to 3 × 102sec−1 at three strain levels. The computed results are in good agreement with the experiments and show similar strain rate and strain rate history effects. Relations are obtained for the temperature dependence of certain parameters in the equations which indicate correspondence between plastic working and temperature and between strain rate sensitivity and temperature.

Development of LSTM networks for predicting viscoplasticity with effects of deformation, strain rate and temperature history

2021 ◽  
pp. 1-30
Author(s):  
Lahouari Benabou
Keyword(s):  
Strain Rate ◽  
Short Term Memory ◽  
Internal State ◽  
Material Behavior ◽  
Temperature History ◽  
Loading Conditions ◽  
Viscoplastic Material ◽  
Temperature Changes ◽  
History Effects ◽  
Deformation Strain Rate

Abstract In this paper, long short-term memory (LSTM) networks are used in an original way to model the behavior of a viscoplastic material solicited under changing loading conditions. The material behavior is dependent on history effects of plasticity which can be visible during strain rate jumps or temperature changes. Due to their architecture and internal state (memory), the LSTM networks have the ability to remember past data to update their current state, unlike the traditional artificial neural networks (ANNs) which fail to capture history effects. Specific LSTM networks are designed and trained to reproduce the complex behavior of a viscoplastic solder alloy subjected to strain rate jumps, temperature changes or loading-unloading cycles. The training datasets are numerically generated using the constitutive viscoplastic law of Anand which is very popular for describing solder alloys. The Anand model serves also as a reference to evaluate the performances of the LSTM networks on new data. It is demonstrated that this class of networks is remarkably well suited for replicating the history plastic effects under all the tested loading conditions.

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.

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.

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.

Constitutive Equations for the Thermomechanical Response of Rene´ 80: Part 2—Effects of Temperature History

1993 ◽  
Vol 115 (4) ◽  
pp. 358-364 ◽  
Author(s):  
V. S. Bhattachar ◽  
D. C. Stouffer
Keyword(s):  
Constitutive Equations ◽  
Temperature History ◽  
Nickel Base Superalloy ◽  
State Variable ◽  
History Effects ◽  
Variable Approach ◽  
Effects Of Temperature ◽  
Nickel Base ◽  
Nonisothermal Conditions ◽  
Base Superalloy

The unified constitutive equations for Rene´ 80 developed by Bhattachar and Stouffer (1992) are used to predict the thermomechanical fatigue (TMF) response of a Nickel base superalloy Rene´ 80 between 649°C and 1093°C. Predictions using these equations suggest that temperature history effects are significant during TMF, and that the TMF response of Rene´ 80 cannot be predicted completely using only isothermal parameters. It is postulated without metallurgical observations that the two deformation mechanisms in Rene´ 80, planar slip at low temperatures and dislocation climb at high temperatures, produce characteristic microstructures which interact under nonisothermal conditions to produce extra hardening that is not present during isothermal deformation. A state variable approach has been used to model this interaction. The nonisothermal model with temperature history effects could successfully predict the initial and saturated TMF response, and block isothermal response of Rene´ 80 from several tests between 649°C and 1093°C.

Determining Deformation Behavior of AISI 9310 Steel Varying Temperature and Strain Rate for Aerospace Applications

2021 ◽  
Author(s):  
Adanma Akoma ◽  
Kevin Sala ◽  
Chase Sheeley ◽  
Lesley D. Frame
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Elevated Temperatures ◽  
Test Sample ◽  
Material Behavior ◽  
Image Correlation ◽  
Sample Length ◽  
Stress Behavior ◽  
Flow Stress Behavior ◽  
The Impact

Abstract Determination of flow stress behavior of materials is a critical aspect of understanding and predicting behavior of materials during manufacturing and use. However, accurately capturing the flow stress behavior of a material at different strain rates and temperatures can be challenging. Non-uniform deformation and thermal gradients within the test sample make it difficult to match test results directly to constitutive equations that describe the material behavior. In this study, we have tested AISI 9310 steel using a Gleeble 3500 physical simulator and Digital Image Correlation system to capture transient mechanical properties at elevated temperatures (300°C – 600°C) while controlling strain rate (0.01 s-1 to 0.1 s-1). The data presented here illustrate the benefit of capturing non-uniform plastic strain of the test specimens along the sample length, and we characterize the differences between different test modes and the impact of the resulting data that describe the flow stress behavior.

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