scholarly journals A Combined Experimental and Numerical Approach That Eliminates the Non-uniqueness Associated With the Johnson-cook Parameters Obtained Using Inverse Methods

2021 ◽  
Author(s):  
Nishant Ojal ◽  
Harish P. Cherukuri ◽  
Tony L. Schmitz ◽  
Kyle T. Devlugt ◽  
Adam W. Jaycox
Keyword(s):  
Strain Rate ◽  
Strain Hardening ◽  
Cutting Forces ◽  
Inverse Method ◽  
Material Model ◽  
Numerical Approach ◽  
Thermal Softening ◽  
Analytical Models ◽  
Initial Yield Stress ◽  
Softening Behavior

Abstract Johnson-Cook constitutive model is a commonly used material model for machining simulations. The model includes five parameters that capture the initial yield stress, strain-hardening, strain-rate hardening, and thermal softening behavior of the material. These parameters are difficult to determine using experiments since the conditions observed during machining (such as high strain-rates of the order of 10 5 /sec - 10 6 /sec) are challenging to recreate in the laboratory. To address this problem, several researchers have recently proposed inverse approaches where a combination of experiments and analytical models are used to predict the Johnson-Cook parameters. The errors between the measured cutting forces, chip thicknesses and temperatures and those predicted by analytical models are minimized and the parameters are determined. In this work, it is shown that only two of the five Johnson-Cook parameters can be determined uniquely using inverse approaches. Two different algorithms, namely, Adaptive Memory Programming for Global Optimization (AMPGO) and Particle Swarm Optimization (PSO), are used for this purpose. The extended Oxley’s model is used as the analytical tool for optimization. For determining a parameter’s value, a large range for each parameter is provided as an input to the algorithms. The algorithms converge to several different sets of values for the five Johnson-Cook parameters when all the five parameters are considered as unknown in the optimization algorithm. All of these sets, however, yield the same chip shape and cutting forces in FEM simulations. Further analyses show that only the strain-rate and thermal softening parameters can be determined uniquely and the three parameters present in the strain-hardening term of the Johnson-Cook model cannot be determined uniquely using the inverse method. A combined experimental and numerical approach is proposed to eliminate this determine all parameters uniquely.

Effects of Constitutive Parameters on Thickness of Phase Transformed Adiabatic Shear Band for Ductile Metal Based on Johnson-Cook and Gradient Plasticity Models

2006 ◽  
Vol 15-17 ◽  
pp. 609-614 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Phase Transformation ◽  
Strain Rate ◽  
Strain Hardening ◽  
Yield Stress ◽  
Thermal Softening ◽  
Flow Shear ◽  
Stress Strain ◽  
Static Yield ◽  
Flow Shear Stress ◽  
Static Yield Stress

Gradient-dependent plasticity where a characteristic length is involved to consider the microstructural effect (interactions and interplaying among microstructures due to the heterogeneous texture) is introduced into Johnson-Cook model considering the effects of strain-hardening, thermal softening and strain rate sensitivity. Effects of initial static yield stress, strain-hardening coefficient and exponent, strain-rate and thermal-softening parameters on the occurrence of phase transformation and the thickness of phase transformed adiabatic shear band (ASB) in deformed ASB are numerically investigated. Higher initial static yield stress, strain-hardening coefficient, strain-rate parameter and lower strain-hardening exponent lead to earlier occurrence of phase transformation (lower plastic shear strain). Effect of thermal-softening parameter on plastic shear strain corresponding to the onset of phase transformation is not monotonous. Transformed ASB is located at the center of deformed ASB since the position has higher temperature exceeding the temperature of phase transformation. The thickness of transformed ASB increases with decreasing flow shear stress and the increasing tendency becomes slow. For the same flow shear stress, the thickness of transformed ASB is wider for higher initial static yield stress, strain-hardening coefficient and exponent, strain-rate and thermal-softening parameters. Compared with classical elastoplastic theory applicable to completely homogenous material, gradient-dependent plasticity considering the microstructural effect predicts that phase transformation occurs earlier and that the thickness of transformed ASB changes with flow shear stress.

scholarly journals A numerical approach for the modelling of forming limits in hot incremental forming of AZ31 magnesium alloy

2021 ◽  
Author(s):  
Davide Campanella ◽  
Gianluca Buffa ◽  
Ernesto Lo Valvo ◽  
Livan Fratini
Keyword(s):  
Room Temperature ◽  
Incremental Forming ◽  
Material Model ◽  
Numerical Approach ◽  
Forming Limit ◽  
Material Strength ◽  
Wall Angle ◽  
Analytical Expression ◽  
The Poor ◽  
Specific Material

AbstractMagnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25–400 °C and wall angle in a range of 35–60°. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity.

scholarly journals Understanding the Strain Path Effect on the Deformed Microstructure of Single Crystal Pure Aluminum

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1189
Author(s):  
Yingjue Xiong ◽  
Qinmeng Luan ◽  
Kailun Zheng ◽  
Wei Wang ◽  
Jun Jiang
Keyword(s):  
Strain Rate ◽  
Single Crystal ◽  
Strain Path ◽  
Mechanical Response ◽  
Pure Aluminum ◽  
Lattice Rotation ◽  
Softening Behavior ◽  
Theoretical Support ◽  
Commercial Applications ◽  
Electron Back Scattered Diffraction

During plastic deformation, the change of structural states is known to be complicated and indeterminate, even in single crystals. This contributes to some enduring problems like the prediction of deformed texture and the commercial applications of such material. In this work, plane strain compression (PSC) tests were designed and implemented on single crystal pure aluminum to reveal the deformation mechanism. PSC tests were performed at different strain rates under strain control in either one-directional or two-directional compression. The deformed microstructures were analyzed according to the flow curve and the electron back-scattered diffraction (EBSD) mappings. The effects of grain orientation, strain rate, and strain path on the deformation and mechanical response were analyzed. Experimental results revealed that the degree of lattice rotation of one-dimensional compression mildly dependents on cube orientation, but it is profoundly sensitive to the strain rate. For two-dimensional compression, the softening behavior is found to be more pronounced in the case that provides greater dislocations gliding freeness in the first loading. Results presented in this work give new insights into aluminum deformation, which provides theoretical support for forming and manufacturing of aluminum.

scholarly journals Identification of the LLDPE Constitutive Material Model for Energy Absorption in Impact Applications

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1537
Author(s):  
Luděk Hynčík ◽  
Petra Kochová ◽  
Jan Špička ◽  
Tomasz Bońkowski ◽  
Robert Cimrman ◽  
...  
Keyword(s):  
Strain Rate ◽  
Material Model ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Linear Low Density Polyethylene ◽  
Stress Strain ◽  
Rate Dependent ◽  
Constitutive Material Model ◽  
Principal Directions ◽  
Constitutive Material

Current industrial trends bring new challenges in energy absorbing systems. Polymer materials as the traditional packaging materials seem to be promising due to their low weight, structure, and production price. Based on the review, the linear low-density polyethylene (LLDPE) material was identified as the most promising material for absorbing impact energy. The current paper addresses the identification of the material parameters and the development of a constitutive material model to be used in future designs by virtual prototyping. The paper deals with the experimental measurement of the stress-strain relations of linear low-density polyethylene under static and dynamic loading. The quasi-static measurement was realized in two perpendicular principal directions and was supplemented by a test measurement in the 45° direction, i.e., exactly between the principal directions. The quasi-static stress-strain curves were analyzed as an initial step for dynamic strain rate-dependent material behavior. The dynamic response was tested in a drop tower using a spherical impactor hitting a flat material multi-layered specimen at two different energy levels. The strain rate-dependent material model was identified by optimizing the static material response obtained in the dynamic experiments. The material model was validated by the virtual reconstruction of the experiments and by comparing the numerical results to the experimental ones.

A Modified Peric Model for Al-Mg Alloy Sheet with Rate-Independent Initial Yield Stress at Warm Temperatures

2019 ◽  
Vol 287 ◽  
pp. 3-7
Author(s):  
Yong Zhang ◽  
Qing Zhang ◽  
Yuan Tao Sun ◽  
Xian Rong Qin
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Yield Stress ◽  
Constitutive Models ◽  
Mg Alloy ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Dependent Flow

The constitutive modeling of aluminum alloy under warm forming conditions generally considers the influence of temperature and strain rate. It has been shown by published flow stress curves of Al-Mg alloy that there is nearly no effect of strain rate on initial yield stress at various temperatures. However, most constitutive models ignored this phenomenon and may lead to inaccurate description. In order to capture the rate-independent initial yield stress, Peric model is modified via introducing plastic strain to multiply the strain rate, for eliminating the effect of strain rate when the plastic strain is zero. Other constitutive models including the Wagoner, modified Hockett–Sherby and Peric are also considered and compared. The results show that the modified Peric model could not only describe the temperature-and rate-dependent flow stress, but also capture the rate-independent initial yield stress, while the Wagoner, modified Hockett–Sherby and Peric model can only describe the temperature-and rate-dependent flow stress. Moreover, the modified Peric model could obtain proper static yield stress more naturally, and this property may have potential applications in rate-dependent simulations.

scholarly journals Fully Atomistic Molecular Dynamics Computation of Physico-Mechanical Properties of PB, PS, and SBS

Nanomaterials ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 1088 ◽  
Author(s):  
Yang Kang ◽  
Dunhong Zhou ◽  
Qiang Wu ◽  
Fuyan Duan ◽  
Rufang Yao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Strain Rate ◽  
Strain Hardening ◽  
Md Simulation ◽  
Md Simulations ◽  
Strain Rates ◽  
Young’S Moduli ◽  
Plastic Modulus ◽  
Styrene Butadiene ◽  
Butadiene Styrene

The physical properties—including density, glass transition temperature (Tg), and tensile properties—of polybutadiene (PB), polystyrene (PS) and poly (styrene-butadiene-styrene: SBS) block copolymer were predicted by using atomistic molecular dynamics (MD) simulation. At 100 K, for PB and SBS under uniaxial tension with strain rate ε ˙ = 1010 s−1 and 109 s−1, their stress–strain curves had four features, i.e., elastic, yield, softening, and strain hardening. At 300 K, the tensile curves of the three polymers with strain rates between 108 s−1 and 1010 s−1 exhibited strain hardening following elastic regime. The values of Young’s moduli of the copolymers were independent of strain rate. The plastic modulus of PS was independent of strain rate, but the Young’s moduli of PB and SBS depended on strain rate under the same conditions. After extrapolating the Young’s moduli of PB and SBS at strain rates of 0.01–1 s−1 by the linearized Eyring-like model, the predicted results by MD simulations were in accordance well with experimental results, which demonstrate that MD results are feasible for design of new materials.

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