72 results on '"Daniel E. Green"'
Search Results
2. Experimental and Numerical Evaluation of DP600 Fracture Limits
- Author
-
Yang Song, Iman Sari Sarraf, and Daniel E. Green
- Published
- 2022
- Full Text
- View/download PDF
Catalog
3. Damage Evolution in DP600 Sheets Using a Combined Finite Element—Cellular Automata Model
- Author
-
Iman Sari Sarraf, Daniel E. Green, Yang Song, and Javad Samei
- Published
- 2022
- Full Text
- View/download PDF
4. Investigation of various necking criteria for sheet metal formability analysis using digital image strain data
- Author
-
Yang Song, Daniel E. Green, and Alexandra Rose
- Subjects
0209 industrial biotechnology ,Digital image correlation ,Materials science ,Strain (chemistry) ,Forming processes ,High resolution ,02 engineering and technology ,Digital image ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,visual_art ,visual_art.visual_art_medium ,Formability ,General Materials Science ,Composite material ,Sheet metal ,Necking - Abstract
The precise determination of the forming limit strains of a sheet metal is necessary in order to accurately predict the onset of failure in sheet metal forming processes. The method used to detect the onset of necking (i.e. the necking criterion) is a most important factor in formability analysis as it significantly affects the forming limit strains. Many different necking criteria have been developed, which take advantage of the flexibility and high resolution of digital image correlation (DIC) strain measurements. Several time-dependent and time/geometry-dependent necking criteria were carefully investigated in order to evaluate their ability to reliably and consistently detect the onset of necking of TRIP780 sheet specimens that were stretch-formed over a hemispherical punch. It was found that the geometry-dependent, surface slope criterion was the most robust and consistent criterion of those evaluated. more...
- Published
- 2019
- Full Text
- View/download PDF
5. Mechanisms of die wear and wear-induced damage at the trimmed edge of high strength steel sheets
- Author
-
Z. Cui, Daniel E. Green, Sandeep Bhattacharya, and Ahmet T. Alpas
- Subjects
Materials science ,Stress–strain curve ,High strength steel ,02 engineering and technology ,Surfaces and Interfaces ,Mechanical press ,Flow stress ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Shear (sheet metal) ,020303 mechanical engineering & transports ,Brittleness ,0203 mechanical engineering ,Mechanics of Materials ,Martensite ,Materials Chemistry ,Trimming ,Composite material ,0210 nano-technology - Abstract
Die wear during trimming of advanced high strength steel (AHSS) sheets deteriorates the edge quality of trimmed sheets. In this work, the mechanisms of AISI D2 steel trim die wear and their effects on plastic deformation and fracture behaviour of the sheared edge of DP980 steel sheet were examined. A mechanical press equipped with D2 inserts was used to trim DP980 sheets with a clearance of 0.14 mm (10%). Abrasion and microchipping were identified as the wear mechanisms operating at the upper die, with microchipping becoming more dominant after 60,000 trimming cycles. The burr height and the length of the burnish zone of sheared DP980 sheets increased linearly with the chipped die edge percentage. The shear strains in the shear effected zone (SAZ) were estimated using martensite displacements as metallographic markers in the ferrite matrix as a function of the depth beneath the sheared edge. The depth of SAZ, and the plastic strains at a given depth within the SAZ increased with the number of trimming cycles. Correlation of the local stress and strain values generated in the SAZ showed that a saturation flow stress was reached near the sheared edge. The damage in SAZ occurred in the form of crack formation at the martensite/ferrite interfaces and fracture of martensite. Die wear reduced the tensile ductility of the DP980 sheets, and the fracture mode in tension changed from ductile with localized neck to more brittle sheared edge fracture initiating from surface cracks after 60,000 cycles. more...
- Published
- 2019
- Full Text
- View/download PDF
6. Hardening of A6111-T4 Aluminum Alloy at Large Strains and Its Effect on Sheet Forming Operations
- Author
-
Sergey Fedorovich Golovashchenko, Daniel E. Green, Natalia Reinberg, and Amir Hassannejadasl
- Subjects
010302 applied physics ,Materials science ,Computer simulation ,Mechanical Engineering ,Alloy ,02 engineering and technology ,STRIPS ,Flow stress ,engineering.material ,Plasticity ,021001 nanoscience & nanotechnology ,01 natural sciences ,Power law ,law.invention ,Mechanics of Materials ,law ,0103 physical sciences ,Hardening (metallurgy) ,engineering ,General Materials Science ,Composite material ,0210 nano-technology ,Tensile testing - Abstract
In a number of sheet metal stamping and joining processes, the material undergoes large plastic deformation exceeding the range of plastic strain achievable in a standard tensile test prior to material plastic instability. In order to extend the range of effective strains, the multistep rolling process was employed which enabled prestraining of aluminum sheet above 2.0 of true strain. Tensile testing of rolled samples was used to identify the flow stress corresponding to the level of prestrain: By varying the prestrain level, several data points were obtained for the studied flow curve. The numerical simulation using Abaqus software for the cold rolling process of aluminum strips confirmed that majority of the strip is deformed in plane strain compression condition. Performed simulation of the LDH test determined that earlier fracture might occur if the curve obtained via rolling–tensile testing approach is used versus traditional power law approximation and Voce law approximation. The results of simulation for the multistep drawing of a cylindrical cup revealed possible wrinkling in the die entry area during redrawing stage of the process if the rolling–tensile testing flow curve is employed. more...
- Published
- 2019
- Full Text
- View/download PDF
7. Influence of Specimen Preparation Methods on the Mechanical Properties and Superplastic Behavior of AA5083 Sheets
- Author
-
Iman Sari Sarraf, Leo Kiawi, Mohammad Shirinzadeh Dastgiri, Eugene Ryzer, and Daniel E. Green
- Subjects
Yield (engineering) ,Materials science ,Machining ,Scanning electron microscope ,Ultimate tensile strength ,Surface roughness ,Superplasticity ,Surface finish ,Composite material ,Tensile testing - Abstract
The process used to fabricate tensile specimens inevitably introduces imperfections at their edges, which can affect the resulting experimental mechanical properties. It has been reported that, for ambient temperature testing, tensile specimens prepared by less aggressive machining methods yield more accurate data due to the absence of plastic deformation at the edges. However, for superplastic forming (SPF) where forming is performed at elevated temperatures, the results are different. In this study, AA5083 sheet specimens were prepared using different machining methods: wire-electro-discharge machining, waterjet cutting, and conventional milling. Mechanical properties were determined from tensile tests carried out at 450 °C and at a quasi-static strain rate. The edges of tensile specimens were observed under optical and scanning electron microscopes (SEM) both before and after testing. It was found that milled specimens resulted in greater values of total elongation. The microscopic investigation revealed that specimens whose edges have a lower arithmetic mean roughness (Ra) have greater values of elongation. The SEM investigation also revealed that micro-cracks are more prevalent at the edges of specimens that have a greater surface roughness. Therefore, tensile specimens used to characterize sheet mechanical properties in view of SPF applications should be fabricated by a process that yields a lower surface roughness, such as conventional milling. more...
- Published
- 2021
- Full Text
- View/download PDF
8. Damage evolution and void coalescence in finite-element modelling of DP600 using a modified Rousselier model
- Author
-
Iman Sari Sarraf, Daniel E. Green, and Arash Jenab
- Subjects
Coalescence (physics) ,Void (astronomy) ,Materials science ,Mechanical Engineering ,Uniaxial tension ,02 engineering and technology ,Mechanics ,Strain rate ,urologic and male genital diseases ,021001 nanoscience & nanotechnology ,Finite element method ,Condensed Matter::Materials Science ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Ultimate tensile strength ,Volume fraction ,Void volume ,General Materials Science ,0210 nano-technology - Abstract
Numerical simulations of uniaxial tensile deformation of DP600 steel were carried out using a modified Rousselier ductile damage model at different strain rates ranging from 0.1 to 100 s−1. Since the original Rousselier model does not consider any secondary void nucleation or coalescence criteria, it was modified by including a strain-controlled void nucleation function, a coalescence criterion and a void growth acceleration function as the post-coalescence regime identifier. The predicted flow behaviour, the evolution of damage and critical strain and void volume fraction at the onset of coalescence were assessed to evaluate the performance of the proposed model at each strain rate. In addition, X-ray tomography analysis was employed to evaluate the void volume fraction predicted by each void coalescence criterion. The modified Rousselier model showed good agreement with the experimentally determined strain and void volume fraction at the onset of coalescence. Also, it could successfully predict the damage distribution and the final damage geometry of DP600 tensile specimens. more...
- Published
- 2018
- Full Text
- View/download PDF
9. Experimental and numerical analyses of formability improvement of AA5182-O sheet during electro-hydraulic forming
- Author
-
Ahmet T. Alpas, Sergey Fedorovich Golovashchenko, Daniel E. Green, and Arash Jenab
- Subjects
0209 industrial biotechnology ,Materials science ,business.product_category ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,Conical surface ,Strain rate ,021001 nanoscience & nanotechnology ,Electro hydraulic ,Industrial and Manufacturing Engineering ,Finite element method ,Computer Science Applications ,Stress (mechanics) ,020901 industrial engineering & automation ,chemistry ,Aluminium ,Modeling and Simulation ,Ceramics and Composites ,Die (manufacturing) ,Formability ,Composite material ,0210 nano-technology ,business - Abstract
The formability of electro-hydraulically formed AA5182-O aluminium sheet was investigated by means of experimental testing and numerical modelling. The experimental results were compared with quasi-static, as-received forming limit curve (FLC) and were used to calibrate a finite element model of EHF. It is found that the formability improvement of AA5182-O sheets was insignificant when electro-hydraulically formed without a die. However, when specimens were electro-hydraulically formed with sufficient energy into 34 or 40° conical dies, the effective strain measured in safe grids increased by 40 and 70% respectively when compared with a conservative quasi-static FLC. Finite element simulation results suggested that a combination of different mechanical parameters contributed to the formability improvement. The increased strain rate in areas close to the apex of the speimen, the negative stress triaxiality just before specimens contact the die, and significant compressive through-thickness stress generated by high-velocity impact all contributed to the improvement of formability in electro-hydraulic die forming. more...
- Published
- 2018
- Full Text
- View/download PDF
10. Numerical analysis of damage evolution and formability of DP600 sheet with an extended Rousselier damage model
- Author
-
I. Sari Sarraf, Y. Song, Daniel E. Green, and D.M. Vasilescu
- Subjects
Coalescence (physics) ,Void (astronomy) ,Materials science ,business.industry ,Applied Mathematics ,Mechanical Engineering ,Numerical analysis ,02 engineering and technology ,Structural engineering ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Finite element method ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Modeling and Simulation ,Hardening (metallurgy) ,Formability ,General Materials Science ,Composite material ,0210 nano-technology ,business ,Plane stress ,Necking - Abstract
Dual phase (DP) steel sheets are increasingly being used for automotive applications due to relatively high strength and formability. In the current work, Marciniak formability tests were carried out to determine the forming limit curve (FLC) of DP600 steel sheet, and an extended version of Rousselier’s ductile damage model, which accounts for void nucleation, growth and coalescence was used to simulate the tests and predict strain localization and failure for three different strain paths: uniaxial tension, plane strain and biaxial tension. In addition, a combination of flat rolling and uniaxial tension tests were used to generate the extended flow curve of the material. Damage evolution in terms of Rousselier scalar damage variable and void volume fraction was assessed for each simulation condition. The FLC as well as neck and fracture morphologies and geometries were obtained from finite element simulations of the Marciniak tests and compared to experimental results. The sensitivity and dependency of the predicted necking limits, damage distribution and geometry predicted by the Rousselier damage model to the type of hardening model, strain path, void nucleation function and void coalescence criterion are discussed. The modified Rousselier model was shown to successfully predict the FLC, damage distribution and the final damage geometry of DP600 sheets. more...
- Published
- 2018
- Full Text
- View/download PDF
11. Sliding and impact induced damage on industrial-scale D2 die inserts during trimming of advanced high strength steel using optical interferometry
- Author
-
Jimi Tjong, Ahmet T. Alpas, Daniel E. Green, A. Rose, and Z. Cui
- Subjects
animal structures ,Bearing (mechanical) ,Materials science ,business.product_category ,viruses ,Surfaces and Interfaces ,Edge (geometry) ,Condensed Matter Physics ,Trim ,Surfaces, Coatings and Films ,law.invention ,Fracture toughness ,Mechanics of Materials ,law ,Materials Chemistry ,Fracture (geology) ,Die (manufacturing) ,Trimming ,Profilometer ,Composite material ,business - Abstract
Die wear during trimming of advanced high strength steel (AHSS) sheets adversely effects the edge quality of trimmed sheets. Due to the large size of the industrial scale dies, it is difficult to measure the wear at the trim edge of the die inserts as a function of the number of trimming cycles. In this work, an optical surface profilometry method was used to determine sliding wear and impact damage on AISI D2 die inserts used to trim 1.4-mm DP980 sheets through a semi-industrial scale trimming press. Reduced peak height (Spk) and reduced valley depth (Svk) were determined by establishing the bearing ratio curves in the damaged areas of the trim dies as a function of the number of trimming cycles up to 80,000 trimming cycles. The evolution of the total volumetric loss and wear rate on the sliding planes of the upper and lower dies showed a change in wear behaviour after 60,000 trimming cycles due to increased chipping. The sliding-induced percentage of total volumetric loss (SPOTV) decreased with the number of trimming cycles on the upper sliding plane revealing that the main damage mechanism changed from sliding-induced wear to impact fracture. The dominant damage mechanism on lower sliding plane was fracture induced as SPOTV on the lower sliding plane remained low constant value of 18% and evidenced by chipping observed on the trim die edge. The performance of trim dies could be improved by increasing the fracture toughness of the lower die and increasing the wear resistance of the upper die by applying proper coatings. more...
- Published
- 2022
- Full Text
- View/download PDF
12. Formability enhancement of DP600 steel sheets in electro-hydraulic die forming
- Author
-
Daniel E. Green, Jia Cheng, and Sergey Fedorovich Golovashchenko
- Subjects
0209 industrial biotechnology ,business.product_category ,Materials science ,Strain (chemistry) ,Metallurgy ,Metals and Alloys ,02 engineering and technology ,Conical surface ,Edge (geometry) ,021001 nanoscience & nanotechnology ,Electro hydraulic ,Industrial and Manufacturing Engineering ,Computer Science Applications ,020901 industrial engineering & automation ,Modeling and Simulation ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium ,Die (manufacturing) ,Formability ,Composite material ,0210 nano-technology ,business ,Sheet metal ,Electrohydraulic forming - Abstract
The objectives of this paper are to quantify the increase in formability of DP600 steel sheets in electrohydraulic die forming (EHDF). The conventional (quasi-static) and high strain rate forming limits of this sheet material were experimentally obtained from specimens deformed using Marciniak tests and EHDF tests, respectively. A numerical model of EHDF was developed in order to determine the strain path of sheet metal experiencing large strains. Forming limits obtained from EHDF specimens formed in plane strain into a V-shaped die indicated that, locally near the top edge of the specimen, more than 120% formability improvement was achieved. Moreover, a formability enhancement of more than 60% was achieved in EHDF in biaxial tension using a conical die, provided sufficient discharge energy was applied. It was found that the significant increases in formability in EHDF are associated with the high-velocity impact against the die wall and the consequent high effective strain rate. more...
- Published
- 2017
- Full Text
- View/download PDF
13. Microscopic investigation of failure mechanisms in AA5182-O sheets subjected to electro-hydraulic forming
- Author
-
Daniel E. Green, Ahmet T. Alpas, and Arash Jenab
- Subjects
Coalescence (physics) ,0209 industrial biotechnology ,High strain rate ,Void (astronomy) ,Materials science ,Mechanical Engineering ,Intermetallic ,chemistry.chemical_element ,02 engineering and technology ,urologic and male genital diseases ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,female genital diseases and pregnancy complications ,Cracking ,020901 industrial engineering & automation ,chemistry ,Mechanics of Materials ,Aluminium ,Forensic engineering ,Formability ,General Materials Science ,Composite material ,0210 nano-technology ,Electrohydraulic forming - Abstract
In this study, damage mechanisms in AA5182-O aluminium sheets are investigated using quasi-static (QS) Marciniak tests and high strain-rate electro-hydraulic forming (EHF) process. The results confirm that void nucleation, growth and coalescence are the main damage mechanisms of AA5182-O at both high and low strain rates. The EDS analysis suggests that cracking of Al 3 (Fe-Mn) intermetallic particles is the main source of void nucleation, whereas Mg 2 Si particles do not majorly influence void formation. Void growth analysis suggests that specimens deformed under QS conditions contained more voids in areas away from the sub-fracture surface but specimens deformed at high strain rate exhibit more significant rate of void growth close to sub-fracture areas. Void formation is suppressed by increasing the applied energy in EHF. And more significantly, the growth of voids is suppressed due to the high-velocity impact of the sheet against the die which plays an important role in increasing formability of AA5182-O aluminium sheet in EHF process. When the void percentage increase remains less than about 0.5% AA5182-O can be formed safely. However, when the void percentage increases beyond 0.6–0.8% fracture becomes inevitable. more...
- Published
- 2017
- Full Text
- View/download PDF
14. Effect of rate-dependent constitutive equations on the tensile flow behaviour of DP600 using Rousselier damage model
- Author
-
Arash Jenab, Daniel E. Green, K.P. Boyle, and Iman Sari Sarraf
- Subjects
Void (astronomy) ,Materials science ,Mechanical Engineering ,Metallurgy ,Constitutive equation ,Markov chain Monte Carlo ,macromolecular substances ,02 engineering and technology ,Mechanics ,Strain hardening exponent ,021001 nanoscience & nanotechnology ,Instability ,Finite element method ,symbols.namesake ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Ultimate tensile strength ,lcsh:TA401-492 ,Hardening (metallurgy) ,symbols ,lcsh:Materials of engineering and construction. Mechanics of materials ,General Materials Science ,0210 nano-technology - Abstract
In the current research, the Rousselier ductile damage model was employed to model hardening, plastic instability and damage properties of DP600 during uniaxial tension in a wide range of strain rates (from 0.001 to 1000 s−1). Also, various well-known phenomenological hardening functions, such as Johnson–Cook and KHL as well as a modified version of Johnson-Cook and multiplicative combinations of Voce with other strain-rate hardening functions have been fitted to experimental flow curves via a new combination of non-linear regression and Markov chain Monte Carlo (MCMC) method. The effect of each hardening function on the evolution of the damage parameter, void volume fraction and strain distribution along the gauge length was evaluated throughout the deformation. Also, the onset of instability, geometry of the neck and final fracture were then assessed by comparing the numerical results with experimental data. It is found that the modified JC and Voce-modified JC models can predict the flow behaviour of DP600 more accurately. Additionally, it is shown that the strain hardening rate at large strain levels, as determined by the hardening models, has a considerable effect on the strain map along the specimen, onset of void growth, and progression of damage in the localized area. Keywords: Dual phase steel, Finite element, Modified Johnson–Cook, Markov chain Monte Carlo, Rousselier model, Ductile damage more...
- Published
- 2017
- Full Text
- View/download PDF
15. 3D micromechanical modeling of dual phase steels using the representative volume element method
- Author
-
Daniel E. Green, Javad Samei, Isadora van Riemsdijk, Maedeh Amirmaleki, and Lorna Stewart
- Subjects
010302 applied physics ,Materials science ,business.industry ,Metallurgy ,Flow (psychology) ,Phase (waves) ,Mechanical engineering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,3D modeling ,01 natural sciences ,Mechanics of Materials ,Martensite ,0103 physical sciences ,Volume fraction ,Ultimate tensile strength ,Representative elementary volume ,Metallography ,General Materials Science ,0210 nano-technology ,business ,Instrumentation - Abstract
There is a steady increase in the implementation of dual phase steels in stamped automotive components. Therefore, steel suppliers who develop dual phase steels are interested in predicting the microstructure-properties relationship for optimization of microstructural design. This goal is achievable by micromechanical modeling. The representative volume element (RVE) method has been a popular technique for micromechanical modeling of dual phase steels. It is generally considered that 2D modeling underestimates the flow curves and that 3D modeling predicts the experimental stress-strain curves more accurately. However, much of the research has focused on 2D modeling. This paper develops 3D micromechanical modeling of DP500 and bainite-aided DP600 steels by including statistical quantitative metallography data in the models. More than 3000 grains were analyzed in each steel. Hence, both volume fraction and morphology of martensite were statistically determined. This model predicted the ultimate tensile strength of these two dual phase steels with less than 0.5% error. more...
- Published
- 2016
- Full Text
- View/download PDF
16. Comparison of quasi-static and electrohydraulic free forming limits for DP600 and AA5182 sheets
- Author
-
Alan J. Gillard, Daniel E. Green, Amir Hassannejadasl, Yiteng Liang, Christopher Maris, Sergey Fedorovich Golovashchenko, and Jia Cheng
- Subjects
0209 industrial biotechnology ,business.product_category ,Materials science ,Electric potential energy ,Metallurgy ,Metals and Alloys ,02 engineering and technology ,Gauge (firearms) ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Computer Science Applications ,020901 industrial engineering & automation ,Modeling and Simulation ,visual_art ,Electrode ,Ceramics and Composites ,visual_art.visual_art_medium ,Formability ,Die (manufacturing) ,Composite material ,0210 nano-technology ,Sheet metal ,business ,Electrohydraulic forming ,Quasistatic process - Abstract
Electrohydraulic forming is a pulsed metal forming process that uses the discharge of electrical energy across a pair of electrodes submerged in fluid to form sheet metal at high velocities. Pulsed metal forming processes, including electrohydraulic forming, have been shown to increase the formability of sheet metals. Although significant formability enhancement has been reported for electrohydraulic die forming, there have been conflicting reports about the formability in electrohydraulic free forming (EHFF). Numerical modeling was used to design sheet metal specimen geometries to generate data for specific regions of the EHFF forming limit curve. The electrohydraulic free forming specimens were formed with the precise amount of input energy to cause a neck at the center of the gauge section. The quasi-static and EHFF forming limit curves for both AA5182-O and DP600 sheets were determined in accordance with the conventional North American formability evaluation method to allow for direct comparison. It was found that the forming limits in EHFF increased by approximately 5% major strain for DP600 and 8% major strain for AA5182, relative to their respective as-received FLC. more...
- Published
- 2016
- Full Text
- View/download PDF
17. The Use of genetic algorithm and neural network to predict rate-dependent tensile flow behaviour of AA5182-O sheets
- Author
-
Michael J. Worswick, Daniel E. Green, Arash Jenab, Iman Sari Sarraf, and Taamjeed Rahmaan
- Subjects
010302 applied physics ,Materials science ,Artificial neural network ,business.industry ,Mechanical Engineering ,Constitutive equation ,02 engineering and technology ,Mechanics ,Structural engineering ,021001 nanoscience & nanotechnology ,01 natural sciences ,Flow (mathematics) ,Rheology ,Mechanics of Materials ,0103 physical sciences ,Ultimate tensile strength ,Linear regression ,lcsh:TA401-492 ,lcsh:Materials of engineering and construction. Mechanics of materials ,General Materials Science ,Deformation (engineering) ,0210 nano-technology ,Anisotropy ,business - Abstract
In this study, the tensile flow behaviour of AA5182-O sheet was experimentally obtained in different material directions (RD, DD, and TD) at strain rates ranging from 0.001 to 1000 s−1 and predicted by means of both phenomenological models and neural networks (NNs). Constants in Johnson–Cook (JC), Khan–Huang–Liang (KHL), and modified Voce were calculated using genetic algorithm (GA) and linear regression analysis and used to simulate the uniaxial tension tests. Two types of feed-forward back-propagation neural networks were also trained and validated to predict the rheological behaviour of the alloy without the limitations of a mathematical function. The weights and bias values of each network were then used to simulate uniaxial tensile deformation. Subsequently, the results were compared with experimental flow curves and accuracy parameters were calculated. It was found that the modified Voce constitutive equation was able to predict the flow behaviour of AA5182-O with better accuracy than JC and KHL models. Also, the NN was found to be the most accurate method of predicting the anisotropic rate-dependant behaviour of AA5182-O. Keywords: Phenomenological constitutive model, Genetic algorithm, Artificial neural network, 5000 series aluminium alloys, Moderate strain rates more...
- Published
- 2016
- Full Text
- View/download PDF
18. Prediction of forming limit curves for nonlinear loading paths using quadratic and non-quadratic yield criteria and variable imperfection factor
- Author
-
Morteza Nurcheshmeh and Daniel E. Green
- Subjects
0209 industrial biotechnology ,Materials science ,Yield (engineering) ,business.industry ,Mechanical Engineering ,Mathematical analysis ,Forming processes ,02 engineering and technology ,Structural engineering ,Bresler Pister yield criterion ,Nonlinear system ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,Quadratic equation ,0203 mechanical engineering ,Mechanics of Materials ,lcsh:TA401-492 ,General Materials Science ,lcsh:Materials of engineering and construction. Mechanics of materials ,Limit (mathematics) ,Hill yield criterion ,business ,Variable (mathematics) - Abstract
Industrial sheet metal forming processes often involve complex deformation modes and it is necessary to consider nonlinear loading path effects when predicting forming limit curves. Moreover, the yield criterion plays a critical role in the accuracy of predicted forming limits.In this work the MK analysis was modified to relate the initial imperfection factor to a physical property such as the surface roughness, and the orientation of the imperfection was also allowed to vary. This model was used to predict the strain-based and stress-based forming limit curves (FLC and SFLC) of sheet materials that are subject to either linear or non-linear strain paths.Two different yield criteria were employed in this study, Hill's 1948 quadratic yield criterion and Hosford's 1979 non-quadratic yield criterion. The theoretical model was validated by comparing predicted FLC and experimental FLC curves obtained from the literature. FLCs and SFLCs predicted with these two yield criteria were compared for both linear and nonlinear loading paths.Results showed that both the quadratic and non-quadratic yield criteria predict the FLC with acceptable accuracy however on the whole the non-quadratic yield criterion generally provides a slightly better correlation with experimental data, especially on the right side of the FLC. Keywords: Forming limit curve, Formability, Yield criterion, MK analysis, Sheet metal, Loading path more...
- Published
- 2016
19. Influence of strain path on nucleation and growth of voids in dual phase steel sheets
- Author
-
Daniel E. Green, Javad Samei, Jia Cheng, and Murilo Soares de Carvalho Lima
- Subjects
Area fraction ,Void (astronomy) ,Materials science ,Dual-phase steel ,Mechanical Engineering ,Nucleation ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,lcsh:TA401-492 ,Formability ,General Materials Science ,lcsh:Materials of engineering and construction. Mechanics of materials ,Elongation ,Composite material ,0210 nano-technology ,Plane stress - Abstract
The objectives of this work are to describe the nucleation and growth of voids in DP600 dual phase steel sheets formed along different strain paths, and to investigate the correlation between the micro-mechanisms of damage and the forming limits. DP600 sheet specimens were stretch-formed in uniaxial, plane strain and biaxial tension using the Marciniak–Kuczynski formability test. The evolution of damage in the microstructure was correlated to the formability in each strain path by quantitatively analyzing void density, void area fraction, void aspect ratio and mean void size. Results showed that DP600 steel sheets have less formability in plane strain compared to uniaxial and biaxial tension due to the more rapid elongation and growth of voids. Moreover, the sheets safely deformed to much greater effective strains in biaxial tension due to the smaller mean void size and slower void growth. As proposed by Gurson Gurson (1977) , Tvergaard and Needleman Tvergaard and Needleman (1984) , void volume fraction is an important damage parameter. However, this work shows that void aspect ratio and mean void size also significantly influence the evolution of damage and the formability of dual phase steels. Keywords: Dual phase steel, Microstructure, Strain path, Voids, Forming limit curve more...
- Published
- 2016
20. Springback simulation of advanced high strength steels considering nonlinear elastic unloading–reloading behavior
- Author
-
A. Ghaei, Daniel E. Green, and A. Aryanpour
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Linear elasticity ,Constitutive equation ,Structural engineering ,Plasticity ,Finite element method ,Nonlinear system ,Mechanics of Materials ,lcsh:TA401-492 ,General Materials Science ,Kinematic hardening ,lcsh:Materials of engineering and construction. Mechanics of materials ,Cyclic response ,business ,Sheet steel - Abstract
The stress–strain response of some materials, such as advanced high strength steels, during unloading is nonlinear after the material has been loaded into the plastic deformation region. Upon reloading, the response shows a nonlinear elastic response that is different from that in unloading. Therefore, unloading–reloading of these materials forms a hysteresis loop in the elastic region. The Quasi-plastic–elastic model (Sun and Wagoner, 2011) was modified and combined with both isotropic-nonlinear kinematic hardening and two-surface plasticity models to simultaneously describe the nonlinear unloading response and complex cyclic response of sheet metals in the plastic region. The model was implemented as user-defined material subroutines, i.e. UMAT and VUMAT, for ABAQUS/Standard and ABAQUS/Explicit finite element codes, respectively. Uniaxial loading-unloading tests were performed on three common grades of automotive sheet steel: DP600, DP980 and TRIP780 steel. The model was verified by comparing the predicted material response with the corresponding experimental response. Finally, the model was used to predict the springback of a U-shape channel section formed in a plane-strain channel draw process. The results showed that the model was able to considerably improve springback predictions compared to the usual assumption of linear elastic unloading. Keywords: Plasticity, Constitutive model, Nonlinear elastic unloading, Springback more...
- Published
- 2015
21. A non-associated plasticity model with anisotropic and nonlinear kinematic hardening for simulation of sheet metal forming
- Author
-
Daniel E. Green, Aboozar Taherizadeh, and Jeong Whan Yoon
- Subjects
Materials science ,business.industry ,Applied Mathematics ,Mechanical Engineering ,Bauschinger effect ,Forming processes ,Structural engineering ,Work hardening ,Flow stress ,Plasticity ,Strain hardening exponent ,Condensed Matter Physics ,Mechanics of Materials ,Modeling and Simulation ,visual_art ,visual_art.visual_art_medium ,Hardening (metallurgy) ,General Materials Science ,business ,Sheet metal - Abstract
A material model for more thorough analysis of plastic deformation of sheet materials is presented in this paper. This model considers the following aspects of plastic deformation behavior of sheet materials: (1) the anisotropy in yield stresses and in work hardening by using Hill’s 1948 quadratic yield function and non-constant stress ratios which leads to different flow stress hardening in different directions, (2) the anisotropy in plastic strains by using a quadratic plastic potential function and non-associated flow rule, also based on Hill’s 1948 model and r -values, and (3) the cyclic hardening phenomena such as the Bauschinger effect, permanent softening and transient behavior for reverse loading by using a coupled nonlinear kinematic hardening model. Plasticity fundamentals of the model were derived in a general framework and the model calibration procedure was presented for the plasticity formulations. Also, a generic numerical stress integration procedure was developed based on backward-Euler method, so-called multi-stage return mapping algorithm. The model was implemented in the framework of the finite element method to evaluate the simulation results of sheet metal forming processes. Different aspects of the model were verified for two sheet metals, namely DP600 steel and AA6022 aluminum alloy. Results show that the new model is able to accurately predict the sheet material behavior for both anisotropic hardening and cyclic hardening conditions. The drawing of channel sections and the subsequent springback were also simulated with this model for different drawbead configurations. Simulation results show that the current non-associated anisotropic hardening model is able to accurately predict the sidewall curl in the drawn channel sections. more...
- Published
- 2015
- Full Text
- View/download PDF
22. Wear of D2 Tool Steel Dies during Trimming DP980-type Advanced High Strength Steel (AHSS) for Automotive Parts
- Author
-
Raj Sohmshetty, Daniel E. Green, Sandeep Bhattacharya, and Ahmet T. Alpas
- Subjects
Materials science ,business.industry ,Tool steel ,Metallurgy ,Automotive industry ,engineering ,High strength steel ,Trimming ,engineering.material ,business - Published
- 2017
- Full Text
- View/download PDF
23. Numerical modelling of electrohydraulic free-forming and die-forming of DP590 steel
- Author
-
Amir Hassannejadasl, Sergey Fedorovich Golovashchenko, Daniel E. Green, Javad Samei, and Chris Maris
- Subjects
Materials science ,business.product_category ,Dual-phase steel ,business.industry ,Strategy and Management ,Forming processes ,Structural engineering ,Mechanics ,Management Science and Operations Research ,Strain rate ,Industrial and Manufacturing Engineering ,visual_art ,visual_art.visual_art_medium ,Die (manufacturing) ,Formability ,Deformation (engineering) ,Sheet metal ,business ,Electrohydraulic forming - Abstract
Electrohydraulic forming (EHF) is a high energy rate forming process in which the strain rate in the sheet metal can vary from 5 × 10 2 to 10 5 s −1 depending on various factors. Several mechanisms have been reported to cause an improvement in formability in EHF such as material deformation mechanisms, inertial effects and the dynamic impact of the sheet against the die. EHF is a complex high speed forming process and experimental work alone is not sufficient to properly understand this process. To understand the variation of some influential variables in EHF, electrohydraulic die-forming (EHDF) and free-forming (EHFF) of DP590 dual phase steel were simulated in ABAQUS/Explicit by considering the fluid/structure interactions. Three-dimensional finite element simulations were conducted by modelling the water with Eulerian elements with a view to investigating the effect of released energy on the sheet deformation profile history, strain distribution, loading path and damage accumulation type. The Johnson–Cook constitutive material model was used to predict the sheet behaviour and the parameters in this model were calibrated based on experimental test results available for DP590 at various strain rates. The Johnson–Cook phenomenological damage model was also used to predict the ductile failure (damage accumulation) in both EHDF and EHFF. Predicted final strain values and damage accumulation type showed good agreement with the experimental observations. more...
- Published
- 2014
- Full Text
- View/download PDF
24. The effect of normal stress on the formability of sheet metals under non-proportional loading
- Author
-
Morteza Nurcheshmeh and Daniel E. Green
- Subjects
Work (thermodynamics) ,Hydroforming ,Materials science ,business.industry ,Mechanical Engineering ,Forming processes ,Structural engineering ,Condensed Matter Physics ,Stress (mechanics) ,Compressive strength ,Mechanics of Materials ,hemic and lymphatic diseases ,visual_art ,visual_art.visual_art_medium ,Formability ,General Materials Science ,Composite material ,business ,Sheet metal ,Civil and Structural Engineering ,Plane stress - Abstract
Theoretical and experimental studies have shown that when a compressive stress is applied normal to the sheet surface its formability can be significantly improved. In forming processes such as hydroforming, the normal stress imposed at the surface of the sheet or tube can be very significant in specific locations and it is therefore necessary to account for this stress state when assessing the forming severity of industrial parts. It is also well known that the forming limit curve (FLC) can vary significantly in strain space as a result of non-linear strain paths. In this work, a numerical code based on the Marciniak and Kuczynski (MK) analysis (1967) was developed to predict the FLC of sheet metals by simultaneously accounting for the effects of strain path non-linearity and the normal stress. The FLC predicted with this code can be used to assess the forming severity of parts that are deformed under complex loading conditions in industrial metal forming processes. The predictive FLC model was validated using experimental data in which linear and bi-linear strain paths were applied to different steel and aluminum sheets or tubes under plane stress and three-dimensional stress conditions. This research work has two specific purposes: first, to investigate the influence of the magnitude of the prestrain in bi-linear loading on the sensitivity of the FLC to the normal stress, and second, to study the effect of the normal stress on the path dependence of the FLC. This work showed that, with increasing magnitudes of prestrain the influence of the normal stress on the formability of sheet metal will decrease, regardless of the loading path. Moreover, it was observed that even a significant normal stress will practically not affect the path dependence of the FLC. more...
- Published
- 2014
- Full Text
- View/download PDF
25. On the use of cyclic shear, bending and uniaxial tension–compression tests to reproduce the cyclic response of sheet metals
- Author
-
A. Ghaei, Sandrine Thuillier, Daniel E. Green, and Fabrice Morestin
- Subjects
Simple shear ,Materials science ,Cyclic plasticity ,business.industry ,Mechanical Engineering ,Uniaxial tension ,Cyclic shear ,Bending ,Structural engineering ,Cyclic response ,business ,Compression (physics) ,Industrial and Manufacturing Engineering - Abstract
Simple shear, uniaxial tension–compression and bending tests were used to determine the cyclic behaviour of two sheet metals: DP600 and AKDQ. The Yoshida–Uemori two-surface model along with Hill’s quadratic yield function was used to simulate the behaviour of these two materials in each test. For each test, a set of material constants was identified such that the error between the simulated and experimental responses is minimized. Using the material constants obtained from one test, the other tests were simulated to see whether the set of constants obtained from this test is able to describe the material response in the other tests. The results show that depending on the material, the set of constants obtained from one test may or may not be able to reproduce the material response in the other tests. Finally, each set of constants was used to simulate the springback of a U-shaped part formed in a channel draw process. The predicted springback profiles obtained from each set of constants were compared with the experimental profile. It was found that all three tests are suitable to characterize the behaviour of DP600 sheets in view of predicting the springback of channel sections. For AKDQ, however, the error between the predicted and experimental springback profiles was significant regardless of the type of characterization test performed. But for this channel draw process, simulations based on material data obtained from the reverse bending test provided the best prediction of springback. more...
- Published
- 2014
- Full Text
- View/download PDF
26. In-situ X-ray tomography analysis of the evolution of pores during deformation of AlSi10Mg fabricated by selective laser melting
- Author
-
Carlo Marinelli, Maedeh Amirmaleki, Javad Samei, Daniel E. Green, and Mohammad Shirinzadeh Dastgiri
- Subjects
Coalescence (physics) ,Structural material ,Materials science ,Mechanical Engineering ,Weldability ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Mechanics of Materials ,Volume fraction ,Fracture (geology) ,General Materials Science ,Elongation ,Selective laser melting ,Composite material ,Deformation (engineering) ,0210 nano-technology - Abstract
AlSi10Mg is an interesting structural material due to its high specific mechanical properties, and good weldability which makes it a good candidate for additive manufacturing by selective laser melting. In this paper, the evolution of pores is visualized and quantified in an AlSi10Mg fabricated by selective laser melting using in-situ tension coupled with X-ray computed tomography. Graphical models were produced in order to visualize the evolution of pores, and the volume fraction, density, and mean diameter of pores were determined at each stage of deformation. Significant coalescence of pores was found during post-uniform elongation. Dimples on the fracture surfaces indicate ductile fracture. more...
- Published
- 2019
- Full Text
- View/download PDF
27. Through-Thickness Stresses in Automotive Sheet Metal after Plane Strain Channel Draw
- Author
-
Thomas Gnäupel-Herold, Daniel E. Green, Timothy J. Foecke, and Mark A. Iadicola
- Subjects
Diffraction ,Materials science ,business.industry ,Mechanical Engineering ,Automotive industry ,High resolution ,Structural engineering ,Penetration (firestop) ,Condensed Matter Physics ,Mechanics of Materials ,Residual stress ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,In plane strain ,Composite material ,Sheet metal ,business ,Plane stress - Abstract
A series of samples from four automotive materials - AKDQ, HSLA50, DP600, and AA6022-T43 - were deformed in a channel draw processes with different levels of draw bead penetration. As a result, varying magnitudes of deformations in plane strain mode and residual stresses were obtained. Through-thickness stress profiles were obtained non-destructively using a novel, high resolution X-ray diffraction technique. more...
- Published
- 2013
- Full Text
- View/download PDF
28. Numerical Modeling of Tube Hydropiercing Using Phenomenological and Micro-Mechanical Damage Criteria
- Author
-
Amir Hassannejadasl and Daniel E. Green
- Subjects
Engineering ,Dual-phase steel ,business.industry ,Mechanical Engineering ,Internal pressure ,Structural engineering ,Plasticity ,Fixture ,Finite element method ,Mechanics of Materials ,Fracture (geology) ,Formability ,General Materials Science ,Tube (container) ,business - Abstract
Hydropiercing is an efficient way of piercing holes in mass produced hydroformed parts with complex geometries. By driving piercing punches radially into a hydroformed and fully pressurized tube, holes will be pierced and extruded into the tube-wall. Recent experimental studies have shown that the formability of advanced high strength steel (AHSS) tubes can be increased with the application of internal pressure. In this study, three-dimensional finite element simulations of a tube hydropiercing process of a dual phase steel (DP600) were performed in LS-DYNA, using phenomenological, micromechanical and combined damage criteria. Damage was included in the numerical analysis by applying constant equivalent plastic strain (CEPS), the Gurson-Tvergaard-Needleman (GTN), and the Extended GTN (GTN+JC) model. In order to calibrate the parameters in each model, a specialized hole-piercing fixture was designed and piercing tests were carried out on non-pressurized tube specimens. Of the various ductile fracture criteria, the results predicted with the GTN+JC model, such as the punch load-displacement, the roll-over depth, and the quality of the clearance zone correlated the best with the experimental data. more...
- Published
- 2013
- Full Text
- View/download PDF
29. Microstructural investigations of the trimmed edge of DP980 steel sheets
- Author
-
Raj Sohmshetty, Daniel E. Green, Sandeep Bhattacharya, and Ahmet T. Alpas
- Subjects
Materials science ,business.product_category ,engineering.material ,Edge (geometry) ,Ferrite (iron) ,Martensite ,Tool steel ,Ultimate tensile strength ,engineering ,Crashworthiness ,Die (manufacturing) ,Trimming ,Composite material ,business - Abstract
In order to reduce vehicle weight while maintaining crashworthiness, advanced high strength steels (AHSSs), such as DP980, are extensively used for manufacturing automotive body components. During trimming operations, the high tensile strength of DP980 sheets tends to cause damage of the trim edge of D2 die inserts, which result in deterioration of the edge quality. The objective of this work is to study the damage microstructures at the trimmed edge of DP980 steel sheets as a function of the number of trimming cycles. A mechanical press equipped with AISI D2 tool steel inserts was used to continuously trim 1.4 mm thick sheets of DP980 at a rate of 30 strokes/min. Cross-sectional SEM images of the trimmed edges revealed that the sheared edge quality of the DP980 sheets decreased, indicated by an increase in the burr width, with an increase in the number of trims from 40,000 to 70,000. Plastic strains were estimated using the displacements of the martensite plates within plastic flow fields of ferrite. Sit... more...
- Published
- 2017
- Full Text
- View/download PDF
30. Characterization of Advanced High Strength Steel Sheets in View of the Numerical Prediction of Sidewall Curl
- Author
-
Matthew Rodzik, Chester J. Van Tyne, Ali Aryanpour, Lee M. Rothleutner, and Daniel E. Green
- Subjects
Materials science ,business.industry ,Curl (programming language) ,Numerical analysis ,High strength steel ,General Medicine ,Structural engineering ,Kinematics ,business ,computer ,Characterization (materials science) ,computer.programming_language - Published
- 2013
- Full Text
- View/download PDF
31. Study and Design of a Shear Test for Analysis of the Cyclic Behaviour of Sheet Materials Used in the Automotive Industry
- Author
-
Samsul Alam Sarker, Daniela Pusca, and Daniel E. Green
- Subjects
Engineering ,Visual Arts and Performing Arts ,business.industry ,Architecture ,Automotive industry ,Direct shear test ,business ,Manufacturing engineering - Published
- 2013
- Full Text
- View/download PDF
32. Quantitative Microstructural Analysis of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming
- Author
-
Sergey Fedorovich Golovashchenko, Amir Hassannejadasl, Javad Samei, and Daniel E. Green
- Subjects
Materials science ,Dual-phase steel ,Mechanics of Materials ,Mechanical Engineering ,Ferrite (iron) ,Martensite ,Metallurgy ,Metallography ,Formability ,General Materials Science ,Strain rate ,Deformation (engineering) ,Electrohydraulic forming - Abstract
Under certain conditions, strain rate sensitive materials such as dual phase steels, show formability improvement under high strain rate forming which is known as hyperplasticity. In this research, two commercial dual phase steel sheets, DP500 and DP780, were formed under quasi-static conditions using the Nakazima test and under high strain rate conditions by electrohydraulic forming (EHF) into a conical die. Macro-strains, measured from electro-etched circle grids with an FMTI analyzer, showed remarkable formability improvement in EHF specimens. Micro-strains, i.e., the strains in the ferrite and the martensite, were calculated by quantitative metallography of more than 7000 ferrite grains and 10,500 martensite islands. The goal was to investigate the deformation improvement of the constituents under EHF. Around 20 and 100% deformation improvements were observed in ferrite and martensite, respectively. Furthermore, as a micro-mechanical modeling technique, correlation of the micro-strains with the macro-strains was investigated by applying the mixture rule. Results showed a reasonable correlation between the macro and micro-scale strains; however in banded microstructures, the strain in the martensite should be determined precisely for more accuracy. more...
- Published
- 2012
- Full Text
- View/download PDF
33. On the use of effective limit strains to evaluate the forming severity of sheet metal parts after nonlinear loading
- Author
-
Morteza Nurcheshmeh and Daniel E. Green
- Subjects
Materials science ,business.industry ,chemistry.chemical_element ,Forming processes ,Structural engineering ,Stamping ,Stress (mechanics) ,Nonlinear system ,chemistry ,Aluminium ,visual_art ,visual_art.visual_art_medium ,Formability ,General Materials Science ,Limit (mathematics) ,Sheet metal ,business - Abstract
The conventional forming limit curve (FLC) is significantly strain path-dependent and therefore is not valid for formability evaluation of sheet metal parts that undergo nonlinear loading paths during the forming process. The stress-based forming limit curve (SFLC) is path-independent for all but very large prestrains and is a promising tool for formability evaluation. The SFLC is an ideal failure criterion for virtual forming simulations but it cannot be easily used on the shop floor as there is no straightforward experimental method to measure stresses in stamped parts. This paper presents a theoretical basis for predicting the effective limit strain curve (ELSC) using the Marciniak and Kuczynski (MK) analysis (Int J Mech Sci 9:609–620, 1967, Int J Mech Sci 15:789–805, 1973). Since the in-plane strain components are sufficient to calculate the effective strain, the ELSC can easily be determined from strains measured in the stamping plant, and therefore it is a better alternative to the SFLC for formability evaluation. This model was validated using experimental data for AISI-1012 steel (Molaei 1999) and AA-2008-T4 aluminum alloys Graf and Hosford (Metall Trans 24A:2503–2512, 1993). Predicted results showed that, similar to SFLC, the ELSC remains practically unchanged for a significant range of prestrain values under various bilinear loading paths, but some strain-path dependence can be observed for significant magnitudes of the effective prestrain (ee ≥ 0.37 for AISI-1012 steel and ee ≥ 0.25 for AA-2008-T4 aluminum). more...
- Published
- 2012
- Full Text
- View/download PDF
34. Microstructure Evolution of AS21 Magnesium Alloy via the SIMA Process
- Author
-
Majid Bigdeli Karimi, Javad Samei, Mostafa Hajian Heidary, and Daniel E. Green
- Subjects
Materials science ,Magnesium ,Mechanical Engineering ,Alloy ,Metallurgy ,Sima ,chemistry.chemical_element ,engineering.material ,Condensed Matter Physics ,Microstructure ,Grain size ,Sphericity ,chemistry ,Mechanics of Materials ,engineering ,General Materials Science ,Grain boundary ,Magnesium alloy - Abstract
ASis a relatively new series of Magnesium alloys. The microstructure of this alloy can be improved for semisolid processing. The current research is concerned with the microstructure evolution of AS21 under the strain induced melt activated (SIMA) process. For this purpose, the AS21 alloy is cast and compressed 10-40% at 200 °C. The semisolid heat treatment is completed in a carbonate salt bath at different temperatures between 600-620 °C. The microstructure studies show that there is no favourable microstructure evolution between 600-610 °C. At 615 °C fine globular grains are obtained with the most desired mean grain size and sphericity of 67 µm and 81%, respectively. At 620 °C an undesirable coarsening phenomenon occurs that damages the microstructure globularity. SEM micrographs show that in a successful SIMA processing, the Mg2Si phases are broken into fine particles distributed within the grains and grain boundaries. more...
- Published
- 2012
- Full Text
- View/download PDF
35. Dual Phase Steel Characterization for Tube Bending and Hydroforming Applications
- Author
-
Randy J. Bowers, Daniel E. Green, and Chad Oliver
- Subjects
Hydroforming ,Materials science ,Dual-phase steel ,Mechanical Engineering ,Metallurgy ,Bending ,Nanoindentation ,Condensed Matter Physics ,Tube bending ,Mechanics of Materials ,Martensite ,General Materials Science ,Composite material ,Tube (container) ,Elongation - Abstract
The behaviour of dual phase steel tubes at 600, 780, and 980 MPa strength grades undergoing rotary draw bending and pressure sequence hydroforming is examined. Bending was performed using three different bend ratios. Principal strains were measured at several locations on each tube. It was found that the level of strain experienced by the tubes was independent of steel grade. The outcome of the bending process was stochastic in nature; for a given steel grade and bend ratio, some tubes were successfully formed, while others experienced failure. The proportion of failed tubes was found to increase with higher strength steel grades and tighter bend ratios. Metallographic samples from the extrados of the bent tubes revealed that many of the same microstructural features affecting strength and elongation in uniaxial tensile testing, namely martensite banding and non-metallic inclusions, affected dual phase steel tubes undergoing rotary draw bending. Additionally, a nanoindentation technique was investigated to determine the potential for more detailed microstructural characterization. more...
- Published
- 2012
- Full Text
- View/download PDF
36. A practical method to evaluate the forming severity of tubular hydroformed parts
- Author
-
Daniel E. Green, Morteza Nurcheshmeh, Tirumala S. Angara, and Thomas Wormald
- Subjects
Engineering drawing ,Engineering ,Computer simulation ,business.industry ,Mechanical Engineering ,Process (computing) ,Automotive industry ,Forming processes ,Structural engineering ,Industrial and Manufacturing Engineering ,Computer Science Applications ,Stress (mechanics) ,Control and Systems Engineering ,Robustness (computer science) ,Limit (mathematics) ,business ,Software ,Beam (structure) - Abstract
In view of the prevalence of non-linear strain paths that develop in parts that are formed in multiple stages, such as bent and hydroformed structural components, the conventional forming limit curve (FLC) cannot be used to assess the forming severity of this manufacturing process. A path-independent stress-based forming limit criterion has been shown to be far more suitable to evaluate such parts, and this paper shows how this failure criterion can be effectively used to evaluate tubular hydroformed parts “on the shop floor”. Knowing the strain history in a given location of a part, a shifted FLC can be computed from the stress-FLC and used to determine the safety margin at this location. This methodology was used to evaluate the forming severity of an automotive instrument panel beam. It was found that this approach is user-friendly and provides a significant improvement in the ability to assess process robustness and product quality compared to the conventional method. The FLCs obtained using the proposed method were found to be in good agreement with those predicted with an MK-based calculation code. Finally, it is shown that a numerical simulation of the entire forming process is recommended to confirm the estimated strain path in critical locations and improve the accuracy of the method. more...
- Published
- 2011
- Full Text
- View/download PDF
37. Fabrication of W-12wt%Cu Composites by Powder Metallurgy Method: Activated Sintering
- Author
-
Vesselin Stoilov, Javad Samei, and Daniel E. Green
- Subjects
Fabrication ,Materials science ,Metallurgy ,General Engineering ,Sintering ,chemistry.chemical_element ,Atmospheric temperature range ,Tungsten ,Hot pressing ,Microstructure ,chemistry ,Powder metallurgy ,Melting point ,Composite material - Abstract
One of the most challenging areas in engineering of composite materials is the fabrication of high quality microstructures. This issue is complicated for tungsten composites due to its high melting temperature and this leads to limitations in terms of possible processing techniques. This research investigates the fabrication of W-12%wtCu composites based on powder metallurgy techniques. Due to the very large difference between the melting point of tungsten and copper, there is no common sintering temperature range for them. In this work, 0.5%Wt nickel was added as an activator to decrease the sintering temperature of tungsten using an activated sintering effect. The effects of pressure, sintering time and temperature in solid state and liquid phase conditions were also investigated. While solid state hot pressing did not result in appropriate microstructures, the liquid phase hot pressing provided high quality samples with a relative density of 98.0%. more...
- Published
- 2011
- Full Text
- View/download PDF
38. Evaluation of advanced anisotropic models with mixed hardening for general associated and non-associated flow metal plasticity
- Author
-
Daniel E. Green, Aboozar Taherizadeh, and Jeong Whan Yoon
- Subjects
Materials science ,Cauchy stress tensor ,business.industry ,Mechanical Engineering ,Structural engineering ,Mechanics ,Plasticity ,Finite element method ,Nonlinear system ,Mechanics of Materials ,visual_art ,Hardening (metallurgy) ,visual_art.visual_art_medium ,General Materials Science ,Earing ,Anisotropy ,business ,Sheet metal - Abstract
The main objective of this paper is to develop a generalized finite element formulation of stress integration method for non-quadratic yield functions and potentials with mixed nonlinear hardening under non-associated flow rule. Different approaches to analyze the anisotropic behavior of sheet materials were compared in this paper. The first model was based on a non-associated formulation with both quadratic yield and potential functions in the form of Hill’s (1948) . The anisotropy coefficients in the yield and potential functions were determined from the yield stresses and r-values in different orientations, respectively. The second model was an associated non-quadratic model (Yld2000-2d) proposed by Barlat et al. (2003) . The anisotropy in this model was introduced by using two linear transformations on the stress tensor. The third model was a non-quadratic non-associated model in which the yield function was defined based on Yld91 proposed by Barlat et al. (1991) and the potential function was defined based on Yld89 proposed by Barlat and Lian (1989) . Anisotropy coefficients of Yld91 and Yld89 functions were determined by yield stresses and r-values, respectively. The formulations for the three models were derived for the mixed isotropic-nonlinear kinematic hardening framework that is more suitable for cyclic loadings (though it can easily be derived for pure isotropic hardening). After developing a general non-associated mixed hardening numerical stress integration algorithm based on backward-Euler method, all models were implemented in the commercial finite element code ABAQUS as user-defined material subroutines. Different sheet metal forming simulations were performed with these anisotropic models: cup drawing processes and springback of channel draw processes with different drawbead penetrations. The earing profiles and the springback results obtained from simulations with the three different models were compared with experimental results, while the computational costs were compared. Also, in-plane cyclic tension–compression tests for the extraction of the mixed hardening parameters used in the springback simulations were performed for two sheet materials. more...
- Published
- 2011
- Full Text
- View/download PDF
39. Multi-objective optimization of loading path design in multi-stage tube forming using MOGA
- Author
-
Honggang An, Jennifer Johrendt, Daniel E. Green, and L. M. Smith
- Subjects
Hydroforming ,Engineering ,Bending (metalworking) ,Kriging ,business.industry ,Genetic algorithm ,Process (computing) ,Formability ,General Materials Science ,Structural engineering ,Tube (container) ,business ,Multi-objective optimization - Abstract
Pre-bending is a critical process required prior to hydroforming. The bending has an effect on the tube thickness and strain which will use up a portion of the formability of the as-received tube. To compensate for this loss of formability, a multi-objective optimization method was applied to improve the hydroforming process after pre-bending. A multi-objective genetic algorithm (MOGA) and Kriging surrogate model were used to optimize the loading path. The Kriging model was used to replace the finite element simulation in constraint handling. The optimal loading parameters in the hydroforming process were obtained for a tube that was previously bent 90°, and showed an improvement in reducing the corner radii of the part at the extrados and intrados of the bend (8.73 mm and 11.24 mm for the extrados and intrados of the bend, respectively). The corresponding corner fill expansion (CFE) was improved by 16.7% (or 1.79 mm) compared to the maximum expansion of 10.73 mm obtained experimentally. more...
- Published
- 2011
- Full Text
- View/download PDF
40. A hybrid-constrained MOGA and local search method to optimize the load path for tube hydroforming
- Author
-
Jennifer Johrendt, Daniel E. Green, and Honggang An
- Subjects
Hydroforming ,Engineering ,Mathematical optimization ,business.industry ,Mechanical Engineering ,Constrained optimization ,Industrial and Manufacturing Engineering ,Finite element method ,Computer Science Applications ,Control and Systems Engineering ,Robustness (computer science) ,Path (graph theory) ,Genetic algorithm ,Formability ,Local search (optimization) ,business ,Software - Abstract
The production of a tubular hydroformed part often requires a combination of internal pressure and axial force at the tube ends to fully form the tube to its specified geometry. A successful hydroforming process requires not only achieving a part that conforms to the design specifications, but also ensures that the part has a reasonably uniform thickness distribution and is free of defects, such as wrinkles, severe thinning, or fractures. The load path design (pressure vs. end feed history) largely determines the robustness of the process and the quality of the finished parts. In this paper, a hybrid constrained optimization method was proposed to solve this type of multi-objective problem by coupling a multi-objective genetic algorithm and a local search. The load path design procedure was developed by considering five objectives: four formability objectives (i.e., to minimize the risk of wrinkling, global and local thinning, and fracture) and a geometric objective (to minimize the corner radius). A Kriging predictor was used to accelerate the computation of genetic operations and generate new feasible solutions. Finite element simulations of the hydroforming process were also used after each generation to accurately evaluate the objectives of the offspring, and solutions with rank 1 were retained throughout all generations. Once the Pareto solutions were obtained by multi-objective genetic algorithm, a local search was carried out in the regions of interest with the assistance of visualization. This optimization method was applied to the hydroforming of a straight tube to create a part with an expanded region with a square cross section; the optimum load path produced a very safe part with a corner radius of only 9.115 mm and a maximum thinning of only 23.9%. more...
- Published
- 2011
- Full Text
- View/download PDF
41. Influence of out-of-plane compression stress on limit strains in sheet metals
- Author
-
Daniel E. Green and Morteza Nurcheshmeh
- Subjects
Materials science ,business.industry ,Forming processes ,Structural engineering ,Strain rate ,Strain hardening exponent ,Stamping ,Stress (mechanics) ,visual_art ,visual_art.visual_art_medium ,Formability ,General Materials Science ,Composite material ,business ,Sheet metal ,Plane stress - Abstract
The prediction of the forming limits of sheet metals typically assumes plane stress conditions that are really only valid for open die stamping or processes with negligible out-of-plane stresses. In fact, many industrial sheet metal forming processes lead to significant compressive stresses at the sheet surface, and therefore the effects of the through-thickness stress on the formability of sheet metals cannot be ignored. Moreover, predictions of forming limit curves (FLC) that assume plane stress conditions may not be valid when the forming process involves non-negligible out-of-plane stresses. For this reason a new model was developed to predict FLC for general, three-dimensional stress states. Marciniak and Kuczynski (Int J Mech Sci 9:609-620, 1967) first proposed an analytical method to predict the FLC in 1967, known as the MK method, and this approach has been used for decades to accurately predict FLC for plane stress sheet forming applications. In this work, the conventional MK analysis was extended to include the through-thickness principal stress component (σ3), and its effect on the formability of different grades of sheet metal was investigated in terms of the ratio of the third to the first principal stress components (\( \beta = {{{{\sigma_3}}} \left/ {{{\sigma_1}}} \right.} \)). The FLC was predicted for plane stress conditions (β = 0) as well as cases with different compressive through-thickness stress values (β ≠ 0) in order to study the influence of β on the FLC in three-dimensional stress conditions. An analysis was also carried out to determine how the sensitivity of the FLC prediction to the through-thickness stress component changes with variations in the strain hardening coefficient, in the strain rate sensitivity, in plastic anisotropy, in grain size and in sheet thickness. It was found that the out-of-plane stress always has an effect on the position of the FLC in principal strain space. However, the analysis also showed that among the factors considered in this paper, the strain hardening coefficient has the most significant effect on the dependency of FLC to the through-thickness stress, while the strain rate sensitivity coefficient has the least influence on this sensitivity. more...
- Published
- 2011
- Full Text
- View/download PDF
42. Prediction of sheet forming limits with Marciniak and Kuczynski analysis using combined isotropic–nonlinear kinematic hardening
- Author
-
Daniel E. Green and Morteza Nurcheshmeh
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Bauschinger effect ,Work hardening ,Mechanics ,Condensed Matter Physics ,Forging ,Forming limit diagram ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,Hardening (metallurgy) ,Formability ,General Materials Science ,Sheet metal ,Civil and Structural Engineering ,Necking - Abstract
The forming limit curve (FLC), a plot of the limiting principal surface strains that can be sustained by sheet metals prior to the onset of localized necking, is useful for characterizing the formability of sheet metal and assessing the forming severity of a drawing or stamping process. Both experimental and theoretical work reported in the literature has shown that the FLC is significantly strain-path dependent. In this paper, a modified Marciniak and Kuczynski (MK) approach was used to compute the FLC in conjunction with two different work-hardening models: an isotropic hardening model and a mixed isotropic–nonlinear kinematic hardening model, which is capable of describing the Bauschinger effect. Predictions of the FLC using the MK analysis have been shown to be dependent on the shape of the initial yield locus and on its evolution during work hardening; therefore the hardening model has an influence on the predicted FLC. In this investigation, published experimental FLCs of AISI-1012 low carbon steel and 2008-T4 aluminum alloy sheets that were subjected to various nonlinear loading paths were compared to predictions using both hardening models. The predicted FLCs were found to correlate quite well with experimental data and the effects of strain path changes and of the hardening model on predicted FLCs are discussed. more...
- Published
- 2011
- Full Text
- View/download PDF
43. A numerical method to predict the rate-sensitive hardening behaviour of sheet materials using uniaxial and biaxial flow curves
- Author
-
Daniel E. Green and Iman Sari Sarraf
- Subjects
Materials science ,Numerical analysis ,Hardening (metallurgy) ,Composite material - Published
- 2018
- Full Text
- View/download PDF
44. Prediction of DP600 and TRIP780 yield loci using Yoshida anisotropic yield function
- Author
-
Iman Sari Sarraf and Daniel E. Green
- Subjects
Yield (engineering) ,Materials science ,Thermodynamics ,Anisotropy ,Yield function - Published
- 2018
- Full Text
- View/download PDF
45. Simulation of electrohydraulic free forming of DP600 sheets using a modified Rousselier damage model
- Author
-
Daniel E. Green and Iman Sari Sarraf
- Subjects
History ,Materials science ,Computer Science Applications ,Education - Published
- 2018
- Full Text
- View/download PDF
46. Investigation on the strain-path dependency of stress-based forming limit curves
- Author
-
Morteza Nurcheshmeh and Daniel E. Green
- Subjects
Materials science ,Strain (chemistry) ,Stress path ,business.industry ,Bar (music) ,Mechanics ,Structural engineering ,Stress (mechanics) ,Path dependency ,Range (statistics) ,General Materials Science ,Limit (mathematics) ,business ,Plane stress - Abstract
Path-dependent forming limits have been computed for sheet metals undergoing various combinations of plane stress loading conditions. This paper presents a theoretical model for prediction of stress-based forming limit curves (SFLC) based on the Marciniak and Kuczynski (MK) model. Acceptable agreement was observed between calculated forming limit curves (FLC) and experimental data for AISI-1012 steel (Molaei 1999) and AA-2008-T4 alloys (Graf and Hosford Metallurgical Trans 24A:2503–2512, 1993). In this paper, the path dependency of SFLCs predicted for different non-proportional loading histories has been investigated. For a range of prestrain values in different bilinear loading paths, the SFLC remains practically unchanged. However, some strain path dependency is observed for large values of prestrain (\( \bar{\varepsilon } \geqslant 0.35 \) for AISI-1012 steel) and for abrupt changes in strain path. Nevertheless, the SFLC remains a good failure criterion for virtual forming simulations because the path dependency of SFLCs is much less significant than that of strain-based FLCs. more...
- Published
- 2010
- Full Text
- View/download PDF
47. Axial cutting of AA6061-T6 circular extrusions under impact using single- and dual-cutter configurations
- Author
-
Shun Yi Jin, William Altenhof, Daniel E. Green, and Amitabha Majumder
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Aerospace Engineering ,Ocean Engineering ,Structural engineering ,Deformation (meteorology) ,Dissipation ,Dynamic load testing ,Displacement (vector) ,Finite element method ,Mechanics of Materials ,Automotive Engineering ,Fracture (geology) ,Crashworthiness ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering ,Dynamic testing - Abstract
Experimental and numerical axial cutting of AA6061-T6 circular extrusions under both dynamic and quasi-static loading conditions were completed using single- and dual-cutter configurations to investigate load/displacement and collapse behaviour of the extrusions. Circular specimens with various wall thicknesses were considered for impact and quasi-static testing in this research. A steel cutter (AISI 4140) with four blades, having blade tip widths of 1.0 mm or 0.75 mm and blade lengths of 7 mm or 26.1 mm were used to cut through the extrusions. Straight and curved deflector profiles were used to flare the cut petalled sidewalls and facilitate the cutting system. Further quasi-static cutting tests using dual cutters were completed with or without the presence of a spacer to examine the load/displacement response as an adaptive energy absorption system. Results from the experimental impact tests illustrated that a higher peak cutting force, with a magnitude of approximately 1.09–1.98 times that of the force necessary under quasi-static testing conditions, was needed to initiate the cutting deformation mode. After this initial high force, the load/displacement responses were observed to be similar to those from the quasi-static tests with the exception of minor variations which resulted from material fracture that occurred on the petalled sidewalls during dynamic testing. Larger lengths of cutter blades and the curved deflector eased the flaring of the petalled sidewalls and reduced the occurrence of material fracture. The blade tip width had minor effects on the initial peak cutting force and mean cutting forces for extrusions under impact loading. The mean cutting force from the dynamic tests was determined to be 0.82–1.2 times that from the quasi-static experimental tests. Finally, quasi-static axial crushing of extrusions was completed to compare crashworthiness measures with the adaptive energy absorption system under the cutting deformation mode. A finite element model incorporating an Eulerian formulation was selected for the numerical model to simulate the cutting process. Simulation results generally agreed well with the experimental tests with a maximum over prediction of approximately 33% and 18% for the cutting force under impact and quasi-static loading, respectively. more...
- Published
- 2010
- Full Text
- View/download PDF
48. Semi-implicit numerical integration of Yoshida–Uemori two-surface plasticity model
- Author
-
Aboozar Taherizadeh, Daniel E. Green, and A. Ghaei
- Subjects
Surface (mathematics) ,Engineering ,business.industry ,Mechanical Engineering ,Structural engineering ,Plasticity ,Condensed Matter Physics ,Orthotropic material ,Finite element method ,Numerical integration ,Simple shear ,Quadratic equation ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,business ,Sheet metal ,Civil and Structural Engineering - Abstract
A semi-implicit integration scheme was used to implement the Yoshida–Uemori two-surface model into the finite element method. Hill’s quadratic yield function was employed to account for the orthotropic behaviour of the metal sheet. The model was used to predict the cyclic simple shear response of DP-600. In order to evaluate the capability of the model for sheet metal forming, the model was used to simulate both the forming stage of a channel draw process in the presence of drawbeads and the subsequent springback stage. The results show that the model predicts the springback profile very well, especially at deeper drawbead penetrations. more...
- Published
- 2010
- Full Text
- View/download PDF
49. Experimentally Observed Strain Distributions Near Circular Discontinuities of AA6061-T6 Extrusions During Axial Crush
- Author
-
Amitabha Majumder, N. Turton, William Altenhof, V. Vijayan, Daniel E. Green, Shun Yi Jin, and H. An
- Subjects
Digital image correlation ,Materials science ,business.industry ,Mechanical Engineering ,Aerospace Engineering ,Structural engineering ,Classification of discontinuities ,Discontinuity (geotechnical engineering) ,Mechanics of Materials ,Strain distribution ,Solid mechanics ,Ultimate tensile strength ,Extrusion ,Composite material ,business ,Extensometer - Abstract
An experimental investigation to determine the strain distribution and collapse behaviour for AA6061-T6 square cross-sectional extrusions with and without circular discontinuities under quasi-static axial compressive loading was completed. Three-dimensional digital image correlation (DIC) was utilized for strain assessment. In order to validate the results of the optical strain measurement system, tensile tests were first conducted employing both the DIC technique and a traditional extensometer. Strain observations from both methods were found to be very consistent prior to strain localization in the test specimen. Quasi-static axial crushing tests were then conducted. Extrusions considered for the present research had a nominal side width, wall thickness and length of 38.1 mm, 3.15 mm, and 200 mm, respectively. A centrally-located circular hole with diameter of either 14.29 mm, 10.72 mm or 7.14 mm was incorporated into the extrusion. Square tubes without any discontinuities were also considered in the experimental testing program. Testing results showed that the collapse mode of the extrusion altered from global bending to a cutting and splitting deformation mode with the presence of the circular discontinuity. Strain localization occurred near the vicinity of the holes for all specimens. For discontinuities sized 14.29 mm and 10.72 mm the location of strain localization and the initiation of material fracture was at the edge of the discontinuity while the location for extrusions with a 7.14 mm hole was found to occur at the intersection of the extrusion side walls. Maximum values of the effective strain were found to vary from approximately 60% to 100%. The region of strain localization was consistent with the location where material fracture initiated. more...
- Published
- 2010
- Full Text
- View/download PDF
50. Numerical implementation of Yoshida–Uemori two-surface plasticity model using a fully implicit integration scheme
- Author
-
A. Ghaei and Daniel E. Green
- Subjects
General Computer Science ,Computer science ,Subroutine ,Numerical analysis ,Bauschinger effect ,General Physics and Astronomy ,Forming processes ,General Chemistry ,Plasticity ,Finite element method ,Computational Mathematics ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,Forensic engineering ,Hardening (metallurgy) ,Applied mathematics ,General Materials Science ,Sheet metal - Abstract
The return mapping procedure was used to develop an algorithm for numerical implementation of Yoshida–Uemori two-surface plasticity model into a finite element program. A fully implicit integration scheme is utilized to integrate all plasticity equations. The algorithm was employed to develop user material subroutine (UMAT and VUMAT) for both ABAQUS-Standard and ABAQUS-Explicit codes. The numerical algorithm is quite general and is not limited to any particular yield function. However, as an example, the Yld2000-2d yield function was implemented in the subroutines in order to take the anisotropy of metal sheets into account. Finally, the subroutines were used to simulate the springback of a U-shape channel section. The channels were formed using two different drawbead penetrations and two different sheet materials, i.e. HSLA and AA6022-T43. The forming process and subsequent springback stage was simulated using the same yield function and three different hardening laws: (a) isotropic hardening, (b) a combined isotropic-nonlinear kinematic hardening and (c) the Yoshida–Uemori two-surface model. A comparison of the experimental and predicted channel sidewall profiles shows that the Yoshida–Uemori model generally improves the springback prediction compared to isotropic hardening and combined isotropic-nonlinear kinematic hardening. more...
- Published
- 2010
- Full Text
- View/download PDF
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.