Analysis and Observations of Current Density Sensitivity and Thermally Activated Mechanical Behavior in Electrically-Assisted Deformation

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
James Magargee ◽  
Rong Fan ◽  
Jian Cao
Keyword(s):  
Flow Stress ◽  
Mechanical Behavior ◽  
Electric Current ◽  
Current Density ◽  
Rapid Heating ◽  
High Strength ◽  
Thermally Induced ◽  
Thermally Activated ◽  
Electrically Assisted ◽  
Wide Range

The flow of electric current through a metal during deformation has been observed to reduce its flow stress and increase its ductility. This observation has motivated the development of advanced “electrically-assisted” metal forming processes that utilize electric current to assist in the forming of high-strength and difficult-to-form materials, such as titanium and magnesium alloys. This method of heating provides attractive benefits such as rapid heating times, increased energy efficiency due to its localized nature, as well as the ability to heat the workpiece in the forming machine thus eliminating the transfer process between oven heating and forming. In this paper, a generalized method is proposed to relate applied electric current density to thermally activated mechanical behavior to better understand and improve the processing of metals during electrically-assisted deformation. A comparison is made of engineering metals studied experimentally as well as in the literature, and it is shown that the method provides insight into what some researchers have observed as the occurrence or absence of a “current density threshold” in certain materials. A new material parameter, “current density sensitivity,” is introduced in order to provide a metric for the relative influence of current density on a material's thermally activated plastic flow stress. As a result, the electric current necessary to induce thermal softening in a material can be estimated in order to effectively parameterize a wide range of advanced electrically-assisted forming processes. Thermally induced changes in material microstructure are observed and discussed with respect to the underlying deformation mechanisms present during electrically-assisted deformation. Finally, a strong correlation between thermally activated mechanical behavior and elastic springback elimination during sheet bending is demonstrated.

Investigation of Deformation Behavior of SS304 and Pure Copper Subjected to Electrically Assisted Forming Process

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Tianhao Jiang ◽  
Linfa Peng ◽  
Peiyun Yi ◽  
Xinmin Lai
Keyword(s):  
Elevated Temperature ◽  
Flow Stress ◽  
Constitutive Model ◽  
Electric Current ◽  
Deformation Behavior ◽  
Pure Copper ◽  
Annihilation Process ◽  
Forming Process ◽  
Electrically Assisted ◽  
Dislocation Movement

Both electrically assisted tension (EAT) and thermally assisted tension (TAT) tests were performed on SS304 and pure copper to decouple the influence of elevated temperature from electric current on flow stress and ductility. It is found that the reduction on flow stress and ductility of SS304 are more dependent on the elevated temperature than electric current, but electric current has a stronger effect by 10% on reducing flow stress and ductility of pure copper than the elevated temperature does. As the flow stress and ductility of two metals are related to the dislocation evolution, a constitutive model considering both storage and annihilation process of dislocation was established to describe the effect of electric current and temperature on dislocation movement. It is found that electric current accelerated the annihilation process of dislocation in pure copper up to 20% in EAT compared with that in TAT, but such phenomenon was rarely observed in SS304. Furthermore, attempts have also been made to distinguish the influence of elevated temperature with that of electric current on microstructure evolution and it is also found that the formation of [111] crystals in pure copper is nearly 10% less in EAT than that in TAT.

scholarly journals New Principles of Polymer Composite Preparation. MQ Copolymers as an Active Molecular Filler for Polydimethylsiloxane Rubbers

Polymers ◽  
2021 ◽  
Vol 13 (17) ◽  
pp. 2848
Author(s):  
Ivan B. Meshkov ◽  
Aleksandra A. Kalinina ◽  
Vadim V. Gorodov ◽  
Artem V. Bakirov ◽  
Sergey V. Krasheninnikov ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Mechanical Behavior ◽  
Polymer Composite ◽  
High Strength ◽  
Traditional Methods ◽  
Silicone Elastomers ◽  
Promising Alternative ◽  
Elongation At Break ◽  
Solvent Removal ◽  
Wide Range

Colorless transparent vulcanizates of silicone elastomers were prepared by mixing the components in a common solvent followed by solvent removal. We studied the correlation between the mechanical behavior of polydimethylsiloxane (PDMS)-rubber compositions prepared using MQ (mono-(M) and tetra-(Q) functional siloxane) copolymers with different ratios of M and Q parts as a molecular filler. The composition and molecular structure of the original rubber, MQ copolymers, and carboxyl-containing PDMS oligomers were also investigated. The simplicity of the preparation of the compositions, high strength and elongation at break, and their variability within a wide range allows us to consider silicone elastomers as a promising alternative to silicone materials prepared by traditional methods.

scholarly journals Determining Material Data for Welding Simulation of Presshardened Steel

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 740
Author(s):  
Jonny Kaars ◽  
Peter Mayr ◽  
Kurt Koppe
Keyword(s):  
Flow Stress ◽  
Room Temperature ◽  
Rapid Heating ◽  
Welding Process ◽  
High Strength ◽  
Cost Ratio ◽  
Material Data ◽  
Automotive Body ◽  
Nugget Growth ◽  
Martensitic State

In automotive body-in-white production, presshardened 22MnB5 steel is the most widely used ultra-high-strength steel grade. Welding is the most important faying technique for this steel type, as other faying technologies often cannot deliver the same strength-to-cost ratio. In order to conduct precise numerical simulations of the welding process, flow stress curves and thermophysical properties from room temperature up to the melting point are required. Sheet metal parts made out of 22MnB5 are welded in a presshardened, that is, martensitic state. On the contrary, only flow stress curves for soft annealed or austenitized 22MnB5 are available in the literature. Available physical material data does not cover the required temperature range or is not available at all. This work provides experimentally determined hot-flow stress curves for rapid heating of 22MnB5 from the martensitic state. The data is complemented by a comprehensive set of thermophysical data of 22MnB5 between room temperature and melting. Materials simulation methods as well as a critical literature review were employed to obtain sound thermophysical data. A comparison of the numerically computed nugget growth curve in spot welding with experimental welding results ensures the validity of the hot-flow stress curves and thermophysical data presented.

Constant Current Density Compression Behavior of 304 Stainless Steel and Ti-6Al-4V During Electrically-Assisted Forming

2011 ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears
Keyword(s):  
Stainless Steel ◽  
Flow Stress ◽  
Current Density ◽  
Elevated Temperatures ◽  
Shape Change ◽  
Electrical Current ◽  
304 Stainless Steel ◽  
Constant Current ◽  
Constant Current Density ◽  
Electrically Assisted

A metal forming technique which has more recently come of interest as an alternative to processes that use elevated temperatures at some stage during manufacturing is Electrically-Assisted Forming (EAF). EAF is a processing technique which applies electrical current through the workpiece concurrently while the material is being formed. At present, this method has only been studied on an experimental level in laboratory settings, and the heuristic results show increased fracture strain, reduced flow stress, and reduced springback; the enhanced process capability is beyond the range that would be expected from pure resistive heating alone. Thus far, when applying the electrical current through the workpiece during deformation, the current magnitude flowing through the workpiece has remained constant. Hence, for a compression loading, the current flux or density decreases as a result of an increasing specimen area. This work examines the effect of a non-constant current density (NCCD) and a constant current density (CCD) on the deformation behavior of 304 Stainless Steel and Ti-6Al-4V during uniaxial compression testing. Additionally, the application of a CCD is used to modify existing empirically-based EAF flow stress models for these materials. From this testing, it is shown that a CCD during forming can significantly reduce the flow stress of the material as compared to the NCCD tests. The reductions in the flow stress were increased at higher strains by approximately 30% and 15% for the 304 Stainless Steel and Ti-6Al-4V, respectively. More importantly, these flow stress curves are better representative of how the material responds to an applied electrical current as the specimen shape change is removed from the results. Also, the NCCD tests were approximated using an existing empirically-based EAF flow stress model and the CCD tests concluded that a new flow stress predictor model be introduced.

The Effect of Pulse Electric Current on the Mechanical Properties and Fracture Behaviors of Aluminum Alloy AA5754

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Kunmin Zhao ◽  
Rong Fan
Keyword(s):  
Flow Stress ◽  
Energy Density ◽  
Current Density ◽  
Pulse Current ◽  
Maximum Flow ◽  
Total Elongation ◽  
Electric Currents ◽  
Electrically Assisted ◽  
Heating Effects ◽  
Pulse Electric

The influences of pulse electric currents at energy density levels of 0.105 J/mm3 and 0.150 J/mm3 on AA5754's flow stress and elongation are investigated. Different combinations of current density and pulse duration are carried out for each energy density. The non-Joule heating effects in electrically assisted forming (EAF) are revealed since the temperatures generated by the electric currents of the same energy density are identical. It is observed that a pulse current helps reduce AA5754's flow stress and increase its elongation. At the same level of energy density, as the current density increases, the instant drop of stress increases as well as the elongation, although the maximum flow stress remains almost unchanged. A theoretical model is proposed that can predict the stress drop during electrically assisted forming. The fracture surfaces of AA5754 subject to pulse currents are observed and analyzed. The dimples of fracture continue to decrease until they completely disappear as the density of pulse current increases. The suppression of voids nucleation and growth by a pulse current leads to the increase of total elongation.

scholarly journals Feasibility of a Two-Stage Forming Process of 316L Austenitic Stainless Steels with Rapid Electrically Assisted Annealing

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 815 ◽  
Author(s):  
Viet Luu ◽  
Thi Nguyen ◽  
Sung-Tae Hong ◽  
Hye-Jin Jeong ◽  
Heung Han
Keyword(s):  
Mechanical Behavior ◽  
Electric Current ◽  
Strain Curve ◽  
Single Pulse ◽  
Stress Strain Curve ◽  
Forming Process ◽  
Stress Strain ◽  
Two Stage ◽  
Post Annealing ◽  
Electrically Assisted

The post-annealing mechanical behavior of 316L austenitic stainless steel (SUS316L) after electrically assisted (EA) annealing with a single pulse of electric current is experimentally investigated to evaluate the feasibility of a two-stage forming process of the selected SUS316L with rapid EA annealing. A tensile specimen is deformed to a specific prestrain and then annealed by applying a single pulse of electric current with a short duration less than 1 s. Finally, the specimen is reloaded until fracture. The stress-strain curve during reloading shows that the flow stress of the SUS316L significantly decreases, which indicates the occurrence of EA annealing. The electric current also increases the maximum achievable elongation of the SUS316L during reloading. The stress-strain curve during reloading and the microstructural observation suggest that the effects of EA annealing on the post-annealing mechanical behavior and microstructure strongly depend on both the applied electric current density (electric current per unit cross-sectional area) and the given prestrain. The results of the present study suggest that the EA annealing technique could be effectively used to improve the formability of SUS316L when manufacturing complex parts.

Comparisons of Constitutive Models for Steel Over a Wide Range of Temperatures and Strain Rates

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Farid Abed ◽  
Fadi Makarem
Keyword(s):  
Flow Stress ◽  
Strain Hardening ◽  
Shear Bands ◽  
Constitutive Models ◽  
Steel Structures ◽  
High Strength ◽  
Stress And Strain ◽  
Strain Rates ◽  
Wide Range ◽  
Strain Hardening Behavior

This study investigates and compares several available plasticity models used to describe the thermomechanical behavior of structural steel subjected to complex loadings. The main purpose of this comparison is to select a proper constitutive model that can later be implemented into a finite element code to capture localizations (e.g., shear bands and necking) in steel and steel structures subjected to low- and high-velocity impact. Four well-known constitutive models for viscoplastic deformation of metals, i.e., Johnson–Cook (JC), Zerilli–Armstrong (ZA), Rusinek–Klepaczko (RK), and Voyiadjis–Abed (VA), have been investigated and compared with reference to existing deformation data of HSLA-65 and DH-36 steel conducted at low and high strain rates and various initial temperatures. The JC, ZA, and RK models reasonably describe the flow stress and the strain hardening behavior only in the certain ranges of strain, strain rate, and temperature for which the models were developed. This was attributed to the inaccurate assumptions used in developing these models. In contrast, the VA model most effectively describes the flow stress and strain hardening in which very good predictions are observed for the constitutive behavior of high strength steel over a wide range of strains, strain rates, and temperatures.

Investigation of the Electroplastic Effect Through Nominally Equal Energy Deformation

2018 ◽  
Author(s):  
Brandt J. Ruszkiewicz ◽  
Laine Mears
Keyword(s):  
Current Density ◽  
High Current Density ◽  
High Strength Steels ◽  
High Strength ◽  
Electrical Energy ◽  
Process Performance ◽  
Advanced High Strength Steels ◽  
Electrically Assisted ◽  
Lightweight Metals ◽  
Material Bodies

To increase the fuel economy of their fleets, automotive OEMs are turning to lightweighting their vehicles through multi-material bodies. This involves forming and joining of materials with high strength to weight ratios such as aluminum and advanced high strength steels. These metals come with the downside of decreased formability and increased springback compared to conventional automotive steels. Electrical augmentation has been shown to decrease springback and increase formability in sheet forming and represents a potential solution to the use of new lightweight metals. Applied electricity is traditionally measured as a current density, however this measure struggles to represent elevated strain rate manufacturing processes. This paper examines other predictors of electrically assisted process performance such as electrical energy and power through comparison of nominally equivalent waveforms. It is found that energy is a better predictor of process performance than current density, but is dependent on the ability to predict process temperature. The leading predictive electrically assisted temperature model is examined in depth through testing of 13 different parameter sets. It is found that the model is unable to predict the correct temperature at a high current density and that the transient stress drop cannot predicted for any of the electrical cases.

scholarly journals Development of Electrically Assisted Rapid Heating for Metal Forming of Hot-Stamping Process

2016 ◽  
Vol 5 (3) ◽  
pp. 66 ◽  
Author(s):  
Mahmudun Nabi Chowdhury ◽  
Dinh Thi Kieu Anh
Keyword(s):  
Electric Current ◽  
Metal Forming ◽  
Rapid Heating ◽  
Hot Stamping ◽  
Heating Time ◽  
Surface Heating ◽  
Specimen Length ◽  
Contact Points ◽  
Electrically Assisted ◽  
Length Direction

<p class="1Body">Two different concepts of electrically assisted (EA) rapid heating of Al–Si coated hot-stamping steels are compared. In “along the surface” EA heating (or simply EA surface heating), the electric current is simply applied to a specimen by clamping the each end of the specimen length with a set of flat rectangular electrodes. In “through the thickness” EA heating (or simply EA thickness heating), the electric current is applied to a specimen by attaching a set of electrodes with multiple contact points on upper and lower surfaces of the specimen. While the EA surface heating generally requires a shorter heating time due to a higher electrical resistance in the length direction, the EA thickness heating also may provide a technical advantage that the heating area can be more easily configured in a case of partial austenization.</p>

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