Analysis of the Electric and Thermal Effects on Mechanical Behavior of SS304 Subjected to Electrically Assisted Forming Process

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Tianhao Jiang ◽  
Linfa Peng ◽  
Peiyun Yi ◽  
Xinmin Lai
Keyword(s):  
Thermal Effect ◽  
Electric Current ◽  
Yield Stress ◽  
Additional Stress ◽  
Forming Process ◽  
Activation Effect ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Electrically Assisted ◽  
Tension Tests

Significant improvements in deformation resistance and ductility of metals are observed in the electrically assisted forming (EAF) process. Both electroplastic effect (EPE) induced by electric current and thermal effect associated with Joule heating have been proposed to explain the phenomenon. However, there are still arguments in the contribution of the EPE in EAF process. In this paper, both electrically assisted tension tests (EAT) and thermally assisted tension tests (TAT) were conducted on SS304 specimens at the same temperature. The existence of EPE is investigated, and the contribution of EPE is also distinguished with thermal effect numerically by considering the initial yield stress, dislocation hardening, and martensite phase transformation. It is shown when the temperature is around 34 °C, the electric current of 50 A/mm2 in EAT induces additional stress reduction of 16% in the short-range internal stress (effective stress) involved in the initial yield stress and volume reduction of 45.2% in martensite formation compared with results in TAT. However, the effect is not obvious for the cases of 100 A/mm2 and 150 A/mm2 when the temperature is above 100 °C. By comparing the storage coefficient and recovery coefficient of dislocation in EAT and TAT, it indicates that electric current has no additional activation effect on dislocation movement of SS304.

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

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

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

Springback Evaluation of 304 Stainless Steel in an Electrically Assisted Air Bending Operation

2016 ◽  
Author(s):  
Abdelrahim Khal ◽  
Brandt J. Ruszkiewicz ◽  
Laine Mears
Keyword(s):  
Electric Current ◽  
General Term ◽  
Bending Test ◽  
304 Stainless Steel ◽  
Forming Process ◽  
Cross Sectional ◽  
Air Bending ◽  
Research Fields ◽  
Electrically Assisted ◽  
Microstructural Evaluation

Driven by the automotive industry’s drive towards lightweighting, electrically assisted forming (EAF) is one of the most rapidly growing research fields in bulk deformation, and is classified under the general term “Electrically-Assisted Manufacturing (EAM)”. In EAF electric current (continuous or intermittent) is applied to a metallic sheet during the forming process, leading to numerous advantageous effects that have been studied and proven by several research groups and for different structural metals, such as reduced forming load and flow stress, increased formability, and reduction (or even elimination) of springback. Electrically-assisted bending (EAB) is a recent evolution of EAF technique, with the aim of capitalizing on the aforementioned advantages of EAF technique. In this work the effects of the EAB process on the final springback in an air bending test are identified, with the metal sheet being bent under different electrical field conditions. In addition, a comparison between the effects of applying the current during forming versus post forming are investigated. It was found that in general, higher current density (amount of current through cross sectional area of specimen (A/mm2), more frequent pulse period, and longer pulse duration all resulted in a greater degree of springback reduction. A microstructural evaluation showed no change in grain size in the presence of electric current.

Alternative Control of an Electrically Assisted Tensile Forming Process Using Current Modulation

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears
Keyword(s):  
Electric Current ◽  
Current Flow ◽  
Current Level ◽  
Temperature Gradients ◽  
Material Strength ◽  
Alternative Control ◽  
Forming Process ◽  
Control Material ◽  
Model Based Control ◽  
Electrically Assisted

Electrically assisted forming is a technique whereby metal is deformed while simultaneously undergoing electric current flow. Using this process, electric current level becomes a new degree of freedom for process control. In this work, we present some alternative control architectures allowing for new avenues of control using such a process. The primary findings are architectures to allow for forming at constant force and forming at constant stress levels by modulating electric current to directly control material strength. These are demonstrated in a tensile forming operation, and found to produce the desired results. Combining these control approaches with previous and contemporary efforts in modeling of the process physics will allow for system identification of material response properties and model-based control of difficult-to-observe process parameters such as real time temperature gradients.

Evaluation of Uniaxial Tensile Behavior under Pulsed Current for Electrically Assisted Warm Forming of Light Weight Alloys

2017 ◽  
Vol 744 ◽  
pp. 254-258
Author(s):  
Jung Han Song ◽  
Injea Jang ◽  
Suh Yun Gwak ◽  
Jun Ho Bang ◽  
Yong Bae Kim ◽  
...  
Keyword(s):  
Electric Current ◽  
Test System ◽  
Warm Forming ◽  
Uniaxial Tensile ◽  
Light Weight ◽  
Test Results ◽  
Forming Process ◽  
Uniaxial Test ◽  
Electrically Assisted ◽  
Deep Drawing Test

In this study, the electric current effects in the deformation of light weight alloys are investigated to improve the formability. To begin with, a test system is built up to carry out the tensile test with heavy electric current flowing through the specimen. The evolutions of the flow stresses and failure elongations were obtained using this test system. The thermal and athermal effect such as electro-plastic effect of metallic materials induced by high density current make significant reduction of the flow stress, which is beneficial to the forming process of less formable metal. From the uniaxial test results, pulse current-assisted deep drawing test were conducted. The experimental results demonstrate that electrically assisted warm forming provides lower energy consumption and higher efficiency.

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.

Sensitivity Analysis of Material Parameters on Spring-Back of NC Bending of High-Strength TA18 Tube

2012 ◽  
Vol 472-475 ◽  
pp. 1003-1008 ◽  
Author(s):  
Pei Pei Zhang ◽  
Mei Zhan ◽  
Tao Huang ◽  
He Yang
Keyword(s):  
Elastic Modulus ◽  
Strain Hardening ◽  
Yield Stress ◽  
Strain Hardening Exponent ◽  
Spring Back ◽  
Initial Yield Stress ◽  
Material Parameters ◽  
Strength Coefficient ◽  
Initial Yield ◽  
Nc Bending

Spring-back is one of the key factors affecting the forming quality of the NC bending of high-strength TA18 tubes (TA18-HS tubes). Since material parameters have a direct influence on stress and strain fields during the bending and after unloading, the springback of TA18-HS tubes after NC bending depends on material properties to a great degree. In order to study the effect of material parameters, the sensitivity of material parameters on spring-back of TA18-HS tubes is analyzed in this study, using the numerical simulation and the multi-parameters sensitivity analysis method. The results show the following: (1) The springback angle has a positive correlation with the strength coefficient and initial yield stress, and has a negative correlation with the elastic modulus and strain hardening exponent. Besides, with the increase of elastic modulus, the fluctuation of springback goes gently; with the increase of the strength coefficient and initial yield stress, the fluctuation of springback goes abruptly; but with the variation of the strain hardening exponent, the springback fluctuates slightly; (2) The elastic modulus is the most sensitive material parameter on spring-back, the strength coefficient and initial yield stress rank the second and third, respectively, and the strain hardening exponent is the last. The achievement of the study is valuable to eliminate the non-sensitivity parameters, simplify the optimization project, and improve the spring-back prediction capability.

Alternative Control of an Electrically-Assisted Tensile Forming Process Using Current Modulation

2013 ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears
Keyword(s):  
Electric Current ◽  
Current Flow ◽  
Current Level ◽  
Temperature Gradients ◽  
Material Strength ◽  
Alternative Control ◽  
Forming Process ◽  
Control Material ◽  
Model Based Control ◽  
Electrically Assisted

Electrically-assisted forming is a technique whereby metal is deformed while simultaneously undergoing electric current flow. Using this process, electric current level becomes a new degree of freedom for process control. In this work we present some alternative control architectures allowing for new avenues of control using such a process. The primary findings are architectures to allow for forming at constant force and forming at constant stress levels by modulating electric current to directly control material strength. These are demonstrated in a tensile forming operation, and found to produce the desired results. Combining these control approaches with previous and contemporary efforts in modeling of the process physics will allow for system identification of material response properties and model-based control of difficult-to-observe process parameters such as real time temperature gradients.

Numerical Simulation of Perforated Hollow Sphere Structures (PHSS) to Investigate Mechanical Properties

2009 ◽  
Vol 620-622 ◽  
pp. 275-278 ◽  
Author(s):  
Andreas Öchsner ◽  
Seyed Mohammad Hossein Hosseini ◽  
Markus Merkel
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Yield Stress ◽  
Elastic Properties ◽  
Hollow Sphere ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Inner Sphere ◽  
New Type

This paper investigates the uniaxial mechanical properties of a new type of hollow sphere structures. For this new type, the sphere shell is perforated by several holes in order to open the inner sphere volume and surface. The mechanical properties, i.e. elastic properties and initial yield stress, of perforated hollow sphere structures in a primitive cubic arrangement are numerically evaluated for different hole diameters and different sphere wall thicknesses.

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