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Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion, resulting in enhanced room temperature formability. The exact mechanism of the formability improvement is not yet established. The contribution of interrupted motion in the ductility improvement has been studied through stress relaxation phenomena in uniaxial tensile (UT) tests. However, the reason for improved formability observed when employing servo press is complicated due to the additional contribution from frictional effects. In the present work, an attempt is made to decouple the friction effect on formability improvement numerically. The improved formability is studied using a hole expansion test (HET). The limit of forming during hole expansion is modeled using the Hosford–Coulomb (HC) damage criteria, which is implemented as a user subroutine in a commercial explicit finite element (FE) software. Only the contribution of stress relaxation is accounted for in the evolution of the damage variable during interrupted loading. Therefore, the difference between simulation and experimental hole expansion ratio (HER) can be used to decouple the friction effect from the overall formability improvement during hole expansion. The improvement in HER due to stress relaxation and friction effect is different. The study showed that the model effectively captures the hole expansion deformation process in both monotonic and interrupted loading conditions. Compared to stress relaxation, friction effect played a major role during interrupted HET.


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Does friction contribute to formability improvement using servo press?

Show Author's information Kali PRASAD1,( )Aishwary GUPTA2,Hariharan KRISHNASWAMY1( )Uday CHAKKINGAL3Dilip K. BANERJEE4Myoung-Gyu LEE2
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India
Material Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg 20899, USA

† Kali PRASAD and Aishwary GUPTA contributed equally to this work.

Abstract

Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion, resulting in enhanced room temperature formability. The exact mechanism of the formability improvement is not yet established. The contribution of interrupted motion in the ductility improvement has been studied through stress relaxation phenomena in uniaxial tensile (UT) tests. However, the reason for improved formability observed when employing servo press is complicated due to the additional contribution from frictional effects. In the present work, an attempt is made to decouple the friction effect on formability improvement numerically. The improved formability is studied using a hole expansion test (HET). The limit of forming during hole expansion is modeled using the Hosford–Coulomb (HC) damage criteria, which is implemented as a user subroutine in a commercial explicit finite element (FE) software. Only the contribution of stress relaxation is accounted for in the evolution of the damage variable during interrupted loading. Therefore, the difference between simulation and experimental hole expansion ratio (HER) can be used to decouple the friction effect from the overall formability improvement during hole expansion. The improvement in HER due to stress relaxation and friction effect is different. The study showed that the model effectively captures the hole expansion deformation process in both monotonic and interrupted loading conditions. Compared to stress relaxation, friction effect played a major role during interrupted HET.

Keywords:

servo press, hole expansion test (HET), dual phase steel, finite element (FE) analysis, Hosford–Coulomb (HC) ductile fracture model
Received: 08 March 2022 Revised: 03 May 2022 Accepted: 21 September 2022 Published: 06 January 2023 Issue date: May 2023
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Publication history

Received: 08 March 2022
Revised: 03 May 2022
Accepted: 21 September 2022
Published: 06 January 2023
Issue date: May 2023

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© The author(s) 2022.

Acknowledgements

The authors would like to express their gratitude to ArcelorMittal for providing the steel utilized in this study. Authors affiliated to Indian Institute of Technology Madras gratefully acknowledge the funding received from the Institute of Eminence Research Initiative project on materials and manufacturing for futuristic mobility.

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