Assistant Professor, Department of Mechanical Engineering, Indian Institute of Technology Patna Supervisors: Dr. soumitra Tarafder, Prof. Sankar Dhar, and Prof. Tim Hilditch Address: R&D, Tata Steel Limited, Jamshedpur- 831001, India
The influence of the central hole-edge condition on the hole expansion ratio (HER) of four automo... more The influence of the central hole-edge condition on the hole expansion ratio (HER) of four automotive-grade steel sheets is experimentally investigated in this work. The punched hole shows inferior HER for all selected automotive-grade steel sheets than the wire-electrical discharge machined (WEDM) hole. The finite element simulation approach is used to determine the influence of the coefficient of friction and spring-back on HER. With an increased coefficient of friction, the punch force increases. Material near the inner edge of the central hole comes out in the direction of the sliding punch in the presence of friction. Spring-back has a small effect on HER, and its importance increases for lesser HER materials.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2022
Hole expansion ratio (HER) is widely used to quantify the stretch-flangeability of sheet metal. H... more Hole expansion ratio (HER) is widely used to quantify the stretch-flangeability of sheet metal. HER is determined from the maximum limit of successful expansion of a central hole by a conical punch. The central hole edge is prepared by the punching process. Around 45° cracks are noticed at the central hole edge after successfully completing the hole expansion test. HER of punched hole correlates with uniaxial tensile properties like yield strength, ultimate tensile strength, total elongation, post-uniform elongation, and coefficient of normal anisotropy. Comparisons of strength (yield strength, ultimate tensile strength), anisotropy (coefficient of normal anisotropy) and deformation (total elongation, post-uniform elongation) parameters among steel grades are essential to relate HER among steel grades. Interstitial free steel is the highest, and SPFH steel is the lowest HER among the four steel grades. HER correlates nicely with the notch mouth opening displacement at peak load.
This study explores the impact of pre-strain on the uniaxial tensile stress-strain behavior of ex... more This study explores the impact of pre-strain on the uniaxial tensile stress-strain behavior of extra deep drawing (EDD) steel at varying strain rates. The EDD steel blanks were subjected to a uniaxial pre-strain of 15 % in either the transverse or rolling direction. Subsequently, uniaxial tensile tests were conducted at different strain rates, both orthogonal and parallel to the initial pre-straining direction. The study also investigates the alterations in yield stress (YS), ultimate tensile strength (UTS), uniform elongation (UEL), total elongation (TEL), and strain energy absorption (SED, represented by the area under the tensile stress-strain curve) at diverse strain rates after pre-straining. The experimental findings indicate that pre-straining is advantageous for enhancing YS, UTS, and SED. However, this improvement comes at the expense of UEL or TEL. A square crush tube, which shares similarities with automotive components, was examined to assess the crash performance of several automotive structural parts during crash events. A validated constitutive model was used to predict the square tube's energy absorption and crush performance under high-velocity conditions for different pre-straining scenarios.
Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys... more Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys. During loading, the stress concentration due to defect results in poor tensile ductility and fatigue performance. A physics-based defect tolerant design approach is used in the present work to calculate the uniaxial tensile performance of cast ADC12 Aluminum alloys. The proposed model elucidates the correlation between tensile ductility and the dimensions of material defects. It derives a material constant referred to as the critical defect size, which is determined through a combination of uniaxial tensile testing on specimens with defects and employing finite element simulations. The proposed approach calculates well the tensile properties such as complete tensile stress-strain curve, ultimate tensile strength, and uniaxial tensile elongation.
The primary obstacles to utilizing additively manufactured metallic alloys in industry are their ... more The primary obstacles to utilizing additively manufactured metallic alloys in industry are their inadequate ductility and manufacturing imperfections. Defects in the alloys can result in stress concentration, which can further deteriorate their tensile ductility and fatigue performance. In this study, defect tolerant design methods based on physics are explored to forecast the fatigue performance of 17-4 PH stainless steel that has been additively manufactured. A cyclic plastic zone size-based finite element approach is proposed in this work to predict the fatigue performance of additively manufactured alloys. Initially, defects will be identified from the microstructure of the material, and a finite element model will be created from the microstructure; then, a kinematic hardening model will be used to determine the size of cyclic plastic zone around all defects. The largest size of cyclic plastic zone will cause failure and be identified as a killer defect, and the fatigue life will be calculated on the basis of that killer defect. The proposed method predicts the fatigue life of additively manufactured alloys well.
Advances in Industrial and Manufacturing Engineering, 2021
Abstract Sheet metal forming industry widely adopted the forming limit curve (FLC) as a limiting ... more Abstract Sheet metal forming industry widely adopted the forming limit curve (FLC) as a limiting criterion in sheet metal forming. Regardless of its commercial importance, controlling factors of FLC are not systematically investigated up to date. The present paper comprehensively discussed the effect of different influencing factors on FLC, including limiting strain determination method, punch geometry, microstructure, pre-straining path, strain rate, and temperature. Different tensile properties and their correlations with FLC are also investigated. The introduction of microstructural features such as reducing void nucleation sites i.e., non-coherent particles, evenly distribution of fine hard phases, the introduction of twin and transformation induced plasticity (TRIP & TWIP), are favourable for higher FLC.
Transactions of the Indian Institute of Metals, 2021
Hole expansion ratio (HER) is extensively used in the sheet metal forming industry to assess the ... more Hole expansion ratio (HER) is extensively used in the sheet metal forming industry to assess the sheet metal’s stretch-frangibility limit. Cold-rolled dual-phase steel (DP 590) showed planar anisotropy during the uniaxial tensile test. Hill-48 yield criterion was selected to represent the planar anisotropy of DP 590 steel sheet. Material constants i.e. anisotropic yield stress ratios of Hill-48 yield criterion were calculated from the r -values (Lankford coefficient) determined from the uniaxial tensile test. The finite element simulation result showed that the thickness reduction was maximum at 45° to rolling direction during hole expansion, and a crack was visible in the same location during hole expansion experimentation. HER of DP 590 steel and crack location were successfully predicted from the finite element model for Wire-Electrical Discharge Machine cut central hole edge in the present work.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2021
In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied e... more In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied experimentally based on the Nakajima test method. A forming limit diagram is successfully constructed using universal sheet metal forming machine by offline measuring the strains of deformed specimens. In-process strain measurement based on a digital image correlation technique is also performed for a few selected samples to compare the results with manual strain measurement techniques. All the deformed specimens are also characterized to correlate the sample geometries with hardness values and microstructure. It is observed that the hardness value gradually decreases with an increase in sample width for all the deformed specimens up to the width of 150 mm, except for full-width sample of 200 mm. Microstructural analysis reveals that the morphology of ferrite grains changes with the sample geometry in all the deformed specimens. Microstructural characterization at the top surface of the s...
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2020
Alteration of forming and failure limits due to planar anisotropy of the sheet metal significantl... more Alteration of forming and failure limits due to planar anisotropy of the sheet metal significantly affects the safe forming operation region and finally successfully manufacturing of a sheet metal formed component. This article presents the effect of planar anisotropy on uniaxial tensile properties, forming and failure limits of cold-rolled ferritic and dual-phase steels. In-situ three dimensional digital image correlation technique is used to measure the evolution of local strain components during uniaxial tensile test. For both the steels, necking limit is highest for the specimen at an orientation of 90° to rolling direction, while failure limit is highest for those specimen whose orientation is 45° to rolling direction for ferritic steel, and both 0° and 90° to rolling direction for dual-phase steel. Uniaxial tensile deformation path for ferritic steel holds lower slope than dual-phase steel as depicted in major versus minor strain plot.
The influence of the central hole-edge condition on the hole expansion ratio (HER) of four automo... more The influence of the central hole-edge condition on the hole expansion ratio (HER) of four automotive-grade steel sheets is experimentally investigated in this work. The punched hole shows inferior HER for all selected automotive-grade steel sheets than the wire-electrical discharge machined (WEDM) hole. The finite element simulation approach is used to determine the influence of the coefficient of friction and spring-back on HER. With an increased coefficient of friction, the punch force increases. Material near the inner edge of the central hole comes out in the direction of the sliding punch in the presence of friction. Spring-back has a small effect on HER, and its importance increases for lesser HER materials.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2022
Hole expansion ratio (HER) is widely used to quantify the stretch-flangeability of sheet metal. H... more Hole expansion ratio (HER) is widely used to quantify the stretch-flangeability of sheet metal. HER is determined from the maximum limit of successful expansion of a central hole by a conical punch. The central hole edge is prepared by the punching process. Around 45° cracks are noticed at the central hole edge after successfully completing the hole expansion test. HER of punched hole correlates with uniaxial tensile properties like yield strength, ultimate tensile strength, total elongation, post-uniform elongation, and coefficient of normal anisotropy. Comparisons of strength (yield strength, ultimate tensile strength), anisotropy (coefficient of normal anisotropy) and deformation (total elongation, post-uniform elongation) parameters among steel grades are essential to relate HER among steel grades. Interstitial free steel is the highest, and SPFH steel is the lowest HER among the four steel grades. HER correlates nicely with the notch mouth opening displacement at peak load.
This study explores the impact of pre-strain on the uniaxial tensile stress-strain behavior of ex... more This study explores the impact of pre-strain on the uniaxial tensile stress-strain behavior of extra deep drawing (EDD) steel at varying strain rates. The EDD steel blanks were subjected to a uniaxial pre-strain of 15 % in either the transverse or rolling direction. Subsequently, uniaxial tensile tests were conducted at different strain rates, both orthogonal and parallel to the initial pre-straining direction. The study also investigates the alterations in yield stress (YS), ultimate tensile strength (UTS), uniform elongation (UEL), total elongation (TEL), and strain energy absorption (SED, represented by the area under the tensile stress-strain curve) at diverse strain rates after pre-straining. The experimental findings indicate that pre-straining is advantageous for enhancing YS, UTS, and SED. However, this improvement comes at the expense of UEL or TEL. A square crush tube, which shares similarities with automotive components, was examined to assess the crash performance of several automotive structural parts during crash events. A validated constitutive model was used to predict the square tube's energy absorption and crush performance under high-velocity conditions for different pre-straining scenarios.
Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys... more Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys. During loading, the stress concentration due to defect results in poor tensile ductility and fatigue performance. A physics-based defect tolerant design approach is used in the present work to calculate the uniaxial tensile performance of cast ADC12 Aluminum alloys. The proposed model elucidates the correlation between tensile ductility and the dimensions of material defects. It derives a material constant referred to as the critical defect size, which is determined through a combination of uniaxial tensile testing on specimens with defects and employing finite element simulations. The proposed approach calculates well the tensile properties such as complete tensile stress-strain curve, ultimate tensile strength, and uniaxial tensile elongation.
The primary obstacles to utilizing additively manufactured metallic alloys in industry are their ... more The primary obstacles to utilizing additively manufactured metallic alloys in industry are their inadequate ductility and manufacturing imperfections. Defects in the alloys can result in stress concentration, which can further deteriorate their tensile ductility and fatigue performance. In this study, defect tolerant design methods based on physics are explored to forecast the fatigue performance of 17-4 PH stainless steel that has been additively manufactured. A cyclic plastic zone size-based finite element approach is proposed in this work to predict the fatigue performance of additively manufactured alloys. Initially, defects will be identified from the microstructure of the material, and a finite element model will be created from the microstructure; then, a kinematic hardening model will be used to determine the size of cyclic plastic zone around all defects. The largest size of cyclic plastic zone will cause failure and be identified as a killer defect, and the fatigue life will be calculated on the basis of that killer defect. The proposed method predicts the fatigue life of additively manufactured alloys well.
Advances in Industrial and Manufacturing Engineering, 2021
Abstract Sheet metal forming industry widely adopted the forming limit curve (FLC) as a limiting ... more Abstract Sheet metal forming industry widely adopted the forming limit curve (FLC) as a limiting criterion in sheet metal forming. Regardless of its commercial importance, controlling factors of FLC are not systematically investigated up to date. The present paper comprehensively discussed the effect of different influencing factors on FLC, including limiting strain determination method, punch geometry, microstructure, pre-straining path, strain rate, and temperature. Different tensile properties and their correlations with FLC are also investigated. The introduction of microstructural features such as reducing void nucleation sites i.e., non-coherent particles, evenly distribution of fine hard phases, the introduction of twin and transformation induced plasticity (TRIP & TWIP), are favourable for higher FLC.
Transactions of the Indian Institute of Metals, 2021
Hole expansion ratio (HER) is extensively used in the sheet metal forming industry to assess the ... more Hole expansion ratio (HER) is extensively used in the sheet metal forming industry to assess the sheet metal’s stretch-frangibility limit. Cold-rolled dual-phase steel (DP 590) showed planar anisotropy during the uniaxial tensile test. Hill-48 yield criterion was selected to represent the planar anisotropy of DP 590 steel sheet. Material constants i.e. anisotropic yield stress ratios of Hill-48 yield criterion were calculated from the r -values (Lankford coefficient) determined from the uniaxial tensile test. The finite element simulation result showed that the thickness reduction was maximum at 45° to rolling direction during hole expansion, and a crack was visible in the same location during hole expansion experimentation. HER of DP 590 steel and crack location were successfully predicted from the finite element model for Wire-Electrical Discharge Machine cut central hole edge in the present work.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2021
In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied e... more In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied experimentally based on the Nakajima test method. A forming limit diagram is successfully constructed using universal sheet metal forming machine by offline measuring the strains of deformed specimens. In-process strain measurement based on a digital image correlation technique is also performed for a few selected samples to compare the results with manual strain measurement techniques. All the deformed specimens are also characterized to correlate the sample geometries with hardness values and microstructure. It is observed that the hardness value gradually decreases with an increase in sample width for all the deformed specimens up to the width of 150 mm, except for full-width sample of 200 mm. Microstructural analysis reveals that the morphology of ferrite grains changes with the sample geometry in all the deformed specimens. Microstructural characterization at the top surface of the s...
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2020
Alteration of forming and failure limits due to planar anisotropy of the sheet metal significantl... more Alteration of forming and failure limits due to planar anisotropy of the sheet metal significantly affects the safe forming operation region and finally successfully manufacturing of a sheet metal formed component. This article presents the effect of planar anisotropy on uniaxial tensile properties, forming and failure limits of cold-rolled ferritic and dual-phase steels. In-situ three dimensional digital image correlation technique is used to measure the evolution of local strain components during uniaxial tensile test. For both the steels, necking limit is highest for the specimen at an orientation of 90° to rolling direction, while failure limit is highest for those specimen whose orientation is 45° to rolling direction for ferritic steel, and both 0° and 90° to rolling direction for dual-phase steel. Uniaxial tensile deformation path for ferritic steel holds lower slope than dual-phase steel as depicted in major versus minor strain plot.
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Papers by Surajit Kumar Paul