Factors governing hole expansion ratio of steel sheets with smooth sheared edge

Yoon, Jae Ik; Jung, Jens; Lee, Hak Hyeon; Kim, Gyosung; Kim, Hyoung Seop

doi:10.1007/s12540-016-6346-5

Cited by 57 publications

(31 citation statements)

References 30 publications

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“…After a reduction in force of 20 N, which indicates cracking, the process was stopped. The expansion ratio of cracking diameter and pre-punched hole diameter provides information on cracking resistance [9,10]. To investigate the influence of strain hardening and the notch effect, samples with deburred cutting edges, solution annealed samples and solution annealed samples with deburred cutting edges were compared with untreated samples.…”

Section: Fig 3 Microscopic Image Of Cross-section With Distances Ofmentioning

confidence: 99%

Investigation of a partial, inductive short-time heat treatment of thin metal sheets integrated into the forming process

Clausius

Maier

2018

MATEC Web Conf.

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Flanging is a widespread method in the sheet metal working industry to connect same or different materials by forming. Especially the sealing technology makes high demands on the flanging process: a low sheet thickness of the inner eyelet is necessary for proper sealing. The outer edges of the neck rings are mostly manufactured by shear cutting. The quality of the cut surface and the level of the local strain hardening influence decisively the limit of the flanging process by possible cracking. This paper is focused on the dependencies of these factors regarding thin metal sheets of different materials with a thickness down to 100 μm. It could be shown that strain hardening has a stronger effect on the process limits compared to the notch effect of the sheet edges when using standard values for the clearance of the shear cutting tool. Furthermore, a process is investigated with a partial inductive short-time heat treatment of the most deformed edge area. Due to the low thickness of the material and low heat capacities related thereto, it is possible to integrate a recrystallization annealing as single step into the forming process. As a result, the strain hardening can be removed from the affected zone directly between two forming steps to increase the process limits.

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Section: Fig 3 Microscopic Image Of Cross-section With Distances Ofmentioning

confidence: 99%

Investigation of a partial, inductive short-time heat treatment of thin metal sheets integrated into the forming process

Clausius

Maier

2018

MATEC Web Conf.

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“…The strain behavior at the hole edge during the hole expansion test occurs similarly to the strain in the tensile test . In general, steels with lower ultimate tensile strength, higher elastic ratio, higher total elongation, higher post‐uniform elongation, lower strain hardening exponent, and higher normal anisotropy (

\overset{false¯}{r}

) show higher hole expansion ratio (HER). In addition, the crystallographic texture causes plastic anisotropy and affects the formability of steels .…”

Section: Introductionmentioning

confidence: 97%

“…The punching process shows a lower HER compared to machining and wire cutting as a result of strain hardening and formation of microvoids and microcracks at the hole edge . Microvoid nucleation occurs at the ferrite/martensite interfaces and through martensite cracking .…”

Section: Introductionmentioning

confidence: 99%

Microstructure, Crystallographic Texture, and Stretch‐Flangeability of Hot‐Rolled Multiphase Steel

Moura

Ferreira

Martins

et al. 2020

steel research int.

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The microstructure, crystallographic texture, strain hardening in the hole edge‐punched and stretch‐flangeability of hot‐rolled multiphase sheet steel is investigated by scanning electron microscopy, electron backscatter diffraction, and microhardness measurements. The results show that the strain hardening in the hole edge‐punched is not the main factor that influences the hole expansion ratio. The bainite fraction, average grain area, and kernel average misorientation distribution mean are microstructure factors that improve the hole expandability and reduce the effect of strain hardening in the hole edge‐punched on the hole expansion ratio. The crystallographic texture affects the hole expandability. The high intensity of {332}<113>α and {111}<112>α components that have higher normal anisotropy (rtrue¯) also reduces the effect of strain hardening at the hole edge‐punched. The cracks propagate through the interfaces following the banded microstructure direction at the hole edge‐punched during the punching process. The gamma distribution analysis of the kernel average misorientation distribution indicates that there are different energy transfer (β parameter) and dislocation densities due to different cooling rates.

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“…Researchers reported the presence of micro-cracks and dimples at the shear edge of the central hole. 16–19 For the same reason, researchers recently established correlation between HER and fracture toughness. 17,18,20,21…”

Section: Introductionmentioning

confidence: 99%

“…One of the prime reasons is the hole edge condition. 16–19 Central hole of the hole expansion test sample is normally prepared by punching process. Researchers reported the presence of micro-cracks and dimples at the shear edge of the central hole.…”

Section: Introductionmentioning

confidence: 99%

Fundamental aspect of stretch-flangeability of sheet metals

Paul

2018

Proceedings of the Institution of Mechanical Engineers, Part B:

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Stretch-flangeability of sheet metal is normally represented by hole expansion ratio. Hole expansion ratio cannot be determined from uniaxial tensile test though uniaxial tensile deformation occurs at the hole’s edge, because of fundamental difference in deformation and damage processes present between hole expansion test and uniaxial tensile test. It is proposed that only localized necking is observed in hole expansion test; however, diffuse necking followed by localized necking is observed in uniaxial tensile test of sheet metal. It is noticed that the hole expansion ratio is marginally higher than maximum diffuse neck strain determined from uniaxial tensile test with local strain measurement by digital image correlation technique. The absence of diffuse neck in hole expansion test with defect-free central hole (i.e. electrical discharge machined hole) results far higher hole expansion ratio than uniform elongation of the material.

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Factors governing hole expansion ratio of steel sheets with smooth sheared edge

Cited by 57 publications

References 30 publications

Investigation of a partial, inductive short-time heat treatment of thin metal sheets integrated into the forming process

Investigation of a partial, inductive short-time heat treatment of thin metal sheets integrated into the forming process

Microstructure, Crystallographic Texture, and Stretch‐Flangeability of Hot‐Rolled Multiphase Steel

Fundamental aspect of stretch-flangeability of sheet metals

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