• Title/Summary/Keyword: Hole Expansion Test

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Development of the technique for prediction of the hub-hole crack with the punching effect (펀칭 효과를 고려한 허브홀의 파단 예측기법 개발)

  • Lee J. S.;Ko Y. K.;Huh H.;Kim H. K.;Park S. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.362-365
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    • 2005
  • The hub hole is usually formed with a flanging process followed by a blanking process of a ]tole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, hole expansion tests are carried out with respect to various hole conditions to verify the hole condition effect on the hole expansion ratio. The hole of specimens is made by machining or punching. In the case of punching, two different punching clearances are used for making the hole. From the results of test, fracture mechanism of the hole expansion is explained.

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Study on Deformation Characteristics of Hole Expansion Test and Its Applicability (구멍확장시험의 변형특성 및 활용성 연구)

  • Han, S.S.;Lee, H.Y.
    • Transactions of Materials Processing
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    • v.28 no.3
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    • pp.154-158
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    • 2019
  • The hole expansion tests using conical punch, flat punch or hemispherical punch are widely used for stretch flangeability verification of HSS. In this study, we investigate the strain distribution on the shear edges of the hole expansion test using grid marking and a projector. A small crack at the edge is distributed, resulting in a large gap between the HER and the crack strain. The strain distribution at the edges is irregular due to anisotropy of sheet metal. While an edge perpendicular to the rolling direction indicate a lower strain level compared to an edge parallel to the rolling direction, edge cracks occur at the edge perpendicular to the rolling direction. To predict the manifestation of edge cracks in FE analysis, the result of the hole expansion test with a crack strain measurement may well be a better tool than FLD. In this case, the level of strain and the direction of the edge relative to the rolling direction should be well considered.

Non-linear Correlation Between Hole Edge Condition and Hole Expansion Ratio (구멍 파단면 상태와 구멍확장률 간의 비선형 상관관계 분석)

  • Jeong, B.S.;Cho, W.;Park, S.;Jung, J.;Na, H.;Han, H.N.
    • Transactions of Materials Processing
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    • v.30 no.2
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    • pp.74-82
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    • 2021
  • Stretch-flangeability, which is the ability of sheet steels to be deformed into complex shapes, is a critical formability property in automobile body parts. In this study, the center-hole for hole expansion test, which is normally used to evaluate the stretch-flangeability of sheet steels, was prepared by both punching and electrical discharge machining (EDM) methods. Hole expansion ratio (HER) of punched hole was far lower than the HER of EDM drilled hole because of damage/crack in hole-edge due to punching process. The effect of hole-edge condition on HER was quantified by mechanical, fractographic and geometric factors. Based on these factors, the empirical equation used to determine HER for various sheet steels was derived using non-linear regression.

Study on Stretch Flangeability Test Method with Straight Shear Line Specimen (직선 전단 시편을 이용한 신장 플랜지성 평가법 연구)

  • Han, S.S.;Lee, H.Y.
    • Transactions of Materials Processing
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    • v.31 no.1
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    • pp.23-28
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    • 2022
  • Although the hole expansion test is currently the most commonly used method to evaluate the stretch flangeability of HSS, it has been criticized due to its poor repeatability and reproducibility for test results. This paper focuses on the development of a new measurement method to investigate the stretch flangeability of HSS. Two materials (DP590, DP980) were investigated with a hole expansion test and a developed test method. Test results showed that the developed test method could be used as one stretch flangeability test to help identify relevant parameters of the shearing process to avoid edge cracking.

Development of Hole Expansion Test for Sheet Materials Using Pattern-Recognition Technique (형태 인식 기술을 이용한 판재의 홀 확장성 평가 시스템 개발)

  • Jang, Seung Hyun;Kim, Chan Il;Yang, Seung Han;Kim, Young Suk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.2
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    • pp.161-168
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    • 2013
  • Nowadays, one of the most interested area of automobile industry is the production of vehicle which has collision safety and ability to produce less amount of $CO_2$. The achievement of such a dual performance is done by choosing the materials like dual phase steel, ferrite bainite steel, etc. These steels have been used in automotive chassis and body parts, and also used to be formed by hole flanging to meet the goal of strength and design requirement. The formability of sheet material was experimented by hole expansion test and the judgement relies on human eye and his experience. This manual judgement involves many errors and large deviation. This paper develops the automatic crack recognition system which finds a crack based on CCD image to complement the problem of the current method depending on human's sense.

Effect of laser shock peening and cold expansion on fatigue performance of open hole samples

  • Rubio-Gonzalez, Carlos;Gomez-Rosas, G.;Ruiz, R.;Nait, M.;Amrouche, A.
    • Structural Engineering and Mechanics
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    • v.53 no.5
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    • pp.867-880
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    • 2015
  • Mechanical fastening is still one of the main methods used for joining components. Different techniques have been applied to reduce the effect of stress concentration of notches like fastener holes. In this work we evaluate the feasibility of combining laser shock peening (LSP) and cold expansion to improve fatigue crack initiation and propagation of open hole specimens made of 6061-T6 aluminum alloy. LSP is a new and competitive technique for strengthening metals, and like cold expansion, induces a compressive residual stress field that improves fatigue, wear and corrosion resistance. For LSP treatment, a Q-switched Nd:YAG laser with infrared radiation was used. Residual stress distribution as a function of depth was determined by the contour method. Compact tension specimens with a hole at the notch tip were subjected to LSP process and cold expansion and then tested under cyclic loading with R=0.1 generating fatigue cracks on the hole surface. Fatigue crack initiation and growth is analyzed and associated with the residual stress distribution generated by both treatments. It is observed that both methods are complementary; cold expansion increases fatigue crack initiation life, while LSP reduces fatigue crack growth rate.

Thermal Characteristics of Foams and Discharge of Fire-Protection Foam Spray Nozzle (폼 분무 노즐 방사 분포 및 폼의 열적 특성 연구)

  • Kim, Hong-Sik;Kim, Youn-Jea
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.1 s.232
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    • pp.151-158
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    • 2005
  • A characteristic of discharge for a foam spray nozzle with various parameters was investigated. The discharge patterns from a fire foam spray nozzle are important to evenly spray over a maximum possible floor area. Two parameters of a foam spray nozzle were chosen, and compared with those from the standard one. Also, in order to evaluate the performance of discharged foam agents used to protect structures from heat and fire damages, the thermal characteristics of fire-protection foams were experimentally investigated. A simple repeatable test for fire-protection foams subjected to fire radiation was developed. This test involves foam generation equipment, a fire source for heat generation, and data acquisition techniques. Results show that the bubble size of foam is increased by large inside diameter of orifice or closed air hole, but phenomenon of discharge angle and expansion ratio is opposite. For the case of the open air hole, liquid film of a circular cone discharges with formation, growth, split and fine grain. In case of the closed air hole, a pillar of foam solution discharges with that. Though the temperature gradient in the foam increases with increased foam expansion ratio. it is not change with increased intensity of heat flux.

Prediction of fracture in hub-hole expansion with a defected-edge model (결함을 가지는 모델을 이용한 허브 홀 확장에서의 파단 예측)

  • Lee Jong-Sup;Huh Hoon
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.05a
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    • pp.131-134
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    • 2004
  • The hub hole is usually formed with a stretch flanging process followed by a blanking process of a hole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, the blanked region of a hole surface is modeled by a defected-edge finite element for stretch flanging simulation. The analysis deals with the level of defect in the blanked region in order to identify the formability in the real process. The analysis provides the formability depending on the level of defect and seeks the way to match the level of defect to that of the real surface. The approach makes the analysis possible to deal with the formability of the high strength steel and predict the fracture at the hole surface during the stretch flanging simulation.

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Hydrogen Aging During Hole Expanding Tests of Galvanized High Strength Steels Investigated Using a Novel Thermal Desorption Analyzer for Small Samples

  • Melodie Mandy;Maiwenn Larnicol;Louis Bordignon;Anis Aouafi;Mihaela Teaca;Thierry Sturel
    • Corrosion Science and Technology
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    • v.23 no.2
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    • pp.145-153
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    • 2024
  • In the automotive industry, the hole expanding test is widely used to assess the formability of punched holes in sheets. This test provides a good representation of formability within the framework defined by the ISO 16630 standard. During hole expanding tests on galvanized high strength steels, a negative effect was observed when there was a delay between hole punching and expansion, as compared to performing both operations directly. This effect is believed to be caused by hydrogen aging, which occurs when hydrogen diffuses towards highly-work hardened edges. Therefore, the aim of this study is to demonstrate the migration of hydrogen towards work-hardened edges in high strength Zn-coated steel sheets using a novel Thermal Desorption Analyzer (TDA) designed for small samples. This newly-developed TDA setup allows for the quantification of local diffusible hydrogen near cut edges. With its induction heating and ability to analyze Zn-coated samples while reducing artifacts, this setup offers flexible heat cycles. Through this method, a hydrogen gradient is observed over short distances in shear-cut galvanized steel sheets after a certain period of time following punching.

Forming Characteristics of Laser Welded Tailored Blanks II : Stretch Flange Forming Characteristics (레이저 용접 테일러드 블랭크의 기본 성형특성 II : 신장플랜지 성형특성)

  • Park, Gi-Cheol;Han, Su-Sik;Kim, Gwang-Seon;Gwon, O-Jun
    • Transactions of Materials Processing
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    • v.7 no.1
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    • pp.36-48
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    • 1998
  • In order to analyze the stretch flange forming characteristics of tailored blanks. laser welded blanks of different thickness and strength combinations were prepared and hole expansion tests were done. The stretch flange formability of laser welded blanks was reduced as increasing the deformation restraining force($strength{\times}thickness$) ratio between two welded sheets. Simulation of stretch forming mode deformation and comparson with experimental results showed that the stretch flange formabili-ty was influenced not only by the difference of the deformation restraining forces between two base sheets but also by the difference of the deformation restraining forces between base sheet and weld. Therefore the stretch flange formability was reduced more rapidly than tensile elongation as increas-ing the deformation restraining force ration. It was also found that simulation of stretch flange forming was more accurate when material properties of weld was given.

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