Stretch flangeability of AHSS automotive grades versus cutting tool clearance, wear, angle and radial strain gradients

Larour, P.; Hinterdorfer, J.; Wagner, Leopold; Freudenthaler, J; Grünsteidl, A; Kerschbaum, Martin

doi:10.1088/1757-899x/1238/1/012041

Cited by 9 publications

(6 citation statements)

References 11 publications

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“…Based on the gradients, it can be inferred that the strains are considerably higher closer to the edge compared to the results from the first measurement section. Strain gradients close to the hole edge have been shown in simulations to be affected by the punch shape and to have proportional ratio to logarithmic hole expansion test results [5]. The major strain levels in the radial direction were generally higher in NHE specimens, the one exception being KWI F specimen.…”

Section: Major Strain Distribution Inwards From the Edgementioning

confidence: 97%

“…Flat-top punch tests have been shown to have considerably lower HER compared to the conical punch ISO test depending on the material [4,5], whereas the results of hemispherical test set-ups have been reported being closer to the values of ISO HER [2,5]. In addition to punch shape and hole edge condition, microstructure of the material is also known to have effects on the hole expansion.…”

Section: Introductionmentioning

confidence: 96%

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Strain evolution during hole expansion testing of 800 MPa tensile strength hot-rolled steels

Plosila

Kesti

Kaijalainen

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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One limitation of the standardized ISO 16630 hole expansion test is that it provides only one result: limiting hole expansion ratio (HER). In practice, steels with similar HER values can have different cut edge forming behavior due to possible differences in strain localization tendencies. Digital image correlation (DIC) strain measurement during formability testing allows more in-detail analysis of strain-state near the cut edge. In this paper, strain evolution during hole expansion testing was investigated for three 800 MPa tensile strength grade hot-rolled strip steels. The steels were selected to have differences in microstructures and anisotropies of mechanical properties. Two different hole expansion test methods with DIC strain measurement were utilized to investigate different edge loading scenarios: in-plane stretching with a flat-top punch and more out-of-plane stretching with a hemispherical punch. Test holes were prepared according to ISO 16630 standard. In order to examine strain evolution and localization during testing, strains were measured with circle-shape sections around the hole in various distances from the cut edge. Strain localization behavior was investigated in different sheet directions and the effect on the hole expansion ratio was evaluated. Results show considerable differences in the cut edge forming behavior between the investigated materials.

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Section: Major Strain Distribution Inwards From the Edgementioning

confidence: 97%

Section: Introductionmentioning

confidence: 96%

Strain evolution during hole expansion testing of 800 MPa tensile strength hot-rolled steels

Plosila

Kesti

Kaijalainen

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

View full text Add to dashboard Cite

show abstract

“…The geometry of edges can be measured with 3D microscopy [ 25 ], replica techniques with image processing [ 16 ], and panoramic images of cut edges [ 26 ]. Although these measurement methods have already been suggested, they are still used to measure only the characteristic zone length or to perform qualitative analyses.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Hole Expansion Ratio for Advanced High-Strength Steel with Image Feature Analysis of Sheared Edge

Jeong

Lee

et al. 2023

Materials

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The punching process of AHSS induces edge cracks in successive process, limiting the application of AHSS for vehicle bodies. Controlling and predicting edge quality is substantially difficult due to the large variation in edge quality, die wear induced by high strength, and the complex effect of phase distribution. To overcome this challenge, a quality prediction model that considers the variation of the entire edge should be developed. In this study, the image of the entire edge was analyzed to provide a comprehensive evaluation of its quality. Statistical features were extracted from the edge images to represent the edge quality of DP780, DP980, and MART1500 steels. Combined with punching monitoring signals, a prediction model for hole expansion ratio was developed under punch conditions of varying clearance, punch angle, and punch edge radius. It was found that the features of grayscale variation are affected by the punching conditions and are related to the double burnish and uneven burr, which degrades the edge quality. Prediction of HER was possible based on only edge image and monitoring signals, with the same performance as the prediction based solely on punching parameters and material properties. The prediction performance improved when using all the features.

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“…The strain limit of a sheared edge is usually lower than the defined by the Forming Limit Curve (FLC) for edge cracking sensitive materials [2,3]. This is due to the damage introduced in the edge during the trimming, shearing or punching process.…”

Section: Introductionmentioning

confidence: 99%

Effect of pre-strain on edge formability of high strength steels for chassis applications

Payà,

Lara,

Frómeta

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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There is a high level of uncertainty in the prediction of edge cracking during the design and manufacturing of high strength sheet metal products. Edge ductility is a complex parameter to measure since it is not an intrinsic property of the material, but it also depends on the trimming strategy/parameters that have been applied to the edge (edge preparation method, cutting/punching clearance, etc.). Furthermore, most forming processes involve more than one operation where the material can be deformed in a first stage, then trimmed or punched and further deformed in a final forming step to obtain the desired shape. Therefore, in order to design a robust and safe forming process able to predict the risk of edge cracking, it is crucial to understand the influence of pre-strain on the residual formability of trimmed edges. This paper analyses the effect of different pre-strain levels and paths (uniaxial tension, plane strain and equi-biaxial stretching) on the sheared edge ductility of a Complex Phase (CP) steel and a high strength low alloy (HSLA) steel used for automobile chassis applications. To this purpose, rectangular specimens are cut out from pre-strained samples and punched. Hole Tension Tests (HTTs) in combination with Digital Image Correlation (DIC) are carried out to determine the edge fracture strain of undeformed and pre-strained samples. The results are discussed in terms of major strains obtained from DIC. The proposed methodology allows describing the edge cracking sensitivity of high-strength steel sheets as a function of the pre-deformation state and can be useful to predict the risk of edge cracking more accurately in forming simulations.

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Stretch flangeability of AHSS automotive grades versus cutting tool clearance, wear, angle and radial strain gradients

Cited by 9 publications

References 11 publications

Strain evolution during hole expansion testing of 800 MPa tensile strength hot-rolled steels

Strain evolution during hole expansion testing of 800 MPa tensile strength hot-rolled steels

Prediction of Hole Expansion Ratio for Advanced High-Strength Steel with Image Feature Analysis of Sheared Edge

Effect of pre-strain on edge formability of high strength steels for chassis applications

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