Evaluation of edge formability in high strength sheets through a fracture mechanics approach

Frómeta, David; Lara, A.; Parareda, Sergi; Casellas, Daniel

doi:10.1063/1.5112704

Cited by 17 publications

(9 citation statements)

References 9 publications

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“…QF has the highest strain levels before strain localization as well as the highest local peak strains. The levels of uniform strain are similar in F and CP, but the withstood local stains are comparatively smaller in F. This could indicate that F has local ductility issues that could be related to fracture toughness, as steels with higher fracture toughness can display higher strains at fracture [13]. Higher HER results may be possible by increasing the mean major strain before the fracture occurrence around the hole edge.…”

Section: Major Strain Distribution Along the Edgementioning

confidence: 95%

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 Along the Edgementioning

confidence: 95%

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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“…Schneider et al [11] have gathered an overview of different methods, including an approach to describe different loading scenarios in a variety of tests by strain gradient. One approach has been presented by Frometa et al [12], who showed that during edge forming, steels with greater fracture toughness create higher strain at fracture, together with a lower cutting clearance sensitivity.…”

Section: Introductionmentioning

confidence: 99%

An approach to describe edge ductility

Kesti

Folmerz

Vierelä

et al. 2022

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

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One of the challenges of utilizing advanced high-strength steels is their limited ability to withstand the forming of cut edges. Large production quantities of parts often lead to mechanical punching/shearing processes in blank preparation, providing a challenging starting point for forming processes. The most commonly used edge ductility test is the ISO 16630 hole-expansion test to describe stretch-flangeability properties. However, this method has been widely criticized for its large-scatter, unreliable results and the fact that it covers only a certain stress-strain state of cut edge forming. In addition, it does not provide enough data to be reliably used in forming simulations to predict edge failures. This paper presents an approach to create a more comprehensive way of describing overall edge ductility. Multiple edge forming test methods coupled with digital image correlation (DIC) were selected in order to investigate different edge loading scenarios in both open and closed trim line forming situations. Data regarding limiting local strain before cracking was collected for several steel grades, and results are gathered in 2D and 3D “Edge FLC”-figures. Attempts to utilize these results for simulation purposes are also presented. Results indicate that this approach can be useful to evaluate overall edge forming limits.

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“…From the works of Yoon et al [2] and Casellas et al [3] worked on the high strength steel sheets and observed that the correlation between the edge crack resistance and fracture toughness of the material. The same methodology has been further investigated for the edge formability of dual phase and complex phase steel [4][5] for their resistance to crack propagation. Such high strength steel, which is fulfill the requirements of increased ductility, high initial strain hardening rate, high strength with high formability attributes [6] is the dual phase (DP) steel.…”

Section: Introductionmentioning

confidence: 99%

Effect of the intermediate quenching on fracture toughness of ferrite-martensite dual phase steels

Sunil¹,

Rajanna²

2020

Frattura Ed Integrità Strutturale

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The main aim of the research work is to examine the fracture toughness of the dual phase steels prepared using the intermediate quenching method. The ferrite-martensite dual phase (DP) steel is produced using low carbon micro alloyed steel by the heat treatment and intercritical quenching technique using various intercritical temperatures such as 740,760,780,800 and 820oC. The samples of the produced dual phase steel are analyzed for their microstructure using optical microscope. The fracture toughness investigations for the dual phase steel have been carried out using ASTM standard testing procedure. From the results it is observed that the fine distribution and equal volume fraction of ferrite and martensite phases at 780oC. The effect of which, the A780 steel has demonstrated excellent fracture toughness which is the result of intermediate quenching technique. The fractography analysis it is clear that the ductile initiated brittle fracture is occurred which is due to the increased hard martensite phase and the increment in the stress accumulation at the ferrite which also leads to the higher elongation.

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Evaluation of edge formability in high strength sheets through a fracture mechanics approach

Cited by 17 publications

References 9 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

An approach to describe edge ductility

Effect of the intermediate quenching on fracture toughness of ferrite-martensite dual phase steels

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