Automated hole expansion test with pneumatic crack detection

Leonhardt, André; Kräusel, Verena; Paar, Uwe

doi:10.1088/1757-899x/480/1/012026

Cited by 5 publications

(4 citation statements)

References 3 publications

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“…The test is conducted until the chosen crack detection method generates a stopping signal. The principle layout of the testing device and procedure for the HET with pneumatic crack detection is shown in [9].…”

Section: Test Setupmentioning

confidence: 99%

“…The test was stopped when the air pressure dropped by 0.0045 bar (within 5 data points). As the drop in air pressure was detected automatically using the control of the testing machine, smaller stopping values were applied compared to [9]. A decrease of the force value between 0.01 and 0.1 kN was used to stop the HET with the force drop method.…”

Section: Experimental Studiesmentioning

confidence: 99%

“…• Force measurement: Detection of force drop during crack formation [5] • Video capturing/digital image processing (DIP): Recording and evaluation of the complete test as well as crack detection by test engineer or software during or after the test [6][7] • Digital image correlation (DIC): Crack detection by evaluation of displacements and strains [8] In [9], a new crack detection method was introduced using a drop of air pressure. Instead of an open die, a closed pressure vessel was used.…”

Section: Introductionmentioning

confidence: 99%

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Validation of pneumatic crack detection in hole expansion test

Leonhardt,

Haas,

Kunke

2024

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

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According to the standard ISO 16630, the hole expansion test (HET) has to be stopped at the instant when the first through-thickness crack appears at the edge of the hole. The detection of the crack is challenging, since the maximum opening width should not exceed 0.1 mm at the inner diameter according to the newest version of the standard from 2017. A pneumatic crack detection has been introduced in which a pressure drop is used to identify the through-thickness crack. In the present paper, this method for stopping the hole expansion test is validated. It was tested for steels with different edge crack sensitivities and compared to stopping with force drop method. Therefore, the curves of pressure and force have been analysed. The influence of hole insertion method (shear cutting or abrasive water jet cutting) as well as specific hole expansion parameters (punch speed, air pressure) have been investigated. Besides the expanded diameters to evaluate the edge crack sensitivity, the opening width of the edge cracks were analysed to determine the suitability of the crack detection methods for different hole expansion ratios (HER).

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Section: Test Setupmentioning

confidence: 99%

Section: Experimental Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Validation of pneumatic crack detection in hole expansion test

Leonhardt,

Haas,

Kunke

2024

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

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“…This method may be insufficient for some materials and test conditions, as multiple microcracks may appear simultaneously, requiring additional approaches. Leonhardt et al [10] employed an automated pneumatic system to detect the crack. The authors concluded that the developed approach exhibits sufficient sensitivity to accurately determine the HER for different process parameters, e.g., cutting clearance and initial hole diameter.…”

Section: Introductionmentioning

confidence: 99%

Application of Digital Image Processing Techniques to Detect Through-Thickness Crack in Hole Expansion Test

Cruz

Amaral

Santos

et al. 2023

Metals

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Advanced high-strength steels (AHSS) have become increasingly popular in the automotive industry due to their high yield and ultimate tensile strengths, enabling the production of lighter car body structures while meeting safety standards. However, they have some setbacks compared to conventional steels, such as edge cracking through sheet thickness caused by forming components with shear-cut edges. When characterizing the formability of sheet metal materials, the hole expansion test is an industry-standard method used to evaluate the stretch-flangeability of their edges. However, accurately visualizing the first cracking is usually tricky and may be subjective, often leading to inconsistent results and low reproducibility with some impact of the operator on both direct and post-processing measurements. To address these issues, a novel digital image processing method is presented to reduce operator reliance and enhance the accuracy and efficiency of the hole expansion test results. By leveraging advanced image processing algorithms, the proposed approach detects the appearance of the first edge cracks, enabling a more precise determination of the hole expansion ratio (HER). Furthermore, it provides valuable insights into the evolution of the hole diameter, allowing for a comprehensive understanding of the material behavior during the test. The proposed method was evaluated for different materials, and the corresponding HER values were compared with the traditional method.

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