Abstract
In this paper, we propose a new method to estimate the hole expansion ratio (HER) using an integrated analysis system. To precisely measure the HER, three kinds of analysis methods (computer vision, punch load, and acoustic emission) were utilized to detect edge cracks during a hole expansion test. Cracks can be recognized by employing both computer vision and a punch load analysis system to determine the moment of crack initiation. However, the acoustic emission analysis system has difficulty detecting the instant of crack appearance since the magnitude of the audio signal is drowned out by noise from the press, which interrupts the differentiation of crack configuration. To enhance the accuracy for determining the HER, an integrated analysis system that combines computer vision with punch load analysis, and improves on the shortcomings of each analysis system, is newly suggested.
Highlights
Advanced high-strength steels (AHSSs) have been widely applied to body-in-white (BIW) structures for both weight reduction and crass worthiness because they exhibit higher tensile strength compared with conventional mild steels [1,2,3]
Unexpected edge fractures occur during the metal forming process due to low sheared edge cracking resistance, which prevents their use in automotive body applications [4,5]
The hole expanding process, which is defined in the ISO 16630-2009 standard, consists of punching a hole on a test specimen and using a conical punch with 60 degrees at the top which moves upward to extend through the thickness of the AHSS sheets [10]
Summary
Advanced high-strength steels (AHSSs) have been widely applied to body-in-white (BIW) structures for both weight reduction and crass worthiness because they exhibit higher tensile strength compared with conventional mild steels [1,2,3]. Unexpected edge fractures occur during the metal forming process due to low sheared edge cracking resistance, which prevents their use in automotive body applications [4,5]. Predicting edge cracks utilizing numerical simulations with a forming limit diagram is difficult since strain at the edge is less than that of the forming limit curves, which gives rise to enormous issues in manufacturing BIW structures with AHSS sheets [6,7]. To predict the edge cracks of AHSS sheets during the stamping and flanging process, hole punching and expansion tests (which are common methods to evaluate edge stretchability) are utilized in industries for estimating the quantitative amounts of edge fracture resistance [8,9]. The hole expansion ratio (HER) is an index to determine the flangeability of a material, which is calculated using the ratio of the initial inner diameter to the final inner diameter, where the final crack occurs on the sheared edge surface [11]
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