Extended evaluation of Erichsen cupping test results by means of laser speckle

• Erichsen cupping test was used to determine the height of the cup LN-IE at the moment of localized necking.
• Information on the cup height LN-IE is a new supplementary parameter to the standard Erichsen Number IE.
• A method of localized necking detection based on the phenomenon of laser speckle was developed.
• Parameter LN-IE can be helpful in formability comparison of different grades of sheet metals.
• The differences in heights between LN-IE and IE for three different grades of sheet metals were revealed.

Erichsen cupping test has usually been used to determine the height of the cup at the moment of sheet metal fracture, defined as the Erichsen Number IE. The paper presents a proposal of using Erichsen cupping test to determine the additional parameter – the height of the cup LN-IE at the moment of localized necking in sheet metal, which usually precedes fracture of sheet metal. For this purpose, a method of localized necking detection was developed. It is based on the phenomenon of laser speckle. The results of height measurements were presented for three different grades of sheet metals used in the automotive industry: 5754 H22 aluminum alloy, DC04 deep drawing steel, and Dogal 800DP high strength steel. The differences in cup heights at the moments of localized necking (LN-IE) and fracture (IE) of the tested sheet metals were in the range of 0–8%.