While the Erichsen cupping test was originally developed to measure the stretch-form capability of metal sheets, any coating applied onto the sheet's surface experiences the same strains as its substrate. With that, the Erichsen cupping test has now also become a standard method used to assess the formability, ductility and adhesion of coatings. The coated test sheet is clamped between a sheet holder and a die, and then formed with a hardened ball punch. The ball punch continues its trajectory through the coated sheet at a specified speed until a fine, continuous crack appears in the sheet. Both the coating and the sheet are then examined for behavior and degree of defect.
