A BETTER SHEET-FORMABILITY TEST

Instability predictions are important in sheet-metal forming processes , one such instability being splitting failures due to localized necki ng. The majority of such sheet-metal industrial splitting failures occ ur near to the plane-strain state. Therefore, sheet-metal industries h ave always been looking for an ''ideal'' formability test which allows them to evaluate sheets for their ability to resist splitting failure s under near plane-strain conditions. Several formability tests have b een developed in the past but none have been very successful. Presentl y, a new test has been designed, constructed and used to evaluate the formability of different sheet materials. The results from this new te st are compared with standard limiting-dome-height (LDH) tests and fin ite-element simulations. The results show that the new test is more re producible, more closely follows the desirable plane strain path and t akes roughly 1/6 of the time to perform relative to the LDH test. Stra in measurements and finite-element simulations have revealed that the improvements are a result of the new test geometry, which produces a m ore stable and repeatable plane-strain state near to the splitting fai lure locations. The failure heights in the new tests were predicted us ing a section analysis finite-element program, SHEET-S.