A better sheet-formability test

Instability predictions are important in sheet-metal forming processes, one such instability being splitting failures due to localized necking. The majority of such sheet-metal industrial splitting failures occur near to the plane-strain state. Therefore, sheet-metal industries have always been looking for an “ideal” formability test which allows them to evaluate sheets for their ability to resist splitting failures under near plane-strain conditions. Several formability tests have been developed in the past but none have been very successful. Presently, a new test has been designed, constructed and used to evaluate the formability of different sheet materials. The results from this new test are compared with standard limiting-dome-height (LDH) tests and finite-element simulations. The results show that the new test is more reproducible, more closely follows the desirable plane strain path and takes roughly 1/6 of the time to perform relative to the LDH test. Strain measurements and finite-element simulations have revealed that the improvements are a result of the new test geometry, which produces a more stable and repeatable plane-strain state near to the splitting failure locations. The failure heights in the new tests were predicted using a section analysis finite-element program, SHEET-S.