FEA-based development of a new tool for systematic experimental validation of nonlinear strain paths and design of test specimens

To achieve high accuracy in finite element simulation, it is beneficial to model forming limit curves (FLCs) for nonlinear strain paths, since FLCs based on linear strain paths inaccurately predict the failure of parts that undergo nonlinear strain paths. Standardized Nakajima or Marciniak tests are used to create a FLC for linear strain paths. For common strain paths, the shapes of the specimens are well-known. Only a limited set of nonlinear strain paths can be generated by using these tests. For example, a biaxial strain path can be generated, and then the test specimen can be cut to generate a uniaxial strain path. However, the other way around is not possible. Therefore, it is important to develop a new tool that can systematically investigate all kinds of nonlinear strain paths. This paper describes a newly developed deep drawing tool that exhibits these properties. Large specimens with homogeneous strain in the centre can be generated for any strain state. These specimens are sufficiently large that a second test specimen can be cut out to generate another strain path using Nakajima or Marciniak tests. The shape of blank for uniaxial, plane and biaxial strains are presented and analysed both numerically and experimentally. A nonlinear strain path consisting of a uniaxial strain path followed by a biaxial strain path is shown as an example.