Prediction of formability for multi-linear strain paths

The prediction of formability is one of the most important tasks in sheet metal process simulation. The common criterion in industrial applications is the Forming Limit Diagram (FLD), which is standardized in ISO 12004-2. It is only applicable for linear strain paths. However, in most industrial experimental and simulation cases non-linear strain paths occur. To resolve this problem, a phenomenological approach is introduced, the so-called Generalized Forming Limit Concept (GFLC). The GFLC enables prediction of lo-calized necking on arbitrary non-linear strain paths. Furthermore, mapping multi-linear strain paths appears highly complex in practice and involves a range of testing equipment, e.g. different specimens, testing machines and tools. One possibility to overcome this extensive effort is to use a modified Nakajima specimen, which is subjected to different strain paths in consecutive stages with intermittent 3D cutting operations. Another method is offered by a modified biaxial tensile test. This principle allows testing of materials under multi-axial strain states. Conventionally the main application of the biaxial tensile test is the identification of the yield loci in the first quadrant of the stress space at low strain values. Since the achievable strain in the specimen center of the common cruciform samples is limited, an optimization of the specimen geometry was performed to allow determining forming limits of metal under multi-axial strain states at comparable strain levels to the conventional Nakajima samples.     «

The prediction of formability is one of the most important tasks in sheet metal process simulation. The common criterion in industrial applications is the Forming Limit Diagram (FLD), which is standardized in ISO 12004-2. It is only applicable for linear strain paths. However, in most industrial experimental and simulation cases non-linear strain paths occur. To resolve this problem, a phenomenological approach is introduced, the so-called Generalized Forming Limit Concept (GFLC). The GFLC enabl...     »