Hydroforming of thick walled tubes Process description, simulation concept and advanced failure criteria

Hydroforming is an appropriate process to produce thick walled parts like T-pieces, elbows and reducers. For the production of these parts it is very important to have a reliable and easy to handle virtual tool to predict forming results. Standard methods for the simulation of hydro formed parts base upon processes using a shell element formulation and implement a forming limit curve (FLC) for crack prediction. But the forming limit curve is limited to the case of linear strain paths. The initial FLC is no longer valid in the case of nonlinear strain paths. Because of the geometric specifications of the investigated parts – thick walls, compact dimensions, high strains – and the known limitations of the forming limit curve – which don´t accord to the hydro forming process – these standard simulation methods are not applicable for the present investigations. A new approach to simulate thick walled hydro formed parts is the use of a volume element formulation in combination with a more complex failure criterion, which gives information about the risk of ductile normal fracture and ductile shear fractures with nonlinear strain paths.