In this work, the influence of non-proportional strain paths as well as a change in the loading direction on three sheet metal materials is investigated. By applying a wide range of interdisciplinary measuring methods, from the macroscopic to the microscopic world, the reason for the material behaviour is analysed. In order to still be able to predict failure after such complex strain paths, a phenomenological approach based on the Generalised Forming Limit Concept (GFLC) is developed and validated using an actual component.