Limits of Deformability in Hot Forming

Gernot Trattnig

Research output: ThesisDoctoral Thesis


The failure of metal components during industrial forming processes, due to the generation of cracks or fracture is an important economic and technical problem. Typically failure occurs due to ductile fracture, via the formation of voids and their subsequent growth and coalescence through the forming process. Ductile fracture has been extensively studied, mostly with investigations devoted to failure under tensile loading. However, in the present case the dominant strains of interest during forming are compressive. Therefore this work considers the special conditions in cold and hot forming processes, the changes in stress state, forming temperature, strain rate and heat treatment. The influence of these parameters on failure was evaluated through experiments performed on austenitic steel at room temperature and on a nickel-base alloy under hot forming conditions. Finite element simulations were also performed to obtain a better understanding of the damage process in the examined specimens. Results show that a decreasing stress triaxiality ratio increases the fracture strain exponentially, this is also valid for very low stress states. Under hot forming conditions the temperature induced microstructure and the strain rate sensitivity are shown to determine the fracture behaviour. This knowledge was used to subsequently evaluate existing fracture criteria and determine their usability to describe hot forming processes.
Translated title of the contributionGrenzen der Umformbarkeit in der Warmumformung
Original languageEnglish
  • Pippan, Reinhard, Assessor A (internal)
  • Buchmayr, Bruno, Assessor B (internal)
Publication statusPublished - 2010

Bibliographical note

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  • hot forming cold forming deformability stress state stress triaxiality ratio predamage fracture criteria damage criteria

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