Effect of strain hardening and normal anisotropy on admissible values of strain and stress in pipe-bending processes

The paper aims at discussing the effect of hardening exponent and normal anisotropy index values on admissible values of bending angle and strain in cold bending of thin- and thick-walled steel pipes. A condition of distributed instability onset was adopted as a limiting criterion for the process. The analysis reveals that higher indexes of hardening and material anisotropy result in larger values of admissible strain and bending angle. The neutral axis position corresponding to the critical instability onset is shown to be shifted toward compressed layers of the pipe. The fracture problem associated with the bending process is presented.