Material Model Describing Cyclic Elastic-Plastic Deformation of Roller Levelling and Straightening Processes

The presented material model describes the elastic-plastic stress-strain course of cyclic tension-compression deformation with variable amplitudes. The result is a hysteresis curve. Each hysteresis curve consists at maximum of three parts. Part I starts on a linear course originating from elastic strain or elastic recovery and ends at a defined point N. When the strain runs past this point, part II then follows as a non-linear function where the superposition of a logarithmic function with a parabola proved to be in good coincidence with the real material behaviour. When the strain reaches a point T, linear hardening begins as part III. For the application of the model in practice, a file of data from special tests with cyclic tension-compression deformations is necessary. The material model can be applied as a subsystem in a roller straightening process model. It has been successfully used in practice. The detrimental residual stresses were significantly reduced as well as the straightness of the rails was improved.