Identification of a strain-aging model accounting for Lüders behavior in a C-Mn steel

Abstract

Strain-aging constitutive models are suitable to simulate the formation and propagation of Lüders bands in complex specimens and components. The identification of the corresponding material parameters is difficult because the strain localization phenomena associated with the Lüders behavior must be taken into account. The spurious mesh dependence of standard finite element simulations of Lüders band propagation is illustrated in the present work and removed using a strain gradient plasticity model. Furthermore the gradient approach introduces a characteristic size corresponding to the finite dimension of the Lüders band front as observed from strain field measurements. The parameters are identified from the experimental measurement of the peak stress and plastic strain carried by the band for a C-Mn steel over a temperature range from −150°C to room temperature and for several strain rates. The validity of the model is tested on 3D simulations of the Lüders band propagation in a strain gradient plasticity medium.

Keywords:

• Lüders bands
• computational mechanics
• strain gradient plasticity
• strain localization
• parameter identification
• static strain aging

Acknowledgments

The authors would like to acknowledge the financial support from Electricité de France (EDF Les Renardières). Also the technical support from Willy Vincent and Christophe Sonnefraud (EDF-MMC) is greatly acknowledged for the help in performing mechanical tests and DIC. Special thanks are due to Prof. C. Berdin (University Paris-Sud) for her help and for her ideas about this work.