Micro-mechanical studies on the effect of the stress triaxiality and the Lode parameter on ductile damage

• Unit cell calculations have been performed covering a wide range of stress triaxialities and Lode parameters.
• Stress state dependent damage criterion is proposed.
• Stress state dependent damage rule is proposed.
• Functions depending on stress triaxiality and Lode parameter are proposed and parameters are identified.
• Numerical results from unit cell calculations and from the continuum damage model show good agreement.

The paper deals with the effect of stress state on the damage behavior of ductile metals. The continuum damage model has been generalized to take into account the effect of stress state on damage criteria as well as on evolution equations of damage strains. Different branches are considered corresponding to various damage mechanisms depending on stress intensity, stress triaxiality and the Lode parameter. Basic material parameters are identified using experiments with differently notched tension and shear specimens. To be able to get more insight in the complex damage and failure behavior additional series of three-dimensional micro-mechanical numerical analyses of void containing unit cells have been performed. These calculations cover a wide range of stress triaxialities and Lode parameters in the tension, shear and compression domains. The numerical results are used to show general trends, to develop equations for the damage criteria, to propose evolution equations of damage strains, and to identify parameters of the continuum model.