A numerical approach to evaluate roughness effects on localization and damage in sheet materials

In dualphase steels damage initiation can be triggered by interface debonding between ferrite and ferrite or ferrite and martensite, by martensite breaking, or by strain localization in the ferritic matrix. The roughness of sheet materials strongly influences the damage initiation and accumulation of dualphase steel, because roughness provokes local strain concentrations which accelerate the evolution of ductile damage. The presented study quantifies the effect of surface roughness on strain localization and ductile damage evolution in a numerical simulation framework established on different scales. On the macro-scale, an uncoupled phenomenological ductile damage mechanics model is applied to ductile material failure. On the microscale, sub-models are investigated that contain information on surface roughness profiles. Two different conditions are investigated: i.) samples that have been only grinded, ii.) samples that have been grinded and polished. In both cases, the surface roughness is characterized by white light confocal microscopy, and the raw data of these experimental measurements are used as input data for a numerical algorithm that reproduces surfaces with the same statistical roughness profiles. The numerical studies reveal the pronounced influence of surface roughness on material resistance against ductile failure.