Influence of Size Effect to Constitutive Model and Damage Evolution in Micro Scaled Plastic Deformation under Different Strain Rate

Abstract

In micro scaled plastic deformation, feature size effect and grain size effect will affect strain energy and fracture strain of ductile fracture. The main reason of this effect is the portion of the free grain of the surface layer increases when the specimen size increases or grain size decrease, and thus affects the flow stress. However, the influence of these two size effects to the flow stress of micro scaled plastic deformation under high strain rate is not revealed. In tandem of this, the isothermal stress-strain relationship of high strain rate is obtained via the split Hopkinson pressure bar(SHPB), and a new micro scaled constitutive model of high strain rate based on Johnson-Cook constitutive model with size factor is established. A hybrid fracture model, which combines this micro scaled constitutive model of high strain rate and Freudenthal fracture criterion, is thus proposed. In-depth understanding of the influence of these two size effects to fracture exist in plastic deformation under different strain rates is revealed, and methodology for surface improvement of ultra-precision raster fly cutting is provided.