Numerical study on the size effect in the ultra-thin sheet's micro-bending forming process

Size effect is the most challenging problem for the development of metal micro-forming technologies, and the urgent requirement for understanding the size effect is presented. In this paper, size effect phenomena in the ultra-thin sheet's micro-bending forming process are studied numerically based on the concept of strain-gradient plasticity. Results show that the sheet's mechanical response is strongly influenced by the sheet thickness. When the sheet's thickness is close to the material characteristic length, the deflection curve and the distributions of stress and strain are greatly different from those predicted by classical plasticity. If the sheet's thickness is considerably larger than the material characteristic length, the size effect disappears and the results tend to be the same as those predicted by classical plasticity. Hence, in the micro-forming process, the size effect should be taken into account in the selection of the technical parameters.