A comparison of strain gradient and conventional plasticity theories and their application to surface texturing

Abstract

<p>There have been considerable requirements for improved products of sheet metal in automobile industry. A quick and economical route to new products is to design novel surface textures of varying scales for improved product enhancement in better optical appearance and formability. The critical deformation in the surface texturing is on the order of only a few microns, and can not be accurately predicted by the classical plasticity due to the size effect. The theory of strain gradient plasticity has been developed to capture the size effect based on the concept of geometrically necessary dislocations (GNDs). A selected strain gradient theory has been implemented into the finite element (FE) model to simulate the surface texturing process. A 3D FE model was developed to simulate the rolling process of sheet metal which has band-type feature on the original surface. The numerical results show that a textured roller can efficiently modify the band-type feature without changing the whole mechanical property of the sheet. Size effect has significant contribution to the magnitude of the rolling force. A FE model was developed to simulate the tensile test of the sheet with textured surface. A textured surface of the sheet is prepared through the indention on the sheet surface. The results show that the textured surface becomes harder due to the strain gradient effect, and finally improves the formability of the sheet.</p>