NUMERICAL SIMULATIONS OF UNEXPECTED PHENOMENA IN PLANE-STRAIN COMPRESSION OF MULTILAYERED BLOCKS

In the preceding work we encountered several peculiar phenomena in pla ne strain upsetting of oxide-free pure copper blocks which are set in multilayered manners without bonding. That is, the interfaces of block s under certain experimental conditions become strongly wavy, and shea r-band fracture takes place under the condition that the blocks are pr ecompressed up to an extremely high strain. Furthermore, when two tape red blocks are set in the forms of an hourglass and a barrel, the inte rface in each case remains slightly wavy. In this paper, numerical sim ulations by means of the elastic-plastic finite element method in plan e strain conditions are carried out to ascertain whether these phenome na take place by nature or due to some experimental error. The results show that in the case of 2-, 3-, and 7-layered rectangular blocks whe re Cu-H is assumed as the material, the wavy interface reappears, and that in the case of 2-layered rectangular blocks where Cu-O is assumed , the interface remains almost flat. When the n-value, which describes the work-hardening property of the material, is assumed to decrease i n proportion to the increase of equivalent strain, the interface becom es more wavy for the higher rate of the n-value's decrease. These nume rical results imply strongly that such waviness of the interfaces is d ue to a diffuse -type plastic instability. Next, in the simulations of the shear-band formation, we see that such a band appears more readil y for a lower n-value, at which extrusion of the material in the shape of a thin sheet is also observed at the bottom portion. This result s hows that such shear-band formation is due to a localized-type plastic instability. Finally, regarding the hourglass- and barrel-type specim ens designed with two tapered blocks, the interface shows smaller wavi ness as the tapering is sharper. Based on the calculations performed h ere, we conclude that the previous experimental results can be well si mulated numerically, and that, therefore, these unexpected phenomena m ay take place by nature, not due to any error in the experimental oper ation.