MODELING CENTRAL BURSTING IN THE EXTRUSION OF PARTICULATE-REINFORCED METAL-MATRIX COMPOSITE-MATERIALS

Elastic-viscoplastic damage constitutive equations for particulate rei nforced metal matrix composite (MMC) materials have been used to inves tigate central burst formation in extrusion. The equations have been i mplemented into finite-element software with which extrusion processes for a range of area reductions and volume fractions of particulate re inforcement have been simulated. The analyses carried out have enabled an extrusion limit diagram to be established for a particle reinforce d aluminium matrix composite. The results show that for volume fractio n of reinforcement up to approximately 20%, the influence of the volum e fraction of particle on central bursting is small compared with the process parameters area reduction and semi-cone die angle. Hence, the method of selection of process parameters to avoid central bursting in MMC materials is likely to be the same as that for monolithic materia ls. The results show that with increasing volume fraction of reinforce ment, significant changes in the patterns of damage evolution occur, w ith increasing volume fraction leading to the development of damage in the central region of the extrudate that does not exist for lower vol ume fractions. However, increasing the volume fraction of reinforcemen t tends to decrease the Level of surface damage developing within the extrudate. (C) 1997 Elsevier Science Ltd.