THE EFFECTS OF INTERFACE CONSTRAINTS ON THE DEFORMATION OF PASTES

The numerical simulation of paste processing operations for optimising the design and operating variables is critically dependent on the accuracy of the governing equations. Within this set of equations, the constitutive relationship and wall stress boundary conditions have to be determined empirically from model deformations involving simple geometries. The paper describes a detailed examination of one such method involving the compression of cylindrical specimens between parallel rigid platens using Plasticine as a model paste. It is established that the stress-strain behaviour of this mateial can be determined to a good approximation from the pressure distribution across the faces of the specimens. However, the wall stress boundary conditions cannot be obtained reliably. The problems and limitations of the procedure investigated here are generic to altenative methods such as ram extrusion or normal hardness.