SQUEEZE-FLOW OF A HERSCHEL-BULKLEY FLUID

Squeeze-flow experiments of a Herschel-Bulkley material between two ri gid plates, investigated both experimentally and computationally by Ad ams et al. (J. Non-Newtonian Fluid Mech. 71 (1997) 41) are compared ag ainst an approximate analysis for generalised Newtonian fluids present ed by Sherwood and Durban (J. Non-Newtonian Fluid Mech. 62 (1996) 35), for the case in which the interface between the material and the plat es is lubricated. The analysis presented here assumes a rigid-viscopla stic material, rather than the elastic-viscoplastic material of Adams et al., but the viscoplastic model for how is identical. However, the shear stress boundary condition at the plates differs from the Coulomb friction law of Adams et al.: the shear stress is here assumed to be a constant fraction of the effective stress land consequently turns ou t to be independent of position). A simple expression for the total fo rce required to push the plates together is obtained for the case when friction at the plates is small. Agreement between this expression an d the experimentally-measured force is good at high strain, though the elastic deformation observed prior to yield is not captured by the ri gid-viscoplastic analysis. (C) 1998 Elsevier Science B.V. All rights r eserved.