plastic fluid

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A fluid in which the shear force is not proportional to the shear rate (non-Newtonian) and that requires a finite shear stress to start and maintain flow. Most drilling muds are characterized as either plastic or pseudoplastic fluids.

See: Bingham plastic modelHerschel–Bulkley fluidnon-Newtonian fluidpower-law fluidpseudoplasticrheologyshear rateshear stressviscosity