A slip boundary condition is derived for the flow of a viscous fluid over a solid surface, using the theory of thermal activation process. The slip velocity is proportional to the hyperbolic sine of the shear stress on the solid surface, and the slip boundary condition reduces to Navier's slip boundary condition for the flow of Newtonian fluids under small shear stresses. There exists a critical shear stress determining the onset of the slip flow.

EBSD mapping of a welding zone ((A) image of crystal orientation, (B) pole figure, (C and D) EBSD color, black-white images of the joint); variation of the thickness of the Fe₂Al₅IMC layer with the simulation time.