Each wheel rolling would lead to slip of the metal microstructure, and the accumulation of microstructure slip formed the plastic flow layer. The thickness of the plastic deformation layer could represent the wear degree of the material surface.
The hardness of the material with lower hardness increased greatly after the rolling test, and the plastic deformation was obvious near the wear surface with a thicker plastic flow layer. Experimental studies show that the change rate of hardness before and after the test determined the plastic deformation of the material.
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If the thickness of the laminar flow layer is ([h.sub.L]), then the annulus in which the fluid flows can be divided into upper and lower parts.
A new expression for the thickness of laminar flow layer may be developed from this study.
However, it appears that the central flow velocity is higher when no die is fitted, this being assessed by examining the displacement of the central flow layer. The poor condition of the sample prepared without a die results from effects arising on vulcanization, the pressure exerted during the process being low.
In addition, it was also observed that as extrusion proceeded, owing to the folding effect generated by the flow across the face of the piston, the number of the flow layers moving into the capillary increased, the thickness of the individual flow layers becoming thinner, except for the central flow, owing to the relatively high velocity of the flow at the barrel centre.
where [V.sub.r] = d(V(z))/dz d is relative velocity of flow layers
, [E.sub.0] is initial energy.
These streamlines will never cross, meaning that there is no interchange of fluid elements among the outer and inner recirculating flow layers. If three particles are put in the positions of the a, b and c streamlines respectively, their trajectories are shown as in the same Figure.
Theoretically speaking, if the orientation of the hole is along the flow direction, the interchanged quantity is greatest, but in different recirculating flow layers, the flow direction and velocities of fluid elements in the mixing section are not in agreement, as illustrated by the trajectories of three particles at the left side of Fig.
The volumes of the flow layers
in the barrel were determined by measuring directly the XY coordinates of the inner and outer surfaces of the individual layers from the specimens produced in the rheometer.