Frictional properties
The tab Frictional Properties shows the window in which the frictional properties of the weave are calculated.
The Frictional Properties tab
1. Select boundary conditions
Select the boundary conditions: the temperature, normal pressure, and the velocity range. The velocity ranges from v_slip_min to v_slip_max and n_points determines the number of points which are taken within this range. The model will be evaluated for each velocity point in the range. For a quick calculation you can set the number of points to 3 or 5. Use more points for a smooth curve.
2. Select side
Select the side of the fabric which is in contact with the tool surface and select the slip direction. The contours of the surface of the weave are different for slip in the warp and weft direction respectively. Two unique situations can be distinguished:
3. Set limits
The model is only valid when hydrodynamic lubrication (HL) is the dominant friction type. As a rule of thumb: when the film thickness drops below the filament diameter, the friction type changes from hydrodynamic lubrication to mixed lubrication (ML) or boundary lubrication (BL). Selecting the lower limit explicitly sets the minimal film thickness to the filament diameter.
An upper bound for the model is given by the point where the stick condition no longer holds and wall slip occurs. The shear stress at which wall slip occurs depends on temperature, pressure, adhesive energy and molecular mass. Currently, only a constant maximum shear stress can be set. Setting the maximum shear stress will cut of wall shear stresses above the tau_max value.
More details on the limits can be found in the article.
4. Plot / Clear
Clicking the plot button will start the calculation. You can watch the progress of the calculation in the Matlab command window. When the calculation is done, the results will be plotted. You can remove a graph by clicking the Clear button.
5. Export
Export the data to the Matlab workspace. Select the curve and the variables you want to export.
Graph A
Graph A shows the average interface traction. It is the apparent shear stress acting on the fabric weave. Multiply this value with the area of the weave and it will give you the total friction force.
Graph B
The coefficient of friction, which is ratio of the apparent interface traction and the normal pressure. The coefficient of friction is actually not a good way to characterise hydrodynamically lubricated systems, but popular. It is better to express the frictional properties in terms of shear stresses / traction.
Graph C
The minimal film thickness predicted by the model. The minimal film thickness is the thickness of the polymer fluid film that separates the weave from the tool.
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