1970 Volume 27 Issue 304 Pages 505-518
Sliding tests were carried out on noncrystalline polycarbonate plates by dragging the nickel-coated steel spheres or cones across the surface. The force of friction and the width of the track were measured, and the contributions of the deformation around the groove and the orientation of the molecular chains in the neigbourhood of the groove to the friction resistance were estimated.
In the range of the load R between 0.1 and 200g, it was found that the friction F obeyed the relation of the type, F=αRn, and the cross-sectional area of plowing A obeyed the law, A=βRm.
Whereas the results for glass surface accorded with the theory of adhesion in plastic contact were n=1, in the same range of load, the results for polycarbonate plates deviated from the theory and the observed values of exponent n and m did not remain constant but varied as follows:
(1) When the spherical pieces of larger radius were slided more quickly (10mm/min) with loads from 0.1 to about 10g at room temperature, the adhesion terms in the elastic contact was effective, that is, n=0.7.
(2) When the spherical pieces of smaller radius were slided either quickly with heavy loads (10 to 200g) or slowly (1mm/min) with light loads (0.1 to 10g), the elastic plowing terms were predominant for the friction force and the exponent n becomes 1. For sharp-edged cone sliders similar results were obtained under light loads (0.1 to 2g) regardless of sliding speeds: that is, n=0.7 in agreemant with the theoretical values. In these cases the friction marks of track were not observed because of elastic recovery of deformation.
(3) When the small spherical pieces were slided at high temperature from 160 to 170°C, the values of n and m increased somewhat with the mechanical losses of visco-elastic hysteresis around groove: that is, n=2.5, m=1.3 at 160°C and n=4, m=1.6 at 170°C. Above 170°C, however, the friction force decreased again by the presence of plastic flow at regions of contact.
(4) When the sharp-edged cones were slided on the polycarbonate plate under the loads from 2 to 200g at room temperature, friction forces were influenced by the orientation of the molecular chains at the boundaries of groove accompanied with plastic deformation. It was found that the value of n increased more than m (=1). The degree of orientation of molecular chains which was related to the amount of displacement in the regions around the groove was estimated from extinction angles under a polarization microscope. While these orientation could not occur when slided quickly (10mm/min) with light loads (under 120g), the orientation increased to the value which would be observed in the deform strain above the yield point, when slided with heavy loads (above 120g) or slided slowly (1mm/min) with the load from 2 to 200g.
In the cases of (3) and (4), the observed values of n were larger than those of m. These results could be explained by the dependencies of yield pressure on the load and speed during plowing the polymers.
