Abstract
This paper describes a study of the shear strength S, the indentation hardness or yield pressure P and the coefficient of friction μ of polythene, P.T.F.E., Kel-F and Perspex over a temperature range from -100°C up to +80°C. In contrast to metals, the plastics show large changes in their strength properties over the temperature range used, and the confusing effect of surface films on the friction has been eliminated. According to the adhesion theory of friction μ is approximately equal to S/P. In these experiments it is found that μ varies closely with the ratio S/P, but the quantitative agreement is good only with polythene. With Perspex and Kel-F the observed values of μ are consistently larger than S/P, while with P.T.F.E. the values of μ are considerably lower. It is concluded that the adhesion theory can explain the friction behaviour of the plastics examined, the apparent discrepancies being due to the enhanced strength of the junctions under the high localized pressures existing at the interface (Perspex and Kel-F) or to structural factors which give a low intrinsic adhesion at the sliding interface (P.T.F.E.).