Dry sliding friction of ethylene vinyl acetate blocks: Effect of the porosity

This study is the first attempt to investigate the dry sliding friction characteristics of ethylene vinyl acetate (EVA) blocks with varying porosity (α) values. The sliding friction tests indicated that the porosity significantly influenced the friction coefficient (i.e., the friction coefficient decreased with α when α < 50% and increased with α when α > 50%). The EVA blocks with a higher porosity (α > 80%) showed larger friction coefficients than the non-porous EVA block. Contact area observations on a glass plate revealed an elastic collapse at the anterior part of the porous EVA blocks with a higher porosity. A simplified model considering the elastic collapse of porous EVA blocks via elastic buckling of the cell walls explained the effect of the porosity on the friction coefficient in terms of adhesion friction. Thus, the higher α provided larger contact areas as a result of the increase in the elastic collapse area at the anterior part of the apparent contact area, thereby resulting in high friction coefficients. These results may provide an insight into new usages of porous polymers as high friction materials.