The adhesion and strength properties of ice

Abstract

This paper describes a study of the adhesion of ice to various solids. If water is frozen on to a clean metal surface the interface is stonger than the ice and fracture occurs within the ice itself. The detailed behaviour depends on the stresses developed near the interface. If tensile stresses are high the failure is brittle and the breaking stress is temperature independent. If the tensile stresses are below a critical limit the failure is ductile, and the breaking stress increases linearly as the temperature is reduced below 0°C. Ductile failure appears to be determined by the onset of a critical creep rate and the variation of breaking stress with temperature may be explained in this way. This view is supported by the observation that small quantities of dissolved salts which increase the creep rate of ice produce a parallel reduction in the adhesive strength. Surface contaminants on metals reduce the adhesion by a very large factor and it is suggested that this is due primarily to a reduction in the area over which strong metal/ice adhesion occurs. The adhesion of ice to polymeric materials differs from the adhesion to metals. The inter­facial strength appears to be less than the strength of ice and failure occurs truly at the interface. Friction experiments carried out with clean and lubricated metals and polymers sliding on ice provide a measure of the shear strength of the solid/ice interface. The results show a marked parallelism with those obtained in the adhesion experiments; this again emphasizes the close connexion between the friction and adhesion of solids. This study has some bearing on the de-icing of aircraft and of ships sailing in polar seas. The results suggest that ice layers may be removed most readily if brittle fracture can be achieved. Constraint of the ice inhibits brittle fracture and the forces to produce ductile failure are considerably greater. These forces may, however, be reduced by adding small quantities of suitable salts, since these reduce the resistance to ductile flow if the system is above the eutectic temperature. Finally, hydrophobic materials show a very low adhesion; this is particularly marked in the adhesion of ice to polytetrafluoroethylene.