The area of contact between a small sphere and a flat surface

Abstract

Abstract Measurements have been made of the area of contact between a small sphere and a flat surface under load. The spheres were of steel or tungsten carbide, 1 mm in diameter. The fiat specimens were of fused silica, soda-lime glass and sapphire. The loads ranged from 5 to 900 g. With a steel ball on soda lime glass, good agreement was obtained between measured values and those calculated by Hertzian theory. However, for fused silica and sapphire the measured radii were significantly larger than the calulated radii. The contact radius was also measured on fused silica at much higher loads, corresponding to the first appearance of a ring crack. In many eases the crack appeared at the edge of the contact area, which was again larger than the calculated area. Discrepancies between these results and some previous work are discussed.