On edge chipping in cylindrical surfaces

Edge chipping is a basic failure mode in natural, biological and synthetic materials. This work extends earlier studies on edge chipping in orthogonal surfaces to curved ones using solid or hollowed glass cylinders. Vickers indentation is made on the cylindrical surface near a flat edge (Case 1) or on the flat section near the outer (Case 2) or inner (Case 3) cylindrical surface. This brings in a new parameter h/R, the normalized distance from edge. The evolution of damage is observed in-situ using a video camera. For Cases 1 and 2 the chip morphology and chipping load are insensitive to h/R except for Case 2 where the chip becomes narrower as h/R is increased. For Case 3 no surface breaking occurs, although the resulting internal damage may be of concern in applications to opaque materials. A simple analysis is developed which predicts well the effect of surface curvature on chip morphology. The resulting analytical relationships may be applied to such diverse fields as flint knapping, material shaping tools and fracture of mammalian teeth. An interesting aspect of edge chipping is that it facilitates easy means for quantifying fracture toughness in fragile materials. This approach is employed here to as-received silica aerogel cylinders.