Abstract
Contact strength tests were carried out in soda lime glass plate with a small ceramic sphere. As the ring crack initiation stress changes with increasing the contact angle, the peculiar tensile strength of glass is not applicable as the criterion of initiation strength. Initiation strength including steep stress distribution was discussed from the viewpoint of fracture mechanics. Stress inclination changes with increasing the contact angle. Crack lengths which cause the ring crack initiation are extremely short and a submicron order. The ring crack occurs also even at a position away from the contact circle because stress level is high. Arranging the phenomenon by the stress intensity factor, the ring crack was caused in the fracture toughness value of glass. Therefore, the application of the stress intensity factor is appropriate as the evaluation parameter of the ring crack initiation. Furthermore, a probabilistic evaluation equation can be expressed using stress intensity factor and Weibull modulus in which a contact angle and an effective volume are considered.
