Hertzian fracture of a borosilicate glass at room temperature and at 77 K

Hertzian fracture tests on 10 mm thick plates of Borofloat® 33 glass (Schott, Germany) have been carried out at room temperature and at 77 K using smooth tungsten carbide (WC) spheres of radii 1, 1.5, 2, 2.5, 3, 3.57, and 4 mm as indenters. Cooling of the test samples down to 77 K has had a marked effect on the Hertzian fracture loads, which are up to at least 5 times higher than the corresponding loads determined at room temperature. It is suggested that this increase in the fracture loads occurs because at 77 K there is no static fatigue of the glass. Since most of the Hertzian fracture tests from 1880s to date have been carried out under ambient conditions involving static fatigue, the results obtained are flawed and conclusions drawn from them are unreliable. Our experimental results obtained from Hertzian fracture tests at 77 K are more reliable.