Space and time effects of stress on cracking of glass

Space effect of applied stresses on cracking was investigated by examining the influence of the stress gradient around an embedded particle on the cracking and fracture of the glass. On the other hand, the effect of the stress time was investigated by studying (1) the delayed cracking and fracture after unloading and (2) the effect of loading rate on the cracking and fracture. It is discovered that particles smaller than 0.2 mm in diameter cause low risk of spontaneous breakage to tempered glass. Fracture strength but also the breakage risk increase with residual stresses on the glass surface. The results obtained from ball-on-ring tests indicate that the strength of glass would increase greatly with the loading rate, which confirmed the time dependence of the fracture in glass.