Delayed Fracture of Glass under Tension, Torsion and Radial Pressure

Abstract

A PLAUSIBLE explanation¹ of delayed fracture of glass is that cracks initially present in the unstressed material gradually extend when glass is loaded. As the cracks extend, the stress at the ends of the cracks increases, until it becomes equal to the maximum stress which the glass can even momentarily withstand ; catastrophic fracture then occurs. Other factors being constant, the rate of crack spreading would be expected to depend on the stress at the end of the largest and most unfavourably orientated crack. Delayed fracture in tension and torsion would therefore be expected to occur in equal times, when the glass is subjected to equal principal tensile stresses.