Use of Crack Branching Data for Measuring Near-Surface Residual Stresses in Tempered Glass

An analytical procedure based on fracture mechanics is used to obtain the amount of residual stress in glass from measurements on the fracture surface. The technique utilizes the measurement of microcrack branching distances, known as the mirror — mist boundary, which occur at a critical crack branching stress intensity (Km) value. This procedurre shows that σArm1/2YF(θ) =σRr1/2m+Ψ0, where σA is the applied stress, rm is the microcrack branching radius, σR is the residual stress, YF (θ) is the crack‐border correction factor, and Ψ0 is a material constant based on Km. Thus, the equation is that of a straight line with the slope equal to the magnitude of the residual stress. Data for tempered glass from the literature are used to demonstrate the applicability of the technique.