Estimation of swelling stresses from crack-terminating angles

Cracks terminating at free surfaces are affected by local stresses in the surface region. The crack front retards under residual compressive stresses compared with the crack contour in the absence of stresses. This effect had been used in [1] for identifying compression in the surface of chemically toughened and ion-exchanged soda-lime glass surfaces. In [2] the same effect was proven for swelling stresses due to the silica/water reaction. In the present report, the stresses in the surface layers are predicted based on results for soda-lime glass. For silica heattreated in humid environments, compressive stresses in the order of about -130 MPa to -170 MPa are obtained.