Method of testing brittle materials such as glasses and sitals under conditions of biaxial compression

Abstract

1. We have created a new method of studying the deformation and rupture resistance of commercial glasses and sitals under conditions of biaxial compression (largely eliminating the effect of high contact stresses on the resultant strength and elasticity characteristics) by gluing the ends of the samples into depressions in the metallic bearings with self-hardening compositions; this procedure also enables us to make a valid estimate of the effects of other factors, such as various boundary conditions, the presence of apertures, glued joints, sharp edges and chamfers, mechanical damage, and the etching (pickling) of the lateral surface on the technical strength of brittle materials. 2. We have found that reliable data regarding the strength of glasses and sitals may be obtained more consistently by using fairly rigid loading devices, preserving the initial contour conditions over the whole range of sample loading, and eliminating possible damage attributable to loss of stability. 3. We have established that elastic compressive strains in glasses and sitals amounting to at least 2.5% may be measured reliably by means of paper-based strain-gage sensors glued to the fire-polished lateral surface by means of epoxy resin heat-treated at 150°C for 7 h and containing (wt. %): epoxy resin ED-6 74, dibutylphthalate 14.8, and polyethylene polyamine 11.2. 4. Using the method so developed, we have obtained fresh data regarding the strength of sheet glass subject to linear and plane compression, which, being comparable quantities, may correspond to the first theory of strength or the Mohr criterion. 5. Under conditions of axial and biaxial compression over the whole range of loads studied (right up to the rupture point), sheet glass constitutes an elastic material with a rectilinear stress-strain diagram.