Biaxially curved glass with large radii—determination of strength using the coaxial double ring test

Abstract

The coaxial double ring test is used for determining the surface strength of flat glass e.g. as it is described in existing standards. The main idea of this test setup is to generate a defined area of surface tensile stress, which is uniform in all directions within the load ring. Thus, the orientation of surface flaws does not influence the test results. Furthermore, the defined area with uniform stress allows a statistical evaluation with regard to the flaw distribution and therefore a prediction for deviating area sizes is possible. For biaxially curved glass, the generation of such an area of uniform tensile stress is not easily possible in a test setup. However, for large radii of curvature and low glass thicknesses it is possible to flatten the specimen during the test and to generate an area of uniform tensile stress with increasing load. This contribution shows under which geometrical conditions the coaxial double ring test can also be used for biaxially curved glass.