Ring-on-ring testing of thin, curved bi-layered materials

The bi-axial ring-on-ring test is a convenient method to determine elastic modulus and fracture strength of brittle materials in plate geometry. However, standard analytical relationships appear to be limited to flat isotropic samples with discrete ratios of thickness to loading/support ring radii. In addition to the necessity to consider residual stresses due to differences in thermal expansion for bi-layered materials, the curvature of thin components complicates the analysis of the experimental data. Experimental and finite element modeling results are presented for thin curved bi-layered materials with substrates of different elastic behavior. Basis for the analysis are experimental results obtained for solid oxide fuel cells with anode substrates in oxidized and reduced state. A testing procedure and its limits are outlined that permits to extend the use of standard analytical relationships to curved bi-layered specimens with the aim to determine the properties of the mechanically dominating support material.