Vergleich biaxialer Versuchsmethoden zur Festigkeitsmessung von Keramiken
Research output: Thesis › Master's Thesis
Strength determination is an essential tool to successfully develop and improve ceramic materials. In many cases, samples are available as thin discs or plates. In those cases, biaxial testing offers the opportunity to test these samples without any further preparation. Common biaxial testing methods include the Ball-on-Three-Balls-Test (B3B), the Piston-on-Three-Balls-Test (P3B) and the Ring-on-Ring-Test (RoR). For this thesis, such tests were conducted on alumina discs as well as square LTCC-plates and compared using Weibull-Theory. The influence of various inter-mediate layers (Teflon, rubber), which are recommended to reduce friction, was evaluated. To support these findings, Finite-Element-Analysis was conducted on alumina discs tested by the RoR-method to analyse the effects of possible deviations from ideal conditions. More specifically, the influence of friction between sample and fixture as well as the effects of an inhomogeneous load distribution on the maxi-mum stress were investigated. The experiments demonstrated that it is possible to measure corresponding strength values with all three testing methods. To properly asses the strength using the RoR-test, intermediate layers have to be used. Teflon-foils are better suited for low fracture forces, whereas rubber is recommended for high fracture forces due to Teflon-foils starting to rupture under high loads. If no intermediate layer is used, the materials strength will be underestimated. Finite-Element-calculations show that this effect cannot be explained by the influence of friction and is rather caused by an inhomogeneous load distribution along the load-ring circumference.