ZERODUR® - Bending strength data for mechanically loaded support structures

The request for ZERODUR® substrates enduring higher operational accelerations increases. The integrity of structures such as wobbling mirrors, elements for satellites surviving rocket launches and reticle and wafer stages in microlithography must be guaranteed with low failure probability. Their design requires statistically relevant strength data. The approach using the statistical two parameter Weibull distribution suffered from two problems. The data sets were too small to obtain distribution parameters with sufficient accuracy and also too small to decide on the validity of the model especially for the low failure probability levels that are required for reliable applications. Extrapolations to 0.1 % failure probability led to design strength so low, that higher load applications seemed to be not feasible. New data have been collected with numbers per set large enough to enable tests on the applicability of the three parameter Weibull distribution, which delivers a threshold value for breakage stresses. The data and distributions for several practically relevant surface conditions of ZERODUR will be given and consequences on the strength design of substrates will be discussed.