ZERODUR: bending strength datafor tensile stress loaded support structures

摘要

In the past ZERODUR® was mainly used for mirror and substrate applications, where mechanical loads were given by itsown weight. Nowadays substrates become more sophisticated and subject to higher stresses as consequences of highoperational accelerations or vibrations. The integrity of structures such as reticle and wafer stages e.g. must beguaranteed with low failure probability over their full intended life time. Their design requires statistically relevantstrength data and information.The usual way determining the design strength employs statistical Weibull distributions obtained from a set ofexperimental data extrapolating the results to low acceptable failure probability values. However, in many cases this ledto allowable stress values too low for the intended application. Moreover, the experimental basis has been found to betoo small for reliable calculations.For these reasons measurement series on the strength of ZERODUR® have been performed with different surfaceconditions employing a standardized ring-on-ring test setup. The numbers of specimens per sample have been extendedfrom about 20 to 100 or even much more. The results for surfaces ground with different diamond grain sizes D151, D64and D25 as well as for etched surfaces are presented in this paper.Glass ceramics like all glassy materials exhibit some strength reduction when being exposed to loads above a tensilestress threshold over long time periods. The strength change of ZERODUR® with time will be discussed on the basis ofknown and newly determined stress corrosion data.The results for samples with large numbers of specimens contribute new aspects to the common practice of extrapolationto low failure probability, since they provide evidence for the existence of minimum strength values depending on thestructures surface conditions. For ground surfaces the evidence for minimum strength values is quite obvious. For etchedsurfaces minimum values are to be expected also. However, here closer observation is still needed. The systematicdeviations from Weibull distributions lie below about 5 % failure probability and thus could not be seen in small samplesas they were common in the past.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.