Plates of SiC, TiB 2 and AI7O3 were impacted edge-on with steel projectiles at striking velocities between 20 m/s and 1000 m/s. Fracture propagation in the specimen was visualised by means of a Cranz-Schardin camera within the first twenty microseconds. The phenomenology of damage is discussed and compared for the different types of ceramics. The velocities of single cracks and crack fronts were measured. The experiments were supplemented by ceramographical investigations of recovered fragments. Void nucleation and coalescence could be identified as the failure mechanism in impacted Til^. Résumé-Les bords de plaques de SiC, TiB 2 et AI2O3 furent soumis à l'impact de projectiles d'acier à une vitesse d'impact entre 20 m/s et 1000 m/s. La propagation des fissures dans les spécimens a été visualisée par moyen d'une caméra Cranz-Schardin pendant les premières 20 lis après l'impact. La phénoménologie des dégâts est discutée et la comparaison a été faite entre les différents types de céramique. La vitesse des fissures simples et des fronts de fissures a été mesurée. Les essays furent complémentés par l'analyse céramographique d'éclats retrouvés. La nucléation de vides et la coalescence ont pu être identifiées comme mechanismes de défaillance dans le TÏB 2 soumis à l'impact.

The conditions for crack nucleation under impact loading were investigated systematically for four glasses which differ in their chemical composition, hardness and material density. Edge-on impact experiments were carried out with blunt steel cylinders within the velocity range from 20 m/s to 1000 m/s. The propagation of shock waves, of primary and secondary cracks and crack systems and the growing of crack systems from nucleated centers were observed by means of a Cranz-Schardin camera in a shadow optical arrangement

.. "."The Research reported in this document has been made possib-..4_.e through the support and sponsorship f the UaS. Govern-"bment through its European Research Office of the U.S rmyHn optical measurinq technique in cornbir, at ion with high speed photography is provided to solve the problem of this contract, the investiqation of wave and fracture phenomena in opaque ceramic materials. Surface disturbances caused by these mechanical events will deflect reflected liqht from its ordinary direction and thus give rise for shadow patterns which carn be photographed. Specimens with the dimensions 100mm by 100mm by 10mm shall be impacted on one of the smaller surfaces by a projectile in order to generate these % events. One of the two larger surfaces has to be flat and smooth like an optical mirror for the application of the optical method. It is, therefore, a maior task within this contract and the first step of the investigation procedure, .. to develop preparation methods to achieve a reflecting surface on each specimen. It is, however, expected that different materials reouire different polishing techniques for example because of their different hardnesses. The light reflecting power will also not be sufficient for the purpose.'of high speed registration with most materials. In this_ c.1-5es it is provided, therefore, the polished surface being coated by a thin metal layer in order to increase its ref lect ivi ty. f specimen of boroncarbide rB 4 C) with the desired dimensions has been made available by rTL, Watertown, for preliminary studies. The hardness of this material, however, is very high so that special techniques have to be applied. After some trials with directly available means which did not lead to the intended results a machining program (grinding, lapping etc.) has been started using diamond tools only. Work on this is still not completed since parts of these techniques are not yet established.In parallel to this work it has also been intended to prepare specimens of alumina, for it is believed that with this material results can be obtained easier than with boroncarbide4-Attempts, however, to receive samples of a special materi from MTL have not been successful yet. Consequently, some specimens of alumina have been purchased from a German company. These are presently in the preparation phase. Also in this case these procedures have been started with grinding to get plane surfaces. Lapping and polishing will follow. ,q"i %

Abstract:The damage evolution in the transparent glass-ceramic ZERODUR, when impacted by pointed and blunt steel cylinders, was investigated in a high-speed photographic study.

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