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This report documents the experimental investigation of wave and fracture phenomena in monocrystalline sapphire. This research includes comparisons with glass and complements the Ernst Mach Institut investigation of ceramics and glasses that was published subsequently in ARL-CR-214, 'Experimental Investigations of Wave and Fracture Phenomena in Impacted Ceramics and Glasses'. A detailed discussion of wave phenomena and fracture phenomena is included, as well as a discussion of an electric emission method for wave and fracture detection. The work was made possible by the state of the art, high speed photographic capability available at the Ernst Mach Institut, specifically two 24-spark Cranz Shradin cameras, which can be used both in transmission and reflectance. Sapphire tiles were impacted by both spherical and flat projectiles and the generation of pressure waves and disintegration effects were observed. Twenty four high quality photographic images could be obtained at predetermined time intervals of less than 1 microsecond.

Ceramic/GRP (Glass Reinforced Plastic) composite targets were inspected by hemispheric alloy projectiles (L= 55 mm, D = 17 mm, m = 214 g) at velocities of about 1000 m/s. The impact velocities were chosen close to the balisitic limit of this projectile-target combination, which was determined from parametric tests conducted by the U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, USA. The GRP laminates were S-2 Glass/Polyester fabricated by Simula, Inc. of Phoenix, Arizona, USA. Simula also glued the ceramic tiles to the S-2 glass using standard assembly techniques to maintain a consistent bond-interface thickness. The ceramic used in these tests was sintered AD995 alumina produced by Coors Ceramic of Golden, Colorado, USA. The 152-mm-x 152-mm- and 40-mm-thick ceramic tiles were confined in a steel frame and glued to the 40-mm-thick GRP panels. The GRP panels were in two sizes: 300 mm x 300 mm or 600 mm x 600 mm square. The dynamic bulging of the GRP panels during penetration was observed by means of two Cranz-Schardin high-speed cameras in side view and top view simultaneously. Distance-time curves of the bulging of the GRP panels are derived from the camera recordings for both panel sizes, and the damage of the targets is described.

Ceramic/GRP composite targets were impacted by hemispherically nosed tungsten alloy projectiles (L = 55 mm, D = 17 mm, m = 214 g) at velocities of about 1000 m/s. The impact velocities were chosen close to the ballistic limit of this projectile-target combination which was determined from parametric tests conducted by the U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, USA. The GRP (Glass Reinforced Plastic) laminates were S-2 Glass/Polyester fabricated by Simula Incorporated of Phoenix, Arizona, USA. Simula also glued the ceramic tiles to the S-2 glass using standard assembly techniques to maintain a consistent bond-interface thickness. The ceramic used in these tests was sintered AD995 Al203 ceramics which is nominally 99.5 % pure, produced by Coors Ceramic of Golden, Colorado, USA, under the tradename "CAP-3". The tiles of the dimensions 152 mm x 152 mm and 40 mm thickness were confined in a steel frame and glued to the GRP panels of 40 mm thickness and sizes of either 12" x 12" or 24" x 24" square. (MM)

Four types of glass which differ in their chemical composition, hardness and material density and tiles of SiC, TiB2, and Al203 were impacted edge-on with blunt steel projectiles at striking velocities between 20 m/s and 1000 m/s. The propagation of shock waves and primary and secondary cracks and crack systems and the growing of crack systems from nucleated centers were visualized by means of a Cranz-Schardin high-speed camera within the first 20 microseconds before the projectile penetrated the target more than a few millimeters. The concept of damage velocity was introduced to describe the different damage processes quantitatively. All four types of glass revealed a similar behavior. The damage velocity equaled terminal crack velocity at low loadings, rose to transversal wave velocity when nucleation occurred and approached longitudinal wave velocity with very high loadings. Unlike glass, the ceramics generated different types of cracks, and different fracture velocities were observed at one impact velocity in one specimen. One had to distinguish between the velocity of continuously growing cracks, including the secondary cracks with sharp edges, fuzzy crack traces and crack fronts. In each of the ceramics, the damage velocity increased with increasing striking velocity and approached the longitudinal wave velocity at high loadings. A terminal crack velocity was found for one type of fracture in SiC. Ceramographical investigations of TiB2 fragments have shown that cracks within large grains as well as intercrystalline cracks are generated by coalescence of voids. jg

Four types of glass which differ in their chemical composition, hardness and material density and tiles of SiC, TiB2, and Al2O3 were impacted edge-on with blunt steel projectiles at striking velocities between 20 m/s and 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 visualized by means of a Cranz-Schardin high-speed camera within the first twenty microseconds, before the projectile penetrated the target more than a few millimeters. The concept of damage velocity was introduced to describe the different damage processes quantitatively. All four types of glass reveal a similar behavior. The damage velocity equals terminal crack velocity at low loadings. Other than in glass, in the ceramics different types of cracks are generated and different fracture velocities were observed at one impact velocity of continuously growing cracks, including the secondary cracks with sharp edges, fuzzy crack traces and crack fronts. In each of the ceramics the damage velocity increases with increasing striking velocity and approaches the longitudinal wave velocity at high loadings. A terminal crack velocity was found for one type of fracture in SiC. Ceramographical investigations of TiB2 fragments have shown that cracks within large grains as well as intercrystalline cracks are generated by coalescence of voids.

Experiments have been performed to investigate the fracture behaviour of pressure wave loaded alumina tiles. The waves were produced by impacting steel projectiles at a speed range between 100 and 1200m/s. The investigation of the damage generation phase was made possible by a newly developed special loading and observation arrangement. The tiles were impacted edge on and observed was one of the large surfaces by a photographic high speed technique in combination with the shadow optical method. The aim was to observe the fracture appearance and, based on this, to understand energy absorbing processes. The results were compared with those of earlier experiments with glass slabs. It was found that alumina behaves quite different than glass. From a fracture mechanics point of view it was most surprising that no distinct terminal crack velocity could be found as was expected and was experienced with glass. Keywords: Alumina; High speed photography; Shadow optical method; Terminal crack velocity; Specific wave energy; Energy absorption mechanism; Crack nucleation; Fractography.

A H. C. L. Senfio Advocato Qvondam Immatricvlato, Vorlageform des Erscheinungsvermerks: Lipsiae Impensis Car. Franc. Koehleri. 1796.

A H. C. L. Senfio Advocato Qvondam Immatricvlato, Vorlageform des Erscheinungsvermerks: Lipsiae Impensis Car. Franc. Koehleri. 1796.