The ballistic failure mechanisms and sequence in semi-infinite supported alumina tiles
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The ballistic failure mechanisms and sequence in semi-infinite supported alumina tiles Dov Sherman and D. G. Brandon Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel (Received 1 July 1996; accepted 27 January 1997)
The basic ballistic failure mechanisms and their sequence occurring in dense alumina tiles during projectile penetration were investigated. The alumina tiles were supported by semi-infinite support blocks made of three different materials. Initially, a drop-weight test (DWT) was used to gain an insight into the damage mechanisms and sequence during quasi-static impact conditions. The quasi-static damage mechanisms were compared with the damage obtained in 0.3 cal. armor-piercing tests (APT). The DWT’s results suggested the following sequence of quasi-static failure mechanisms: Radial tensile cracks, associated with the low tensile strength of the ceramic formed initially, as a result of the bending induced by local deformation at the opposing surface. Subsequently, a shear-dominated cone crack propagated from the edge of the contact zone. If sufficient energy was available, crushing of the material beneath the contact zone developed during the final stages of failure. It is shown that these so-called “quasi-static” damage mechanisms, identified from the DWT’s, also corresponded to the damage mechanisms and sequence during APT’s.
I. INTRODUCTION
Monolithic ceramics have been evaluated for their ballistic performance and the results have led to a well-established understanding of the requirements for ceramic armor.1–3 The failure mechanisms occurring during projectile penetration are diverse and include deflection of the projectile, erosion of the projectile and target,4–6 shock-wave propagation and reflection,4,7 as well as crack initiation and coalescence.8–11 These mechanisms may also be affected by the rigidity and inertia of the armor module,4 the constraints introduced by the mounting system, and the design of the backing layer.4 Each mechanism may play a role in determining the minimum weight of armor required to defeat a given threat. As the kinetic energy of the projectile is absorbed during the penetration process, some mechanisms will become ineffective while others become important. Mechanisms that are critical for one threat may be unimportant or absent in the defeat of a different threat. The damage resulting from standard projectile impacts on a brittle target has been studied over a period of at least 20 years. More basic studies have used spherical (ball-bearing) projectiles,12–14 planar impact configurations, or Hopkinson bar tests.15 The results of all these tests are consistent, at least as far as projectile impact on a brittle target is concerned, and they correspond to the three phenomena of cracking, crushing, and erosion. An important parameter determining damage mechanisms during projectile penetration is the projectile J. Mater. Res., Vol. 12, No. 5, May 1997
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