Abstract
Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young’s modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.
Highlights
Research on improving the ballistic performance of ceramics is a dynamic subject, as is made necessary by the ever-increasing threat level of bullets
It is assumed that toughening of ceramics is synonymous for improved ballistic performance which has led to the widespread effort to reinforce ceramics with the aim of improving their strength and fracture toughness, and the multi-hit capability [2]-[4]
Of particular interest in toughening efforts is a synergistic combination of toughening mechanisms including microstructure design and particle or fiber reinforcement
Summary
Research on improving the ballistic performance of ceramics (including multi-hit capability) is a dynamic subject, as is made necessary by the ever-increasing threat level of bullets. Processing, characterisation and ballistic performance evaluations have highlighted the key roles of static mechanical properties and microstructure [1]. While the roles of hardness, sonic velocity, strength and density during ballistic events are relatively well understood, the relevance of fracture toughness is still unclear and controversial. It is assumed that toughening of ceramics is synonymous for improved ballistic performance which has led to the widespread effort to reinforce ceramics with the aim of improving their strength and fracture toughness, and the multi-hit capability [2]-[4]. The multi-hit capability is shown to be a function of crack resistance that significantly affects the fragmentation process during ballistic impact on ceramics [5]. Of particular interest in toughening efforts is a synergistic combination of toughening mechanisms including microstructure design and particle or fiber reinforcement
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