Design and Processing of Alumina Plate Composites for Ballistic Nacre Alumina Structures
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Design and Processing of Alumina Plate Composites for Ballistic Nacre Alumina Structures A. Haynes1,2, L. Reinhardt2, C. Lim1,2 1
U.S. Army Armaments Graduate School at Picatinny Arsenal, Picatinny Arsenal, NJ, United States Armaments Engineering Analysis and Manufacturing Directorate, U.S. Army Research Development and Engineering Center, Picatinny Arsenal, NJ, United States. 2
ABSTRACT
Nacre is a hierarchical multi-composite matrix consisting of mineral plate-like structures stacked up similar to brick and mortar. When impacted with a projectile this type of structure is expected to reduce the overall shock loading into the system as well as projectile velocity as a consequence of variations in structural stiffness between the composite plates and the organic interlayers. Bio-mimicked nacre derived from alumina as the base ceramic is also shown to have increased fracture toughness over an alumina monolith. One challenge to building the nacre alumina structure is the design and processing of the composite mineral plates which should be comprised of roughly 90-95% nano-filler and 5-10% organic binder. In order for these plates to accurately mimic the nacre mineral plates they must also emulate aspect ratios on the order of 1:10 to 1:20. This paper will discuss the design and processing of nacre-alumina plates for studies into the impact behavior of nacre composites.
INTRODUCTION Ceramics offer the advantage of being lightweight with comparable strength to metals. However the inherent brittle nature of these materials deem them unsuitable in structural applications that subject them to multi-axial load states. For this there have been many attempts to overcome the brittle behavior without sacrificing strength and toughness by incorporating the ceramic into a composite matrix. One novel approach studied by researchers is the imitation of structures found in nature [1-2]. Towards this goal, the oyster shell has been studied and exploited to assess the contributions of the materials and its nacre structure for enhancing impact resistance and strength [3]. Nacre is a multi-level composite structure composed primarily of nano-grained aragonite composite plates self-assembled into a stacked structure with an organic binder. By having this layered structure, a blunting effect is observed preventing cracks from propagating easily by forcing a tortuous path. The ceramic-polymer interface provides an elasticity mismatch to limit shock propagation by forcing the crack to travel between hard and soft surfaces and interfaces. The stacked structure proves beneficial as it allows for efficient transfer of load stress, functional degradation of the shock load, dissipation of energy, and enhanced resistance to cracking in the composite [5]. Downloaded from https://www.cambridge.org/core. Cambridge University Main, on 06 Jan 2018 at 13:47:25, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2017.631
A significant challenge in imitating these structures is
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