Characterisation and Properties Improvement of Armour Ceramics

Title: Characterisation and Properties Improvement of Armour Ceramics
Authors: Fakolujo, Olaniyi Samuel
Date: 2016
Abstract: As firearms continuously become more sophisticated, there have been commensurate efforts to optimize the ballistic performance of armours, with ceramic materials currently at the forefront of such studies. These efforts have focused on improving processing and microstructural design with reinforcements using dispersion particles, carbon nanotubes (CNT) and boron nitride nanotubes (BNNT). In most studies, ballistic testing has been used to identify parameters affecting the performance. The research documented here focuses on: (1) the investigation of two commercial ceramics, namely silicon carbide (SiC) and zirconia toughened alumina (ZTA). The primary material properties evaluated for the characterization included: hardness, fracture toughness, flexural strength and Young’s modulus. Other properties investigated included the microstructure, porosity/density, and mode of failure or fracture. (2) Ballistic depth of penetration (DOP) testing for six candidate ceramic armour systems including three monolithic ceramics (Al2O3, SiC and B4C) and three nanotube toughened ceramic composites (Al2O3-BNNT, Al2O3-single walled CNT and SiC-BNNT). SiC showed a hardness of 2413 HV, which is far beyond the requirements for armour ceramic. In contrast, ZTA barely met the hardness requirement of 1500 HV, but showed improved toughness of 4.90 MPa m1/2 beyond values reported for monolithic alumina. SiC and ZTA showed that microstructural design improves fracture toughness but processing introduces defects that can substantially reduce other armour related properties such as the strength. The results of the Charpy and drop tower impact tests are in agreement with indentation fracture toughness results suggesting a great degree of reliability of this cost efficient method. The addition of nanotubes produced an increase in toughness and a decrease in hardness in the ceramics, which resulted in an overall drop in performance during ballistic depth of penetration (DOP) tests. A microstructure-quasi-static mechanical properties-ballistic performance relationship was established which led to the development of a novel ballistic performance index and a new DOP model. The proposed ballistic performance index yielded a ranking, which agrees better with experimental observations than the currently published indices. The developed semi-empirical model suggests that the ballistic performance of ceramics is improved with increased fracture toughness, reduced flaw size and higher density.
CollectionThèses, 2011 - // Theses, 2011 -