Uniaxial Tensile Strength and Flaw Characterization of SiC-N

Abstract : Large blocks (10.8 29.4 39 cm3) of SiC-N composition were manufactured by BAE Systems (now CoorsTek Vista Operations) using their proprietary pressure-aided densification process. Quasi-static tensile strength was determined using cylindrical uniaxial tension specimens oriented either parallel or perpendicular to the densification direction. Fractography, using a combination of optical and scanning electron microscopy, identified three critical flaw populations: machining damage, agglomerates, and inclusions. The material exhibited a low Weibull modulus and characteristic strength compared to historical data. Two tensile specimen sizes were employed for strength-size scaling analysis yielding strength data as a function of effective volume. Strength-size scaling analysis, though performed, was hampered by the low Weibull modulus and the presence of multiple flaw populations. SiC-N is a common ceramic armor material used in the protection of military ground vehicles (1). Ceramic vehicle armor is usually comprised of an array of square or hexagonal tiles built into a composite armor package. These packages are composed of a series of encapsulated ceramic inserts mounted on a backing material (2). The size and thickness of the embedded ceramic tiles depend upon the specific armor application, but scientific study has been largely limited to tiles less than 40 mm thick, especially versus small caliber threats (1, 3, 4). Research and production of ceramic tiles for the protection of both vehicles and personnel is being actively pursued by several companies in the United States and around the world (5).