Infrared window and dome materials are classified as ceramics, which is a broad term encompassing inorganic, nonmetallic materials. Ceramics are typically brittle, stable at high temperature, and poor conductors of heat and electricity. In this chapter we discuss the mechanical behavior of brittle materials, which are somewhat different from ductile metals.
For example, Fig. 3.1 shows specimens of yttria fabricated for a test of tensile strength. Each piece was gripped at the ends and pulled apart until it broke. If these had been metal, they would have broken in the narrow section near the middle, and all failures would have occurred at nearly the same load. Instead, three of five samples broke in the thick end region, and the load at failure varied over a range of <20%. It is difficult to make meaningful measurements of tensile strength of optical ceramics with specimens similar to those in Fig. 3.1.
Online access to SPIE eBooks is limited to subscribing institutions.