(Dr. Min Zhou, advisor)

"An Experimental Analysis of the Dynamic Failure Resistance of TiB₂/Al₂O₃ Ceramic"

Abstract

High performance ceramics are useful in a wide variety of applications, including machine tool inserts and lightweight armor.  In such applications, the ceramics are subjected to transient mechanical loading under high rates of strain. The mechanical response of materials to dynamic loading is often dramatically influenced by their microstructural characteristics, including phase size, phase morphology, composition and texture.  There is a lack of characterization for the responses of composite TiB₂/Al₂O₃ ceramics to dynamic loading conditions.  A split Hopkinson pressure bar (SHPB) apparatus is used to subject TiB₂/Al₂O₃ specimens to loading under transient stress pulses at strain rates up to 450 s-1.  The duration of the stress pulses is approximately 250 microseconds.  A time-resolved analysis of the mechanical response is carried out using high-speed digital oscilloscopes with a resolution of 500 nanoseconds.  The results are compared with existing data for quasi-static loading conditions.  The materials tested are four TiB₂/Al₂O₃ ceramics.  Each material is composed of 70% Al₂O₃ and 30% TiB₂ by weight and conforms to one of four different microstructural morphologies.  These materials allow the effects of processing and microstructural morphology on performance to be analyzed.

The experiments conducted show that the materials analyzed display a clear increase in compressive strength with increasing strain rate. Microscopic analysis revealed that failure occurred preferentially within the Al₂O₃ phase of each material.  Failure in the Al₂O₃ phase was characteristically through transgranular cleavage, while failure associated with the TiB₂ occurred through a combination of transgranular cleavage and intergranular pull-out and was clearly influenced by microstructure.