The emerging technologies of smart materials and structures have found increasing applications in diverse engineering branches such as aerospace, mechanical, manufacturing and civil engineering, etc. Piezoelectric materials are ideal candidates for functional (smart) materials, and have been a primary focus of attention in the realization of smart (adaptive) structure systems. Due to the fact that piezoelectric materials are very brittle, to find better employment of piezoelectric materials depends on the better understanding of mechanical failure mechanism of piezoelectric materials. Micro-crack is one of the most commonly encountered defects leading to mechanical failure, and it plays an important part in fracture processes. During the entire fracture procedure of a crack, Zener-Stroh crack mechanism controls the initial stage of crack growth and propagation. When the micro-crack is stressed after its propagation, Griffith crack mechanism controls the crack to final fracture. Investigation on Zener-Stroh crack and Griffith crack can help to understand how a crack initiates and gradually grows and find out which cracks constitute an obvious risk for fracture and which do not.

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