Fracture of Ferroelectric / Ferroelastic Ceramics

Many technologically important ceramics are ferroelastic. This includes lead zirconate titanate (PZT), which is a ferroelectric that is widely used for piezoelectric applications, and lanthanum strontium manganate (LSM), which is an electronic conductor that is used as a cathode material in solid oxide fuel cells. The objective of the proposed research is to investigate and understand the overlooked problem of fracture at notches in ferroelastic ceramics subjected to compressive loading. Ceramics are often preloaded in compression to avoid brittle failure. However, preliminary work by us has demonstrated that compression-compression loading of ferroelectric ceramics can produce fracture at surprisingly small far-field stresses. The results of this work have significant implications for the design and performance of ferroelastic ceramic components. The origin of the effect may be the relatively large strain irreversibility produced in ferroelastic ceramics and the tensile stresses that this can generate on unloading. In the case of polar materials, electric displacements at the notch may induce large local electric fields that may produce additional damage. The objective of the research is to investigate the factors that influence fracture, determine the mechanisms for fracture and crack growth and to model the problem using finite element analysis. An important outcome of the work will be an improved knowledge of good design practice for ferroelectric / ferroelastic ceramic components.