The fracture behavior of PZT specimens driven at their resonant frequency by the application of an ac voltage was investigated and compared with fracture behavior of monotonically loaded PZT. Microcracking was observed in the cyclically loaded specimens; above 150"C, the microcracks were dispersed in small clusters, while at T 5 86"C, microcracks were generated in a densely populated region near the failure site (indentation). Macrocrack growth also demonstrated a temperature dependence, with crack growth occurring at T > 150°C but not at T 5 86°C.
Indentation/crack length measurements were used to determine hardness and fracture toughness in twinned and detwinned single crystals of YBa2Cu3O6+δ (YBCO). Hardness was found to be isotropic and unaffected by twin boundaries or moisture; the average hardness value was 9.5 GPa. Fracture toughness (Kc) was determined to be anisotropic with the average value for cracks running perpendicular to the basal plane being approximately twice that of cracks parallel to the basal plane; thus, cleavage is easier along basal planes. In addition, the results suggest a small but measurable anisotropy in Kc between the a and b directions. Twin boundaries were found to toughen YBCO, enhancing Kc by about 25%. Moisture promoted crack growth, degrading Kc by about 35%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.