EXAMINATION OF A WAKE-DILATATION MODEL OF MICROCRACK TOUGHENING IN CERAMICS

An attempt was made to examine the validity of a wake-dilatation model of microcrack toughening in ceramic matrix composites. Model two-phase, particulate composite system was chosen for study. Spheroidized alumina particles with average size 25 and 12μm, respectively, were dispersed in a soda lime silica glass having thermal expansion coefficient greater than the expansion coefficient of alumina. The composite containing 25-μm alumina particles was formulated by selecting a combination of differential thermal expansion and particle size, whereby microcrack toughening is expected to occur most effectively. Another composite containing 12-μm alumina particles was designed as a reference material, in which the condition for the occurrence of microcracking is not met. For both composites, specimens containing 30vol% of alumina particles were prepared by hot-pressing technique. Fracture toughness and R-curve measurements were carried out on each of the composites. Glass-alumina(25μm) composite exhibited a rising R-curve behavior. The experimental results were interpreted on the basis of a wake-dilatation model of microcracking. By evaluating physical parameters involved in the model, its validity was discussed.