Mechanical Properties of CaO–Al2O3–SiO2 Glass-Ceramics Precipitating Hexagonal CaAl2Si2O8 Crystals

Fracture behavior via a flexural test for a newly found CaO–Al2O3–SiO2 (CAS) glass-ceramic (GC) was compared with that of enstatite GC and mica GC, which are well-known GCs with high-fracture toughness and machinability, respectively. By focusing on the nonelastic load–displacement curves, CAS GC was characterized as a less brittle material similar to machinable mica GC, compared with enstatite GC, which showed higher fracture toughness, KIC. The microcrack toughening mechanism in CAS GC was supported by the nondestructive observation of microcracks around the Vickers indentation using the X-ray microcomputed tomography technique. The CAS GC also showed higher transparency than mica GC due to its low crystallinity. Moreover, the precursor glass had easy formability due to its low-liquidus temperature.

An Overall Approach for Microcrack and Inhomogeneity Toughening in Brittle Solids

ABSTRACTBased on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.

ON THE MICROMECHANICS MODELING OF MICROCRACK TOUGHENING IN CERAMIC MATERIALS

The development of advanced ceramic materials with enhanced toughness relies upon the fundamental understanding and accurate modeling of various toughening mechanisms in these materials. In this paper, a rigorous micromechanics approach is proposed to treat the microcrack toughening phenomena in ceramics. The microcracking zone is modeled as a region containing multiple discrete microcracks near the tip of a dominant crack and the main crack-microcrack interactions are studied in detail. The analysis is based upon the use of the complex potentials of Muskhelishvili and an appropriate superposition scheme. The induced stress intensity factor at the main crack is obtained in a general series form and the leading order explicit solution is utilized to investigate the associated shielding and amplification effects and to provide a quantitative analysis of the microcrack toughening. Both a stationary and a steadily growing main crack are considered and the effect of the release of residual stresses has been taken into account. The relationship between the current model and other existing ones is also discussed.