On the estimation and modeling of fracture toughness in structural ceramics in a simple way

摘要

Fracture toughness testing is based primarily on millimeter-scale macro-notches, but the actual brittle fractures in structural ceramics are often associated with surface scratches, flaws or microcracks of only several dozens of microns. Here, the porous ZrB2, the dense ZrB2-SiC and the reinforced ZrB2-SiC-Graphite ceramics were taken as the experimental targets, and a nanosecond laser notching approach was used to fabricate sharp notches with various depths from 10 mu m to 3 mm. The shallow notched fracture toughness value was found to be only 60-80% of the deep notched fracture toughness. Furthermore, the fracture strength and the notch depth followed a linear relationship in double logarithmic coordinates, and the strength value reached the theoretical strength of these three ceramics when extrapolating the notch depth to atomic scale (3 angstrom). Based on this, a new prediction model of fracture toughness in ceramics was established, which agreed well with the experimental results.