Evaluation of Fracture Toughness for Structural Ceramics Using SEPB Specimens (Part 2)

Effect of Residual Stress around an Indentation-Induced Crack as a Starter of Pop-in Precrack

Abstract

Fracture toughness (K_IC) of polycrystalline silicon carbide and alumina was evaluated using a single edge precracked beam (SEPB) technique. A Knoop indentation-induced microcrack was introduced into a specimen, and then a sharp pop-in precrack was followed by appling the bridge indentation method The relative precrack length (a/W) was varied by changing the indentation load (20, 30, 50kgf) and/or the width of support groove (4, 5, 6mm). The precracked specimens were fractured by three-point bending under a cross-head speed of 0.5mm/min at room temperature. K_IC values decreased with the increase in the indentation load in the range of 0.2<a/W<0.8 for silicon carbide and a/W<0.35 for alumina, respectively. The indentation load dependence on the K_IC values was discussed from the residual stress around the indentation-induced crack and the crack mouth opening displacement (CMOD) of SEPB specimens.