Estimation of fracture toughness in ZnO ceramics from indentation crack opening displacement measurements

Crack opening displacement (COD) approach on indentation cracks has been successfully utilized in evaluating the fracture toughness of sintered ZnO samples. The study has been conducted on two varieties of sintered samples, made from commercial and ground ZnO powder, with applied loads of 9.8 and 19.6 N in a Vickers hardness tester. Crack opening profiles along the crack length have been measured by scanning electron microscopy (SEM). Fracture toughness in the ground and sintered ZnO sample has been estimated as 2.44 MPa.m(0.5) using the crack displacement data for the full length. The slightly lower toughness of 2.10-2.16 MPa.m(0.5) measured in the commercial variety of sintered ZnO has been related to the lesser plain strain modulus corresponding to lower density value. The obtained results are within 10% variation of the fracture toughness measured using indentation crack length method for the similar variety of ZnO samples. Irwin's equation validates the fracture toughness results for the near tip data, within 5 mu m from the crack tip. (C) 2019 Elsevier Ltd. All rights reserved.