Fracture Toughness Measurement by Micro-Scratch Tests with Conical Indenter

Micro-scratch tests of copper, polycarbonate, fused silica and soda-lime-silica glass were carried out with Rockwell C diamond indenter. It is the first time in China that scratch method is used to measure fracture toughness of materials. The results show that when the scratch depth was relatively shallow, the spherical area at the top of the indenter must be considered. And the indenter shape function was quite different when the spherical area at the top of the indenter was not considered. After considering the spherical area at the top of the indenter, the fracture toughness by the linear elastic fracture mechanics (LEFM) model is close to that by the energetic size effect law (SEL) model. The fracture toughness by LEFM is in good agreement with that by the single-edge notched beam (SENB) method and the chevron-notched beam (CNB) method or indentation fracture (IF) method. The calculation result was not good when the spherical area at the top of the indenter was not considered. When SEL model was used, the error of fracture toughness estimated by equivalent half-apex angle of projected contact area was smaller than that assessed by equivalent half-apex angle of the perimeter, which was close to that by LEFM model.