Investigation of fracture toughness for a polycrystalline graphite under combined tensile-tear deformation

In the present contribution, mixed mode I/III fracture toughness of a polycrystalline graphite is studied experimentally, numerically and theoretically using a new designed test specimen. A simple disc shape specimen subjected to three-point bending named herein edge notched disc bend (ENDB), is successfully employed for fracture toughness experiments on graphite. This specimen can introduce full combination of modes I and III including pure mode I, pure mode III and complete intermediate mode mixities. Fracture toughness values (K-Ic and K-IIIc) of investigated graphite are obtained for six different mode mixities for and the obtained experimental data are compared with theoretical predictions of two conventional mixed mode fracture theories namely: maximum tangential stress (MTS) and maximum tangential strain energy density (MTSED). It has been observed that the fracture toughness results are in good agreement with the mixed mode I/III curve of MTSED criterion. Consequently, the suggested ENDB specimen can be proposed as a suitable specimen for mixed mode I/III fracture toughness study of based on graphite materials. (C) 2017 Elsevier Ltd. All rights reserved.