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 (KIc and KIIIc) 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 I/III 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.