Assessment of mode I/III fracture toughness of bi-material rock-like ENDB and ENDC specimens

Abstract

Mode I/III fractures at the bi-material interface are common and present unique challenges in civil and geotechnical engineering. However, there are few studies on the mechanical characteristics of bi-material rock-like specimens under mixed-mode I/III loading. This study used bi-material rock-like Edge-notched disc bend (ENDB) specimens and Edge-notched diametrically compressed (ENDC) specimens to investigate their mechanical and fracture characteristics under pure mode I, III, and mixed mode I/III loading. The results showed that the fracture toughness KI > KIII, KI and KIII decreased overall with increasing loading angle(β, α), the KI and KIII of the ENDB specimens are generally lower than that of ENDC specimens. The fracture energy (Wi) of ENDB specimens is gradually increased with the loading mode changed from pure mode I to pure mode III, while the ENDC specimens have a trend of first decreasing and then increasing. Besides, the ENDB specimens exhibit significant torsion fracture, and the torsional angle(θ) gradually increased with loading angle β, in which low-strength material has larger θ than high-strength material. In contrast, ENDC specimens fractured along the interface in pure mode I and mixed mode I/III loading, while fractures along the loading point to the centre of the specimen under pure mode III loading. Moreover, the acoustic emission results show that tearing cracks are more prominent in ENDC specimens than in ENDB specimens. Generally, ENDB specimens show more pronounced tensile/torsional fracture characteristics than ENDC specimens, it’s recommended to be adopted in mode I/III fracture toughness testing for bi-material rock-like materials.