Fracture toughness anisotropy of ultrafine-grained pure copper processed by equal channel angular pressing

Abstract The fracture anisotropy of ultrafine grained pure Cu processed by eight passes of equal channel angular pressing in route BC was investigated based on elastic-plastic fracture mechanics. For different crack planes and different crack propagation directions, both the global fracture initiation toughness measured by JIC and KIC and the crack growth toughness represented by the non-dimensional tearing modulus TR were evaluated by accurately determining the J-integral resistance curves. Furthermore, the crack tip opening displacements at fracture initiation were also measured through crack profile analysis to determine the local crack initiation J-integral Ji. The results demonstrate that the specimen orientation has a pronounced influence on the fracture toughness of the ultrafine grained Cu. Among all the tested orientations, the fracture resistance is highest in the transverse direction with KIC = 99 MPa m1/2 and TR = 100, and lowest in the extrusion direction with KIC = 66 MPa m1/2 and TR = 30. The origin causing the anisotropic fracture toughness is discussed based on detailed fracture appearance characterization and microscale crack path analysis.