Experimental investigation of the quasi-static mixed-mode crack initiation in NiCr/ZrO₂functionally graded materials by digital image correlation

The NiCr/ZrO₂ functionally graded materials (FGMs) were fabricated by the powder metallurgy. To study the effect of material gradient on the mixed-mode crack initiation，two types of fracture samples were prepared：FGM-A corresponding to the specimen with the crack situated on the stiffer side and FGM-B corresponding to the specimen with the crack situated on the compliant side. The quasi-static fracture tests were conducted under the unsymmetrical loading conditions，and the full-field digital image correlation (DIC) was used to obtain the stress intensity factors KⅠand KⅡ. The experimental results show that the kinking angle of FGM-A is less than the one of FGM-B；the crack of FGM-A is shielded by the elastic gradient and the mixed-mode crack initiation is influenced by the elastic gradient and the local fracture toughness.