About application of three dimensional analyses of fracture surfaces in fracture study on nanostructured titanium

Fracture behavior of coarse-grained and nanostructured commercially pure Ti was studied at room temperature and 250 °C. Three dimensional digital elevation models of corresponding fracture surfaces were generated using an automatic fracture surface analysis system and quantitative analyses of fracture surface topography were performed. Average dimple height, crack tip opening displacement COD, and crack opening angle COA were measured. Energy required for formation of dimple structure on fracture surface, fracture toughness, and crack growth resistance were calculated using these results and fracture mechanics relations. It was shown that the correct fracture toughness can be calculated from COD measurements for the nanostructured Ti at room temperature where dislocation glide is the only active deformation mechanism and plastic rotation is insignificant. No correct fracture toughness can be calculated if other deformation mechanisms such as twinning in coarse-grained Ti at room temperature and 250 °C or cooperative grain boundary sliding in nanostructured Ti at 250 °C are active and plastic deformation is more significant. Advantages of application of three-dimensional analysis of fracture surfaces in fracture studies on nanostructured Ti are discussed.