A quantitative fractographic analysis was undertaken in order to relate important microstructural and fractographic features to fatigue fracture in a Ti-28V alloy. Special emphasis is placed on facet characteristics and subsurface cracking in the single-facet and multifacet regions.

The stereological treatment of this problem develops methodologies and relationships based primarily on vertical sections cut through the fracture surface and parallel to the crack propagation direction. The evaluation of fracture profiles (in terms of true length, roughness, and degree of orientation) permits calculation of fracture surface characteristics (such as true surface area, roughness, and type of surface).

True mean facet areas, Ā_facets, are calculated from combined measurements on scanning electron microscope photographs and two parallel, vertical sections along the edge and center of the fracture surface. The values of Ā_facets for the single-facet and multifacet regions are 22.2 ± 4.9 and 12.7 ± 4.0 nm², respectively, with indicated 95 percent confidence intervals. True mean subsurface crack lengths, ¯L_cracks, in the edge section are 0.05 ± 0.07 and 0.16 ± 0.07 mm for the single-facet and multifacet regions, respectively, whereas in the center section the corresponding values are 0.13 ± 0.08 and 0.34 ± 0.13 mm. Based on an upper-lower bound approach, the fracture surface is found to conform most closely to a partially oriented surface with strong planar elements. The results obtained here are consistent with the fatigue crack growth model of Chakrabortty.