Assessment of predominant microstructural features controlling 3D short crack growth behavior via a surrogate approach in Ti-6Al-4V

Abstract

Complex 3D microstructure and mechanical properties can be precisely characterized and linked by employing the X-ray micro-tomography combined with EBSD serial sectioning. Global sensitivity and principal component analysis can be used to rank and coarsen the contributing features that control the mechanical response. Afterwards, by creating surrogate models, the relationship between the most contributing features and mechanical properties can be further analyzed via support vector machines. The aforementioned novel approach was applied to study the relationship between 3D microstructural features and short crack behavior in a Ti-6Al-4V alloy. It was revealed that short crack path, growth rate, and its variation are mainly affected by the interaction with neighboring grains; however, as the short crack front becomes larger, there is a decrease and a change in the importance of those interactions. A high number of grains in contact with long cracked α grains in the loading direction may impose a constraint on the crack opening resulting in low crack growth rates. For the larger crack front, the increase in the shear stress field around the cracked grains leads to crack bifurcations and to the formation of secondary cracks, resulting in a decrease in crack driving forces with low crack growth rates. It was concluded that short crack behavior is strongly affected by the shape, size, and crystallographic features of its neighboring grains, which cause variation in the shear and tensile stress fields resulting in crack growth rate variation.