PSI - Issue 66

Nur Mohamed Dhansay et al. / Procedia Structural Integrity 66 (2024) 87–101 Author name / Structural Integrity Procedia 00 (2025) 000–000

96 10

ZX

XZ

XY

(a)

(b)

(c)

Fig. 7. Crack profile in the ZX, XZ and XY orientations for the bi-modal condition. Fracture surfaces are shown at (a) lower magnification and (b) higher magnification. Crack profile images are shown in (c). Crack propagation is downwards.

Considering crystallographic texture, investigations conducted on fatigue loading CM Ti-6Al-4V have shown faceted fracture, typically, associated to a basal slip system (Bantounas et al., (2009)). The implication being that basal slip is a common cause of crack initiation under fatigue loading conditions. However, both Qui et al. (Qiu et al., (2016)) and Bantounas et al. (Bantounas et al., (2009)) found that crack propagation also occurs on prismatic planes. More specifically, the approach by Bantounas et al. (Bantounas et al., (2009)) showed agreement between highest Schmid factors and active slip systems i.e., the slip system which has the highest Schmid factor will be dominant. More specifically, for misorientation angles between 0 ° and 10 ° the 〈 a+c 〉 pyramidal slip is dominant, between 10 ° and 66.7 ° the 〈 a 〉 basal slip is dominant, and from 66.7 ° to 90 ° the 〈 a 〉 prismatic slip is dominant. What is further shown is that the ZX orientation, has a loading direction in Z, while the XZ and XY has a loading direction in X. This means that while both loading directions has maximum basal slip Schmid factor at 45°, different dominant slip systems will be active. Furthermore, no major difference (8%) between orientation specific crystallographic pole figures were observed. Therefore, it is more likely that anisotropic observations are due to morphological texture as opposed to crystallographic texture. Considering morphological texture, the previous authors (Becker et al., (2020)) found that the α ’ laths act as barriers where laths orientated at ± 45° influence the crack path which result in crack deflection and branching. It was also found that the α ’ lath morphology is dependent on the PBG structure via the habit planes. Thus, for the respective orientations, the crack fronts will experience the PBG and α ’ laths in different ways, i.e. equiaxed in the ZX orientation,