The objective of this work is to develop an understanding of the relationship between hole drilling processes and the fatigue performance of the resulting part in Ti-6Al-4V. This problem is significant, as on the order of one-hundred thousand to a million holes are created in a typical large aircraft, and the limiting performance criterion is usually the fatigue lifetime. The path between the drilling process parameters and the fatigue performance has two main steps: characterization of the thermo-mechanical drill process and assessment of the relationship between the hole integrity left by the drill process and the fatigue performance. Development has been limited by the robustness of previously available thermal characterization systems, poor correlation between drill processes and physical observations of metallic effects, and limited success identifying the key hole integrity characteristics. This work develops robust novel thermal methods which enable integration into current drill process development techniques. The key integrity drivers in the hole wall are identified, characterized, and a system to assess is presented. The thermal and hole integrity trends are presented as guidance for drill process development providing significant opportunities to optimize processes. Thus, this work advances knowledge of the process to fatigue lifetime relationship by correlating the thermo-mechanical drill process to fatigue life in Ti-6Al-4V
