Navid Nasajpour Esfahani
Advisor: Dr. Hamid Garmestani

will propose a doctoral thesis entitled,

Through-Depth Residual Stress Characterization of Laser Powder Bed Fusion Ti-6Al-4V Specimens via Femtosecond Laser Cutting, Digital Image Correlation, and Inverse FEM

On

Friday, August 21, 2026, at 1 PM
Love Room 295

or virtually via Teams:

https://teams.microsoft.com/meet/215690724088599?p=jJaH0L7z0UvgSZkH4x

Committee
Dr. Hamid Garmestani – School of Materials Science and Engineering (advisor)

Dr. Aaron P. Stebner – School of Materials Science and Engineering
Dr. Steven Y. Liang – School of Mechanical Engineering

Dr. Rick Neu – School of Mechanical Engineering

Dr. Preet M. Singh – School of Materials Science and Engineering

Abstract
Residual stress is a critical factor affecting the dimensional accuracy, fatigue performance, and structural integrity of laser powder bed fusion (LPBF) components. While through-depth residual stress can be characterized using incremental material removal techniques, the achievable spatial resolution remains limited, making it difficult to resolve stress variations within individual deposited layers. Improving the depth resolution of residual stress measurements is therefore essential for advancing the understanding of residual stress development and its relationship with the manufacturing process in additively manufactured components. The objective of this research is to develop a high-resolution framework for through-depth residual stress characterization of LPBF Ti-6Al-4V components by integrating experimental measurements with computational modeling. Conventional hole-drilling methods reconstruct residual stress through incremental material removal; however, each material removal step yields only a single residual stress measurement, inherently limiting the spatial resolution of the technique. Although reducing the drilling increment can improve depth resolution, it is constrained by drilling precision, tool geometry, material damage, and measurement uncertainty. Consequently, achieving multiple reliable residual stress measurements within a single LPBF layer remains challenging. To address these challenges, this proposal is organized into three complementary studies that progressively improve the spatial resolution and reliability of through-depth residual stress characterization. The first study develops a Digital Image Correlation (DIC)-based inverse finite element methodology to reconstruct residual stress distributions from full-field displacement measurements obtained during incremental material removal. The second study investigates digitally generated and printed speckle patterns to evaluate their influence on DIC-based residual stress characterization, highlighting the trade-off between the improved repeatability of printed patterns and the higher spatial resolution achieved with conventional spray-painted patterns. Building on these findings, the final study introduces femtosecond laser cutting as an alternative material removal technique capable of producing substantially smaller depth increments while minimizing thermal loading and the possibility of laser-induced stresses. This approach enables multiple residual stress measurements within a single LPBF layer, providing significantly improved through-depth spatial resolution. The proposed methodologies are validated using LPBF Ti-6Al-4V specimens fabricated under different processing conditions and compared with the conventional hole-drilling strain-gauge technique. Together, these studies establish a framework for high-resolution through-depth residual stress characterization and provide the foundation for future development of a fully non-destructive technique for evaluating residual stresses in additively manufactured metallic components.