Strain Mapping in the Vicinity of Cracks Using a Conical Slit Setup for Angular Dispersive Synchrotron X-Ray Diffraction

Background Laser-based powder bed fusion (PBF-LB/M) is a manufacturing technique that enables tailoring of the properties of components towards the application, provided the process parameters are adjusted. However, the process induces residual strain and stresses, influencing, i.e., the fatigue properties. To analyze the residual strain distributions in the vicinity of fatigue cracks in the bulk of specimens a high lateral resolution is necessary, which limits the possible analysis methods to high-energy synchrotron X-ray diffraction. Objective The objective is to propose a viable strategy to determine the (lattice) strain distributions in the vicinity of fatigue cracks in AISI 316L compact-tension specimens manufactured via PBF-LB/M. Methods An angular dispersive high-energy synchrotron X-ray diffraction setup with conical slits is used, to restrict the gauge volume to the center of the specimens. Complementarily, the residual stress distribution near the surface is investigated using the incremental hole-drilling method. Results Along the build direction a compressive residual strain distribution of higher magnitude is found, which is significantly reduced in the vicinity of the crack. Depending on whether the crack opening direction is aligned with the transverse or the build direction, a tensile lattice strain field or a lattice strain field of reduced magnitude is found ahead of the crack tip. Conclusions The results indicate that the proposed strategy is well suited to determine the (lattice) strain distributions in the vicinity of fatigue cracks in the center of the specimens with a sufficient lateral resolution.