Neutron Interferometry Detection of Early Crack Formation in Fatigued Additively Manufactured SS316 Dogbones
Daniel S. Hussey, Hong Yao, Adam J. Brooks, Ali Haghshenas, Jumao Yuan, Caroline G. Lowery, Jacob M. LaManna, David L. Jacobson, Nikolay Kardjilov, Shengmin Guo, Michael M. Khonsari, Leslie G. Butler
Fatigue in selective laser melted (SLM) and conventional SS316 dogbones was studied with neutron imaging methods for attenuation, scattering, and diffraction. To detect the microcrack evolution in fatigued samples,two methods of grating-based neutron interferometry, Talbot-Lau and far-field, were employed. Both interferometry methods detected early crack formation via the dark-field (scattering) images, especially for porous microstructures in the range of 0.6 μm to 2 μm. The dark-field image combines sensitivity tomicron-sized scattering centers at the crack formation with sub-millimeter imaging resolution over a severalcentimeter-sized dogbone. The crack formation observed with neutron interferometry dark-field wasvalidated post-imaging with additional fatigue cycles to fracture, then inspection by scanning electron microscopy (SEM) and optical photography. In the two SLM and conventional fatigued dogbones, crack formation was identified to within 1 mm. Other neutron experiments included neutron attenuation tomography and Bragg edge imaging; neither successfully observed crack formation.