Simultaneous Micro-scale and Continuum-scale Characterization of AF9628 Steel Subjected to Dynamic Loading Conditions

In this dissertation, a novel experimental method to integrate phase-contrast imaging (PCI), stereographic digital image correlation (stereo-DIC), and full-ring x-ray diffraction (XRD) to allow for the simultaneous characterization of polycrystalline metals at 1MHz or higher is presented. A Kolsky bar was integrated into the synchrotron x-ray source in Sector 32 ID-B at the Advance Photon Source (APS) at Argonne National Laboratory. When the sample is dynamically loaded, the diagnostic methods of full-ring XRD, PCI, and stereo-DIC are properly synchronized to record the deformation behavior at both continuum and microstructural scales as a function of the loading history. Proof-of-concept experiments were conducted on a low-alloy high-strength steel, AF9628, which from dynamic loading resulted in multi-axial strain states. Preliminary fracture experiments were performed to gain valuable insight to the effect of triaxiality on the failure of AF9628. These results were then used to plan experiments at the APS accordingly.

Multi-axial strain states were generated from dynamic loading through the notching of tensile specimens at various orientations with respect to the loading. Generally, the force required to fracture the material decreased as notch orientations became more aligned with the direction of loading. The x-ray scattering data was used to perform sequential strain analysis within GSAS-II, and was compared to the strain components calculated from DIC.