In Situ X-Ray Phase Contrast Imaging of an Additively Manufactured High-Solids Loaded Polymer Composite Under Shock-Compression

Additively manufactured (AM) high-solids loaded polymer composites have a large variety of process-induced heterogeneities, often leading to difficulty in controlling or predicting their properties. Although AM opens new pathways to tailoring material performance by design of the micro- and meso-scale structure, it also leads to the generation of heterogeneities with a hierarchy of length scales such as non-uniform constituent distribution, interfaces, and porosities. that can alter the performance. It is important to understand how such heterogeneities, particularly porosity that may be preferentially aligned as a function of print direction, affects the materials’ dynamic response. Conventionally-used diagnostics do not enable temporally- and spatially-resolved measurements of both macroscopic and micro- and meso- level processes occurring during shock compression of the composites. X-ray phase contrast imaging (PCI) is a technique in which both refraction and absorption of x-ray are used to image the 3D structure of a material. Gradients in index of refraction (such as at phase interfaces or shock wave fronts) are highlighted making it possible to probe the interior of a material during an impact experiment. Thus, X-ray PCI can give an unprecedented level of detail due to its high temporal (ns) and spatial (μm) resolutions. In this work, we analyzed the shock compression response of an AM fabricated high-solids-loaded polymer composite impacted in different orientations relative to the printing pattern of the filaments. Previous work indicated that AM composites fabricated with uniform porosity were effectively isotropic at the length scale (2-mm field of view and 2-mm depth of x-ray penetration) required to image using X-ray PCI effectively. Hence, AM composites fabricated with co-linear and log-cabin configurations of build patterns were imaged via microcomputed tomography prior to impact experiments in order to pre-identify porosity locations and forms as well as other process-inherent heterogeneities. Computer-aided analysis was then used with the X-ray PCI data to compare heterogeneous features in the material to the tomography data, to track the observed wave(s) velocity profiles, and to study the temporal and structural properties of shock-wave interactions with voids.