“In-Material” X-PCI Characterization of Effects of Heterogeneities on Shock Compression of High-Solids Loaded Additively Manufactured Polymer Composites*

The shock-compression behavior of additively manufactured (AM) particle-filled polymer composites with different hierarchies of process-inherent heterogeneities is highly complex. The heterogeneities present including pores and aggregated particulates can have random, directional, or stochastic distributions due to layer-by-layer build-up of 3-D structures fabricated by the direct ink writing AM process. Traditional diagnostic methods, such as velocity interferometry enable temporally resolved measurements, but are limited in spatial resolution, which makes it difficult to resolve shock wave interactions with pore/particle interfaces, and the properties measured are based on volume-averaged responses. X-ray phase contrast imaging (X-PCI) enables “in-material” spatial and temporal characterization which makes it ideally suited for investigating the shock-compression response of AM fabricated high-solids loaded polymer composites. Uniaxial-strain plate impact experiments employing X-PCI in conjunction PDV measurements performed at the DCS/APS were used to establish the effects of process-inherent and intentional porosity of varying morphologies arising from collinear and log-cabin layouts of the 3-D printed composite structures. The heterogeneities present in each sample were also characterized using X-CT imaging, prior to the impact experiments. Shock and particle velocities were measured using “in-material” feature tracking from the captured X-PCI images. The measured shock and particle velocity equation of state, as well as the characteristics of shock compression of pores, determined from X-PCI, were correlated with the directionality of the AM filament/layer pattern and 3-D print orientation relative to the shock propagation direction. The results demonstrate a relatively isotropic macro-scale shock equation of state response of the polymer composites considering the scale of heterogeneous features and their directionality relative to the size of the impacted samples. However, the meso-scale response, including the shock compression characteristics of pore collapse, are dominated by the directionality of the pores relative to the direction of shock wave propagation.