Title:
Characterization and effects of heterogeneities on shock compression properties in high-solids loaded additively manufactured polymer composites
Characterization and effects of heterogeneities on shock compression properties in high-solids loaded additively manufactured polymer composites
Author(s)
Wagner, Karla Brooke
Advisor(s)
Thadhani, Naresh N.
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Abstract
High-solids loaded polymer composites contain several hierarchies of heterogeneities and are of interest for use as ceramic green bodies and energetic crystals embedded in a polymer matrix. The recent and rapid growth of additive manufacturing (AM) and the engineering need for more complex geometries and individualized products has led to a surge of interest in fabricating high loading particle composites via AM. In particular, Direct Ink Write (DIW) extrusion involving layer-by-layer deposition of a composite paste made of a high loading of solids and a curable polymer binder is used to fabricate such composites in different geometries and forms. However, DIW-AM introduces further complexity in composites due to formation of process-inherent heterogeneities such as particle aggregation or porosities, which can be random, directional, or stochastic. The structure and composition of such materials vary across several length scales, resulting in processing and mechanical behavior that is difficult to predict or understand.
Shock-compression of heterogeneous particle-filled polymer composites often involves complex interactions, which can make it difficult to predict their dynamic mechanical properties. The shock compression behavior is often dominated by mesoscale defects (including porosity) or interactions of the shock wave with interfaces and particulates. Traditional diagnostic methods, such as velocity interferometry, enable temporally resolved measurements, but are limited in spatial resolution and generally provide volume averaged responses. Spatially resolved measurements are therefore also necessary to provide sufficient information regarding the mesoscale processes which dominate performance of such materials. X-ray phase contrast imaging, a spatially and temporally resolved technique, in conjunction with traditional velocimetry, can enable observation of the effects of hierarchical heterogeneities on shock compression response.
In this work, the effect of print geometry and porosity (process-inherent heterogeneities) on the shock compression response of an additively manufactured high-solids loaded composite is
studied. The composite contains three reinforcing phases: two inorganic particles and one organic particle, all with differing size distributions and morphologies. They are surrounded by a UV curable polymer binder. In order to investigate the effect of these process inherent heterogeneities on shock response, the high-solids loaded composite’s microstructure is first quantitatively characterized via microcomputed tomography imaging and computational analysis in three dimensions. Next, the composite undergoes plate-impact experiments at Argonne National Laboratory’s Advanced Photon Source’s Dynamic Compression Sector, with X-ray PCI used as an in-situ and in-material diagnostic. This is combined with PDV for validation. The phase contrast images are analyzed in order to measure shock and particle velocities directly from the translation of the shock wave and particles over time. Finally, the effects of print geometry, impact direction relative to print orientation, and porosity are studied by combining the aforementioned structural characterization with the shock response of the material determined via X-ray PCI. This reveals that print geometry does result in differing macroscale shock response (quantified with EOS), and that print geometry, impact orientation, and pore morphology all have an effect on microscale shock response (quantified with pore collapse velocity). We expect that these factors, only studied on a relatively small scale in this work, will become more exaggerated as sample size and therefore quantity of heterogeneities grows.
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Date Issued
2024-01-11
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Text
Resource Subtype
Dissertation