Particulate composite material internal deformation measurements using x-ray microtomography and digital volume correlation

Typical particulate composites used in engineering applications consist of complex microstructures with a range of particulate sizes and often high particulate volume fractions (65%-95%). Examples of these are, explosives and rocket propellants for defense and aerospace applications, asphalt concrete materials civil engineering applications and ceramic/ceramic thermal barrier coatings for turbine engines. In the past, X-ray microtomography (X-ray microCT) has been used to study the internal structure of such complex microstructures. The combination of the Digital Volume Correlation (DVC) method and the three-dimensional (3D) imaging X-ray microCT technique is becoming a powerful tool in the mechanics community that provides 3D internal metrology in addition to 3D imaging. In this work, we employ an in-house DVC algorithm to measure deformations within a model composite material – a controlled number of one or a small finite number hard particles in a complaint polymer matrix. In-situ compression experiments are performed inside an X-ray microCT scanner on samples containing different microstructure configurations. To quantitatively and qualitatively study the internal deformations and evolution of failure in 3D, we use a model composite material (cylindrical 15 mm in height and 10 mm in diameter) with a series of different well-controlled microstructure configurations. A simple microstructure arrangement consisted of precisely positioned spherical ceramic inclusion(s) (at most two). A more complex microstructure contained a larger number (20) of randomly positioned spherical alumina inclusions. The final configuration studied contained a precisely positioned irregularly shaped inclusion. The model material consisted of a reinforced polymer matrix, PDMS with 35 µm glass marker particles which were appropriately distributed to serve as the internal speckle pattern required for DVC. Specifically, we studied the 3D displacement and strain fields resulting within the polymer particulate composites with different microstructure arrangements. In addition, we resolved the resolution and accuracy of the DVC analysis technique by successfully comparing the measured results to known elastic solutions (before the occurrence of failure). The second part of this work focused on studying internal flaws and failure evolution as a function of loading. Interfacial debonding was the only failure mode seen in these model composites and was studied quantitatively and qualitatively for the simpler microstructure configurations of a single embedded spherical inclusion or two inclusions one above each other. We also attempted to delay interfacial failure by increasing the surface roughness of a single alumina inclusion sample. Although, in the simpler case of the single and double inclusions the opening(s) was precisely measured, in the more complex interfacial failure patterns of the multiple spheres or the irregularly shaped inclusions, debonding was only qualitatively studied using volumetric 3D renderings