Dealing with Missing Angular Sections in NanoCT Reconstructions of Low Contrast Polymeric Samples Employing a Mechanical In Situ Loading Stage

While in situ experiments are gaining importance for the (mechanical) assessment of metamaterials or materials with complex microstructures, imaging conditions in such experiments are often challenging. The lab-based computed tomography system Xradia 810 Ultra allows for the in situ (time-lapsed) mechanical testing of samples. However, the in situ loading setup of this system limits the image acquisition angle to 140 degrees. For low contrast polymeric materials, this limited acquisition angle leads to regions of low information gain, thus preventing an accurate reconstruction of the data using a filtered back projection algorithm resulting in erroneous microstructures. Here, we demonstrate how the information gain can be improved by selecting an appropriate position of the sample. A low contrast polymeric tetrahedral microlattice sample and a structured sample with specific markers, both scanned over 140 degrees and 180 degrees, demonstrate that the missing structural details in the 140 degrees reconstruction are limited to an angular wedge of about 20 degrees. Depending on the sample geometry and microstructure, applying simple strategies for the in situ experiments allows accurate reconstruction of the data. For the tetrahedral microlattice, a simple rotation of the sample by 90 degrees rotates all relevant surfaces by about 30 degrees to the original illumination direction, creating a more even X-ray illumination for all the projections, thus providing enough X-ray absorption for an accurate reconstruction of the geometry.