Most materials in nature or industry do not behave like ideal solids (Hookean) or fluids (Newtonian), and their constitutive equations are not obvious ab initio. Their multi-scale structure determines a response to strain (- rate) or stress. Although synchrotron X-ray tomography allows capturing structural rearrangement over several length scales at ever faster acquisition rates [1, 2] a platform for rheological surveys capable of inducing different types of flows or deformation in combination with continuous-motion test protocols is still missing. We developed tomo-rheoscopy at TOMCAT, a full-volume time-resolved approach to elucidate microstructural transients and dynamics in different rheometric flow scenarios (Fig.1) and acquisition modes.

Figure 1. Various rheometric flow scenarios that can be investigated with tomo-rheoscopy.

Granular material is found in many different scientific and industrial domains and represents here a great working example. It is well suited for tomographic microscopy, and its rheological behavior poses many open questions [3-5]. Our method allows the continuous imaging of individual grain kinematics (Fig.2) and acquires synchronously relevant macroscopic forces and strains for its mechanical characterization.

Figure 2. Tomo-rheoscopy working principle. For granular materials, the dynamics of individual grains can be tracked over time, permitting a multi-scale analysis of material structure to external stress and strain in a continuous-motion test.

Furthermore, in this project, we extend the range of materials (Fig.3) and test protocols suitable for Tomo-Rheoscopy, integrating it as a universal platform for material testing on the TOMCAT beamline, and make it available to our broad user community.

Figure 3. Examples of various materials that are suitable for tomo-rheoscopic testing. From left to right: a 3D printed metamaterial under compression, a nylon thread under torsion, a penetration test of a tablet.