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.
  1. Mokso, R. et al. GigaFRoST: the gigabit fast readout system for tomography. Journal of Synchrotron Radiation 24, 1250–1259 (2017).
  2.  García-Moreno, F. et al. Tomoscopy: Time-Resolved Tomography for Dynamic Processes in Materials. Advanced Materials 33, 2104659 (2021).
  3.  Andreotti, B., Forterre, Y., & Pouliquen, O. (2013). Granular Media: Between Fluid and Solid. Cambridge, UK, Cambridge University Press, 469 pp.
  4.  Viggiani, G., & Tengattini, A. (2019). Recent developments in laboratory testing of geomaterials with emphasis on imaging. Proceedings of the XVII ECSMGE-2019.
  5. Baker, J., Guillard, F., Marks, B., & Einav, I. (2018). X-ray rheography uncovers planar granular flows despite non-planar walls. Nature Communications, 9(1), 1–9.
  • SNF R'Equip 2021 and PSI
Dr. Stefan Gstöhl,
Dr. Christian Schlepütz,