A Multi-loading, Climate-Controlled, Stationary ROI Device for In-Situ X-ray CT Hygro-Thermo-Mechanical Testing

Abstract

In-situ CT mechanical testing yields a full 3D description of a sample material's behaviour under specific loads. In the literature various devices are proposed which enable in-situ CT hygro-, thermo-or mechanical testing, each with its own merits and limitations. However none of them is able to perform advanced hygro-thermo-mechanical tests on specimens subjected to multiple loading modes, while accurately controlling and measuring the force, displacement, temperature and relative humidity in real time. Therefore, this work proposes an in-situ CT device which allows such multi-faceted experiments. Improvements to the current state-of-the-art devices include: (1) a compact, lightweight and rotationally symmetric design that enables high-resolution CT scans by minimization of wobble during scanning, in practically all labscale CT scanners; (2) a stationary region of interest by loading the sample from both sides, which enables high resolution CT characterization of materials exhibiting a large fracture strain; and (3) improved testing modularity by exchanging clamping methods to allow samples of various sizes (e.g., circular or rectangular) to be inserted in a variety of ways, thereby facilitating complex experiments such as three-or four-point bending tests. Validation experiments demonstrate that stringent requirements on CT resolution, loading and displacement accuracy and climate control are met. Furthermore, the in-situ testing capabilities of the device were validated by CT characterization of the creasing and folding process of multi-layer cardboard under varying (controlled) levels of relative humidity and temperature.

Small-Scale Mechanical Testing

“…Dynamic tests (i.e., tests that are not interrupted for image acquisition) require exceptional stability during rotation in order to minimize movement of the field of view. In the system described by Vonk et al (97), deformations and interlayer damage development can be tracked under controlled conditions of humidity in a cardboard. Using a combination of micro-computed tomography and far-field high-energy diffraction, Nair et al (98) track stress partitioning in individual grains of a cement-quartz mixture, demonstrating that the loss of a diffraction peak from a grain can signal the onset of fracture in these granular materials.…”

Least squares based geometric error measurement for sparse view CT: a 2D simulation study

“…High precision CT is also a very important tool in the in-situ mechanical study of concrete and metal components. Although existing CT imaging systems for in-situ testing use the same approach as most industrial systems: the scanning component is fixed while the sample and in-situ loading device rotates [3][4][5][6], CT scanning of large reinforced concrete and metal components has to be carried out with a fixed loading table and specimen, while the scanning device, i.e. the radiation source and detector, rotates, just as in medical CT.…”