The ability to watch the three-dimensional (3D) evolution of structural materials is a breakthrough in non-destructive characterization. In particular, X-ray tomographic imaging techniques have fou...

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2020.1809544

Characterization of metals in four dimensions

Review of high-speed imaging with lab-based x-ray computed tomography

The aim of this work is to present the quantitative evaluation of the Additive Manufacturing (AM) laser powder bed fusion ( L -PBF) process steps and validation of the FE (Finite Elements) simulation results using the X-ray Computed Tomography (XCT) based approach. The characterization of the production process was made using standard methods, including: laser light diffraction, optical and scanning electron microscopy, hardness examinations, and the investigation of mechanical properties. The XCT method was used to conduct the quality of powder feedstock, the influence of the L -PBF build strategy on the samples’ porosity, and also to evaluate a quantitative analysis of damage behavior before and after ex-situ mechanical testing. The porosity recorded for the powder feedstock was 0.2% and for test samples did not exceed 0.02%. The majority of the observed pores are aligned in patterns connected with the scanning strategy and were arranged in lines appearing along the borders between adjacent stripes. It was observed that increasing the resolution of the XCT scanning significantly influenced the mapping of the shape of pores and – to a lesser extent – the recorded porosity. The comparison of geometry deviations after numerical simulation and tensile test for FE models obtained with different XCT resolutions allowed to show differences in the geometry of experimentally and numerically damaged test samples.

X-ray Computed Tomography for the ex-situ mechanical testing and simulation of additively manufactured IN718 samples

Polylactic acid (PLA) porous composite scaffolds with three different infill patterns were subjected to compression testing. The composites were fabricated by 3D printing based on Fused Filament Fabrication (FFF) technology. Stress-strain curves were obtained which allowed to identify Young’s modulus, yield point and residual strain of samples. 3D tomography images were taken before and after deformation. Comparison between images corresponding to a particular sample were used to identify deformation and failure mechanisms.

Mechanical properties and failure mechanisms of 3D-printed PLA scaffolds: A preliminary study

The thermal stability of gypsum-based materials, and in this context, especially their long-term behavior, is the background of our current research activities. A comprehensive investigation program was compiled in which detailed examinations of various model materials exposed to thermal loads were carried out. The understanding of the partly not entirely consistent state of knowledge shall be sharpened especially by in situ observations of the thermally induced conversion reaction of gypsum into hemihydrate. The temporal course of the reaction was investigated non-destructively by in situ investigations in a high-resolution X-ray computed tomography setup, and the experiment was accompanied by detailed characterizations of the microstructure and composition. In this contribution, selected results of experiments with a high-purity natural gypsum rock as the model substance are presented. Studying the influence of temperature on the reaction showed that, even under supposedly dry conditions, the reaction could take place at much lower temperatures than usually reported in the literature. It was demonstrated that the transformation of gypsum into hemihydrate could take place at a temperature of already 50 °C. The results indicated that even under “classical” heating conditions in a conventional oven, the dissolution and crystallization processes in water films on the mineral surfaces could be suggested to be a driving force for the reaction. A corresponding reaction model, which took these aspects into account, was proposed in this work.

/pdf/reactivity-of-gypsum-based-materials-subjected-to-thermal-3uqrhyl15f.pdf

Reactivity of Gypsum-Based Materials Subjected to Thermal Load: Investigation of Reaction Mechanisms.

In the past few years, dynamic computed tomography (CT) approaches or uninterrupted acquisitions of deforming materials have rapidly emerged as an essential technique to understand material evolution, facilitating in situ investigations ranging from mechanical deformation to fluid flow in porous materials and beyond. Developments at synchrotron facilities have led this effort, pointing to the future of the technique. In the laboratory, recent developments at TESCAN XRE have made it possible to image, reconstruct and inspect dynamic processes in the laboratory with a temporal resolution below 10 s, meaning that an entire acquisition from 0 to 360° is completed within 10 s. The aim of this study is to explore the challenges and innovations that have led to the ability to perform high speed, dynamic acquisitions. A unique horizontally rotating gantry based micro-CT system was developed to facilitate complex in situ experiments. In doing so, the sample stays fixed while source and detector are uninterruptedly rotating around a vertical axis. In this work, the dynamic CT method with this rotating gantry based system will be described by two application examples: (1) deformation and collapse of a delicate beer foam and (2) in situ baking process of pastry. For the pastry baking process, an oven was needed to reach baking temperature. In a conventional micro-CT system, where the sample rotates, it is not so obvious to rotate an oven with sensor and heating cables. On the other hand, the delicate foam of a collapsing beer head is able to rotate, but because of the tangential convection during fast rotation (<10 s), it could influence the bubble detachment and liquid drainage and thus also the foam degradation. To investigate both processes, a horizontally rotating gantry based micro-CT is required. For both examples it was possible to quantify the key parameters such as pore size and distribution to better understand the rise and fall of porous foams. These examples will highlight the recent progress in adapting micro-CT workflows to accommodate uninterrupted imaging of dynamic events and point to opportunities for future continued development. LAY DESCRIPTION: Micro-CT allows the nondestructive visualisation of internal structures and is being used routinely in the field of Material Science, Geoscience, Life Science and more. Because of its nondestructive aspect, micro-CT is optimal to take repetitive scans of the same sample over time. The combination of taking different scans over time is so called time-resolved CT. By doing so, crucial insights can be obtained on how materials form, deform and perform over time or under certain external conditions. TESCAN XRE have made it possible to image, reconstruct and inspect dynamic processes in the laboratory with a temporal resolution below 10 s. The dynamic CT method will be described through the lens of two application examples: (1) deformation and collapse of a delicate beer foam and (2) in situ baking process of pastry. These examples will highlight the recent progress in adapting micro-CT workflows to accommodate imaging of dynamic events and point to opportunities for future continued development.

M.A. Boone

Papers

Innovations in laboratory-based dynamic micro-CT to accelerate in situ research.