Granular materials are one of the most important materials in several industries such as civil engineering, agriculture, and energy production. They are a collection of distinct macroscopic particles. Although, these materials are very simple to be described they exhibit highly different mechanical behavior under quasi-static and dynamic loading conditions. Traditionally, glass beads have been considered as a benchmark granular material for the fundamental understanding of the mechanics of granular materials under complex mechanical loadings. In this study, we intend to characterize the compressive behavior of glass beads under confinement using in-situ X-ray micro-computed tomography at low (quasi-static) and high strain (dynamic) rates. For this purpose, a mechanical loading frame with high capacity load/torque cell (45 kN and 300 N⋅m) was integrated into a Nikon 225 kV CT system in order to provide the in-situ three-dimensional (3D) X-ray tomography images with an effective voxel size of 5 µm during the quasi-static experiments. At high strain rates, samples with similar bulk densities to the quasi-static samples are compressed using a long split Hopkinson pressure bar system at different strain levels. The maximum compressive strain at each experiment is controlled using a stop-ring technique that stops the displacement of the incident bar at the predefined strain level. Using different ring stoppers at different heights, samples are dynamically compressed up to different strain levels and later imaged with the tomography system to acquire their volumetric images. In the case of low strain rates, a similar sample is compressed, and subsequently, its volumetric images are captured at the same set of strain levels as the dynamically compressed samples using the long split Hopkinson pressure bar system. The volumetric images at each strain level are then analyzed to determine three-dimensional morphologies and to investigate and compare the damage and failure mechanism of the glass beads at quasi-static and dynamic loading conditions. Explicit finite element models, which are based on the actual configurations of glass beads acquired by X-ray scans, with the consideration of the interaction between the beads, and incorporation of element deletion technique and brittle cracking damage model, are developed to simulate the quasi-static and dynamic compression experiments. The simulation results such as load-deflection curves and failure modes are compared with the experimental observations. The comparison between quasi-static and dynamic conditions at similar strain levels can enrich our understanding of the time-dependent behavior of the granular materials in order to improve the accuracy and robustness of the existing constitutive laws.


Quasi-Static and Dynamic Confined Compressive Behavior of Glass Beads by In-Situ X-Ray Micro-Computed Tomography

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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