Annual review of condensed matter physics

X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information nee...

https://www.tandfonline.com/doi/pdf/10.1179/1743280413Y.0000000023

Quantitative X-ray tomography

Microfluidic technologies have emerged recently as a promising new route for the fabrication of uniform emulsions. In this paper, we review microfluidic methods for synthesizing uniform streams of droplets and bubbles, focusing on those that utilize pressure-driven flows. Three categories of microfluidic geometries are discussed, including co-flowing streams, cross-flowing streams, and flow focusing devices. In each category we summarize observations that have been reported to date in experiments and numerical simulations. We describe these results in the context of physical mechanisms for droplet breakup, and simple theoretical models that have been proposed. Applications of droplets in microfluidic devices are briefly reviewed.

https://iopscience.iop.org/article/10.1088/0022-3727/40/19/R01/pdf

Microfluidic methods for generating continuous droplet streams

Discrete element models for non-spherical particle systems: From theoretical developments to applications

DEM/CFD-DEM Modelling of Non-spherical Particulate Systems: Theoretical Developments and Applications

We investigate the properties of packings of frictionless non-spherical particles utilizing a dynamic particle expansion technique. We employ superquadric particles (superellipsoids), which allows us to explore how a broad range of particle shapes affect both the macroscopic and the local configurational properties of the system. We smoothly transition from spherical particles possessing only translational degrees of freedom to large aspect ratio non-spherical grains where rotational degrees of freedom are highly important. We demonstrate that the degree of anisotropy and local surface curvature of the particles have a profound effect on their packing properties, determining whether a random or an ordered packing is readily formed.

https://www.maths.tcd.ie/~garyd/Publications/Delaney2010_EPL_PackingSuperellipsoids.pdf

The packing properties of superellipsoids

/pdf/rheology-of-ordered-foams-on-the-way-to-discrete-16med1e6ib.pdf

Rheology of ordered foams—on the way to Discrete Microfluidics

Jamming is a popular and versatile soft robotic mechanism, enabling new systems to be developed that can achieve high stiffness variation with minimal volume variation. Numerous applications have been reported, including deep-sea sampling, industrial gripping, and use as paws for legged locomotion. This review explores the state-of-the-art for the three classes of jamming actuator: granular, layer and fibre jamming. We highlight the strengths and weaknesses of these soft robotic systems and propose opportunities for further development. We describe a number of trends, promising avenues for innovative research, and several technology gaps that could push the field forwards if addressed, including the lack of standardization for evaluating the performance of jamming systems. We conclude with perspectives for future studies in soft jamming robotics research, particularly elucidating how emerging technologies, including multi-material 3D printing, can enable the design and creation of increasingly diverse and high-performance soft robotic mechanisms for a myriad of new application areas.

https://www.mdpi.com/2076-0825/9/4/104/pdf

A Review of Jamming Actuation in Soft Robotics

DEM modelling of non-spherical particle breakage and flow in an industrial scale cone crusher

Investigating how tightly objects pack space is a long-standing problem, with relevance for many disciplines from discrete mathematics to the theory of glasses. Here we report on the fundamental yet so far overlooked geometric property that disordered mono-disperse spherical bead packs have significant local structural anisotropy manifest in the shape of the free space associated with each bead. Jammed disordered packings from several types of experiments and simulations reveal very similar values of the cell anisotropy, showing a linear decrease with packing fraction. Strong deviations from this trend are observed for unjammed configurations and for partially crystalline packings above 64%. These findings suggest an inherent geometrical reason why, in disordered packings, anisotropic shapes can fill space more efficiently than spheres, and have implications for packing effects in non-spherical liquid crystals, foams and structural glasses.

/pdf/disordered-spherical-bead-packs-are-anisotropic-4xo30hfsf7.pdf

Gary W. Delaney

Papers

The packing properties of superellipsoids

Rheology of ordered foams—on the way to Discrete Microfluidics

A Review of Jamming Actuation in Soft Robotics

DEM modelling of non-spherical particle breakage and flow in an industrial scale cone crusher

Disordered spherical bead packs are anisotropic