The flow of liquid polydimethylsiloxane (PDMS, Dow Corning Sylgard 184, 10 : 1 base to cross-linker ratio) in open, rectangular silicon microchannels, with and without a coating (100 nm) of poly-tetra-fluoro-ethylene (PTFE), was studied. Photolithographic patterning and etching of silicon wafers was used to create microchannels with a range of widths (∼5-50 μm) and depths (5-20 μm). Experimental PDMS flow rates in both PTFE-coated and uncoated channels were compared to an analytical model based on the work of Lucas and Washburn. The experimental flow rates matched the predicted flow rates reasonably well when the channel aspect ratio (width to depth), p, was less than 2. For channels with p > 2, the observed flow rates progressively lagged model predictions with increasing p. The experimental data, including zero flow rates in certain high aspect ratio PTFE-coated channels, can largely be explained by changes in the front and upper meniscus morphology of the flow as the channel aspect ratio is varied. The results strongly suggest that meniscus morphology needs to be taken into account to accurately model capillary flow in microchannels, especially those with large aspect ratios.

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In situ TEM straining allows probing deformation mechanisms of ultrafine-grained and nanocrystalline metals. While obtaining statistically meaningful information about microstructural changes using conventional bright-field/dark-field imaging or diffraction is time consuming, automated crystal orientation mapping in TEM (ACOM-TEM) enables tracking orientation changes of hundreds of grains simultaneously. We use this technique to uncover extensive grain rotations during in situ tensile deformation of a freestanding, ultrafine-grained aluminum film (thickness 200 nm, mean grain size 180 nm). During loading, both the fraction of grains that undergo rotations and the magnitude of their rotations increase with strain. The rotations are partially or fully reversible in a significant fraction of grains during unloading, leading to notable inelastic strain recovery. More surprisingly, the direction of rotation remains unchanged for a small fraction of grains during unloading, despite a sharp reduction in the applied stress. The ACOM-TEM measurements also provide evidence of reversible and irreversible grain/twin boundary migrations in the film. These microstructural observations point to a highly inhomogeneous and constantly evolving stress distribution in the film during both loading and unloading.

This study focuses on the possible uses of physics engines, and more specifically the Bullet physics library, to simulate granular systems. Physics engines are employed extensively in the video gaming, animation and movie industries to create physically plausible scenes. They are designed to deliver a fast, stable, and optimal simulation of certain systems such as rigid bodies, soft bodies and fluids. This study focuses exclusively on simulating granular media in the context of rigid body dynamics with the Bullet physics library. The first step was to validate the results of the simulations of direct shear testing on uniform-sized metal beads on the basis of laboratory experiments. The difference in the average angle of mobilized frictions was found to be only 1.0°. In addition, a very close match was found between dilatancy in the laboratory samples and in the simulations. A comprehensive study was then conducted to determine the failure and post-failure mechanism. We conclude with the presentation of a simulation of a direct shear test on real soil which demonstrated that Bullet has all the capabilities needed to be used as software for simulating granular systems.

A physics engine is computer software which provides a simulation of certain physical systems, such as rigid body dynamics, soft body dynamics and fluid dynamics. Physics engines were firstly developed for using in animation and gaming industry; nevertheless, due to fast calculation speed they are attracting more and more attention from researchers of the engineering fields. Since physics engines are capable of performing fast calculations on multibody rigid dynamic systems, soil particles can be modeled as distinct rigid bodies. However, up to date, it is not clear to what extent they perform accurately in modeling soil behaviour from a geotechnical viewpoint. To investigate this, examples of pluviation and vibration-induced densification were simulated using the physics engine called Bullet physics library. In order to create soil samples, first, randomly shaped polyhedrons, representing gravels, were generated using the Voronoi tessellation approach. Then, particles were pluviated through a funnel into a cylinder. Once the soil particles settled in a static state, the cylinder was subjected to horizontal sinusoidal vibration for a period of 20 seconds. The same procedure for sample preparation was performed in the laboratory. The results of pluviation and vibration tests were recorded and compared to those of simulations. A good agreement has been found between the results of simulations and laboratory tests. The findings in this study reinforce the idea that physics engines can be employed as a geotechnical engineering simulation tool.