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This work presents experimental characterization and numerical modeling of laterally deflecting polydimethylsiloxane (PDMS) membranes under pneumatic actuation. The device for this study is a membrane valve seat that partially closes a perpendicular fluid microchannel, fabricated using single-layer soft lithography. Membranes with thickness between 8 and 14 µm have been experimentally tested up to 207 kPa, and maximum lateral displacement beyond 20 µm has been demonstrated. Investigation of geometric parameters by factorial design shows that the height of the membrane is more dominant than the width and thickness, and this is attributed to the zero-displacement boundary condition at the foot of the membrane where it is bonded to a flat substrate. A numerical model that incorporates hyperelastic material testing data shows close agreement with the deflection behavior of experimental samples, accurately predicting that a membrane of 10 µm thick, 100 µm wide and 45 µm tall deflects approximately 13 µm at 207 kPa. Simulation further shows that sidewall effects from bulk compression of the elastomer material in the actuation cavity have a significant effect, reducing maximum displacement by as much as 15% over predictions based on deformation that is limited strictly to the membrane only. Experimental yield, SEM imaging and stress simulations emphasize that the membrane foot region requires the greatest attention in terms of process development.

Emerging technologies commonly known as "rapid prototyping" fabricate solid objects directly from computer models by building parts in thin layers. Three-dimensional printing is one such process that creates engineering prototypes and tooling by joining powder particles selectively on a layer-by-layer basis. The powder-based approach offers tremendous flexibility in geometry and materials, but it makes layer position accuracy a fundamental concern for dimensional control in the vertical direction. Ideally, each powder layer is generated at a vertical position that remains fixed, at a prescribed distance with respect to a machine reference. However, compressive loads imparted to a stack of layers (by the weight of subsequent layers, for example) may cause the layers to displace downward. Develops a model for layer displacement using experimental data for compressibility and applied load. Compares predictions made from the model to measured displacements, and the predictions successfully captured the relative magnitudes of actual errors at various positions within layered powder beds. Position changes were most severe in the middle regions of the powder beds, with diminishing magnitude towards the top and bottom. Uses aluminium oxide powder in two different sizes (approximately of 10-micron and 30-micron diameter) and two different shapes (platelet and spherical) in the studies. The average measured displacement in a 76.2mm deep bed ranged from 23 microns for a 30-micron platelet-shaped powder to over 260 microns for a 9micron platelet-shaped sample.

This paper studies the effect of flow channel scaling on fuel cell performance. In particular, the impact of dimensional scale on the order of 100 micrometers and below has been investigated. A model based on three-dimensional computational flow dynamics has been developed which predicts that very small channels result in significantly higher peak power densities compared to their larger counterparts. For experimental verification, microchannel flow structures fabricated with varying sizes in SU-8 photoepoxy have been tested with polymer electrolyte membrane electrode assemblies. The experimental results confirm the predicted outcome at relatively large scales. At especially small scales ͑Ͻ100 m͒, the model ͑which does not consider two-phase flow͒ disagrees with the measured data. Liquid water flooding at the small channel scale is hypothesized as a primary cause for this discrepancy.