This paper investigates the fatigue behaviour of polylactic acid (PLA) parts processed by fused deposition modelling (FDM) additive manufacturing process. PLA is becoming a commonly used thermoplastic in open-source FDM machines for various engineering applications and it is essential that mechanical properties and performance of FDM-processed PLA parts must be properly understood. Very little data exist on the fatigue performance of PLA parts processed by FDM additive manufacturing. This study looks at the effect of part build orientations on the tensile fatigue properties of PLA material. A Cube 3D printer was used to print dog-bone test specimens in three (X, Y and 45°) different build orientations. These dog-bone parts were based on ASTM D638 standard and were cyclically tested at 80, 70, 60 and 50 % nominal values of the ultimate tensile stress by using a Zwick Z010 universal testing machine. Results show that in static loading, the FDM-processed PLA parts in X build orientation exhibit higher tensile stress, in the range of 60-64 % of that of injection moulded PLA material, compared to those built in Y and 45°orientations. But under tensile cyclic loading condition, the parts in 45°build orientation show higher fatigue life than the parts in X and Y build orientations for the same percentage of applied static loads. This paper adds knowledge to fill the gap on the fatigue characteristics of the PLA parts processed through FDM and would be useful in engineering design applications of such parts subjected to cyclic loading conditions.

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Numerical investigation of mixing in microchannels with patterned grooves.

To improve mixing, obstacles have been placed in the channel to try to disrupt flow and reduce the diffusion path. The disruption to flow velocity field alters the flow direction from one fluid to another. In this way, convection may occur to enhance the mixing. Ideally, properly designed geometric parameters, such as layout and number of obstacles, improve the mixing performance without increasing the pressure drop. In this work, the commercial computational fluid dynamics (CFD) tool for microfluidics is used to study the mixing of two liquids in a "Y" channel. The results indicate that asymmetric layout of the obstacle has more effect on the mixing than the number of obstacles. Placing obstacles in the microchannels is a novel method for mixing in microfluidic devices, and the results can provide useful information in the design of these devices.

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