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.
This paper describes a novel technique for bonding polymeric-microfluidic devices using microwave energy and a conductive polymer (polyaniline). The bonding is achieved by patterning the polyaniline features at the polymer joint interface by filling of milled microchannels. The absorbed electromagnetic energy is then converted into heat, facilitating the localized microwave bonding of two polymethylmethacrylate (PMMA) substrates. A coaxial open-ended probe was used to study the dielectric properties at 2.45 GHz of the PMMA and polyaniline at a range of temperatures up to 120 • C. The measurements confirm a difference in the dielectric loss factor of the PMMA substrate and the polyaniline, which means that differential heating using microwaves is possible. Microfluidic channels of 200 µm and 400 µm widths were sealed using a microwave power of 300 W for 15 s. The results of the interface evaluations and leak test show that strong bonding is formed at the polymer interface, and there is no fluid leak up to a pressure of 1.18 MPa. Temperature field of microwave heating was found by using direct measurement techniques. A numerical simulation was also conducted by using the finite-element method, which confirmed and validated the experimental results. These results also indicate that no global deformation of the PMMA substrate occurred during the bonding process.
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