This work provides a structural analysis of small-scale 3D-printed wind turbine ribs subjected to compression. The ribs were manufactured according to NACA 23015 and NACA 633618 geometries, with polylactic acid (PLA) and polylactic acid with carbon fiber additives (CF-PLA). In addition, holes were manufactured into the sample bodies by either 3D printing or drilling for being compared with solid samples. The compression testing was performed by following the ASTM 695D standard, whereas the beginning and propagation of delamination were assessed with the ASTM 5528 standard. Experimental results revealed that 3D-printed built-in holes provided higher compression strength, hence higher structural efficiency, than the drilled samples. Significant improvement by adding carbon fiber additives into the PLA resin system in comparison to raw PLA was detected for at least one of the studied airfoil profiles. NACA geometries also represented a key parameter for avoiding stress concentration areas, as the FEM modeling supported. However, in damaged areas, fracture mechanisms were observed such as bead-bridging, which is a key parameter in reinforcing and consolidating the specimen bodies. Working in better interphase bonding and different additives between beads and layers is highly suggested for future studies.
The effects of varying interfacial conditions between two contacting hollow cylinders on the propagation of helical Lamb waves are studied. Experiments were carried out on two aluminum hollow cylinders (114 mm in outer-diameter and 6 mm of wall thickness) axially loaded by a horizontal press to control contact interfacial stiffness. An ultrasonic measurement setup using broadband transducers, with semispherical contact probes coupled to the cylinders surface, in a pitchcatch configuration is presented. Time-frequency representation (TFR) is employed to accurately perform mode identification of ultrasonic captured signals. The effect of different interfacial contact conditions in mechanically joined cylinders into propagation parameters of helical Lamb waves is studied. Finally, a comparison of sensitivity, between Lamb waves in straight and helical propagating paths, under different interfacial conditions is presented.
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