Percorrer por autor "Cláudio, Ricardo"
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- Design optimization of cruciform specimens for biaxial fatigue loadingPublication . Baptista, Ricardo; Cláudio, Ricardo; Reis, L.; Guelho, I.; Freitas, M.; Madeira, J. F. A.In order to correctly assess the biaxial fatigue material properties one must experimentally test different load conditions and stress levels. With the rise of new in-plane biaxial fatigue testing machines, using smaller and more efficient electrical motors, instead of the conventional hydraulic machines, it is necessary to reduce the specimen size and to ensure that the specimen geometry is appropriated for the load capacity installed. At the present time there are no standard specimen’s geometries and the indications on literature how to design an efficient test specimen are insufficient. The main goal of this paper is to present the methodology on how to obtain an optimal cruciform specimen geometry, with thickness reduction in the gauge area, appropriated for fatigue crack initiation, as a function of the base material sheet thickness used to build the specimen. The geometry is optimized for maximum stress using several parameters, ensuring that in the gauge area the stress is uniform and maximum with two limit phase shift loading conditions. Therefore the fatigue damage will always initiate on the center of the specimen, avoiding failure outside this region. Using the Renard Series of preferred numbers for the base material sheet thickness as a reference, the reaming geometry parameters are optimized using a derivative-free methodology, called direct multi search (DMS) method. The final optimal geometry as a function of the base material sheet thickness is proposed, as a guide line for cruciform specimens design, and as a possible contribution for a future standard on in-plane biaxial fatigue tests.
- Development of composites of PLA filled with different amounts of rice husk fibers for fused deposition modelingPublication . Pereira, Daniel F.; Branco, A.C.; Cláudio, Ricardo; Marques, Ana C.; Figueiredo-Pina, C. G.Polylactic acid (PLA) has been used as a matrix material to produce composites with natural fibers, which present several advantages, being one of them the addition of value to agricultural waste. Thus, this study aims to develop a PLA 3D filament with the incorporation of a waste agriculture product (rice husk (RH)). For that, RH fibers were prepared, and PLA was loaded up to 20% RH. The filaments were obtained by extrusion. Finally, samples were produced by fused deposition modeling (FDM). The fibers and filaments’ density and thermal stability (TGA) were determined, and their chemical structure changes due to alkali treatment were accessed by Fourier Transform Infrared Spectroscopy (FTIR). Printability tests were performed, and printed samples were characterized in terms of density, water absorption, and mechanical behavior (compression, tensile, and flexural tests). The results showed that the alkali treatment changed the chemical structure of RH fibers and TGA showed that the filaments did not degrade significantly until 250ºC. The best printability was achieved with 5% of HR content and was the one that showed the lowest mechanical properties reduction. Overall, the present work showed that RH fibers can be successfully used as a filler in PLA filaments for FDM.
- STEM KIT: Teachers’ NotebookPublication . Guedes, Mafalda; Piteira, Martinha; Nunes, Nuno; Cláudio, Ricardo