Three‐dimensional (3D) printing processes are nowadays leading the charge in transforming traditional art, engineering, and manufacturing processes. In this study, the structural and thermal behavior of commercially available filaments composed of synthetic poly(acrylonitrile‐co‐butadiene‐co‐styrene) thermoplastic as well as poly(lactic acid) and poly(lactic acid)/polyhydroxyalcanoate reinforced with bamboo (Bambusa sp.) wood flour composite biothermoplastics were assessed by differential scanning calorimetry and infrared spectroscopy, aiming to understand the modifications that occur at the molecular level during their 3D printing. It has been determined that the biothermoplastic materials undergo both molecular reorientations related to tacticity increase and crystallinity decrease when submitted to 3D printing extrusion, while the synthetic thermoplastic undergoes crosslinking due to its butadiene component. All of the studied materials present good water stability (with water uptake values between 0.8% and 24%), and the water absorption follows a pseudo‐Fickian mechanism. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019.
Material Extrusion-Based Additive Manufacturing Process (ME-AMP) via Fused Filament Fabrication (FFF) offers a higher geometric flexibility than conventional technologies to fabricate thermoplastic lightweight sandwich structures. This study used polylactic acid/polyhydroxyalkanoate (PLA/PHA) biodegradable material and a 3D printer to manufacture lightweight sandwich structures with honeycomb, diamond-celled and corrugated core shapes as a single part. In this paper, compression, three-point bending and tensile tests were performed to evaluate the performance of lightweight sandwich structures with different core topologies. In addition, the main failure modes of the sandwich structures subjected to mechanical tests were evaluated. The main failure modes that were observed from mechanical tests of the sandwich structure were the following: face yielding, face wrinkling, core/skin debonding. Elasto-plastic finite element analysis allowed predicting the global behavior of the structure and stressing distribution in the elements of lightweight sandwich structures. The comparison between the results of bending experiments and finite element analyses indicated acceptable similarity in terms of failure behavior and force reactions. Finally, the three honeycomb, diamond-celled and corrugated core typologies were used in the leading edge of the wing and were impact tested and the results created favorable premises for using such structures on aircraft models and helicopter blade structures.
Balsa wood is a natural cellular material with an excellent resistance-toweight ratio that is ideal for manufacturing the core of sandwich structures. In this study, sandwich specimens with a carbon-fiberreinforced polymer (CFRP) skin and a balsa wood core were tested with static and dynamic loading. Three-point flexural tests in static regime determined the mechanical characteristics of the CFRP-balsa specimens that were needed for subsequent fatigue strength tests. Also, experimental research was performed on the Charpy impact response of the CFRP-balsa sandwich specimens. This study implemented an accelerated fatigue testing method to identify and predict the mean fatigue life of the CFRP-balsa sandwich specimens subjected to cyclic fatigue via three-point flexural tests. Using the accelerated fatigue and the three-point flexural testing methodology on the CFRP-balsa sandwich specimens, the testing period was reduced by 11.9 times, and thus the material costs necessary for the tests were also reduced. Also, the breaking surfaces were analysed to reveal the failure modes of CFRP-balsa specimens subjected to static and fatigue tests at threepoint flexural and at impact tests.
This study concerns the use of the fused filament fabrication technique to create models of the landing gear of an unmanned aircraft. These components are made of filament with short fibers (chopped fibers) of carbon fiber and fiberglass. In order to identify the material with the high mechanical strength, the designed models were subjected to a finite element analysis and to a three-point bending test, followed by a microscopic examination of the tested components. Following a comparative study, both the finite element analysis results and the three-point bending test results provided similar results, with a relative error of 2%, which is acceptable in the aviation field. After analyzing all the results, it was found that the carbon fiber-reinforced polymer material has the highest mechanical performance, with a bending strength of 1455 MPa. Among the fused filament fabricated landing gears, the one with the best mechanical performance was polyethylene terephthalate with short carbon fiber, which had a bending strength of 118 MPa. Microscopic analysis of the landing gear models, manufactured by the fused filament fabrication process, indicated the typical defects of composite filaments: voids and interlayer voids.
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