Fueled by their excellent stiffness-to-weight ratio and the availability of mature manufacturing technologies, filament wound carbon fiber reinforced polymers represent ideal materials for thin-walled laminate structures. However, their strong anisotropy reduces structural resistance to wall instabilities under shear and buckling. Increasing laminate thickness degrades weight and structural efficiencies and the application of a dense internal core is often uneconomical and labor-intensive. In this contribution, we introduce a convex linear semidefinite programming formulation for truss topology optimization to design an efficient non-uniform lattice-like internal structure. The internal structure not only reduces the effect of wall instabilities, mirrored in the increase of the fundamental free-vibration eigenfrequency, but also keeps weight low, secures manufacturability using conventional three-dimensional printers, and withstands the loads induced during the production process. We showcase a fully-automatic procedure in detail for the design, prototype manufacturing, and verification of a simply-supported composite machine tool component, including validation with roving hammer tests. The results confirm that the 3D-printed optimized internal structure almost doubles the fundamental free-vibration eigenfrequency, allowing to increase working frequency of the machine tool, even though the ratio between elastic properties of the carbon composite and the ABS polymer used for 3D printing exceeds two orders of magnitude.
This paper deals with the design of the carbon fibre composite driveshaft. This driveshaft will be used for connection between piston engine and propulsor of the type of axial-flow fan. Three different versions of driveshaft were designed and produced. Version 1 if completely made of Al alloy. Version 2 is of hybrid design where the central part is made of high strength carbon composite and flanges are made of Al alloy. Adhesive bond is used for connection between flanges and the central CFRP tube. Version 3 differs from the version 2 by aplication of ultrahigh-strength carbon fibre on the central part. Dimensions and design conditions are equal for all three versions to obtain simply comparable results. Calculations of driveshafts are described in the paper.
Considering a possible use of carbon fiber reinforced polymers (CFRP) in automotive gearboxes, this paper investigates influence of oil on mechanical properties of CFRP. This particular research was a part of wide-focused project whose goal was to design a gearbox using large proportion of CFRP in order to reduce mass and noise. Part of this design was a filament wound shaft. In order to investigate an influence of oil on such part, 18 test specimens were manufactured. The specimens were simple tubes 15 x 9.9 x 300 mm with layup similar to the designed shaft. One half of the specimens was tested immediately and the other one after immersing in gearbox oil at elevated temperature of 80 °C for 83 days. Both test groups were then compared. The specimens were tested statically and dynamically in 4-point bending setup. Immersed specimens were regularly weighted, and mass progress was watched expecting diffusion behavior. The results have shown likely no negative effect of oil on CFRP and no oil diffusion in the material. Both flexural stiffness and maximal force increased and degradation of stiffness during cyclical loading decreased after oil exposure.
Carbon fiber reinforced polymers (CFRP) have an enormous potential in mass reduction of vehicles and therefore also CO2 emissions. Also, their contribution to noise reduction is considerable. There are, however, challenges during designing as CFRP are not isotropic materials so each application has to be viewed individually according to the current function. The goal of presented project was in using the advantages of CFRP materials for application in gearbox design for an electric vehicle and a research of potential for mass and noise reduction. There was a reference conventional gearbox provided by project partners KIMM (Korea Institute of Machinery and Materials) and Samyang company. The gearbox in electric vehicle is a significant source of noise because of high RPM and absence of combustion engine, so using CFRP can help in noise reduction. The high RPM also lead to higher frequencies that are uncomfortable for people. The first goal was to design and manufacture a CFRP gearbox casing and embedded differential case. That includes specification of material, layout and shape with use of FEM analysis in order to achieve sufficient mechanical properties comparable with those of the reference gearbox. These properties include for example stiffness of casing in bearings in order to achieve small deflection of shafts and thus better contact of gears. Another part of this project was done in order to explore a potential use of filament-wound shafts in gearboxes. There were several versions of hybrid shafts (CFRP/steel) manufactured and then steel gear rings were bonded on the surface of the shafts. There was also a reference steel shaft manufactured. The shafts were later tested on closed-loop test stand and the results of noise, vibration and transmission error of CFRP shafts were compared with the reference steel shaft. Another comparison was focused on evaluation of mass and moment of inertia reduction.
In this contribution, we design a minimum-weight truss reinforcement of a thin-walled composite beam, such that the fundamental free-vibrations eigenfrequency of the beam is increased to a specific value. The reinforcement structure is designed using techniques of topology optimization and produced using additive manufacturing, in order to achieve economical design and minimize manual interventions in the fabrication process. Finally, an experimental validation of theoretical outcomes is performed on an additively manufactured prototype.
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