Browsing by Author "Treviso, Alessandra"

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Development of a CAE-basedapproach for the concurrent design, manufacturing and testing of hybrid metal-composite spur gears
(Università della Calabria, 2020-02-19) Catera, Piervincenzo Giovanni; Furgiuele, Franco; Mundo, Domenico; Treviso, Alessandra
Trends in emission limitations and fuel efficiency impose a more efficient energy exploitation in many application fields of mechanical systems. In this direction, the lightweighting of mechanical structures represents a powerful strategy, above all in the transportation industry, where geared transmissions play a key role. Here, these components are designed in such a way that performance criteria are met at the minimum weight, without compromising the requirements of reliability and safety. In this context, the aim of the present work is the development of new strategies for the design of geared systems, where the concept of gear body lightweighting with geometrical modifications is substituted by the one applied to the material, in order to improve the strength-to-weight ratio and reduce vibrations in the overall mechanical system. In particular, the research is focused on innovative methods for the simulation, manufacturing and testing of a hybrid gear, in which a metal rim is joined with a composite body. In detail, the contribution of the gear body stiffness is studied by means of a multi-scale approach, which starts from the interaction between matrix and fibres at the micro-scale to derive the lamina properties at the macro-scale. In this way, the anisotropy of the composite material can be accounted for, leading to an accurate modelling and evaluation of the mechanical properties of the gear. Additionally, two assembly techniques are used for joining the rim part to the body, which include adhesive bonding and interference fitting. Both techniques are analysed with experimental modal tests to characterize dynamic stiffness and damping in comparison to a lightweight metal gear with the same mass. At the same time, non-linear finite element (FE) simulations are executed for the evaluation of the static transmission error and meshing stiffness. Finally, the last part of the work deals with the experimental analysis of a hybrid gear pair during meshing in a dedicated test-rig, where the dynamic behaviour is analysed with respect to the variation of applied torque and rotational velocity. Noise and vibration behaviour of a solid-hybrid gear pair is compared to that of a pair composed by a solid and a lightweight metal gear. Experimental results show the great potentiality of the multi-material approach in mechanical power transmissions.
Finite Element models for the dynamic analysis of composite and sandwich structures
(2015-12-16) Treviso, Alessandra; Mundo, Domenico; Tournou, Michel
The use of lightweight multi-layered materials is dramatically changing the design process and criteria in many engineering fields. The transportation industry, for example, is facing major challenges in order to replace traditional materials while keeping at least the same level of passengers’ comfort and safety. In particular, the Noise, Vibration and Harshness (NVH) performances are affected by the novel combination of high stiffness and low density. If the aeronautic industry still heavily relies on testing to assess designs’ validity, such an approach cannot be applied to the automotive industry for the development costs would be too high. It is therefore necessary to identify CAE tools capable of giving realistic, reliable and cost-effective predictions of multi-layered structures’ behaviour under dynamic loadings. An often overlooked problem is that of damping which is generally higher in composite and sandwich structure but rarely it is also efficiently exploited, so that in most cases the classic approach of applying NVH treatments is followed. However, this procedure has a detrimental effect on the attained weight saving and on the global dynamic performance of lightweight structures, therefore leading to unsatisfactory results. Moreover, the variability of mechanical properties due to the low repeatability of some manufacturing processes can also have an impact on the global behaviour of the as-manufactured component. An early integration of damping prediction and an estimate of possible stiffness variations due to the manufacturing can actually lead to better designs in less time. In this thesis these challenges are tackled from the Computer Aided Engineering (CAE) point of view, thanks to the introduction of a novel finite element for the prediction of the damped response of generic multi-layered structures and the proposition of a CAMCAE approach to introduce manufacturing simulations at an early stage in the design and analysis process. In the first chapters, different analytical and numerical approaches for the modelling of multi-layered structures are presented and used for the development of a 1D finite element. The results of the mono-dimensional analysis show that zigzag theories are a cost-effective and accurate alternative to solid finite element models, motivating the development of a 2D element for the analysis of plates and shells. With respect to previous investigations on zigzag theories, the current study focus on their use for modal parameters prediction, i.e. eigenfrequencies, mode shapes and damping. It will be shown that compared to classic models, the zigzag elements are able to predict the dynamic response, damped and undamped, of beam, plates and shells with the same accuracy of 3D models but at a much lower computational cost. In the last chapter, the available homogenisation methods for the analysis of long fibres composites are reviewed and compared to more refined models based on manufacturing simulation algorithms. Results show that changes in manufacturing parameters lead to substantially different results. The goal is to show that CAM/FE coupling is possible already at an early design stage and that manufacturing simulations can be used as a mean to further optimise the performance of composite structures. As a final stage, an example of coupling between zigzag theories and manufacturing simulations is presented. Despite some limitations, the proposed methods increase the accuracy of the analysis and gives a better understanding of lightweight multi-layered structures. Further research could focus on the use of the developed zigzag elements for fatigue analysis and delamination modelling as well as detailed modelling of drop-off regions in the framework of CAM tools improvements