Dipartimento di Ingegneria Meccanica, Energetica e Gestionale - Tesi di Dottorato
Permanent URI for this collectionhttps://lisa.unical.it/handle/10955/100
Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Ingegneria Meccanica, Energetica e Gestionale dell'Università della Calabria.
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Item 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, AlessandraTrends 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.Item Toughening mechanisms and damage tolerance of bioinspired interfaces(Università della Calabria, 2020-03-06) Morano, Chiara; Furgiuele, Franco; Alfano, MarcoBiologically inspired designs were deployed into selective laser sintering of polyamide substrates to study the mechanics of adhesion and debonding of adhesive bonded structural interfaces. In particular, through extensive series of experiments and simulations, the present study covers the effect of hollow channels, mimicking the base plate of the Amphibalanus amphitrite, and of sinusoidal interfaces, resembling those observed in sutures joints, on the mechanics of crack propagation in adhesive bonds. A model material system comprising adhesively bonded 3D printed substrates in the Double Cantilever Beam (DCB) configuration was selected for the analyses. Adhesive bonding and subsequent mechanical tests revealed the occurrence of a crack trapping effect, which hinders crack propagation and enhances energy dissipation with respect to the baseline interface. The use of bioinspired structures is shown to improve the performances of adhesive joints, enabling damage tolerance and, in the case of subsurface channels, also a weight reduction. Numerical simulations, carried out using finite element analysis (FEA) with interface elements, were also executed to gain a deep understanding of all mechanisms observed experimentally. The simulations were able to mimic the serrated behavior observed in experimental load-displacement responses, which was due to the snap-through interfacial cracking mechanism, i.e., a sudden and almost instantaneous growth of apparently stable cracks. Moreover, the mechanisms of fracture observed in the experiments (e.g., nucleation of a secondary crack at the interface) were reproduced with good accuracy in finite element simulations. The overall analysis demonstrates that is possible to improve joints effective fracture toughness by modifying joints architecture, even without any modification of adhesive type and/or interface properties (e.g., surface energy). This study further confirms that additive manufacturing represents a powerful platform for the experimental study of bio-inspired materialsItem Analysis of mechanical properties of cold spray coatings for tribological and vacuum applications(Università della Calabria, 2020-07-13) Magarò, Pietro; Furgiuele, Franco; Maletta, Carmine; Tului, MarioCold Gas Dynamic Spray (CGDS) is a process in which solid particle are accelerated in a de Laval nozzle toward a substrate. At the impact, if the particle velocity exceeds a critical value, i.e. the critical velocity, particles undergo plastic deformation and the consequent adiabatic shear instability provides material flow and heat for bonding. This phenomenon is the main driving force for the adhesion of the coating to the substrate. Compared other thermal spray techniques, since it utilizes kinetic rather than thermal energy for deposition, it offers several technological advantages; in fact, residual stresses, oxidation and chemical reactions can be avoided. Materials such as metals, ceramics, composites and polymers can be deposited using cold gas dynamic spray, creating new opportunities in order to obtain particular properties; in fact, good coatings using hard metals can be obtained with the purpose to enhance the tribological properties of such mechanical components. Therefore, the expected qualitative leap in using CGDS is magnified in harsh environments with great benefits predicted in design flexibility gains, precision improvements, production time reductions, cost reduction, integration of additional embedded functionalities. The purpose of this thesis is to demonstrate the possibility to obtain good deposits of Stellite-6 with the aim to enhance the surface resistance during sliding condition, while mechanical and vacuum properties of pure titanium coatings were analyzed for possible application in ultra high vacuum (UHV) systems at the European Organization for Nuclear Research (CERN). This thesis, firstly, analyzes the effects of process parameters on mechanical and tribological properties of Stellite-6 coatings. The gas pressure and temperature as well as the traverse speed of the deposition torch were considered as significant process parameters. The aim is to overcome some technical issues arising in the cold spray deposition of hard anti-wear metallic coatings, such as Stellite-6, due to their high strength and melting point. A High-Pressure CGDS equipment was used and systematic studies were carried out for a deeper understanding of the effects of all investigated process parameters. A particular focus has been put on the substrate temperature, that can be regarded as an indirect process parameter. This latter, in fact, was monitored in-situ during deposition by infrared thermography (𝐼𝐼𝐼𝐼). The microstructure was analyzed by both optical and scanning electron microscopic observations. Mechanical properties were analyzed by instrumented micro- and nano-indentation measurements. Hardness (𝐻𝐻) and Young's modulus (𝐸𝐸) were considered as affective parameters to estimate the inter-particle cohesion strength and the work hardening of the coating. Results revealed that the substrate temperature, that is affected by the process parameters, plays a fundamental role in the coating formation process, and, both mechanical and tribological properties, of CGDS Stellite-6 coatings are mainly affected by the impact temperature of the particle-substrate system. It is also well-known that this alloy undergoes several physical changes at the interface during dry sliding while is sensitive to the loading conditions and environment. Due to these micro-structural alterations, the wear behavior of the alloy is modified, which linear Archard-like wear models could not capture. To better understand the wear performance a Stellite-6 coatings in-situ, a mechanistic model of wear would be desirable, so a systematic experimental study was performed. Tests were done under combinations of sliding speed (0.1–0.5 𝑚𝑚/𝑠𝑠) and contact pressure (0,5–5 𝑀𝑀𝑀𝑀𝑀𝑀). Platelet wear and subsurface cracking was seen in high speed tests, as well as evidence of plastic deformation at the wear surface. These results suggest the platelet wear observed is more likely a consequence of adhesive wear. On the other hand, in low speed conditions detachment and pull-out phenomena mainly affect the worn surface of coatings leading to a type of fatigue wear known as “nano-grain wear” that does not allow to use the wear model proposed by Archard. Unique to this study, the cross-sectional nano-indentation study showed the stiffness of material at and below wear interface to drop significantly. The last section was aimed by the necessity to overcome some technical issues, usually experienced during pure titanium deposition. These latter are mainly related to poor coating compactness and adhesion to the substrates. These technical issues become even more stringent when dealing with vacuum systems as they could affect the leak tightness and gas release in UHV. Preliminary micrographic observations were carried out to select the optimal values of the process parameters, that are pressure (𝑝𝑝) and temperature (𝑇𝑇) of the propellent gas. Mechanical properties of deposits were subsequently analyzed at the nano/micro and macro scale by instrumented indentations and adhesion tensile tests respectively. Vacuum properties were analyzed by outgassing rate measurements, thermal desorption spectroscopy (TDS) and helium tightness tests. Indentation results revealed that compact and homogeneous coatings can be obtained if high energy deposition parameters (𝑝𝑝~4 𝑀𝑀𝑀𝑀𝑀𝑀,𝑇𝑇~1000° 𝐶𝐶) are applied. However, a limited adhesion strength on stainless steel substrates is the main technical issue of the coating process. Outgassing and TDS tests revealed an abnormal nitrogen release that is attributed to gas entrapped during deposition or during the production stage of the Ti powders as N2 is used in the gas atomization process. Finally, helium leak rates were found to be incompatible with UHV requirements applied in modern particle accelerators. Much higher helium leak rates were detected along the interface between the coating and the substrate than through the thickness. These results confirm that the interface represents the weakest point of the bi-material system. Further studies are needed to solve this technical issue.