Zinno, Alberto (2010) Multiscale Approach for the Design of Composite Sandwich Elements. [Tesi di dottorato] (Inedito)

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Abstract

In the present work, composite sandwich components, that perfectly match the challenging demands of lightweight and more customized structures, have been characterized and designed as a roof panels of a railway vehicle. The most critical issue related to the design and assessment of composite sandwich structures are discussed and analyzed in a multiscale procedure. A multiscale procedure has been developed using knowledge-based procedure for the optimal stiffness design of composite sandwich structures under some classified design rules. Recent developments of multifunctional design tools, integrating structural and functional features, enables a next step toward the exploitation of the composite sandwich benefits in a wide range of applications In particular new phenolic impregnated composite skins have been characterized and involved in sandwich configuration for load carrying components. The selected composite materials have been analyzed with different core configuration and the use of both numerical and analytical tools have been assessed with particular attentions to various failure mode that can be expected.. However, the use of fiber reinforced composite materials presents a significant challenge with respect to the methods of joining to be used in body fabrication. At this aim the project provides the characterization of potential joining techniques available to the railway industry involving both composite and aluminum components. Problems related to strength and durability of the joints have been experimentally characterized. The durability of composites, in addition to being dependent on loading conditions, is strongly dependent on the environmental conditions, in terms of the specific combinations of temperature, relative humidity, exposure to electro-magnetic radiation, to solvents, acid and alkaline conditions and of their (cyclic) evolution during time. Since the degradation process of a composite sandwich structure depends on the environmental conditions, type of skins and core material, and production process, mechanical properties through accelerated ageing tests have been performed in order to predict long-term performances of sandwich composites and to determine the correlation between mechanical damage and aging due to different environmental factors.. In addition to the aforementioned issues, in order to reliably predict the structural safety of composite sandwich structures, understanding the adverse effect of in-service impact events (e.g. impact and penetration damage) has become important in the transportation industry. Both quasi static and dynamic impact have been experimentally analyzed in the present study and the damage mechanism have been related to the type of impact events. Finally optimization and validation of the designed sandwich structures have been performed by means of finite element simulation.

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