Manufacturing, characterization and modelling of advanced materials

Research focus

The Peer review has evaluated this group as Average

The future generations of aircraft will possibly need the adoption of composite materials for large parts of their primary structure (e.g. A380, B787, AB609), preferably implementing some advanced applications like smart structures and nano-functionalized materials. Therefore, the research is focused towards the development of material systems, manufacturing technologies and analysis techniques for overcoming their typical drawbacks like cost, degradation, brittleness and even difficulty in numerical investigation, experimental testing-monitoring and capability in exploiting real efficiency. These reasons led to the study of FML, smart and functionalized materials, suited numerical approaches, as well as efficient and ”green” technologies, as summarized here below. FML (fibre metal laminates), constituted by co-cured aluminium sheets and fibreglass plies lay-up, thanks to favourable structural efficiency, fatigue and impact damage tolerance have become an appealing alternative to composite and aluminium alloys in the aeronautical field. Constitutive materials and laminates were characterised for providing data related to elastic properties, plastic behaviour of aluminium sheets after curing processes and fibreglass plies multiple-damage mechanisms. Inelastic response, damage mechanics and fatigue behaviour were also experimentally tested and numerically analysed. Presently, main research focuses are: a) environmental ageing and residual performance, i.e. static and fatigue characterisation of laminates and joints at different temperatures, percent moisture absorption and types of low-energy-impact damages; b) evaluation of typical damage growth rate and environmental conditions; c) investigation and comparison of technological cycles and structural efficiency of viable repairing techniques; d) evaluation and comparison of NDI inspection procedures and accuracy assessment; e) buckling and fatigue-buckling behaviour of panels. Aerospace research pursues reduction of production/maintenance/repairing costs, safety levels preservation and operational efficiency, reliability and affordability improvements. To this purpose, smart materials should be conveniently adopted. The activity of the Materials and Technology Unit was particularly focused towards the study of smart structures, made of host composites embedding sensors (Bragg’s grating fiber optics (FBG)) and/or actuators (piezo-ceramics plates (PZT) or fibers (MFC), shape memory alloys (SMA) wires/strips). The issue of numerical simulation was successfully faced. Characterization of sensors/actuators/structures was completed through DSC, DMA tests. Embedding technologies were assessed, considering mechanical, thermal, chemical compatibility. Special methodologies (quick-pack unit) were developed, as well as original techniques for MFC production. Passive and active invasivity of actuators/sensors were investigated (thermal/mechanical analysis). Training strategies for OWSM and TWSM were set-up, as well as Joule and Peltier heating/cooling methods. Multiplexed WDM and TDM acquisition techniques for FBG were adopted in view of technological and structural health monitoring. Recently, two innovative material research areas were born, dealing with environmentally-friendly and functionalized materials. Biocomposites (biodegradable matrices + vegetable fibres) were considered for a/c interiors, in terms of mechanical, dynamic, impact behaviour and interface efficiency. Nano-functionalized materials were studied as self-healing polymers and super-hydrophobic plasma-coatings for polymer-matrixcomposites a/c lifting surfaces. Complex 3-D stress-states in thick laminates cannot be FEM-analyzed using layered shells. Once interlaminar cracks nucleate, their propagation depends on interlaminae toughness and crack-propagating available energy. Accordingly, laminate ultimate load-carrying capability prediction requires both highly refined FEM schemes and knowledge of interlaminar behaviour. Among the numerical approaches able to accomplish such objectives, attention was focused on interface (cohesive) elements to represent interlaminae. This enables the capturing of complex interlaminar states-of-stress, even for linear analyses at acceptable computational cost, and gives good correlation (nucleation zone, damage propagation, failure modes). Being Fibre Metal Laminates a promising class of materials when damage tolerance, buckling and impacts are concerned, a constitutive model was also developed to represent their overall behaviour, considering both aluminium sheets plasticity and composite plies inelasticity. It implements a bi-phasic material law and models the inelastic response through continuous damage-mechanics approaches. Good correlation was obtained when modelling damage propagation, post-buckling and impact phenomena. In the field of advanced technologies, new routes were investigated for composites (VaRTM), fiber metal laminates and smart materials. Fibre infusion technologies (RTM and VaRTM) to produce advanced composites are raising interest in the aerospace industry. Benefits in terms of product quality and Research topic 4.2 - Manufacturing, characterization and modelling of advanced materials 2-51 performance, process cleanness and cost are expected. At DIA, infusion process mechanisms were studied; reinforcing fabrics and tows permeability measurements were developed to investigate the resin transport mechanisms during infusion in relation to fibre characteristics (material, dimensions, packing, wettability) and fabric distribution (number of layers, areal weight). The capability to produce high-thickness composite laminates by closed-mould vacuum-assisted RTM process were approached to estimate benefits/limitations, as well as viability of FO embedding for health monitoring. Besides, original procedures were set-up to produce curved FML components, through a mixed approach exploiting filament-windingdeposition and oven-curing. Finally, manufacturing technologies of smart structures were developed (training, embedding, inspection, assessment).

Dipartimento di afferenza

Dipartimento di Ingegneria Aerospaziale

Docenti afferenti

Giuseppe Sala (Full Professor)
Luca Di Landro (Associate Professor, at DIA since 2005)