The need for new measurement techniques able to assess the nanofiller dispersion is still receiving great consideration when nanocomposites are developed. This occurs since different routes to disperse nanostructures generate molecular changes in polymer matrices that promote complex polymer–polymer and polymer–nanofiller interactions, which make difficult a suitable estimation of the dispersion. In this paper, ultrasonic waves at different frequencies and power were used for preparing nanocomposite samples and for evaluating the nanofiller dispersion. First, a patented method was used to disperse multiwall carbon nanotubes (MWCNTs) in polyamide 12 through extrusion assisted by low-frequency and high power ultrasound (with frequency ranging between 20 and 50 kHz). This “green” processing method was able to induce different states of dispersion of the nanofillers, as well as chemical modifications to polymer chains promoting branching reactions. Then, ultrasonic dynamic mechanical analysis (UDMA with ultrasound frequency in the megahertz range) was used to estimate the dispersion of the different nanocomposite samples. Compared to rheological measurement methods, UDMA provided a better estimation of the quality of dispersion, being sensitive both to the complex molecular architectures in polymer matrices and to the scattering due to MWCNT agglomerates.

A new procedure for the alignment of carbon nanotubes in a thermosetting matrix is proposed in this study. The two-step approach is based on (i) the alignment of carbon nanotubes (CNTs) in thermoplastic fibres by electrospinning and (ii) the transfer of these nanocompositefibres into a reactive thermosetting resin, in which they are easily soluble. After fibre dissolution, the CNTs remain aligned in the cured thermosetting matrix. The proof of concept is demonstrated by producing electrospunpolymethyl methacrylate (PMMA) fibres filled with single wall carbon nanotubes (SWCNTs) in the form of unidirectional tape, which are then solubilised into a vinylester (VE) matrix. The PMMA is easily dissolved by the styrene present in the VE resin, leaving SWCNTs aligned in the cured VE network, as confirmed by Raman spectroscopy studies. A 50% increase in elastic modulus (SWCNT 1.3 wt.%) has been obtained by dynamic mechanical analysis carried out in tensile mode at 1 Hz. Thanks to its ability to orient carbon nanotubes in a thermosetting matrix, the proposed method can be exploited also to transfer oriented nanofillers into continuous fibre composites, thus obtaining multiscale or hierarchical composites.

An overview of the current state of art of the ultrasonic treatment technology applied to polymer melts is presented. The research and technological advancements of the ultrasonic treatment as applied to development of polymeric materials are discussed. An analysis of the technological progress shows that the mechanism of the effects of ultrasound on polymer melts is not fully understood at present. Such lack in fully understanding the mechanism could limit the use of this versatile technology in future applications. Based on the critical analysis of the research progress to date, some key issues for a deeper understanding of the chemical and physical effects of ultrasound on polymer melts are identified.

Waterlogged wood samples of Ulmus sp. and Fraxinus sp. from the ancient harbor of Otranto in Southern Italy were radiocarbon dated by accelerator mass spectrometry (AMS) and examined for physical and chemical changes to assess the degree of degradation. The analyzed woods were dated to the 2nd half of the twelfth – 1st half of the thirteenth centuries AD. The results of all the used methods (maximum water content, basic density, shrinkage, XRD analysis and holocellulose content) indicated a low level of degradation in the inner part of the wooden find. The outer and middle part, on the other hand, showed a greater degradation level. An important result is the identification of a not homogeneous degradation in the different parts of the examined wooden block, which will affect the design of the consolidating treatment

Experimental organic–inorganic hybrid systems, based on silane functionalized difunctional and trifunctional epoxy resins and an alkoxysilane precursor mixture, containing small amounts of ammonium molybdate, are evaluated for potential use as adhesives cured at ambient temperatures. The precursor resin mixtures are found to exhibit a large increase in viscosity with a pseudoplastic behavior. Scanning electron microscopy (SEM) analysis shows the existence of siloxane domains with nanometric dimensions, except for the presence of microscopic molybdate particles. By monitoring the evolution of the glass transition temperature (Tg) during curing, varying the thickness of the specimens between 0.2 and 4.5 mm, it is found that the organic–inorganic hybrids display a significant increase in the final Tg over the parent unmodified epoxy resins, particularly in thin specimens and when ammonium molybdate is added. Small-angle X-ray scattering (SAXS) spectra show that the dimensions and typographic features of thick and thin specimens are similar, both containing an agglomeration of primary particles of 5-6 nm.

The growing use of reinforcement preforms during composite manufacturing requires resin soluble binders which significantly affect the properties of crosslinking thermosetting resins. In this study, for the first time the influence of an epoxy preforming binder on the curing kinetics and chemorheological behavior of a crosslinking epoxy matrix was studied. The results proved that the addition of the binder lead to a significant change of the curing behavior suggesting that the epoxy binder was an essential component needed to complete the stoichiometry of the resin-hardener mixture. The developed kinetic and chemorheological model of the experimental results could be used for process optimization

The influence of chemical treatments based on novel organic products on the consolidation of deteriorated wood by insect attack was evaluated on two hardwoods and one softwood: fir (Abies alba), beech (Fagus sylvatica) and deciduous oak (Quercus sp.). Degraded and intact specimens of the three wood species were impregnated with two different chemical treatments aimed to verify the potential synergic action of the novel products on wood. Then, the specimens were subjected to bending, compression parallel to the grain, impact, hardness and water absorption tests. Untreated specimens of the same botanical species, both degraded and non-degraded, were examined for comparison purposes. The experimental results showed a different effectiveness of the proposed chemical treatments to improve the mechanical and absorption properties of degraded wood. The most effective treatment was the one assuming the concurrent use of the studied novel consolidants. The species more susceptible of the enhancement in mechanical properties were fir and beech. The observed differentiations were most likely caused by the different structure of the botanical species considered, leading to a consequent different product penetration in the wood structure. The dimensional stability in terms of water repellent and antiswelling efficiency, after a three-month immersion in deionized water, was found to improve in all the treated wood specimens. Overall, experimental results showed that the impact of the chemical treatments was higher on degraded samples than on intact ones.

The article investigates the effects of long term environmental aging on thermal and mechanical properties of epoxy-silica hybrids. These nanostructured materials, prepared by non-aqueous sol-gel process and in situ generation of nanosilica during epoxy curing at room temperature, present the potential to be used as cold-cured adhesives for civil engineering and Cultural Heritage applications. A specifically developed conditioning procedure for these cold-cured nanostructured materials was applied before moisture/ water absorption tests. The work evidenced the superior durability of the studied epoxy-silica hybrid, which kept its performances in severe, but realistic, environmental conditions with respect to traditional epoxy adhesives. The reduction in the glass transition temperature and mechanical properties of the studied epoxy-silica hybrid, observed in the first weeks of environmental aging, was followed by a significant recovery. This was attributed to two concomitant phenomena: the reactivation of the incomplete curing reactions in the epoxy domains and the continuation of the condensation reactions in the siloxane domains activated by the absorbed water. Finally, the Fickian behavior, presented by the studied epoxy-silica hybrid, was used as an indirect indication of the homogeneity of achieved microstructure, with well dispersed silica nanostructures in the epoxy network

An epoxy–silica hybrid was produced from a mixture of an amine-silane functionalized bisphenol-A resin and a siloxane precursor derived from tetraethoxysilane with small amounts of glycidoxypropyltrimethoxysilane coupling agent. The low temperature curing characteristics and final properties of the hybrid system were compared to those of two epoxy controls. Examinations were carried out by differential scanning calorimetry, dynamic mechanical analysis, electron microscopy, thermogravimetric analysis, UV–Vis spectroscopy, SAXS and densitometry. The modulus, strength and ductility were measured in 3-point bending mode at 23 and 50 C. The siloxane hybridization of the original epoxy resin was found to increase the glass transition temperature (Tg) of cold cured systems by more than 10 C and to produce large improvements in mechanical properties. The study has also provided new insights for the events taking place during gelation, vitrification and curing to the equilibrium state.

Continuous inductionwelding for thermoplasticmatrix composites requires an accuratemodeling of the temperature distribution in the laminates, depending on the electromagnetic field. In this work, a transient threedimensional finite element (FE)model was developed in order to study the heat transfer phenomena, and melting and crystallization in the welding area during the continuous induction welding of carbon fiber reinforced Poly(ether ether ketone) (CF/PEEK) laminates. The multiphysics problemwas solved by coupling electromagnetic and heat transfer equations considering matrix melting and crystallization behavior. The model was able to simulate the continuous process along a linear path at a constant speed. The computed temperatures were in good agreement with experimental measurements. Several numerical simulation were used for selecting a processing window as a function of coil speed and current, for the welding of CF/PEEK joints. The results of welding experiments were evaluated by single lap shear tests and morphology characterization of the welded interfaces and fracture surfaces.

Ultrasonic metal welding has been applied for joining aluminum AA5754 sheets to a thermoset matrix composite consisting in a carbon fiber reinforced epoxy resin (CF/epoxy). To overcome the limitations of thermosetting resins, that, unlike thermoplastic polymers, cannot melt due to their chemical structure, a thermoplastic film of Polyamide 6 (PA6) has been used as a surface layer of the CF/epoxy stack before curing. The functional surface created on the thermoset matrix composite enables a fast welding with a metallic sheet. By a proper selection of welding energy and force, an average adhesion strength of 34.8 MPa has been obtained on CF/epoxy-PA6-AA5754 ultrasonically welded joints. The morphological characterization has revealed that the aluminum-composite interface is characterized by carbon fibers in a direct contact or even embedded in aluminum, whose surface presents pores and crevices due to the pronounced plastic deformation of the Al interfacial area

Abstract Two fusion bonding techniques typically used for thermoplastic matrix composites, such as ultrasonic and induction welding, were applied for joining thermosetting matrix composites. A proper modification of the composite layup was proposed, i.e. a thermoplastic film of Poly-vinyl butyral (PVB) was added as a last ply in the stacking sequence of carbon fibre epoxy prepregs, typically used in aeronautical applications. After matrix curing, an intermingled thermoplastic-thermoset polymer zone at the surface of composite was obtained. The composite containing the thermoplastic film was used for fabrication of single lap joints by ultrasonic and induction welding, exploiting the melting of the thermoplastic film. The joint properties and the chemical compatibility and adhesion of PVB to the carbon fiber-epoxy prepregs were studied by mechanical testing and microstructural analysis

The approach for joining thermosetting matrix composites (TSCs) proposed in this study is based on the use of a low melting co-cured thermoplastic film, added as a last ply in the stacking sequence of the composite laminate. During curing, the thermoplastic film partially penetrates in the first layer of the thermosetting composite, leading to macro-mechanical interlocking as the main connection mechanism between the thermoplastic film and the underlying composite. After curing, the thermosetting composite joints with the thermoplastic modified surface can be assembled by welding. Welding of the TSC-TSC joints is performed by ultrasonic and induction welding. The weld strength is investigated by morphological characterization of cross sections and failure surfaces and by mechanical testing. The effect of the thermoplastic film thickness on the welding process and on its outcome is also analyzed. Both induction and ultrasonic welding mostly result in good-quality welded joints. The welding process used as well as the initial thickness of the thermoplastic film are found to have a significant effect on the final thickness of the weld line and on the location of failure. Thicker thermoplastic films are found to ease the welding processes.

Ultrasonic propagation was used to provide heat and pressure in order to perform impregnation and consolidation during production of thermoplastic matrix composites. For this purpose, a new experimental set-up, integrating a laboratory filament winding machine with a horn and a compaction roller, was developed. The heat transfer phenomena occurring during continuous impregnation and consolidation were simulated solving by finite element (FE) analysis the energy balance equations in 2D accounting for the heat generated by ultrasonic waves, the melting characteristics of the matrix and the movement of the thermoplastic commingled roving. The temperature distribution in the composite, predicted by the numerical simulations, was validated by temperature measurements during the production of E-glass/polypropylene cylinders, with the optimized parameters obtained by the FE analysis. The ultrasonic consolidated composite cylinders were characterized by low void content and a shear modulus comparable with that obtained by the micromechanical analysis.

The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to changes in the viscoelastic characteristics of the curing resin, since the velocity is related to the resin storage modulus and density, while the attenuation is related to the energy dissipation and scattering in the curing resin. The paper reviews the results obtained by the authors’ research group in the last decade by means of in-house made ultrasonic set-ups for both contact and air-coupled ultrasonic experiments. The basics of the ultrasonic wave propagation in polymers and examples of measurements of the time-evolution of ultrasonic longitudinal modulus and chemical conversion of different thermosetting resins are presented. The effect of temperature on the cure kinetics, the comparison with rheological, low frequency dynamic mechanical and calorimetric results, and the correlation between ultrasonic modulus and crosslinking density will be also discussed. The paper highlights the reliability of ultrasonic wave propagation for monitoring the physical changes taking place during curing and the potential for online monitoring during polymer and polymer matrix composite processing

The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from weathering, both natural and artificial. Both techniques revealed an increase in the crystallinity index (CI) of cellulose when wood was subjected to weathering. An increase in the size of crystallites was also observed by XRD measurements. These results were related to the reduction of the amorphous fractions of wood, and, consequently, to the enrichment of the relative crystalline content. Thanks to FT-IR analysis, the degradation of hemicellulose was observed for uncoated samples after exposure to artificial weathering. The effect of weathering was less evident on coated samples because of the protective action of the coating. A good correlation between the crystallinity indexes obtained from FT-IR and XRD was found. The experimental results proved that the proposed method may be a very useful tool for a rapid and accurate estimation of the degradation level of wood exposed to weathering. This methodology can find application in the field of conservation and restoration of wooden objects or in the industry of wood coatings.

The work is addressed to investigating the potentiality of calcination of organic-inorganic (O-I) hybrids as a feasible approach to produce silica particles, at mild temperature conditions and with tailored morphology. Two different innovative hybrid systems were obtained through sol-gel process with a siloxane content ranging from 6 to 26wt%. The two O-I hybrids differed for i) the organic matrix (methacrylic or epoxy), ii) its crosslinking mechanism (photopolymerization for methacrylic systems or thermal cold-cure for epoxy systems) and iii) the rate ratio between solgel and crosslinking reactions. Different characterization techniques were used to understand the effect of composition and curing method on the morphology of the silica obtained from O-I hybrids after calcination in air. The results confirm the morphology and properties of silica particles in terms of surface and porosity may be tailored over a wide range by varying the composition and nature of organic and inorganic precursors of hybrids

The potential improvement of physical and mechanical properties in nanostructured composites can be fully exploited by proper distribution of the nanofillers in the polymer matrix, which strongly affects both their final properties and processability. A nanofilled thermosetting polymer can be used as a matrix for continuous fibers when the alignment of a high aspect ratio nanofiller is achieved: in this case a hierarchical composite is obtained. In this work a new processing technology for the production of hierarchical polymer based composites is proposed. First, the alignment of graphene nanoplatelets (GNPs) in thermoplastic fibers of amorphous polyetylene terephthalate (PETg) is achieved by a fiber spinning process. The obtained nanocomposite fibers with a very high filler content (10 wt%) are then transferred into a reactive epoxy resin. After dissolution of PETg, the nanofillers remained oriented in the thermosetting matrix. The characterization of the obtained nanocomposites has been carried by means of different experimental techniques which provided complementary results.

The use of polyether polyols is common in the polyurethane (PU) industry, particularly for soft PU applications. In particular, viscoelastic foams, characterized by slow recovery after compression, are obtained using poly(ethylene oxide) (PEO) polyols. Nanofilled polyols can be used for the production of viscoelastic foams with improved fire-resistance properties. The high polarity of polyetherpolyols is responsible for a poor affinitywiththeorganicmodifiersusedincommercialorganicallymodified montmorillonite (omMMT). The aim of the work reported here was the development of a procedure for enhanced polyether polyol intercalation using modified MMT. The exfoliation of the lamellar nanofiller is obtained during the mixing stage of the polyol and the MMT. The MMT is modified using polyetheramines with different amounts of ethylene oxide/propylene oxide. Aftermixingwith the modifiedMMT, the polyol shows an increase in viscosity by three orders of magnitude, and the diffraction angles of the MMT measured by X-ray analysis decrease to values lower than 1.5◦. The intercalated structure is preserved after the curing stage, when isocyanate is added to the polyol/omMMT. The resulting PU has an irregular open-cell structure, and is characterized by a higher flame resistance compared to unfilled PU. Organically modified MMT was prepared, having an improved affinity with polyether polyols. The modified MMT has an improved compatibility with the PEO-based polyether polyols commonly used for soft PU foam production. The properties of the nanofiller can be tailored by varying the type and amount of organicmodifier. A strongly intercalated/exfoliated structure is obtained aftermixing the polyol with the omMMT.

Novel epoxy-silica hybrid systems based on silane-functionalized epoxy resins containing interpenetrating silica domains were investigated as structural adhesives with the aim to achieve a good retention of properties when the adhesives are exposed to severe environmental conditions or weathered. Durability experiments have been conducted on the experimental hybrid adhesives by monitoring their mechanical properties, on both cast specimens and on adhesive joints composed of cylindrical concrete or masonry blocks, in ordinary conditions or after exposure to different environmental agents (moderate temperature, immersion in water, outdoor exposure).

High power ultrasound was used in order to mould thermoplastic composites in a process including the simultaneous fibers impregnation and plies consolidation. An experimental equipment, made of an ultrasonic device implemented on a filament winding machine, was developed. During winding, a titanium horn is put in contact with thermoplastic layer and its melting point is reached. Several cylindrical speciments were fabricated and their physical, mechanical and morphological properties were investigated. Temperature field obtained during in-situ consolidation through heat generated by ultrasonic waves propagation was modeled using finite element (FE) analysis in order to optimize process parameters

In the last years there has been a considerable interest in a new class of materials, known as organic–inorganic (O-I) hybrids, which present unique characteristics arising from the combination of organic and inorganic components. Recently, epoxy-based O-I hybrids, consisting of epoxy resins with interpenetrating silica domains, have been optimized by the authors. The methodology for their production is based on the sol-gel technology, involving the hydrolysis and condensation of metal alkoxides in aqueous solution, which is able to bind chemically, at nanometric scale, the organic phase with the inorganic one. These novel hybrid systems present superior properties then those of the parent resins. The presence of nanostructured co-continuous organic and inorganic domains, in fact, allows to achieve higher glass transition temperatures, greater mechanical properties and enhanced adhesion to different substrates than those experienced by epoxy resins. Thanks to their peculiarities, these epoxy-based hybrid systems have been investigated by the authors as potential “cold-cured” adhesives, i.e. to be cured at ambient temperature and to be used in Cultural Heritage for restoration of artefacts and consolidation of masonry structures. The main interest in cold-cured epoxy-silica hybrids lies, in fact, in the possibility of overcoming the main limitations of conventional cold-cured epoxy resins, currently used as adhesives and matrices for FRP (Fiber Reinforced Plastics) in the restoration and repair of ancient masonry structures. They require, in fact, long curing times, while, due to the incomplete cure, the glass transition temperature (Tg) of the final products can only achieve values about 10-20°C higher than the temperature used for the curing process. Moreover, the Tg of cold-cured epoxies can decrease to even lower values through the absorption of water, due to plasticization phenomena caused by strong association of OH of water with NH groups of the epoxy. The aim of this chapter is to analyse the properties of the organic–inorganic epoxy-based hybrid systems, highlighting their potential as efficient, structural and non-structural, adhesives for Cultural Heritage.

simple procedure for the alignment of graphene nanoplatelets (GNPs) in a thermosetting matrix is presented. First, the alignment of GNPs in thermoplastic fibers of amorphous polyetylene terephthalate (aPET) is achieved by a fiber spinning process. The nanocomposite fibers, obtained with a very high filler content (10 wt%), are then transferred into a reactive epoxy resin. After dissolution of aPET, the nanofillers remained oriented in the thermosetting matrix. The characterization of the obtained nanocomposites has been carried by means of different experimental techniques which provided complementary results. The proposed method has the potential to be used in the manufacturing of hierarchical composites, by introducing nanofilled microfibers into continuous fibers reinforced composites.

In this work, a finite model able to evaluate the evolution of resin pressure as a function of temperature and degree of reaction, accounting for viscosity changes, during autoclave cure cycles has been developed. The model also includes a kinetic and rheological model whose input parameters have been experimentally determined by Differential Scanning Calorimetry and rheological analysis. The predicted resin pressure for different lay up, including breather thickness, and for different cure cycles has been compared with the results of experimental characterization of void evolution.

The engineering aspects associated with the development of nanocomposites involve either their final properties either their processability. Both are affected by the distribution of nanofiller in the matrix and by the aspect ratio of the nanofiller. A nanofilled thermosetting resin can be exploited as a matrix for continuous fibers when the alignment of a high aspect ratio nanofiller is achieved: in this case a hierarchical composite is obtained. A new procedure for the alignment of nanofillers in a thermosetting matrix is proposed in this study. The two-step approach is based on i) the alignment of nanofillers (carbon nanotubes, graphene, ect.) in thermoplastic fibers by a fiber spinning processes and ii) use of these nanocomposite fibers as a carrier to bring aligned nanofillers into a reactive thermosetting resin. These fibers, soluble in the thermosetting resin, release the nanofillers orientated according to the direction in which fibers are positioned, even after the matrix curing. The proof of concept is demonstrated by producing melt spun polyetylene terephtalate (PETg) fibers filled with graphene nanoplatelets (GNP) and multi-wall carbon nanotubes (MWCNT) with a very high filler content (up to 10 wt%) in view of producing a hierarchical composite

A finite element (FE) model able to evaluate both the evolution of resin flow, degree of reaction and void formation during autoclave cure cycles was developed. The model was implemented using a commercial epoxy matrix widely used in aeronautic field. The FE model also included a kinetic and rheological model whose input parameters were experimentally determined by Differential Scanning Calorimetry and rheological analysis. The FE model was able to predict the evolution of degree of reaction with very good agreement with the experimental data. Moreover, the predicted resin losses were lower than 3% of the overall composite resin content.

During autoclave processing of composites for high-performance applications, it is mandatory to limit the porosities, which mainly depend on the hydrostatic pressure in the resin. This pressure, which is not constant during heating being affected either by resin flow either by elastic stress in the fiber stack, can be significantly different from the autoclave pressure. Modeling of resin flow and stress in the fiber stack is a key issue for prediction of the resin hydrostatic pressure, which can be related to void development. Also, the viscosity of the thermosetting matrix is a relevant parameter since it is not constant but evolves during curing going through a minimum and then increasing to an infinite value at gel point. In this work, a viscoelastic model is adopted to calculate the evolution of resin pressure during an autoclave cycle up to gelation, accounting for viscosity and degree of reaction changes. Therefore, the model includes a kinetic and rheological model whose input parameters have been experimentally determined by Differential Scanning Calorimetry and rheological analysis. The predicted resin pressure for three case studies associated to different composite and bleeder thicknesses and reinforcement materials have been discussed

Thermoplastic matrix composites are finding new applications in different industrial area, thanks to their intrinsic advantages related to environmental compatibility and processability. The approach presented in this work consists in the development of a technology for the simultaneous deposition and consolidation of commingled thermoplastic rovings through to the application of high energy ultrasound. An experimental equipment, integrating both fiber impregnation and ply consolidation in a single process, has been designed and tested. It is made of an ultrasonic welder, whose titanium sonotrode is integrated on a filament winding machine. During winding, the commingled roving is at the same time in contact with the mandrel and the horn. The intermolecular friction generated by ultrasound is able to melt the thermoplastic matrix and impregnate the reinforcement fibers. The heat transfer phenomena occurring during the in situ consolidation have been simulated solving by finite element (FE) analysis, an energy balance accounting for the heat generated by ultrasonic waves and the melting characteristics of the matrix. To this aim, a calorimetric characterization of the thermoplastic matrix has been carried out to obtain the input parameters for the model. The FE analysis has enabled to predict the temperature distribution in the composite during heating and cooling. The simulation results have been validated by the measurement of the temperature evolution during ultrasonic consolidation. The reliability of the developed consolidation equipment has been proved by producing hoop wound cylinder prototypes using commingled continuous E-glass rovings and polypropylene filaments. The consolidated composite cylinders are characterized by high mechanical properties, with values comparable with the theoretical ones predicted by the micromechanical analysis.

An experimental set-up for the ultrasonic consolidation of commingled thermoplastic rovings has been developed. It integrates a laboratory filament winding machine with the sonotrode of an ultrasonic welding head. A commingled roving made of polypropylene and glass fibers was used to fabricate several prototypes of cylinders of different thicknesses. The physical, mechanical and morphological properties of consolidated composite specimens were measured and related to the different processing conditions. The heat transfer phenomena which occur during consolidation of these rovings were simulated solving, by finite element analysis, the energy balance accounting for the heat generated by ultrasound and the melting characteristics of the thermoplastic matrix

An experimental set-up for ultrasonic cure monitoring has been developed at the Laboratory of Composite Materials (University of Salento). The obtained results demonstrate that ultrasonic wave propagation is able to detect and monitor the physical changes taking place during curing of thermosetting matrices. Moreover, the set-up has the potential for online monitoring during composite processing

The mechanical and electrochemical behavior of ultrasonic spot welded hybrid joints, made of AA5754 aluminum and carbon fiber reinforced epoxy with a co-cured thermoplastic surface layer, was studied. The effect of the welding parameters (energy and force) and the thickness of a thermoplastic film, applied as an upper ply in the composite lay-up, on the development of adhesion strength, was investigated. The best mechanical results were obtained when the welding parameters were able to achieve a large bonding area of mechanical interlocking between naked carbon fibers and aluminum and a better load distribution. The electrochemical results excluded the possibility of galvanic corrosion between aluminum and composite adherends thanks to the insulating action provided by the thermoplastic film

The finite element method (FEM) has been applied to simulate the ultrasonic wave propagation in a multilayered transducer, expressly designed for high-frequency dynamic mechanical analysis of polymers. The FEM model includes an electro-acoustic (active element) and some acoustic (passive elements) transmission lines. The simulation of the acoustic propagation accounts for the interaction between the piezoceramic and the materials in the buffer rod and backing, and the coupling between the electric and mechanical properties of the piezoelectric material. As a result of the simulations, the geometry and size of the modelled ultrasonic transducer has been optimized and used for the realization of a prototype transducer for cure monitoring. The transducer performance has been validated by measuring the velocity changes during the polymerization of a thermosetting matrix of composite materials.

L’invenzione propone un metodo per la produzione di un materiale composito fibro-rinforzato consolidato mediante il trattamento tramite energia ultrasonora di un substrato grezzo di tipo commingled, costituito da fibre di rinforzo secche e fibre di matrice polimerica termoplastica (Figura 1). Tramite il trattamento ultrasonoro si ottengono in un'unica operazione le fasi di rammollimento e/o fusione delle fibre di matrice termoplastica, le fasi di impregnazione delle fibre di rinforzo secche e le fasi di consolidamento del composito finale solitamente eseguite, secondo lo stato della tecnica nota, separatamente e secondo fasi successive.

Organic-inorganic hybrids made of an organic phase based on epoxy oligomer and an inorganic phase consisting of silica nanodomains wherein the organic phase based on epoxy oligomer is polymerizable at room temperature and the silica nanodomains are produced in situ thanks to a modified sol-gel process carried out in the absence of organic or aqueous solvents and their use as adhesives or matrices for composite materials used in the rehabilitation, repair, consolidation and restoration of infrastructure and cultural heritage as well as in related methods, are disclosed.