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Despite their scarce resistance to humid or wet conditions, natural fiber reinforced composites (NFRCs) seem to be able to partially recover their performances under discontinuous exposition to marine environment. To investigate this peculiarity, flax fiber reinforced composite was at first subjected to salt-fog spray condition at 35 °C for 15 and 30 days, respectively, and then stored in ‘‘dry” condition (i.e., 50% R.H. and 22 °C) between 0 and 21 days. The performances evolution was evaluated through flexural tests, water uptake and contact angle measurements. Moreover, the morphology of fractured mechanical samples was examined by using 3D optical microscope and scanning electron microscope (SEM). Flax fiber reinforced composite experienced phenomena of both reversible and irreversible degradation during the wet phase thus evidencing a relevant mechanical recovery thanks to the drying. Quite interestingly, the laminate showed an almost complete recovery of the flexural strength, meaning that this property is more strictly related to mainly reversible aging phenomena whereas the greater stiffness loss is more probably due to irreversible ones.

This paper aims to investigate the ability of an eco-friendly and cheap treatment based on sodium acetate solutions to improve the mechanical properties of flax fiber-reinforced composites. Flax fibers were treated for 5 days (i.e., 120 h) at 25 °C with mildly alkaline solutions at 5%, 10% and 20% weight content of the sodium salt. Quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests were carried out to evaluate the mechanical properties of the resulting composites. Fourier transform infrared analysis (FTIR) was used to evaluate the chemical modification on the fibers surface due to the proposed treatment, whereas scanning electron microscope (SEM) and helium pycnometry were used to get useful information about the morphology of composites. It was found that the treatment with 5% solution of sodium acetate leads to the best mechanical performance and morphology of flax fiber-reinforced composites. SEM analysis confirmed these findings highlighting that composites reinforced with flax fibers treated in 5% sodium acetate solution show an improved morphology compared to the untreated ones. On the contrary, detrimental effects on the morphology as well as on the mechanical performance of composites were achieved by increasing the salt concentration of the treating solution.

In this study, the use of natural fibres (flax and basalt) in combination with a recyclable epoxy matrix based on cleavable amines is suggested for improving the sustainability of marine industry. In addition, a new and eco-friendly anodizing process based on tartaric sulfuric acid solution (TSA) and a pore widening step in a NaOH aqueous solution was carried out on aluminium alloy (AA5083) to evaluate its effect on the adhesion strength and damage tolerance after low velocity impact of co-cured adhesive joints with a basalt fibre reinforced and recyclable laminate. The durability in marine environment was simulated by exposing samples to salt-fog spray conditions over a period of 90 days. Results highlighted the potential of the proposed natural fibre composites, even though the interfacial adhesion with the recyclable matrix needs to be improved, while the anodizing treatment significantly increased the damage tolerance of the joints irrespective of ageing, impact energy and temperature compared to the reference joints.

Il cambiamento climatico e la necessità di ridurre il consumo energetico degli edifici sono argomenti chiave del dibattito politico, scientifico, economico e culturale. Un dibattito al quale si è voluto dare il proprio contributo sin dall’anno accademico 2010-2011 con la prima edizione del Master in Materiali e Tecniche Innovative per l’Edilizia Sostenibile (MeTIES) dell’Università degli Studi di Palermo insieme al Consorzio Universitario per l’Ateneo della SiciliaOccidentaleedel Bacino del Mediterraneo (UNISOM), perseguendo il preciso obiettivo di formare una generazione di professionisti che sappiano padroneggiare le nuove tecnologie per ripensare il modo di “costruire”. Tutti gli studenti che hanno seguito il master, nelle diverse edizioni, hanno avuto modo di mettere a frutto le competenze acquisite durante il corso in un ambito lavorativo. Si è voluto contribuire al dibattito sulle possibili strade da perseguire per lo sviluppo sostenibile attraverso la formazione di “operatori” che abbiano la capacità di individuare, sviluppare e proporre soluzioni possibili e concrete per l’efficientamento energetico degli edifici. Il libro contiene alcune risposte operative alle necessità di un settore che sarà sempre di più al centro delle scelte economiche e politiche dei prossimi decenni.

It is well-known that the addition of randomly dispersed particles in polymers influences their linear viscoelastic behavior and dynamic mechanical properties. The aim of this study was to describe the viscoelastic behavior of an epoxy resin modified by waste glass and rubber particles using the linear fractional spring-pot model. Unlike complex classical exponential models, fractional models, being only two-parameter dependent, make it easier to characterize the viscoelastic behavior of materials. Isothermal relaxation and single frequency sweep temperature dynamic tests were carried out in a dynamic mechanical analyzer DMA150 by varying the content of the particles from 0 to 20% by weight. Overall, the results of this study evidence that using waste materials as additives for polymer compounds is a practical and sustainable possibility when it comes to modifying their viscoelastic properties.

This paper presents an experimental testing of a pultruded glass fiber reinforced polymer (FRP) structure used for emergency applications continuing the discussion presented in a previous paper (part 1) where the study of the characteristics of material and elements are presented. First, the design of the composite structure and components and the evaluation of the structural behavior by means of numerical and analytical approach according to current regulatory codes are described. In this frame, the global and local response was observed according to load paths deriving from the design loads at limit states. Then, the experimental test on a full-scale 2D model is presented at different load configurations up to the failure of the composite structure, comparing the experimental results with the load capacity predicted by the numerical model. The results indicate that the high performances of the structure provide a very good capacity in view of facing service loads and also in extreme conditions. Moreover, it was observed that the actual capacity obtained by the experimental test is much higher compared to the bearing capacity provided by the design according to current technical codes.

Giant wild reed Arundo donax L. is an aggressive agricultural species with remarkable features such as fast-growing, untapped economic potential, eco-friendliness, and high specific properties (e.g., high strength/weight and modulus/weight ratios). Here, the bending properties of giant reed were studied at a molecular level to evaluate the effect of the conditions used during the preparation for their applications (also referred to as treatment conditions). The aim was to achieve new information potentially useful to suggest new possible applications of A. donax L. for structural applications in modern buildings. In this study, green reeds collected in a Sicilian plantation were dried for 2000 h in a climatic chamber under humidity-temperature-controlled conditions, then fully dried in an oven and finally re-moistened through two different procedures. The combination of different analytical techniques (such as calorimetry and fast field cycling NMR relaxometry) revealed that giant reed bending properties are strongly affected by the presence of bound water. In particular, it has been evidenced that a progressive enhancement of bending characteristics is obtained when the interactions between residual water and A. donax L. fibers become progressively stronger. For this reason, it can be suggested that fibers having different plasticity can be produced by modulate the heating treatment to regulate the amount of bound water inside A. donax L. fibers.

The goal of this paper is to evaluate the effectiveness of a cost-effective and eco-friendly treatment based on the use of sodium citrate (Na3C6H5O7) on the mechanical properties of flax fiber reinforced composites. To this scope, flax fibers were soaked in mildly alkaline solutions of the sodium salt at different weight concentration (i.e., 5%, 10% and 20%) for 120 h at 25 °C. The modifications on fibers surface induced by the proposed treatment were evaluated through Fourier transform infrared analysis (FTIR), whereas scanning electron microscope (SEM) and helium pycnometer were used to obtain useful information about composites morphology. The effect of the concentration of the treating solution on the mechanical response of composites was determined through quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests. The results revealed that composites reinforced with flax fibers treated in 10% solution exhibit the best mechanical performances as well as the lowest void contents. SEM analysis supported these findings showing that, by treating fibers in solutions with concentration up to 10%, composites having better morphology can be manufactured, in comparison to untreated ones. Conversely, higher Na3C6H5O7 concentrations negatively affect both the morphology and the mechanical properties of composites.

This paper aims to propose and characterize a sustainable hydraulic mortar entirely obtained by the reuse of waste materials, with marble slurry coming from quarries in the north-western Sicily and glass powder coming from a waste collection plant in Marsala (Province of Trapani). The first was used as raw material to produce the mortar binder by a kilning and slaking process, while the second was used as a pozzolanic additive. The chemical and morphological characterization of the marble slurry was done by XRD, FTIR, STA and SEM analyses. Glass powder was analyzed through particle size distribution measurements, XRD and standard pozzolanic tests. Hydraulic mortars constituted by slaked lime from kilned marble slurry and waste glass powder (LGS) were prepared beside commercial Natural Hydraulic Lime (NHL) based mortars (NGS) and air-hardening lime (LSS)-based mortars. Mechanical and absorption properties of the mortars were investigated as a function of the grain size of the glass powder by means of three-point bending and compressive strength tests, capillary uptake, helium pycnometry and simultaneous thermal analysis. The results demonstrated that the formulation LGS exhibits significantly improved mechanical and absorption properties compared to air-hardening mortars (LSS). It confirms the possibility of producing a more sustainable hydraulic mortar exclusively from waste materials for civil engineering.

Nowadays, there is a growing need to reduce the environmental impact generated by the use of inorganic materials for building applications. The aim of this work is to investigate the bio-lime based mortar flexural toughness improvement due to the addition of common reed fibers (Arundo donax L.) in order to evaluate their possible application as ductile eco-compatible prefabricated bricks or laying and joint mortars for masonry. Different sets of specimens were tested by varying the fiber weight content and the fiber length. Moreover, chemical treatments with Linseed Oil and Polyethylene glycol (PEG) were performed to improve the physical and mechanical properties of the fibers as well as the fiber/matrix interfacial adhesion. The Mechanical characterization of the neat and treated fibers was performed through Single Fiber Pull-out Test and Single Fiber Tensile Test. The quasi-static mechanical properties of the composites were evaluated through Three-Point Bending and Compressive tests. Finally, an analytical model proposed in the literature has been used to evaluate the parameters that influence the post-fracture behavior of the composites. Overall, the findings of this study are valuable to understand the flexural behavior of new eco-compatible natural fibers reinforced mortars for masonry application providing scientific evidence of the effectiveness of giant reed fibers in the manufacturing of green building materials, as bricks or laying mortars.

Nowadays sustainability is one of the main concept in building construction, both considering energy saving buildings and life cycle assessment of building materials. According to these considerations, in this work the use of recycled and waste materials to produce a binder and the use of a natural fiber as reinforcement are investigated to obtain a sustainable mortar. Particularly, lime is obtained by kilning waste marble slurry from marbles quarries in western Sicily; pozzolanic aggregate is obtained by grinding glass powder from urban waste collection; natural fibers come from a widespread grass: Ampelodesmos Mauritanicus also known as diss. Scanning electron microscopy and helium picnometry have been performed to characterize diss fibers. Samples with different fibers volume percentage have been prepared and subjected to three-point bending and compression tests, in order to verify the modification of resistance related to the presence of fibers; moreover, capillary uptake and thermal conductivity have been evaluated.The results show a great influence of fibers’ percentage on both mechanical and environmental properties of mortars, resulting in lowering of mechanical resistance and thermal conductivity.

The use of natural fibres in cement composites is an expanding research field as their use can improve the mechanical and thermal behavior of cement mortars and reduce their carbon footprint. In this paper two different wild grasses, i.e. Pennisetum Setaceum, also known as crimson fountaingrass, and Ampelodesmos Mauritanicus, also called diss, are used as source of natural fibres for cement mortars. The principal aim is to evaluate the possibility of using the more invasive crimson fountaingrass in place of diss inside cement based vegetable concrete. The two plants’ fibres have been characterized by means of electron microscopy, helium picnometry; moreover, the thermal conductivity of fibre panels has been measured. Mortars samples using untreated and boiled fibres have been prepared. The mechanical characterization have been performed by means of three point bending and compression tests. Thermal conductivity and porosity have been measured to characterize physical modification induced by fibres’ treatment. The results showed better thermal and mechanical properties of diss fibres composites than fountaingrass one and that fibres treatment leads to a decrease of thermal insulation properties.

Fibers are often used as reinforcement of brittle materials, like mortars, in order to modify their mechanical behavior; particularly the modification in post-cracking toughness, induced by low elasticity modulus fibers in the artificial stone material, is the main goal in natural fibers mortar manufacturing. In this work Arundo donax L. fibers are used to reinforce lime mortars according to the characteristics of this plant, very commonly available and with high mechanical properties, similar to bamboo, traditionally used in buildings in Spain. Influence of fibers’ length and weight ratio is studied. Particularly, three different fibers’ lengths, 4, 8 and 12 centimeters, and three weight ratio, 0.5, 1 and 2% are used. The experimental characterization focused on bending and compression tests on mortars’ samples as well as tensile and pull out tests on single fiber. Overall, according to experimental results, mechanical flexural properties of the mortar are significantly improved by the addition of natural fibers at different weight contents and lengths, optimal fibers’ weight ratio and length was individuated.

Cork is a unique material, characterized by small closed cell structures, high insulating properties, very low density, high fire resistance and a very good durability after simple thermal treatment. The main use of cork in the production of stopper and insulating panels obtained with cork grains and a polymeric resin. Usually cork grains used in panel production have a grainsize around 1-2 mm. In this work cork grains have been used as aggregates for natural hydraulic lime mortars by reducing grainsize distribution. Cork grainsize has been reduced by means of a knife mill and divided in three different distributions, i.e. 1, 0.5 and 0.25mm. Mortars have been prepared according to NHL to cork to natural sand volume ratio equal to 2:3:2. Three point bending and compression tests showed that reducing cork grainsize leads to a slight increase in mechanical performance. On the other hand thermal conductivity showed to be independent from cork grainsize. Scanning electron microscope investigation was also performed to better understand these results.

Nowadays glass is widely used in building applications and coupled to steel through adhesive joining. Reliable mechanical characterization of these joints is necessary to design and predict the final structure performance.In this framework, the aim of this paper is to measure the pure shear strength and elastic modulus for design and modelling of adhesive joined glass-to-steel structures.Torsional shear strength and elastic properties of an adhesively bonded glass-to-steel component were measured on several joined steel-to-steel and steel-to-glass samples.An epoxy resin-based adhesive was used as joining material for AISI304 steel and soda-lime glass.The same steel and adhesive were used to obtain steel-to-steel joined sample bars to be tested in asymmetrical four-point bending, for comparison purposes.The indentation elastic modulus of the adhesive, both inside the joined region and as a bulk, was measured by nano-indentation and impulse excitation technique.Finally, the effect of etching on the glass was studied and correlated to the glass-steel joint strength.This study shows that torsion test can be used to provide reliable shear strength values for design and modelling glass-to-steel adhesive joined components.

The aim of the present paper is to study the mechanical performance evolution of pinned hybrid glass-flax composite laminates under environment aging conditions. Hybrid glass-flax fibers/epoxy pinned laminates were exposed to salt-spray fog environmental conditions up to 60 days. With the purpose of assessing the relationship between mechanical performances and failure mechanisms at increasing aging time, single lap joints at varying joint geometry (i.e., hole diameter D and hole distance E from free edge) were characterized after 0 days (i.e., unaged samples), 30 days, and 60 days of salt-fog exposition. Based on this approach, the property&ndash, structure relationship of the composite laminates was assessed on these critical environmental conditions. In particular, a reduction of failure strength for long-aging-time-aged samples was observed in the range 20&ndash, 30% compared to unaged one. Due to the natural fiber degradation in a salt-fog environment, premature catastrophic fractures mode due to shear-out and net-tension were found, related to reduced joint fracture strength. This behavior identifies that this type of joint requires a careful design in order to guarantee an effective mechanical stability of the composite hybrid joint under long-term operating conditions in an aggressive environment.

This paper represents the first effort aimed to the investigation of the pin/hole contact stress and failure mechanisms of epoxy composites reinforced with woven flax fabrics, underwent to tensile bearing tests. In particular, the maximum loads and failure modes are evaluated at varying the laminate geometrical configuration. In order to optimize the use of polymer composites reinforced with flax fibers in structural applications, an experimental failure map, identifying main failure modes of mechanically fastened joints, is obtained as function of hole diameter, distance of the hole from the free edge of the laminate and laminate width. Moreover, a theoretical approach based on the observation that a particular fracture mechanism occurs when its threshold fracture load is lower than the loads of the other competitive ones, is proposed. Main goal of this paper is to give a simple experimental methodology to support the joining design of natural composite laminates reinforced with woven flax fabrics.

In this study, the anodizing process based on the use of tartaric sulfuric acid solution (TSA) was carried out on metal substrate to evaluate for the first time its effect on the adhesion strength and corrosion resistance of aluminium alloy (i.e., AA5083) to fibre (i.e., basalt or glass) reinforced composite adhesive joints for nautical applications. Furthermore, some TSA anodized samples were soaked in a NaOH solution to investigate the influence of this post-immersion step on the joint performances. With the aim to improve the fibre-matrix adhesion in the composite substrate thus further increasing the overall mechanical response of the joint, glass and basalt fibres were treated with a silane coupling agent solution. The corrosion behaviour of the aluminium alloy was studied by electrochemical techniques. Samples morphology was analysed by scanning electron microscopy, while the interaction between aluminium alloy substrate and epoxy resin was studied through contact angle analysis and resin uptake tests. The effectiveness of the silane treatment was examined by means of Fourier transform infrared spectroscopy and quasi-static tensile tests carried out on dry glass and basalt fabrics. The mechanical response of the resulting joints was evaluated by means of quasi-static tensile tests in accordance to ASTM D3528 standard.

The use of natural fibers in cement composites is a widening research field as their application can enhance the mechanical and thermal behavior of cement mortars and limit their carbon footprint. In this paper, two different wild grasses, i.e., Ampelodesmos mauritanicus, also called diss, and Pennisetum setaceum, also known as crimson fountaingrass, are used as a source of natural aggregates for cement mortars. The main purpose is to assess the possibility of using the more invasive crimson fountaingrass in place of diss in cement-based vegetable concrete. The two plant fibers have been characterized by means of scanning electron microscopy (SEM), helium picnometry and thermogravimetric analysis. Moreover, the thermal conductivity of fiber panels has been measured. Mortars samples have been prepared using untreated, boiled and Polyethylene glycol 4000 (PEG) treated fibers. The mechanical characterization has been performed by means of three point bending and compression tests. Thermal conductivity and porosity have been measured to characterize physical modification induced by fibers’ treatments. The results showed better thermal and mechanical properties of diss fiber composites than fountaingrass one and that fiber treatments lead to a reduction of the thermal insulation properties.

The present experimental investigation aims to investigate the effect of salt-fog exposition on the mechanical behaviour of composite/metal riveted joints. To this aim, two kinds of joint were exposed to salt-fog environmental conditions according to ASTM B117 standard, for fifteen weeks. In particular, two composite laminates (i.e. glass fibre and carbon fibre/epoxy composites) were used as composite substrate joined with the metal substrate (i.e. aluminium alloy Al 6060). Single-lap shear tests were carried out in order to evaluate the evolution of the mechanical performances and the damage mechanisms of the riveted joints during the ageing exposition. The results evidence that the mechanical performances (i.e. maximum load and load-displacement slope) of the hybrid joints progressively decrease at increasing ageing time in the considered exposure time. Moreover, glass fibre/epoxy hybrid composite joint showed a higher sensitivity to degradation in salt-fog environmental condition than carbon fibre/epoxy one. As concerns the damage mechanisms, glass fibre/epoxy hybrid composite joint experienced catastrophic cleavage/net tension failure modes regardless the ageing time whereas the progressive bearing failure was the mechanism observed in carbon fibre/epoxy hybrid composite joint during the entire experimental campaign. Corrosion phenomena not significantly affected degradation performances of both joints.

This work describes an experimental mechanical characterisation campaign on composites made out of a quasi-unidirectional basalt fabric. In order to evaluate the ability of commercial basalt fabrics and their composites to meet the potentials of basalt fibers, the work has used raw materials from commercial catalogs with no further modification. Two common manufacturing techniques for medium performance composites have been adopted: vacuum assisted resin infusion, and hand-impregnated vacuum bagging. Two panels, one for each technique, have been fabricated, able to provide a sufficient number of samples for a comprehensive stiffness and strength characterization through Tensile, Flexural, In-Plane Shear, Short Beam Shear, Double Cantilever Beam and End-Notched Flexural tests. Results revealed a significant dependence of the mechanical properties on the manufacturing processes, due to their different ability to fully impregnate the dry fabric assembly, and on the quality of fiber/matrix adhesion. In general, hand-impregnation followed by vacuum bag curing was able to guarantee a better impregnation, which in particular yielded superior Interlaminar Shear Strength and Interlaminar Fracture Toughness performances.

This paper presents an experimental study in the field of structures made of pultruded fiber reinforced polymers (FRP) elements to be used for emergency purposes. A preliminary design of a 3D pultruded glass fiber reinforced polymer structure is presented with the mechanical characterization of the constituting elements. The axial and flexural properties of laminate and I-shaped GRFP profiles are discussed considering the short term creep. In a companion paper, the benefits, the limits and the reliability of the structure analyzed for emergency applications are discussed. In details, the numerical structural analysis of the full-scale 3D model is described followed by the experimental assessment of the structural capacity by a full-scale 2D model.

The use of sheep wool as a filler of cement in order to produce mortar or plaster involves several advantages for environment and energy. Moreover, it is considered as a waste and, therefore, its use is characterized by low cost. The aim of this paper is to evaluate the influence of wool fibers on thermal conductivity and mechanical properties of cement. The samples were prepared using wool fibers, obtained from a breed of Sicilian sheep, with three different lengths (i.e., 1, 6, and 20 mm). Furthermore, in order to evaluate the influence of fiber content, the samples were prepared by varying the fiber weight fraction. The thermal conductivity of the samples was analyzed by using a heat flow meter, whereas the mechanical behavior was studied through compressive tests. In order to validate the thermal measurements, on the experimental data, two theoretical models were applied. The experimental results showed that wool fibers can be used within cementitious matrices to obtain mortars or plasters with enhanced thermal insulation properties. Nevertheless, noticeable decrements in the compressive strength are also found. Therefore, it is needed to find a compromise between these two aspects

The aim of the present paper is to assess the bearing performance evolution of pinned, glass-composite laminates due to environmental aging in salt-spray fog tests. Glass fibers/epoxy pinned laminates were exposed for up to 60 days in salt-spraying, foggy environmental conditions (according to ASTM B117 standard). In order to evaluate the relationship between mechanical failure mode and joint stability over increasing aging time, different single lap joints, measured by the changing hole diameter (D), laminate width (W) and hole free edge distance (E), were characterized at varying aging steps. Based on this approach, the property-structure relationship of glass-fibers/epoxy laminates was assessed under these critical environmental conditions. Furthermore, an experimental 2D failure map, clustering main failure modes in the plane E/D versus W/D ratios, was generated, and its cluster variation was analyzed at each degree of aging.

In this paper, the aging resistance of sandwich structures made with cork agglomerate as core and flax-reinforced polymeric laminates as face sheets was investigated for the first time. In order to evaluate their durability in a hostile environment, a sandwich plate was manufactured by vacuum bagging technique and aged under salt-fog spray conditions, according to ASTM B 117 standard. The evolution of the sandwich mechanical properties during the aging exposition was analyzed by carrying out quasi-static flexural tests and Charpy impact tests both on unaged specimens and on specimens aged for 10, 25, and 60days, respectively. The quasi-static experimental results showed that despite the salt-fog exposition leads to clear decrements in both maximum strength and modulus, the deformation capability of the sandwich structure evidences a noticeable improvement. According to this last result, it was found that the impact strength of the sandwich specimens was clearly increased after the salt-fog exposition evidencing that the studied green sandwich maintains good toughness properties in a hostile environment such as marine.

Aim of this article is the assessment of the bearing mechanical performances of pin-loaded glass laminates as function of their geometrical configuration. To this concern, 32 specimens having different hole diameter (D), laminate width (W), and hole center to laminate free edge distance (E) have been tested under bearing conditions. The maximum bearing stress and the stress-displacement curves were analyzed as function both of hole to laminate free edge distance E and hole diameter D. Moreover, an experimental 2D failure map was created by placing the experimental results (i.e., the kind of failure mechanism occurred for each geometrical configuration) in the plane E/D versus W/D ratios. In order to identify a simplified methodology able to design mechanically fastened joints in an easy and effective way, a simplified theoretical failure map on E/D and W/D axes was proposed. The theoretical model showed a good matching with the experimental results validating the proposed approach. In particular, the proposed simplified failure map highlighted that woven glass fiber composite laminates fastened joints should have E/D and W/D ratios higher than 1.6 and 2.1, respectively, in order to stimulate a progressive bearing failure mechanism and achieve the full laminate strength. Finally, another goal of this article was to assess failure mechanisms evolution by drawing a 3D plot (i.e., at varying E/D and W/D geometrical ratios) of the failure index evaluated for each failure mechanism according to the maximum stress criterion.

The aim of this paper was to evaluate the durability behaviour of glass/steel adhesive joints exposed to salt fog environmental conditions for ten weeks, according to ASTM B117 standard. To this scope, pull-off mechanical tests were carried out in order to evaluate the performances evolution and damage phenomena of the adhesive joints during the ageing exposition. Two different types of adhesives were compared (i.e. epoxy and polyurethane ones). Moreover, the effects of the glass surface condition and the presence of a basalt mat layer within the adhesive thickness were evaluated. The mechanical performances were related with the occurred failure mechanisms. Epoxy-based joints showed higher strength and durability than the polyurethane based ones. Furthermore, frosted glass surface condition and basalt interlayer addition enhanced mechanical durability in salt fog environment of glass–metal dissimilar joints.

Aim of this work is to evaluate the influence of external layers of basalt-mat on the durability behaviour of flax reinforced epoxy composites. To this scope, long-term ageing tests were performed on two different laminates in critical environmental conditions. The first laminate, named Flax, was constituted by stacking ten layers of bidirectional flax fabrics. The second one, named Flax–Basalt, was produced by replacing two external flax layers with two layers of basalt mat for each side of the laminate. Both laminates were exposed to salt-fog environmental conditions, according to ASTM B 117 standard, for 60 days. Five samples per laminate were removed from salt-fog spray chamber and mechanically tested. In particular, quasi-static flexural tests and Charpy impact tests were performed according to ASTM D 790 and ISO 179 standards, respectively. The fracture surfaces of both laminates were evaluated by using an optical 3D microscope. Moreover, five samples per laminate were removed periodically and weighed to evaluate the water absorption. The experimental results showed that the hybridization with basalt fibres can be considered as a practical approach for enhancing the durability of natural fibre composites under salt-fog environment conditions.

This paper reports a study of the flexural behaviour and resultant failure modes in E-glass/polyester pultruded composites. The digital image correlation (DIC) method is used to estimate the effect of fibre orientation on failure behaviour in thick beams, taking into account the presence of continuous filament mat layer (CFM) in the stacking sequence. In particular, the tests were carried out for specimens with off-axis angle of 0°, 7.5°, 15°, 30°, 45° and 90°. The crack initiation and the failure mechanisms depend on the mutual interaction between the stiffness properties of different areas in the stacking sequence. An influence index (I) was introduced to evaluate the magnitude of these phenomena. For small orientation angle (i.e. less than 7.5°), the failure mechanism is not influenced by the central mat layer and the crack starts from the tension region. For angles between 15° and 45°, the influence of the central mat layer is predominant and delamination occurs at the interface between the mat layer and the adjacent one. For 90° angles, the CFM layer does not influence the typical fracture mechanism and transverse matrix cracking occurs.

Aim of the present paper is to evaluate how the bearing behavior of pinned flax composites can be influenced by their exposition to critical environment such as marine one. To this scope, flax fibers/epoxy pinned laminate was exposed up to 60 days to salt-fog environment, according to ASTM B 117 standard. In particular, samples having different hole diameter (D), laminate width (W), and hole center to laminate free edge distance (E) have been tested under single lap bearing tests at varying the aging exposition time. Following this procedure, an experimental 2D failure map clustering main failure modes was created by placing the experimental results in the plane E/D versus W/D ratios, and its variation was analyzed at varying the aging exposition. Experimental results showed that environmental aging induced modification on the mechanical performances of the pinned composite. Furthermore, the failure map, defined by E/D and W/D ratios axes, evidenced a progressive modification of damage mechanisms transitions, at increasing the exposition time. In particular, due to significant reductions of tensile and shear strengths of flax laminate, the progressive fracture by bearing mode was not observed for aged samples, replaced by premature and catastrophic shear out and net tension mechanisms.

Noninvasive X‐ray micro‐computed tomography was applied for a complete quantitative and qualitative analysis of the cellular structure of composite foams constituted by a silicone matrix and a glass production waste filler. Composite foams with different glass filler weight content in the range 0–80% were synthesized and characterized. The tomographic analysis was employed in order to assess the structural heterogeneities, void fraction values, and bubble size distribution for all composite foams. The 3D micro‐CT images analysis, performed at different cross‐sections, highlighted heterogeneous cell growth or more elongated cells in the case of low and high filler content foams, respectively. Batch with 60% of glass filler was identified as a composite foam with effective void fraction values and relatively uniform spheroidal cellular structure (average sphericity 0.723 and diameter 0.107 mm)

This paper deals with the evaluation of the effect of an eco-friendly and cost-effective surface treatment based on the use of sodium bicarbonate on the mechanical properties of flax-reinforced epoxy composites. To this aim, unidirectional fabrics were soaked for five days in 5 and 10% in weight of sodium bicarbonate solution at 25℃. Quasi-static and dynamic mechanical tests were performed and the fracture surfaces of the composites were analyzed through scanning electron microscopy. Results evidenced that this treatment improves the fiber–matrix adhesion thus increasing the performances of the composites. Treating the fabrics with 10% w/w of bicarbonate solution leads to improvements of ∼20 and ∼45% in tensile strength and modulus of the composites, respectively, compared to untreated ones. Furthermore, by increasing the concentration, negligible changes in the glass transition temperature and reductions in the tanδ peak heights were found. The observation of the fracture surfaces confirmed the beneficial effect of the proposed treatment.