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The technology of dry assembly to produce multi-layer panels is an efficient alternative to traditional systems. Eco-sustainable systems are increasingly studied, particularly fiber reinforced composites for external cladding, based on natural fibers. However, the durability of these composites gives serious concern, in particular for their potential use in outdoor applications. To overcome this drawback, hybridization of natural fibers with mineral fibers as basalt ones appears promising. In this paper, the aging resistance of jute-reinforced laminate was compared with those of two hybrid laminates.

The giant reed Arundo donax L. is an aggressive grass widely diffused throughout warm temperate regions. Thanks to its remarkable features as fast-growing, eco friendly and high specific properties (i.e. high strength/weight and modulus/weight ratios), it is widely used in ancient and traditional buildings, especially in the realization of supports for roof cladding and paneling of walls. A better understanding and a consequent standardization of its properties could make it more suitable for general application in the sustainable building industry. Mechanical and viscoelastic properties of the giant reed were studied as a function of the moisture content. To this scope, various sets of reed were considered. A first set of green reeds was collected in a Sicilian plantation. Another set was fully dried in an oven (103°C for 24 h) and finally a further set was remoistened through soaking in 5%, 10% glucose solutions and HAB (heavy alkylate benzene). For each condition investigated, samples were mechanically tested carrying out stress relaxation experiments in three points bending tests configuration, with the aim of studying the effect of moisture content on the viscoelastic properties of the giant reed. Stress relaxation experimental data were fitted using a mathematical spring pot model in order to characterize the material constitutive law and to capture the two parameter of the model ( and ). The experimental results show that it is possible to get a wide range of static (i.e. modulus, strength and ductility) and viscoelastic properties of giant reed by varying the moisture content, making it a suitable material in a wide range of semi structural applications., Academic Journal of Civil Engineering, Vol 33 No 2 (2015): Special Issue - ICBBM 2015

Aim of this work was to investigate the wettability of natural fibres reinforced epoxy composites, subjected to aging tests performed on two different laminates. The first laminate was constituted by stacking ten layers of bidirectional flax fabrics. The second one 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. The results of wettability were compared with those of the water uptake test. Moreover, an analysis of variance was performed in order to evaluate the significance of the parameters that influence the wettability of the structures and their interaction.

Transverse Crack Tension (TCT) samples represent an alternative to End Notched Flexure configurations for the characterization of pure mode II fracture toughness of Fibre Reinforced Polymer composites. TCT is supposed to reproduce a pure Mode II failure mechanism while avoiding the frictional energy dissipation between the flanks of a starter crack. The TCT geometry is that of a unidirectional tensile sample where a number of embedded plies, centered on the middle plane, are cut in the transverse fibres direction. The tensile loading should then activate four symmetric fronts of mode II delamination from the transverse cut tips. The present work describes the implementation of two full field experimental stress analysis techniques: Thermoelastic Stress Analysis (TSA) and a Digital Image Correlation (DIC). These are applied to evaluate the stresses and strains on the through-the-thickness surface of a TCT sample during static and cyclic loading. The stress and strain information carried out by the thermoelastic signal and DIC analysis are analyzed to investigate the effectiveness of the TCT specimen for the purposes of Mode II characterization.

The effect of through-the-thickness compressive stress on the mode II interlaminar fracture toughness is investigated experimentally and replicated numerically. The modified Transverse Crack Tensile specimen recently proposed by the authors is used, together with an experimental device designed to apply a constant transverse compressive stress on the surface of the specimen. Experiments are conducted using IM7/8552 specimens for different compressive stresses, ranging from 0 to 100 MPa, covering all the practical applications commonly encountered in the aeronautical industry (e.g., tightened filled holes or bolted joints). It is shown that the mode II interlaminar fracture toughness increases with the applied compressive through-the-thickness stress. Finally, experiments are replicated using appropriate numerical models based on cohesive elements that take into account frictional effects. A good agreement between numerical predictions and experiments is found.

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.

The work proposes the combined use of a Modified Transverse Crack Tension (MTCT) test coupon and Infrared Thermography, to evaluate the static and fatigue behaviour of Fibre Reinforced Polymer composites under Mode II delamination. Artificial delaminations starters are added to the TCT coupon, whose effects on the Strain Energy Release Rate are discussed. Infrared Thermography and Thermoelastic Stress Analysis are implemented to investigate stresses and delaminations growths on two FRP materials: a pre-preg IM7/8552 carbon fibre-epoxy and a glass-fibre reinforced epoxy laminates. The thermographic, thermoelastic and second harmonic signals have been obtained and used to monitor the onset of instable crack growth under monotonic loading, and the delamination growth under fatigue loading. The use of such full-field non-contact thermographic parameters allows a further and effective insight on the behaviour of TCT specimens, providing useful information for the characterisation of the Mode II delamination behaviour under both static and fatigue conditions.

A new methodology to measure the Mode II interlaminar fracture in fatigue for FRP composites is developed. The proposed methodology uses a Modified Transvers Crack Tensile (MTCT) specimen and is able to characterize the near threshold behavior in a robust, easier and significantly faster way than standard procedures. Analytical formulae, able to link the crack growth rate to the load or strain amplitudes, were found and verified, and their importance was explained, in particular, for what concerns the characterisation of the near threshold behavior. Experiments were performed both in load and strain control, while the delamination growth was monitored using different techniques including the Thermoelastic Stress Analysis (TSA). Experiments showed the reliability and effectiveness of the proposed procedure, and evidence its suitability and compatibility with current industrial material testing and qualification protocols with particular emphasis to industrial environment where a “no growth” design approach is employed.

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.

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.

The present work investigates the behaviour of a Transvers Crack Tensile (TCT) specimen undergoing fatigue loading, by means of a Thermoelastic Stress Analysis (TSA) experimental setup. The TCT is a tensile composite specimen where a number of internal layers are cut through the beam width. The presence of such transverse notch favours the formation of interlaminar Mode II delaminations, starting from the notch tips and propagating between the cut and continuous plies. In this work, a modification is adopted to the classic TCT specimen, where insert films, mimicking artificial delaminations, are laid across the notch tips. This is done with the purpose to favour a pure Mode II and a symmetric and simultaneous delamination. The modified-TCT has been subject to cyclic sinusoidal loading, typical of fatigue characterisations, and monitored at various crack growth stages by TSA. CFRP and GFRP samples have been prepared and analysed, measuring the thermoelastic signal from the edge and front faces of cycling samples. The information gained from TSA has provided a useful insight on the stress distribution settling near the crack tips, and its evolution with crack growth under fatigue. Copyright (C) 2018 The Authors. Published by Elsevier B.V.

The aim of the present work is to evaluate the influence of external layers of glass woven fabric on the pin-hole strength of flax/epoxy laminates. Single lap bearing tests were carried out to evaluate the fastened joint performances depending on laminate stacking sequence. In order to better identify the mechanical behavior of the hybrid laminate, full glass and flax laminates were also compared. In particular, bearing stress and failure mechanisms were investigated at varying joint geometry. Furthermore, an experimental failure map, clustering main failure modes of pinned hybrid composite laminate, was used to better clarify the relationship between mechanical failure and geometrical parameters of joints. The experimental results showed that the presence of external layers of glass fabric in a flax/epoxy laminate positively influences the mechanical performance of mechanically fastened joints. Furthermore, in a hybrid laminate, bearing fracture mechanism occurs for a large range of joint geometries, thus supporting the joining design of flax based composite laminates.

In this paper, the effect of salt-fog exposition on the mechanical behavior of sandwich panels having cork agglomerate core was investigated. In particular, the aim of this research work is to assess the shield function of unidirectional basalt and E-glass reinforced polymer on the aging and failure mechanism of the core when such class of material are destined to operate in hostile environments (e.g., marine environment). To do this, the manufactured sandwich panels were exposed up to 60 days to salt-fog environment, according to ASTM B 117 standard. Unaged and aged specimens were analyzed through three point bending tests after aging time of 10, 25 and 60 days. Digital Image Correlation (DIC) was carried out to perform a strain field analysis of the longitudinal cross-sections. The differences in the mechanical behavior of the synergistic cooperation of the cork core with basalt and glass fiber were highlighted thorough this technique. Moreover, the failure mechanisms related to each combinations for different aging times were described. The experimental results showed that, the intrinsic conditions of the composites (e.g., presence of defects, poor fiber-matrix adhesion), that are strictly linked to the fiber-matrix compatibility and to the impregnation quality, may induce to differences in the local mechanical behavior of the sandwich panels and to a faster aging process of the cork core in the case of basalt fiber skinned sandwich, especially in the first phases of the exposition.

Aging resistance of jute reinforced laminates is compared with two jute/basalt hybrid laminates prepared with different stacking sequences (i.e., sandwich and intercalated configuration). To this aim, composites are exposed to cyclic conditions comprising hygrothermal stress and UV radiation to promote an accelerated aging, for a period of 84 days. Specimens of each laminate are tested after 14, 28, 56 and 84 days, respectively. Quasi-static flexural tests, Charpy impact tests and dynamic mechanical tests are performed according to international ASTM and ISO standards. Furthermore, scanning electron microscopy and differential scanning calorimetry are used to evaluate the morphology of the laminates and the curing residual heat, respectively. Results showed that hybrid laminates exhibit higher impact energy and flexural properties than jute laminates, in addition to greater aging resistance. Moreover, hybrid laminates with sandwich-like configuration show improved aging tolerance in comparison to those with an intercalated configuration.