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ABSTRACTHygromorph BioComposites (HBC) exhibit shape-changing actuated by a moisture content (MC) variation due to their bilayered bioinspired architecture. However, their application in daily meteorologic variation is limited due to relative humidity (RH) and thermal couplings. This work aims to investigate the role of temperature variation on the shape changing of 4D printed continuous flax fibres reinforced HBC so that ThermoHygromorph BioComposites (THBC) are introduced.The responsiveness of the THBC is governed by the MC of the material and the stiffness ratio between the passive and active layer, which are both thermally dependant. An increase in temperature strongly reduces the actuation amplitude while the actuation kinetics is strongly fastened. A 4D-printed HBC structure is designed and submitted to a practical outdoor environmental loading, to understand the impact of daily RH and temperature variations on THBC actuation.

Recent research has been focused on developing high-performance sandwich structures using renewable resources. The adoption of bamboo rings as a core material and bio-based adhesives has emerged as a promising sustainable design solution for panel construction. It is therefore critical to conduct accelerated ageing tests on these materials to evaluate the impact of environmental humidity on their degradation and durability. This study assessed the effects of moisture ageing on the physic-mechanical properties of eco-friendly sandwich panels and their constituents (aluminium skins, bamboo ring core and castor oil bio-adhesive). Mechanical evaluations of sandwich panels with compacted and spaced bamboo ring cores were performed under varying humidity conditions. Bamboo rings exhibited variable bulk density due to swelling and loss of organic material over time. They also demonstrated increased compressive properties after 2 years of natural ageing but reduced performance after 30 days at 100 % relative humidity. The mechanical properties of the bio-based polymer were enhanced through water-ageing exposure. Sandwich panels constructed with compacted bamboo ring cores exhibited higher bending properties than those with spaced ring core architecture, with the latter showing failures characterised by a wrinkling effect on both skins followed by debonding.

Abstract This paper proposes a modified iterative learning control (MILC) periodical feedback-feedforward algorithm to reduce the vibration of a rotor caused by coupled unbalance and parallel misalignment. The control of the vibration of the rotor is provided by an active magnetic actuator (AMA). The iterative gain of the MILC algorithm here presented has a self-adjustment based on the magnitude of the vibration. Notch filters are adopted to extract the synchronous (1 × Ω) and twice rotational frequency (2 × Ω) components of the rotor vibration. Both the notch frequency of the filter and the size of feedforward storage used during the experiment have a real-time adaptation to the rotational speed. The method proposed in this work can provide effective suppression of the vibration of the rotor in case of sudden changes or fluctuations of the rotor speed. Simulations and experiments using the MILC algorithm proposed here are carried out and give evidence to the feasibility and robustness of the technique proposed.

Abstract Acoustic metamaterials are increasingly being considered as a viable technology for sound insulation. Fractal patterns constitute a potentially groundbreaking architecture for acoustic metamaterials. We describe in this work the behaviour of the transmission loss of Hilbert fractal metamaterials used for sound control purposes. The transmission loss of 3D printed metamaterials with Hilbert fractal patterns related to configurations from the zeroth to the fourth order is investigated here using impedance tube tests and Finite Element models. We evaluate, in particular, the impact of the equivalent porosity and the relative size of the cavity of the fractal pattern versus the overall dimensions of the metamaterial unit. We also provide an analytical formulation that relates the acoustic cavity resonances in the fractal patterns and the frequencies associated with the maxima of the transmission losses, providing opportunities to tune the sound insulation properties through control of the fractal architecture.

Abstract Classical approaches to enhance auxeticity quite often involve exploring or designing newer architectures. In this work, simple geometrical features at the member level are engineered to exploit non-classical nonlinearities and improve the auxetic behaviour. The structural elements of the auxetic unit cell are here represented by thin strip-like beams, or thin-walled tubular beams. The resulting nonlinear stiffness enhances the auxeticity of the lattices, especially under large deformations. To quantify the influence of the proposed structural features on the resulting Poisson’s ratio, we use here variational asymptotic method (VAM) and geometrically exact beam theory. The numerical examples reveal that 2D re-entrant type micro-structures made of thin strips exhibit an improvement in terms of auxetic behaviour under compression. For the auxetic unit cell with thin circular tubes as members, Brazier’s effect associated with cross-sectional ovalisation improves the auxetic behaviour under tension; the enhancement is even more significant for the 3D re-entrant geometry. Thin strip-based auxetic unit cells were additively manufactured and tested under compression to verify the numerical observations. The experimentally measured values of the negative Poisson’s ratio are in close agreement with the numerical results, revealing a 66% increase due to the nonlinearity. Simulation results showcase these alternative approaches to improve the auxetic behaviour through simple geometric engineering of the lattice ribs.

Despite the extensive research on renewable resources (RR) and their potential applications in composite materials and sandwich structures, there remains a significant dearth of life cycle assessment (LCA) studies that comprehensively evaluate the efficacy of RR in mitigating environmental impacts (EI). To bridge this gap, the present study aims to investigate twelve different designs of sandwich panels, specifically referred to as Fibre Metal Laminates (FML). These FML combine aluminium skins (2024-T3 and 1200-H14), polymer matrices (Epoxy, Polyester, and Castor oil Bio-PU), natural fibres (Sisal, Coir, and Cynodon spp.), surface treatments for aluminium skins (sanding, NaOH, and Washprimer), and treatments for natural fibres (Ground, NaOH-treatment and untreated). A cradle-to-gate LCA is conducted, and the inventories are modelled using the OpenLCA 1.6.3 and ecoinvent 3.9 cut-off regionalized database. EI are evaluated in twelve categories, including climate change, fossil and nuclear energy use, freshwater (acidification, ecotoxicity and eutrophication), human toxicity (cancer and non-cancer), mineral resources use, ozone layer depletion, particulate matter formation, photochemical oxidant formation, and terrestrial acidification. Impact World+ method for Latin America version 1.251 is employed to calculate EI. Nine Eco-efficiency indicators and trade-off analyses are evaluated to gain insights into design decision outcomes. Among the various panels considered, FML12, manufactured with aluminium alloy 1200-H14 treated only with sanding, castor oil biopolymer and untreated coir fibres, present the most consistent eco-efficiency indicators. The reference scenario considers the average characteristics of FML (both environmental and mechanical) for trade-off analysis. Despite the fifty percent chance of better performance, FML12 is the only panel that shows higher mechanical performance and lower EI compared to the reference scenario. The importance of this article lies in the novel results obtained using the proposed eco-efficiency indicators, which can be expanded in further studies on the topic.

This paper aims to present a hemp-based natural fibres composite value chain that could be implemented in biocomposite structures and replace synthetic fibres. Life cycle assessment (LCA) allows the assessment of the environmental footprint of the hemp fibre reinforcement value chain. This general case is complemented with two hemp fibre reinforcement applications, i.e. (1) a hemp fibre reinforced epoxy-based aircraft dashboard panel and (2) a hemp fibre reinforced epoxy-based biomonocoque for an electric scooter. LCA is also used to assess the environmental footprint of the application cases. All the hemp fibre-based value chain applications shown here demonstrate a lower environmental footprint than the fossil-based reinforcement value chain, particularly regarding the global warming potential, among other impact categories except for the case where the specific tensile strength was used as the functional unit for comparison. Impact categories related to agricultural activities, such as the eutrophication potential, land use, and freshwater consumption, are higher for the hemp-based value chains than for conventional synthetic fibre-based solutions. This study shows how conventional synthetic fibre products have the potential to be replaced by hemp-based natural fibre solutions depending on the required applications, which could lower the environmental footprint and help contribute to the ongoing climate mitigation efforts.

Date palm fibers have been studied as potential reinforcement in composite materials. Their density is equal to 1.22 g.cm−3; making them suitable for use in lightweight applications. In order to efficiently use these fibers and understand their mechanical properties, quasi-static tensile tests and cyclic fiber fatigue tests were performed to determine the mechanical properties. Their internal structure, elementary fibers and porosity were analyzed by scanning electron microscopy. The results show that the mechanical properties are clearly improved by taking into account the porosity by calculating the real section of the fibers by using the imageJ software a cross-sectional pore fraction of the fibers has been determined and the ultimate properties of the pore-free bulky fibers has been calculated with stress and Young’s modulus increased by approx. 54% as compared to the highly porous natural fibers.

Lignocellulosic fibers from date palm are one of the most available biomasses without significant valorization in the world. This work makes use of an experimental Taguchi design with three factors to determine the optimal conditions of three parameters related to date palm leaflets (gauge length, loading speed and fiber position). The paper also shows an analysis of variance for identifying the parameters that provide a maximization of their tensile properties and obtaining a significant linear model for the manufacturing of natural fibers derived from those date palm components. The results show that the factor that most affects the tensile properties of those leaflets is the gauge length, followed by the fiber within the leaflets position. The best properties were obtained for the top part of the leaflets, 20 mm gauge length and 1 mm/min speed. Moisture tests for date palm leaflets have been also carried out; a drying period of 48 h led to a decrease in water content from 53% to 6%.

This work aims to optimize the physicochemical and tensile properties of vascular fibers extracted from a local date palm rachis in Algeria. This fiber has a very specific composition and architecture and is different from the remaining fibers obtained from the six possible parts of the tree. For this purpose, a Taguchi orthogonal array design L16 was applied to reduce the number of experiments. The fibers were extracted from the rachis with two different methods (boiling and retting in water) and treated by NaOH with various concentrations (1%, 2%, 3%, and 5%) and for different durations (1, 4, 8, and 12 h). They were characterized using SEM-EDX, ATR-FTIR, XRD, and TGA to understand the effects of the extraction method and alkali treatment. A statistical treatment of the data was carried out based on the S/N ratio and ANOVA was performed to identify the most significant parameters affecting the tensile strength and the Young’s modulus of the fibers. A desirability function was developed to identify the optimal factors leading to the maximization of the tensile properties.

This work describes the correlations between the ultrasonic pulse velocity (UPV) and physical properties of fibrous-particulate hybrid composites made of glass/carbon fabrics and three different micro-inclusions such as silica particles, recycled carbon fibre powder and Portland cement. A full factorial design (214151) is established to identify the effects of volume fraction, stacking sequence and particle type on the physical properties obtained by Archimedes’ principle. An electroacoustic transducer (50 ​kHz) is used to determine the ultrasonic pulse velocity data. Statistical models reveal correlations between UPV and the physical properties of hybrid composites. The combination of UPV and statistical techniques can identify all constitutive phases, being useful to characterise and estimate physical properties in a hybrid system composed of fibres and microparticles.

The work describes the exploration of the design space by fabrication, modelling and testing of bio-based and humidity-triggered 4D printed shape-changing biocomposites. The aim is to broaden the understanding of the control actuation via printing path tailoring and unlock new potential applications for biomaterials and autonomous actuator design. The composites are made with continuous flax yarns and polylactic acid matrix filaments and exhibit moisture-induced actuation. The actuation capability is first demonstrated by printing a calla lily flower-inspired configuration subjected to 98% relative humidity. This structure did not however achieve the anticlastic double curvature and large actuation targeted. To resolve these issues, cross-ply composite architectures with bent filaments deposited in one layer have then been developed. The amplitude for curvature control ranges obtained were 1.9*10−3mm−1 and 7.9*10−3mm−1 depending on the position on the specimen. Other cross-ply hygromorphs solutions are also proposed, with the orientation of their passive layers ([0°]2) tilted by α degrees (stacking sequence: [-α,α, 90°]). The largest actuation curvature was obtained when α=40°, which increased by 0.0072 mm−1 when compared to α = 0°. The hygromorphs presented in this work are modelled using in an in–house filament scale finite element model able to capture the complexity of the printed hygromorphs architectures.

Abstract Current interest toward ionic liquids (ILs) stems from some of their novel characteristics, like low vapor pressure, thermal stability, and nonflammability, integrated through high ionic conductivity and broad range of electrochemical strength. Nowadays, ionic liquids represent a new category of chemical‐based compounds for developing superior and multifunctional substances with potential in several fields. ILs can be used in solvents such as salt electrolyte and additional materials. By adding functional physiochemical characteristics, a variety of IL‐based electrolytes can also be used for energy storage purposes. It is hoped that the present review will supply guidance for future research focused on IL‐based polymer nanocomposites electrolytes for sensors, high performance, biomedicine, and environmental applications. Additionally, a comprehensive overview about the polymer‐based composites’ ILs components, including a classification of the types of polymer matrix available is provided in this review. More focus is placed upon ILs‐based polymeric nanocomposites used in multiple applications such as electrochemical biosensors, energy‐related materials, biomedicine, actuators, environmental, and the aviation and aerospace industries. At last, existing challenges and prospects in this field are discussed and concluding remarks are provided.

This data article presents four experimental sets of results related to flax fibre composites with epoxy shape memory polymer matrix: water vapor absorption, mass diffusion immersed in water, hygroscopic expansion, mechanical properties. The water vapor absorption tests are described in raw data related to four types of laminates with weights measured at different relative humidity (0%, 9%, 33%, 44%,75%, 85% and 100%). The mass diffusion experiments are related to weights of immersed samples over time. The unidirectional composite hygroscopic expansion is also measured along the fibre longitude and transverse directions. The mechanical properties of flax composite at various temperatures (20°C, 40°C, 60°C, 80°C and 100°C) and humidity environments (50% and immersed) are also described. Load-displacement diagrams of the hygromorph composites are converted into stress-strain diagrams via a compliance calibration, from which the tensile moduli are extracted. The data presented in this article can provide a benchmark for the development of new models, or for the determination of other properties via post processing. The detailed interpretation of the data can be found in [1]. The data is available in the Mendeley Data repository at [2].

This study focuses on the chemical and thermo-physical characterization of date palm fiber, which can be used in the reinforcement of green composites. Alkaline solutions with different concentrations of NaOH (0.5, 1, 2 and 3%) and various immersion times (0.5, 1, 2, 4, 6 and 8h) at room temperature were used to treat fibers obtained from date palm fruit branches. In total, 750 samples were tested, and the results obtained show that the chemical treatment of the fibers can lead to an increase, up to 3 times, of their mechanical properties (strength and Young’s modulus) in quasi-static tensile tests. Due to the dispersion in the experimental data, a statistical approach is required to evaluate the mechanical properties. To better understand the phenomena related to the physico-chemical properties of these fibers, several characterization techniques have been used, namely Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction. The data have been compared with results reported in the literature for other lignocellulosic fibers.

We present here a simplified procedure to manufacture auxetic PU foam via a single direction thermoforming compression process applied to conventional (pristine) open cell foam samples. The auxetic foams produced here have a Poisson’s ratio ν21 ranging from −1 to 0 in the 1–2 plane and a tangent modulus Et2 ranging from 0.2 MPa to 2 MPa. X-ray μ-CT and 3D skeletonization enabled the extraction of the topological parameters of the pristine and the auxetic foams. The auxetic foam is transverse isotropic with cell structures exhibiting a re-entrant shape along the thermoforming compression direction 1. More ribs are also oriented within the transverse plane 2–3, in which the stiffness is larger. Tensile and compression quasi-static tests have been carried out on samples cut along different directions and having various thermoforming compression ratios rc. Auxeticity is present in the in 1–2 plane only for compression ratios between 40% and 80%. Finite Element models for the pristine and auxetic foams have also been built from the μ-CT scanned 3D models. The numerical results show a good agreement with the experimental data and help explaining the deformation mechanisms of these auxetic foams.

The incorporation of cells into tissue engineering scaffolds can be a major challenge. Here, the authors report on anchoring thrombin to cell membranes for the in situ formation of fibrin scaffolds around the modified cells, demonstrate scaffold formation in vitro and show cell survival in vivo.

Abstract This work investigates the mechanical behaviour of a sustainable sandwich panel, consisting of bamboo rings core, treated aluminium skins and epoxy adhesive. A Design of Experiment (DoE) is used to identify the effects of bamboo diameters (30 and 45 mm) and aluminium skin treatments (alkaline degreasing and application of primer) on the mechanical and physical properties of sandwich panels. The aluminium skins treated with the wash primer significantly increase adhesion to the polymer, resulting in greater maximum load, flexural strength, maximum skin stress and maximum core shear stress; while the skins treated with NaOH resulted in a greater flexural and core shear modulus. Relatively more rigid and resistant structures are obtained with Ø30 mm rings, due to the increased surface contact area and the number of constraints on the core. The samples fail due to the skin fracture, implying an efficient face-core bond that is attributed to the proper absorption of the polymer by bamboo and the treatment of the aluminium surface. The proposed panels present good mechanical performance, proving to be a feasible and promising alternative for secondary structural applications.

The use of recycled and renewable components in structural applications supports the development of sustainable lightweight structures. Disposed bottle caps can be used to generate eco-friendly honeycomb cores, especially when combined with other eco-friendly components. A natural fibre-based laminate represents an alternative to synthetic fibres, matrices, and metals in skins for sandwich panels. This study evaluates the use of flax fibre laminates as sustainable skins for sandwich panels made from upcycled bottle caps core. Metallic skin cases are also tested as a reference. The influence of the amount of adhesive used to produce the panels is also investigated in a 22 full factorial design, together with an independent test carried out on samples made from natural fibres. The characterisation against flexural and low-velocity dynamic loads indicates that the flax fibre skin leads to specific core shear and flexural moduli up to 19% higher than in aluminium-based panels. Unidirectional flax fibres, however, reduce the energy absorption during impact. Flexural properties show that the most efficient design involves the least adhesive amount. Finite element models also show a good fit to the experimental results and indicate a 166% increase of energy absorption with the presence of multidirectional fibre laminates.

There has been a growing concern for safety and precautions in the wake of coronavirus SARS-CoV2 pandemic also dubbed as COVID-19, which has caused a major impact at a global scale. This has resulted in many industries accelerating at fast pace new biosafety technologies and improving the already existing ones to deal with this highly contagious virus. Most governments across the globe are also mandating policies focusing on increased biosafety to prevent further spread of the virus and protect key workers such as healthcare agents, store employees and police. The COVID-19 pandemic has exposed huge gaps in the healthcare industry that include lack of effective vaccines and medicines, testing of infection, real-time monitoring of the spread of the virus, inadequate protective equipment, and scarcity of protective and intensive care of patients. Some of these may be attributed to a lack of focused research in biosafety materials. As a consequence of the pandemic, a significant body of research activities has therefore focused on biosafety materials that possess unique properties needed for biosafety applications. This graphical review aims to provide a perspective on the usage of bio-based materials to handle the imposing challenges in biosafety. This review investigates existing developments in bio-based antimicrobial encapsulations as an effective measure to deter the growth of COVID-19 virus on surfaces and minimize its spread through surface contact. This will help researchers develop further strategies in material science to focus on contagious pathogens in the future.

This work describes the bending and shear mechanical properties of a novel concept of sustainable sandwich panel made from unidirectional prepreg flaxtape skins and bamboo rings as a circular core material. A Design of Experiment (DoE) is used to determine the influence of the bamboo diameter and the type of adhesive bonding between core and skins on the equivalent density, flexural and shear properties of these panels. Numerical analysis are also performed using cohesive surface contacts between skins and bamboo rings to investigate the structural behaviour and failure mechanisms of the sandwich panels. The equivalent density is affected by both factors, with an overall decrease when larger bamboo rings and lower density adhesive are used. Although sandwich panels with the larger bamboo rings as core show superior flexural properties and skin stress, smaller bamboo rings cores shows an increase in the core transverse shear modulus. The physical and mechanical characteristics of the adhesives directly affect the failure mode and the overall structural integrity of the panels.

A sandwich structure made of sustainable components is investigated under quasi-static and dynamic conditions. The upcycled plastic bottle caps are used to manufacture a greener circular cell honeycomb core, based on a full factorial design. A recycled PET foil is used as skins, being compared to a classic panel with aluminium skins. The particle-reinforced adhesive is also tested by adding recycled rubber particles, from remoulded tyres, and cement particles. Three-point bending test and a low-velocity drop-tower test are performed on sandwich structures. Flexural modulus has a 19% increase with aluminium skins, while core shear modulus increases by 27% with cement-reinforced PET panels. Energy absorption in quasi-static tests increased by 26% with rubber inclusions in aluminium-based samples, while no significant effect is observed in low-velocity impact tests. Aluminium skins lead to increments of up to 198% for specific energy absorption and 298% for specific maximum load under impact. The satisfactory results of the static and dynamic characterisation of the bottle cap structure highlight the promising characteristic of the reuse of plastic waste in lightweight structural applications.

This work focuses on the fabrication and characterisation of epoxy composites reinforced with natural fibre layers extracted from the inner bast (phloem) of the papaya plant (Carica papaya) under tensile and three-point bending loading. The papaya phloem is composed of fibrous laminas that wrap and reinforce the stem of the plant. A set of quasi-periodically arranged holes disrupt the continuity of these layers, through which the branches emerge. The fibres in each layer constitute an anisotropic honeycomb-like structure, whose elongated cells align along a single preferential direction. Papaya-reinforced epoxy composites are fabricated by hand lay-up and evaluated using two full-factorial designs based on the fibre-to-load direction in longitudinal (0°) and transverse (90°) conditions, for configurations without holes and alternating holes. Composites made with randomly-oriented short fibres are also evaluated along with the first experiment. The tensile and flexural properties obtained are compared to other materials in the literature to assess its potential as a structural material. The results show that the papaya bast fibre layers can be a promising reinforcement for polymeric composites.

Smart biomaterials with an inherent capacity to elicit specific behaviors in lieu of biological prompts would be advantageous for regenerative medicine applications. In this work, we employ an electrospinning technique to model the in vivo nanofibrous extracellular matrix (ECM) of cartilage using a chondroinductive cellulose and silk polymer blend (75:25 ratio). This natural polymer composite is directly electrospun for the first time, into nanofibers without post-spun treatment, using a trifluoroacetic acid and acetic acid cosolvent system. Biocompatibility of the composite nanofibres with human mesenchymal stem cells (hMSCs) is demonstrated and its inherent capacity to direct chondrogenic stem cell differentiation, in the absence of stimulating growth factors, is confirmed. This chondrogenic stimulation could be countered biochemically using fibroblast growth factor-2, a growth factor used to enhance the proliferation of hMSCs. Furthermore, the potential mechanisms driving this chondroinduction at the cell-biomaterial interface is investigated. Composite substrates are fabricated as two-dimensional film surfaces and cultured with hMSCs in the presence of chemicals that interfere with their biochemical and mechanical signaling pathways. Preventing substrate surface elasticity transmission resulted in a significant downregulation of chondrogenic gene expression. Interference with the classical chondrogenic Smad2/3 phosphorylation pathway did not impact chondrogenesis. The results highlight the importance of substrate mechanical elasticity on hMSCs chondroinduction and its independence to known chondrogenic biochemical pathways. The newly fabricated scaffolds provide the foundation for designing a robust, self-inductive, and cost-effective biomimetic biomaterial for cartilage tissue engineering.

Fibre metal laminates (FMLs) are lightweight structures with high structural performance and are suitable for many industrial applications. This work describes the impact behaviour of novel sisal fibre-reinforced aluminium laminates (SiRAL) and their dependence upon the orientations of the fibres, the composite core used and the surface treatment of the metal skins. A cold-pressing technique is used to produce SiRALs in six configurations. The FMLs here also have treated or untreated aluminium skins (2024 T3) and three different types of core materials (0°/90° fabric, ±45° fabric and random matt). The ±45° core treated SiRAL provides the highest energy absorption and deflection properties. The pre-treatment of aluminium skins using sandpaper, deep cleaning and primer significantly affects the delamination of the panels under bending impact. The findings reveal that the SiRAL concept is a promising multifunctional FML suitable for different applications that require lightweight, bending and impact performance, together with sustainability characteristics.

In this study, we investigated the influence of the addition of sisal and glass fibres on the mechanical properties of polymer concrete (PC). These types of concrete are used in many modern civil engineering applications. The prismatic specimens sized according to ASTM C580-02 were elaborated with a PC constituted by 14% constant mass of polyester resin matrix, a granular skeleton based on sand and powder marble. The reinforcement with 60% sand and 26% marble powder adopted in this investigation is the best formulation found in previous authors work. This composition was reinforced by 1 and 2% of sisal and glass fibres, the first one having lengths of 6 mm or 12 mm, however, the second unidirectional cut into bands. These specimens were subjected to 3-point bending monotonic loading. The results obtained were discussed and compared with those obtained for control beams without fibres reinforcement. It is important to note that the incorporation of the glass fibre contributes to an increase of the ultimate load of the polymer composite material produced, however, the addition of the sisal fibre lead to its decreases. In addition, the incorporation of 2% of sisal fibre having 6 mm length leads to a reduction of 26% of the mass of the specimens.

Externally bonded reinforcement using Fiber Reinforced Polymer (FRP) is a good response to the concern represented by the need for rehabilitation of concrete structures. These techniques are more and more attractive because of their fast and low labour costs, very good strength to weight ratio, good fatigue properties, and non-corrosive characteristics of FRP. The present work is an experimental study investigating the mechanical behaviour under a uni-axial loading of short concrete columns reinforced by composite materials. These are constituted of glass fibers GFRP (bidirectional fabric of two surface densities 500 and 300 g/m2), carbon CFRP (unidirectional sheet of density per unit area of 230 g/m2) and polyester and epoxy resin respectively. The investigation aims at demonstrating the effectiveness of FRP reinforcement through highlighting the effect of thickness (FRP number of folds), the nature of the reinforcement (glass, carbon or Hybrid), and the orientation of the fibers. The axial lengths shortening along with the radial expansion are measured using the strain gauges glued to the outer surfaces of the composite jacket via a Wheatstone bridge. These measurements are saved to a PC through an acquisition card. The results obtained clearly show that the columns reinforced with CFRP folds allow an important increase in the compressive rupture stress in comparison with those reinforced with GFRP folds. The gains in compressive strength, in axial and in radial strains of the confined concrete with the different FRPs used are identified and quantified. It has further been demonstrated that the tested columns mechanisms depend strongly on the type of fiber reinforcements.

Nowadays, finding new approaches to attenuate the effects of the catastrophic shear failure mode for reinforced concrete beams is a major challenge. Generally the bending failure is ductile. It allows a redistribution of the stresses providing an early warning, whereas the rupture by shear is fragile and sudden which can lead to detrimental consequences for the structures. This research focuses on the repair of deep beams in reinforced concrete shear subjected to 4-point bending. After being preloaded at different levels of their ultimate loads, the beams are repaired by bonding a composite material made of an epoxy resin reinforced by glass fibers. The main objective of this study is to contribute to the mastery of a new method developed by the authors that consists by banding the cracks in critical zones in order to avoid fragile ruptures due to the shear force. This new technique led to better results in terms of mechanical properties when compared to conventional methods, notably the absence of the debonding of the composite found in the case of the repairs of the beams by bands or U-shaped composites. The feasibility, the performances and the behavior of the beams have been examined. The experimental approach adopted using this new technique has shown the influence of the type of loading on the fatigue behavior. In addition, the repair performed led to a considerable improvement in the fatigue durability of the preloaded beam.

Abstract In this work we describe a theoretical model that predicts the interfacial contact stiffness of fractal rough surfaces by considering the effects of elastic and plastic deformations of the fractal asperities. We also develop an original test rig that simulates dovetail joints for turbo machinery blades, which can fine tune the normal contact load existing between the contacting surfaces of the blade root. The interfacial contact stiffness is obtained through an inverse identification method in which finite element simulations are fitted to the experimental results. Excellent agreement is observed between the contact stiffness predicted by the theoretical model and by the analogous experimental results. We demonstrate that the contact stiffness is a power law function of the normal contact load with an exponent α within the whole range of fractal dimension D(1

This paper describes the structural characteristics of metal rubber (MR) evaluated by X-ray tomography and skeletonisation at microscopic scale. The parameters used to describe the internal structure of the MR were numerically extracted and compared to assess the effect of different MR manufacturing parameters on the mechanical properties of the material. Quasi-static tests were also performed to obtain the stiffness and damping of the metal porous material and to understand their correlation with the topology defining the samples. A simplified helix cell model was used to interpret the mechanical properties of the MR based on the structural parameters identified in this paper. The transverse isotropic stiffness of the MR observed here is partly caused by the distribution of the metal wires, with more helices oriented along the molding direction resulting in smaller equivalent stiffness. The compression, relative density, helix and wire diameters can influence the structural and mechanical characteristics of the MR in a significant manner. Keywords: Metal rubber, Entangled wire mesh, CT scan, Topology, Microstructure parameters, Mechanical property

The behavior of Inconel 718 and 617 panels on the high-speed impact perforation mode at elevated temperatures and ballistic impact limit is here investigated using experimental and numerical methods. Impact tests have been performed using a custom-made two-stage light-gas gun rig, with the specimens being subjected to high temperatures (up to 1007 °C). The panels have been impacted using spherical projectiles with velocities ranging from 0.5 to 2.2 km/s. During the experiments the failure of the targets has been evaluated by varying parameters like the projectile diameter, its density and the oblique impact angle. An analytical model to estimate the residual velocity and the ballistic limit equations has been established. Finite element models (FEM) combined with phenomenological analytical models have been also developed to validate the predictive results obtained by the analytical model. The simulations from the FEM and the analytical models provide a good match with the experimental data. For the two typical cases (normal impact and oblique impact), the shapes and sizes of the damaged holes have been also well predicted by the numerical model. Equivalent diameters of the impacts have also been identified as functions of the velocity, diameter of the projectile and panel thickness. Keywords: Inconel alloys, High velocity impact, High-temperature, Residual velocity, Ballistic limit

Rigid particles have been incorporated into laminated composites, especially to enhance their bending performance attributed to the stiffening of the matrix phase (i) and the increased interlaminar shear resistance (ii). In order to better evaluate the improvement mechanism provided by the particulate inclusions, this work investigates the incorporation of micro-sized silica on the top, bottom and both surfaces of glass fibre laminates, mitigating the interference of the interlocking effect. Three-point bending, and impact tests are performed to evaluate the hybrid glass fibre composites containing 5, 7.5 and 10 wt% of micro silica. In addition, the effect of the micro silica particles into epoxy polymers is verified under tensile, compressive and abrasion tests. A finite element model is developed to simulate the three-point bending test and to better assess the behaviour of the composite laminate. Although silica particles lead to increased compressive modulus of the epoxy polymers, their positive effect on glass fibre composites under flexural loads is more evident when placed on the bottom side of the laminates subjected to the maximum tensile stress. The incorporation of 7.5 wt% silica microparticles at the bottom surface of the laminates achieves higher flexural strength and lower impact resistance.

Phononic metamaterials are capable of manipulating mechanical wave propagation in applications ranging from nanoscale heat transfer to noise and vibration mitigation. The design of phononic metamaterials to control low-frequency vibrations, such as those induced by ground transportation and low-amplitude seismic waves, however, remains a challenge. Here we propose a new design methodology to generate seismic metamaterials that can attenuate surface waves below 10 Hz. Our design concept evolves around the engineering of the multi-layered soil, the use of conventional construction materials, and operational construction constraints. The proposed seismic metamaterials are constructed by periodically varying concrete piles in the host multi-layered soil. We first validate the design concept and the numerical models by performing a lab-scale experiment on the low-amplitude surface wave propagation in a finite-size seismic metamaterial. To the best of the Authors' knowledge, this is one of the few attempts made to date to experimentally understand the vibration mitigation capability of seismic metamaterials. We then numerically demonstrate that the multi-layered seismic metamaterials can attenuate surface waves over a wide frequency range, with the incident wave energy being confined within the softest layer of the shallow layered seismic metamaterials. In addition to the localized wave energy distribution, deep layered seismic metamaterials exhibit broadband cut-off band gaps up to 7.2 Hz due to the strongly imposed constraint between piles and surrounding soil. Furthermore, these cut-off band gaps strongly depend on the constraint between the piles and the bottom layer of the soil and hence can be tuned by tailoring the foundation stiffness. We also evidence the possibility to create constant wave band gaps by introducing hollow concrete piles with pile volume fraction

We present in this work the manufacturing, modeling, and testing of dome-shaped cellular structures with auxetic (negative Poisson's ratio) behavior. The auxetic configurations allow the creation of structures with synclastic (i.e., dome-shaped) curvatures, and this feature is used to evaluate the performance of cellular metamaterials under quasi-static indentation conditions. We consider here different cellular geometries (re-entrant, arrow-head, tri-chiral, hexagonal) and the implications of their manufacturing using 3D printing techniques with PLA material. The dome-shaped configurations are modeled using full-scale non-linear quasi-static and explicit dynamic FE models that represent both the geometry and approximate constitutive models of the PLA filament material derived from tensile tests on dogbone specimens. The cellular metamaterials samples are subjected to indentation tests, with maps of strains obtained through DIC measurements. The correlation between experimental and numerical simulations is good, and shows the peculiar indentation behavior of these cellular structures. We also perform a comparative analysis by simulation of the force/displacement, strain and fracture history during quasi-static loading, and discuss the performance of the different cellular topologies for these dome-shape metamaterial designs.

The microwave properties of composites containing Fe-based ferromagnetic microwires and carbon fibres have been investigated as part of a campaign to bring added functionalities into structural composites. A transmission window observed in 1-6 GHz demonstrates double-negative (DNG), i.e., metamaterial characteristics in the composites containing short-cut carbon fibres and a parallel array of microwires; the metamaterial characteristic is due to the ferromagnetic resonance and a plasmonic behaviour, as short carbon fibres are proved to ameliorate DNG properties through enhancing the impedance of the composites. In parallel, magnetically tunable metamaterial features are realised in composites containing continuous carbon fibres and microwires, which can be switched on/off via rotating the electrical excitation direction. Such structural composites integrated with metamaterial features (termed as metacomposites) are potentially useful for active cloaking applications among others.

The preparation of ultra-thin CFRP laminates, which incorporate a cycloaliphatic epoxy resin reinforced with polyhedral oligomeric silsesquioxane (POSS) reagent nanofiller, using out-of-autoclave procedure is reported. The influence of the amount of POSS within the laminate on the mechanical properties and surface roughness of the laminates is analysed before and after exposure to atomic oxygen (AO) to simulate the effects of low Earth orbit (LEO). The addition of 5 wt% POSS to the base epoxy leads to an increase in both flexural strength and modulus, but these values begin to fall as the POSS content rises, possibly due to issues with agglomeration. The addition of POSS offers improved resistance against AO degradation with the laminates containing 20 wt% POSS demonstrating the lowest erosion yield (1.67 × 10-24 cm2/atom) after the equivalent of a period of 12 months in a simulated LEO environment. Exposure to AO promotes the formation of a silicon-rich coating layer on the surface of the laminate, which in turn reduces roughness and increases stiffness, as evidenced by measurements of flexural properties and spectral data after exposure.

The development of new materials based on industrial wastes has been the focus of much research for a sustainable world. The growing demand for tyres has been every year exacerbating environmental problems due to indiscriminate disposal in the nature, making a potentially harmful waste to public health. The incorporation of rubber particles from scrap tyres into polymeric composites has achieved high toughness and moderate mechanical properties. This work investigates the geometric effects (thickness, width and internal cell angle) of auxetic structures made of recycled rubber composites based on experimental and numerical data. The response surface models integrated with the swarm intelligence and finite element analysis were proposed in order to obtain a range of solutions that provides useful information to the user during the selection of geometric parameters for reentrant cells. The results revealed the cell thickness ranges from 39-40 mm and 5.98-6 mm, and the cell angle range from -0.01 to -0.06º maximize the ultimate strength. The same parameters were able to optimize the modulus of elasticity of rubber auxetic structures, excepting for the angle factor which must be set between -30º and 27.7º. The optimal Poisson's ratio was found when the cell angle ranged from -30º to -28.5º, cell width ranged from 5-5.6 mm and 2 mm in thickness.

The work describes the analytical and experimental characterisation of a class of polymeric composites made from epoxy matrix reinforced with unidirectional natural sisal and banana fibres with silica microparticles and maleic anhydride fabricated by manual moulding. The analytical models, ROM rule of mixtures and Halpin-Tsai approach, have been used in conjunction with a Design of Experiments (DOE) analysis from tensile tests carried out on 24 different composites architectures. The following experimental factors were analyzed in this work: type of fibres (sisal and banana fibres), volume fraction of fibres (30% and 50%) and modified matrix phase by adding silica microparticles (0%wt, 20%wt and 33%wt) and maleic anhydride (0%wt and 2%wt). The ROM approach has shown a general good agreement with the experimental data for composites manufactured with 30%vol of natural fibres, which can be attributed to the strong adhesion found between the phases. On the opposite, the semi empirical model proposed by Halpin and Tsai has shown greater fidelity with composites manufactured from 50%vol of natural fibres, which exhibit a weak interfacial bonding. The addition of microsilica and maleic anhydride in the system did not enhance the adhesion between the phases as expected.

The work described in this paper is related to the effect of adding carbon nanotubes (CNT) on the mechanical properties of polymer-cement composites. A full factorial design has been performed on 160 samples to identify the contribution provided by the following factors: polymeric phase addition, CNT weight addition and water/cement ratio. The response parameters of the full factorial design were the bulk density, apparent porosity, compressive strength and elastic modulus of the polymer-cement-based nanocomposites. All the factors considered in this analysis affected significantly the bulk density and apparent porosity of the composites. The compressive strength and elastic modulus were affected primarily by the cross-interactions between polymeric phase and CNT additions, and the water/cement ratio with polymeric phase factors.

This paper presents a simple methodology to perform a high temperature coupled thermo-mechanical test using ultra-high temperature ceramic material specimens (UHTCs), which are equipped with chemical composition gratings sensors (CCGs). The methodology also considers the presence of coupled loading within the response provided by the CCG sensors. The theoretical strain of the UHTCs specimens calculated with this technique shows a maximum relative error of 2.15% between the analytical and experimental data. To further verify the validity of the results from the tests, a Finite Element (FE) model has been developed to simulate the temperature, stress and strain fields within the UHTC structure equipped with the CCG. The results show that the compressive stress exceeds the material strength at the bonding area, and this originates a failure by fracture of the supporting structure in the hot environment. The results related to the strain fields show that the relative error with the experimental data decrease with an increase of temperature. The relative error is less than 15% when the temperature is higher than 200 °C, and only 6.71% at 695 °C.