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Showing papers in "Composites Part B-engineering in 2017"


Journal ArticleDOI
TL;DR: In this paper, the authors give an overview on 3D printing techniques of polymer composite materials and the properties and performance of 3D printed composite parts as well as their potential applications in the fields of biomedical, electronics and aerospace engineering.
Abstract: The use of 3D printing for rapid tooling and manufacturing has promised to produce components with complex geometries according to computer designs. Due to the intrinsically limited mechanical properties and functionalities of printed pure polymer parts, there is a critical need to develop printable polymer composites with high performance. 3D printing offers many advantages in the fabrication of composites, including high precision, cost effective and customized geometry. This article gives an overview on 3D printing techniques of polymer composite materials and the properties and performance of 3D printed composite parts as well as their potential applications in the fields of biomedical, electronics and aerospace engineering. Common 3D printing techniques such as fused deposition modeling, selective laser sintering, inkjet 3D printing, stereolithography, and 3D plotting are introduced. The formation methodology and the performance of particle-, fiber- and nanomaterial-reinforced polymer composites are emphasized. Finally, important limitations are identified to motivate the future research of 3D printing.

2,132 citations


Journal ArticleDOI
TL;DR: In this paper, the effect on properties of virgin and recycled HDPE/LDPE/Nylon PSW with different reinforcements like sand, natural fibre, hemp fibre, metal powder etc.
Abstract: Plastic solid waste (PSW) of polymers (like: high density polyethylene (HDPE), low density polyethylene (LDPE), Nylon etc.) is creating new challenges, which in today's scenario are major research concerns. A sharp rise has been observed in production of different products based on different plastic material. This huge increase in plastic commodities also increases the waste generation thus creating new challenges. Some researchers have reported work in the field of PSW management with different recycling methods. This paper compiles the different research work done by researchers in this field of recycling and progress in recovery and management of PSW by different methods (i.e. Primary, secondary, tertiary and quaternary) along with the various identification/separation techniques. Further, this paper reviews the effect on properties of virgin and recycled HDPE/LDPE/Nylon PSW with different reinforcements like sand, natural fibre, hemp fibre, metal powder etc.

703 citations


Journal ArticleDOI
TL;DR: In this paper, the surface treatment of carbon fibers is employed to increase the surface functional groups and interfacial adhesion between the CFs and the surrounding polymer matrix, and the thermal, mechanical, and electrical properties of the composites are also discussed.
Abstract: Carbon fibers (CFs) have high specific tensile strength, high modulus, and outstanding wear resistance, and are widely used for the reinforcement of advanced composite materials. CF-reinforced thermoplastic composites have received much attention because of their easy processability and recycling convenience compared with thermosetting composites. Surface treatment of CFs is generally employed to increase the surface functional groups and interfacial adhesion between the CFs and the surrounding polymer matrix. In this review, we explore recent advances in the surface treatment of CFs and preparation of CF/thermoplastic composites. The thermal, mechanical, and electrical properties of the composites are also discussed.

438 citations


Journal ArticleDOI
TL;DR: In this article, the mechanical properties of materials produced by 3D printing based on fused filament fabrication (FFF, analogous to FDM ® ) are investigated. But the main assumption is that the materials behave like laminates formed by orthotropic layers.
Abstract: The objective of this work is the mechanical characterization of materials produced by 3D printing based on fused filament fabrication (FFF, analogous to FDM ® ). The materials chosen are a polylactic acid (PLA) and a PLA reinforced with short carbon fibers in a weight fraction of 15 % (PLA+CF). In view of the FFF nature, which produces specimens layer by layer and following predefined orientations, the main assumption considered is that the materials behave like laminates formed by orthotropic layers. If the 3D printing is made in the 1 − 2 plane, where 1 is the deposition direction and 2 is a direction perpendicular to 1, the mechanical properties obtained are the tensile moduli E 1 and E 2 , the Poisson ratios ν 12 and ν 21 , the shear modulus G 12 and related strength properties. For this purpose, only unidirectional or specially oriented specimens are used. After tests up to material failure, scanning electron microscopy (SEM) is employed to observe fracture surfaces. It was noticed that, in the microstructure of the PLA+CF, the short carbon fibers stay highly oriented with the material deposition direction in the FFF specimens. This fact, and the also observed length of the fibers, explains differences in material properties encountered among the performed experiments.

414 citations


Journal ArticleDOI
TL;DR: In this paper, the nonlinear bending behavior of a novel class of multi-layer polymer nanocomposite beams reinforced with graphene platelets (GPLs) that are non-uniformly distributed along the thickness direction was investigated.
Abstract: This paper studies the nonlinear bending behavior of a novel class of multi-layer polymer nanocomposite beams reinforced with graphene platelets (GPLs) that are non-uniformly distributed along the thickness direction. Nonlinear governing equation is established based on Timoshenko beam theory and von Karman nonlinear strain-displacement relationship. The effective Young's modulus of the nanocomposites is determined by modified Halpin-Tsai micromechanics model. Ritz method is employed to reduce the governing differential equation into an algebraic system from which the static bending solutions can be obtained. A comprehensive parametric study is then conducted, with a particular focus on the influences of distribution pattern, weight fraction, geometry and size of GPLs together with the total number of layers on the linear and nonlinear bending performances of the beams. Numerical results demonstrate the significantly improved bending performance through the addition of a very small amount of GPLs into polymer matrix as reinforcements. It is found that dispersing more GPLs that are in square shape with fewer single graphene layers near the top and bottom surfaces of the beam is the most effective way to reduce bending deflections. Beams with a higher weight fraction of GPLs that are symmetrically distributed in such a way are also less sensitive to the nonlinear deformation.

300 citations


Journal ArticleDOI
TL;DR: In this article, a stress-driven integral constitutive law is proposed to solve the nonlocal elasticity problem in plane and straight nano-beams. But the model is not suitable for the structural design of nano-devices.
Abstract: In the strain-driven model of nonlocal elasticity proposed by Eringen , the elastic strain is defined by a Fredholm integral equation in which the stress is the output of a convolution between the local response to an elastic strain and a smoothing kernel dependent on a nonlocal parameter. In the wake of this proposal, size effects in nano-beams were investigated in literature by adopting a differential formulation considered to be equivalent to the integral one. Recent improvements have however revealed that equivalence requires also the fulfilment of constitutive boundary conditions. Moreover, this strain-driven nonlocal elastic problem has been shown to be ill-posed, being conflicting with equilibrium requirements. A stress-driven integral constitutive law provides the natural way to get well-posed nonlocal elastic problems for application to nano-structures. The new integral constitutive law is formulated with explicit reference to plane and straight nano-beams according to the standard Bernoulli - Euler structural model. The solution procedure based on the stress-driven nonlocal law is described and adopted for the solution of a simple statically indeterminate scheme, thus showing effectiveness of the new model for the structural design of nano-devices.

249 citations


Journal ArticleDOI
TL;DR: In this article, the effect of surface treatment on the morphology, thermal conductivity and dielectric properties of the composites was investigated, and the results revealed that after surface treatment, the interfacial adhension between hBN platelets and PTFE matrix was improved and the in-plane orientation degree of platelets in PTFe matrix decreased.
Abstract: To achieve polymer-based composites for electronic packaging with low dielectric constant, low dielectric loss tangent and high thermal conductivity, silane coupling agent KH550 modified hexagonal boron nitride (hBN) platelets were introduced into PTFE matrix via a cold pressing and sintering method. The effect of surface treatment on the morphology, thermal conductivity and dielectric properties of the composites was investigated. The results revealed that after surface treatment, the interfacial adhension between hBN platelets and PTFE matrix was improved and the in-plane orientation degree of hBN platelets in PTFE matrix decreased, which effectively improvd the thermal conductivity of the composites. The thermal conductivity of hBN-KH550/PTFE composite with 30 vol% filler content is 0.722 W/mK, which is 2.7 folds of pure PTFE. Moreover, the enhanced interfacial adhension and reduced surface hydrophilicity of hBN platelets significantly decreased the interfacial polarization, resulting in not only lower dielectric constant and dielectric loss tangent but also weaker frequency-dependence.

241 citations


Journal ArticleDOI
TL;DR: In this paper, the Young's and shear moduli of the composites with different graphene volume fractions under different temperatures are simulated and discussed, and large discrepancies between the results from the MD simulations and the rule of mixture are observed.
Abstract: This paper investigates the mechanical properties of graphene/PMMA nanocomposite system by using the molecular dynamics simulations. The graphene nanoplates are assumed to be fully exfoliated in the PMMA matrix and are all planar orientated, which are similar to the ones assembled using layer-by-layer technique. The Young's modulus and shear modulus of the composites with different graphene volume fractions under different temperatures are simulated and discussed. The results show that the Young's and shear moduli increase with the increase of graphene volume fraction and decrease as the temperature rises from 300 K to 500 K, while the efficiency of the reinforcement is reduced as the graphene content becomes higher. Simulations of single layer graphene under uniaxial tension, in-plane pure shear and uniformly distributed transverse load are performed and the effective thickness and the elastic moduli of graphene are subsequently determined uniquely. The obtained stiffnesses of graphene are then substituted into the simple rule of mixture to predict the overall mechanical properties of the composite. Large discrepancies between the results from the MD simulations and the rule of mixture are observed.

232 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of GNP and MWCNT, at various filler loadings, on the mechanical, thermal and dielectric properties of epoxy nanocomposites have been investigated.
Abstract: Nano-sized carbons, such as graphene nanoparticle (GNP) and multiwall carbon nanotube (MWCNT), have attracted a great deal of attention due to their extraordinary intrinsic properties. Extensive research has been done on each carbon material for epoxy nanocomposites but only a few have ventured into a comparison study. In this paper, the effect of GNP and MWCNT, at various filler loadings, on the mechanical, thermal and dielectric properties of epoxy nanocomposites have been investigated. The experimental results demonstrate that GNP filled epoxy nanocomposites showed higher thermal and dielectric properties, but slightly lower mechanical properties compared to the MWCNT filled epoxy nanocomposites. The tensile strength, flexural strength, thermal conductivity and dielectric constant of GNP filled epoxy nanocomposites improved up to 11%, 17%, 126%, and 171% respectively, and MWCNT filled epoxy nanocomposites improved up to 26%, 29%, 60%, and 73% respectively.

214 citations


Journal ArticleDOI
TL;DR: In this article, a Round Robin Test was organized by the RILEM Technical Committee 250-CSM and the Italian association Assocompositi in order to experimentally characterize different FRCM systems composed of PBO, carbon, glass, basalt, aramid and steel textiles embedded in cementitious or lime based mortars.
Abstract: Fabric Reinforced Cementitious Matrix (FRCM) materials are composed of a dry fiber grid embedded in an inorganic matrix, which may contain short fibers. These materials are particularly well-suited for the reinforcement of masonry structures due to their high compatibility with the substrate, vapor permeability and durability against environmental agents. The most important information needed for the characterization of these composite systems, for use as strengthening materials of masonry structures, are the tensile behaviour and the shear bond properties. A Round-Robin Test was organized by the RILEM Technical Committee 250-CSM and the Italian association Assocompositi in order to experimentally characterize different FRCM systems composed of PBO, carbon, glass, basalt, aramid and steel textiles embedded in cementitious or lime-based mortars. The systems were tested at different universities and research centers in Europe in order to investigate the influence of samples preparation, test set-up and instrumentation. In this paper, the experimental tests performed on Carbon-FRCM systems are described and discussed. Important aspects are analyzed herein: differences in the testing procedure and instrumentation, influence of textile geometry and mechanical properties of the constituent materials, importance of specimen preparation and curing conditions. Moreover, a comparison between tensile and shear tests is reported in order to determine a reliable procedure towards the complete characterization of an FRCM material.

206 citations


Journal ArticleDOI
TL;DR: In this article, the free vibrations of nano-beams are investigated by making recourse to the novel stress-driven nonlocal integral model (SDM), which provides an effective methodology to describe nonlocal phenomena in NEMS.
Abstract: Nonlocal theories of Continuum Mechanics are widely used in order to assess size effects in nano-structures. In this paper, free vibrations of nano-beams are investigated by making recourse to the novel stress-driven nonlocal integral model (SDM). Equations of motion governing the dynamics of a Bernoulli-Euler nano-beam are consistently formulated and numerically integrated by Matlab. Selected case studies involving structures of nanotechnological interest are examined. Natural frequencies, evaluated according to the SDM, are compared with those obtained by the Eringen differential law (EDM) and by the gradient elasticity theory (GradEla). SDM provides an effective methodology to describe nonlocal phenomena in NEMS.

Journal ArticleDOI
TL;DR: In this paper, a micromechanical model based on the agglomeration of these nanoparticles is considered, where the strong form of the equations governing a plate is solved by means of the Generalized Differential Quadrature (GDQ) method.
Abstract: By means of Non-Uniform Rational B-Splines (NURBS) curves, it is possible to describe arbitrary shapes with holes and discontinuities. These peculiar shapes can be taken into account to describe the reference domain of several nanoplates, where a nanoplate refers to a flat structure reinforced with Carbon Nanotubes (CNTs). In the present paper, a micromechanical model based on the agglomeration of these nanoparticles is considered. Indeed, when this kind of reinforcing phase is inserted into a polymeric matrix, CNTs tend to increase their density in some regions. Nevertheless, some nanoparticles can be still scattered within the matrix. The proposed model allows to control the agglomeration by means of two parameters. In this way, several parametric studies are presented to show the influence of this agglomeration on the free vibrations. The considered structures are characterized also by a gradual variation of CNTs along the plate thickness. Thus, the term Functionally Graded Carbon Nanotubes (FG-CNTs) is introduced to specify these plates. Some additional parametric studies are also performed to analyze the effect of a mesh distortion, by considering several geometric and mechanical configurations. The validity of the current methodology is proven through a comparative assessment of our results with those available from the literature or obtained with different numerical approaches, such as the Finite Element Method (FEM). The strong form of the equations governing a plate is solved by means of the Generalized Differential Quadrature (GDQ) method.

Journal ArticleDOI
TL;DR: In this paper, the postbuckling behavior of GRC laminated plates is modeled using a higher order shear deformation plate theory and the plate-foundation interaction and thermal effects are taken into consideration.
Abstract: Modeling and analysis of the postbuckling behavior of graphene-reinforced composite (GRC) laminated plates are presented in this paper. The GRC plates are in a thermal environment, subjected to uniaxial compression and resting on an elastic foundation. The temperature-dependent material properties of functionally graded graphene-reinforced composites (FG-GRCs) are assumed to be graded in the plate thickness direction with a piece-wise type, and are estimated through a micromechanical model. The postbuckling problem of FG-GRC laminated plates is modeled using a higher order shear deformation plate theory and the plate-foundation interaction and thermal effects are taken into consideration. A two-step perturbation technique is employed to determine the buckling loads and the postbuckling equilibrium paths. The compressive buckling and postbuckling behavior of perfect and imperfect, geometrically mid-plane symmetric FG-GRC laminated plates under different sets of thermal environmental conditions is obtained and is also compared with the behavior of uniformly distributed GRC laminated plates. The results show that the buckling loads as well as the postbuckling strength of the GRC laminated plates may be enhanced through piece-wise functionally graded distribution of graphene.

Journal ArticleDOI
TL;DR: In this paper, the hierarchical structure of natural nacre is mimicked to produce multilayer composite laminates assembled from three dimensional polygonal tablets bonded with organic adhesives.
Abstract: This work presents a novel design, additive manufacturing and modeling approach of three dimensional voronoi-based composite structures that closely mimic nacre's multilayer composite structure. The hierarchical structure of natural nacre is mimicked to produce multilayer composite laminates assembled from three dimensional polygonal tablets bonded with organic adhesives. Furthermore, various complex geometries of the nacreous shells observed from the nature, such as the dome-shaped structure, are developed into three dimensional designs. A novel mapping algorithm is developed to generate complex structures of nacre-like composites that are readily fabricated by unique dual-material 3D printing technology. Preliminary 3D-printed prototypes with complex shapes and material combinations are presented. A novel numerical model of the nacreous composite is proposed, which includes tablet cohesive bonds and interlaminate adhesive layers to mimic the soft organic polymer matrix. The nacreous model is validated against a natural nacre specimen under uniaxial loading. To exemplify a potential application, a scaled model of a nacre-mimetic composite made of Aluminum tablets and Vinylester adhesive is constructed and assessed against blast-induced impulsive loading. The performance of the nacre-like composite panel is investigated in terms of deformation and energy dissipation.

Journal ArticleDOI
TL;DR: In this paper, the CNTs are functionalized by attaching melamine to improve the dispersibility in epoxy matrix and to enhance the interfacial bonding between CNT and matrix, and a significant increase of fracture toughness was observed for 2wt% M-CNT/Epoxy nanocomposite.
Abstract: Carbon nanotubes (CNTs) are considered as high potential filler material to improve the mechanical properties of epoxy nanocomposites. The CNTs are functionalized by attaching melamine to improve the dispersibility in epoxy matrix and to enhance the interfacial bonding between CNTs and matrix. The tensile tests and single edge notch bending (SENB) tests were performed for CNT/Epoxy and M-CNT/Epoxy nanocomposites at various weight fraction of functionalized CNTs. The M-CNT/Epoxy nanocomposites with addition of 2wt% functionalized CNTs exhibited enhancements of Young's modulus by 64% and ultimate tensile strength by 22%. Furthermore, a significant increase of fracture toughness by 95% was observed for 2wt% M-CNT/Epoxy nanocomposite. The homogeneity of CNTs in epoxy matrix has been analyzed and related to the improvement of modulus and strength. The phenomena of crack propagation has been investigated and related to the improvement of fracture toughness.

Journal ArticleDOI
TL;DR: In this paper, the effects of material treatment(s) on the mechanical behaviors of hemp fiber reinforced polypropylene (PP) composites are investigated with different combinations of material treatments(s).
Abstract: Natural fiber reinforced thermoplastic matrix composites have been increasingly used in semi-structural applications in automotive applications because of their good specific strength and modulus, low carbon footprint and recyclability. This research work studies the effects of material treatment(s) on the mechanical behaviors of hemp fiber reinforced polypropylene (PP) composites. The material treatment(s) are realized by chemically treating the hemp fiber with different concentration NaOH and/or adding maleic anhydride grafted polypropylene (MAPP) to the PP matrix. The purpose of the material treatment(s) is to enhance the bonding between the hemp fibers and the polypropylene matrix which otherwise has low surface energy and limited bonding. The mechanical behaviors are investigated with different combinations of material treatment(s) such as 5 wt% MAPP, 5% NaOH treated hemp fiber, 10% NaOH treated hemp fiber, and 5% NaOH + 5 wt% MAPP. 15 wt% and 30 wt% hemp fiber loadings are used in the composites with these material treatments. It is found that the material treatment(s) result(s) in composites with better mechanical properties compared to the composites without any treatment(s). The composites with 5 wt% MAPP addition show the best mechanical properties.

Journal ArticleDOI
TL;DR: In this article, a rheology control method to improve steel fiber distribution and flexural performance of ultra-high-performance concrete (UHPC) by adjusting the rheological properties of the suspending mortar of UHPC before steel fibers are added was developed.
Abstract: This study develops a rheology control method to improve steel fiber distribution and flexural performance of ultra-high-performance concrete (UHPC) by adjusting the rheological properties of the suspending mortar of UHPC before steel fibers are added. Correlations among the plastic viscosity of the suspending mortar, the resulting steel fiber distribution, and flexural properties of UHPC are established. This was done by changing the dosage of viscosity modified admixture (VMA) for investigated UHPC mixtures. The optimal plastic viscosity of the suspending mortar that allows for the optimized fiber distribution and flexural performance of UHPC is determined. The plastic viscosity is correlated with the mini V-funnel flow time, which provides a simple alternative to evaluate the plastic viscosity. For a UHPC mixture with 2% micro steel fibers, by volume, the optimal mini V-funnel flow time of suspending motar was determined to be 46 ± 2 s, which corresponded to the optimal plastic viscosity (53 ± 3 Pa s) that ensures the greatest fiber dispersion uniformity and flexural performance of UHPC. However, increasing the VMA dosage retarded the hydration kinetics and reduced the degree of hydration, compressive strength, and the bond properties of the fiber-matrix interface of UHPC.

Journal ArticleDOI
TL;DR: In this article, a Round Robin Test aimed to the characterization of both bond with the existing substrate and tensile performance of glass fabric (in the form of grids) coupled with inorganic mortar matrices is presented.
Abstract: Fibre-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting, and repairing existing structures. However some problems may arise with the use of traditional FRP (Fiber Reinforced Polymer), particularly when the compatibility with the substrate and the reversibility of the intervention are required, as in case of cultural heritage buildings, or specific exposition conditions may compromise the long term effectiveness of the reinforcement, as in presence of high temperature and humidity. Starting from these considerations new composite materials are emerging as a more effective solution in certain fields of application and under specific service conditions; in this context, mortar-based composite systems, consisting of one or more layers of uni- or bi-directional fibre nets embedded in cement/lime-based matrix layers, can be used as reinforcement of both concrete and masonry structures. However, the research work dealing with these emerging materials and their performances when used as a strengthening system for existing structures is still limited. Both experimental and theoretical investigations are needed in order to deliver reliable design methodologies. In this work, a Round Robin Test aimed to the characterization of both bond with the existing substrate and tensile performance of glass fabric (in the form of grids) coupled with inorganic mortar matrices is presented. The investigation was conducted at fifteen laboratories involved in the RILEM Technical Committee 250-CSM (Composites for the Sustainable Strengthening of Masonry). With the aim of studying the bond behaviour between Fabric Reinforced Cementitious Matrix (FRCM) composites and masonry substrate, single and double lap shear tests were carried out on brick-masonry prisms. Results provide useful informations about the mechanical properties, the bond capacity and the failure mechanisms of different commercially available glass FRCM systems. Finally, critical aspects are underlined to address the progress of the research work.

Journal ArticleDOI
TL;DR: In this paper, a ternary hybrid nanocomposite comprising of thermoplastic polyurethane as matrix and graphene nanoplatelets-carbon nanotubes hybrid (GCNT) as filled inclusion was reported.
Abstract: Hybrid nanocomposites are in the forefront of nanomaterials research owing to their unique ability to enhance the material property due to the existing synergistic effect of the fillers. Here, we report a ternary hybrid nanocomposite comprising of thermoplastic polyurethane as matrix and graphene nanoplatelets-carbon nanotubes hybrid (GCNT) as filled inclusion. The solution blending approach was used to prepare a series of polyurethane nanocomposites with GCNT loading ranging from 0 to 10 wt%. Due to the synergistic interaction of the two kinds of nanofillers, an electrical conductivity of the order of ∼10 −2 S/cm was achieved owing to the formation of a conducting network of CNTs bridging the gaps between graphene nanoplatelets throughout the electrically insulating polyurethane matrix. These hybrid nanocomposites exhibited excellent electromagnetic interference shielding up to −47 dB in the Ku-band of microwave frequency for 10 wt% loaded GCNT sample. In addition, the electromagnetic attributes, such as the real and imaginary permittivity of the nanocomposites as a function of frequency, were also investigated. The present studies, therefore, provides a new avenue for the preparation of hybrid carbon nanomaterials with unique structure and outstanding EMI shielding properties which make these materials as capable aspirants against electromagnetic polluting radiations.

Journal ArticleDOI
TL;DR: In this paper, the authors identify the crash responses and crashworthiness characteristics of bio-inspired sandwich structures composed of carbon fiber reinforced plastic (CFRP) panels and aluminum honeycomb.
Abstract: Nature has provided us with extraordinary resources to tackle design challenges facing in modern society nowadays. The multistate structures inspired by animal shell have proven effective to improve the impact resistance of composite laminate. This study aims to identify the crash responses and crashworthiness characteristics of bio-inspired sandwich structures composed of carbon fiber reinforced plastic (CFRP) panels and aluminum honeycomb. The crash responses, failure mode as well as the effects of core side length, height and impact velocity on peak load and energy absorption were explored herein. The differences of crashworthiness characteristics between the CFRP aluminum honeycomb sandwiches and bare CFRP panel were quantified. Two typical load-displacement relations, namely single-peak and double-hump curves, were observed in the tests. It was noted in the energy-displacement curve, where the slopes corresponding to the failure stages of the upper and lower face-sheets, were greater than that in the honeycomb failure stage, indicating that the bare aluminum honeycomb was of lower energy absorption capacity than the CFRP face-sheet. By comparison, the honeycomb filling was an effective way to improve the impact resistance of CFRP structure, yielding higher energy absorption and lower peak load during the impact. It was also found that the crashworthiness characteristics were more sensitive to the core length than to the core height; and the specific energy absorption (SEA) varied insignificantly with the increase in the core height. It was noted that the peak load, absorbed energy and SEA increased significantly under high impact velocity.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of an extensive experimental program on different combinations of basalt fibre textiles and inorganic matrices organized by RILEM TC 250-CSM (Composites for the Sustainable strengthening of Masonry) involving ten European laboratories.
Abstract: An increasing interest and application is nowadays found for composite systems in construction and rehabilitation industry. The consensus on fibre reinforced composite systems was mainly based on high tensile strength, light weight, relative ease of installation, and resistance to corrosion. However, some drawbacks related to the epoxy (hence, organic) matrices of Fiber-Reinforced Polymers (FRP) have been solved by inorganic ones yielding to novel fibre reinforced composites. In these materials the composite action is mainly achieved through mechanical interlock between the matrix (e.g. a cement- or a lime-based mortar or a geopolymer with the option of chopped fibres and/or low-content polymer addition) and the mesh-like fibrous structure (a textile) that allows the mortar to protrude through the grid's openings. Aiming at the investigation of the mechanical properties and the development of testing procedures for this new family of materials (termed herein as Fabric-Reinforced Cementitious Matrix (FRCM)) the present paper presents the results of an extensive experimental program on different combinations of basalt fibre textiles and inorganic matrices organized by RILEM TC 250-CSM (Composites for the Sustainable strengthening of Masonry) involving ten European laboratories. The tests involve more than 100 specimens: half are tensile tests and the other half are bond tests carried out on prisms made of clay bricks, on three different basalt-based FRCM configurations comprising readily available commercial systems provided by different producers. The scope of this work is aimed not only at presenting a comparative performance assessment of different Basalt FRCM systems, but also at providing meaningful criteria to reliably design and analyse retrofit applications. The relevant round robin test program provides valuable data generated during the experimental activity and statistical analysis thereof; then, based on the various testing approaches employed, the advantages/drawbacks of certain testing factors are summarized and critically assessed, reflecting the experience of involved institutions. It is believed that this represents a crucial step in improving knowledge on innovative retrofit applications and developing standard test methods.

Journal ArticleDOI
Li Zhao1, Xinli Guo1, Ge Chuang1, Qi Li1, Liping Guo1, Xin Shu, Jiaping Liu1 
TL;DR: In this article, polycarboxylate superplasticizer (PC) modified GO (PC@GO) was used to improve the dispersion of GO and the mechanical behavior of cement composites.
Abstract: Graphene oxide (GO) has attracted increasing interests for the use as nano-reinforcement in cement composites. However, the dispersion problem of GO nanosheets in alkaline cement matrix has been restricting its real application. In this paper, polycarboxylate superplasticizer (PC) modified GO (PC@GO) 1 was used to improve the dispersion of GO and the mechanical behavior of cement composites. The results show that PC@GO disperses uniformly in alkaline cement matrix and exhibits reinforcing effects on mechanical behavior of cement composites. With the addition of ∼0.242 wt% PC@GO (PC 0.22 wt%, GO 0.022 wt%) of cement, the compressive strength, flexural strength, Young's modulus and flexural toughness can be increased to 34.10%, 30.37%, 32.37% and 33%, respectively at early days. The toughening mechanism of PC@GO is attributed to its resistance to the formation and growth of cracks based on the characterization of cracks in scanning electron microscope images. This work has opened an effective way to use GO as a nano-reinforcing material for cement composites.

Journal ArticleDOI
TL;DR: In this paper, the use of Fabric Reinforced Cementitious Matrix (FRCM) composites appears as a compatible and effective technique to strengthen masonry structures using direct tensile tests and single lap shear tests.
Abstract: The use of Fabric Reinforced Cementitious Matrix (FRCM) composites appears as a compatible and effective technique to strengthen masonry structures The use of FRCM composites in place of FRP (fiber reinforced polymer) composites provides noticeable advantages in terms of fire and heat resistance and vapor permeability These characteristics are of primary importance in the field of the strengthening historical buildings and monuments This justifies the attention of the scientific community to the mechanical behavior of the FRCM materials with the aim to define exhaustive strengthening design guidelines The experimental research presented in this paper involves direct tensile tests and single lap shear tests It was carried out in the framework of the Technical Committee Rilem TC 250 CSM (Composites for the Sustainable Strengthening of Masonry) Specifically, this paper concerns FRCM systems comprising PBO (polyparaphenylene benzobisoxazole) or Aramid textiles

Journal ArticleDOI
Ömer Civalek1
TL;DR: In this paper, free vibration analysis of conical and cylindrical shells and annular plates made of composite laminated and functionally graded materials (FGMs) is investigated for FGM cases.
Abstract: In this study, free vibration analysis of conical and cylindrical shells and annular plates made of composite laminated and functionally graded materials (FGMs) is investigated. Carbon nanotubes reinforced (CNTR) composite case is also taken consideration for FGM. The equations of motion for conical shell are obtained via Hamilton's principle using the transverse shear deformation theory. To obtain the eigenvalue problem of the system, the method of discrete singular convolution is employed. Material properties are graded in the thickness direction according to a volume fraction power law and four-parameter power law indexes for FGM cases. Five types of distributions of CNTR material are also considered. To verify the accuracy of this method, comparisons of the present results are made with results available in the open literature. Free vibrations of cylindrical shells and annular plates with FGM are treated as special cases. Results are also presented for carbon nanotubes reinforced (CNTR) composite cylindrical shells and annular plates. It is found that the convergence and accuracy of the present DSC method is very good for vibration problem of shells with functionally graded materials (FMG) and CNTR functionally graded materials.

Journal ArticleDOI
TL;DR: In this paper, the physical and mechanical properties of GFRP bars made with vinyl-ester, isophthalic polyester, or epoxy resins were evaluated first, and the long-term performance of these bars under alkaline exposure simulating a concrete environment was then assessed in accordance with ASTM D7705.
Abstract: In the last decade, noncorrosive glass fiber-reinforced-polymer (GFRP) bars have become more widely accepted as cost-effective alternatives to steel bars in many applications for concrete structures (bridges, parking garages, and water tanks). Also, these reinforcing bars are valuable for temporary concrete structures such as soft-eyes in tunneling works. The cost of the GFRP bars can be optimized considering the type of resin according the application. Yet limited research seems to have investigated the durability of GFRP bars manufactured with different types of resin. In this study, the physical and mechanical properties of GFRP bars made with vinyl-ester, isophthalic polyester, or epoxy resins were evaluated first. The long-term performance of these bars under alkaline exposure simulating a concrete environment was then assessed in accordance with ASTM D7705 . The alkaline exposure consisted in immersing the bars in an alkaline solution for 1000, 3000 and 5000 h at elevated temperature (60 °C) to accelerate the effects. Subsequently, the bar properties were assessed and compared with the values obtained on unconditioned reference specimens. The test results reveal that the vinyl-ester and epoxy GFRP bars had the best physical and mechanical properties and lowest degradation rate after conditioning in alkaline solution, while the polyester GFRP bars evidenced the lowest physical and mechanical properties and exhibited significant degradation of physical and mechanical properties after conditioning.

Journal ArticleDOI
TL;DR: In this article, carbon-epoxy composites were subjected to accelerated aging in an aging chamber with controlled conditions of temperature, humidity and UV-radiation, and changes within the material were evaluated by Fourier-Transform Infrared (FTIR) Spectroscopy, Dynamic Mechanical Analysis (DMA), interlaminar shear strength and compressive strength, Scanning Electron Microscopy (SEM), and also in terms of mass variation.
Abstract: The influence of operational environments on the long-term durability of structural components fabricated with carbon fiber reinforced composites is an ongoing concern. Exposures to ultraviolet radiation, temperature cycles and moisture are known to degrade the polymeric matrix. In this work, carbon-epoxy composites were subjected to accelerated aging in an aging chamber with controlled conditions of temperature, humidity and UV-radiation. Changes within the material are evaluated by Fourier-Transform Infrared (FTIR) Spectroscopy, Dynamic Mechanical Analysis (DMA), interlaminar shear strength and compressive strength, Scanning Electron Microscopy (SEM), and also in terms of mass variation. Although significant changes in mechanical properties were not observed, the effects of accelerated aging on the composite material were evidenced by mass loss, fiber exposure, chemical alterations, increased crack density in interlaminar shear tests and fiber buckling in fractured specimens after compression testing.

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TL;DR: In this paper, the roles of nanoparticles aggregation/agglomeration in the interfacial/interphase and tensile properties of polymer nanocomposites are discussed and quantitatively characterized in some samples using known models.
Abstract: In this article, the roles of nanoparticles aggregation/agglomeration in the interfacial/interphase and tensile properties of polymer nanocomposites are discussed. The interfacial/interphase and tensile levels are quantitatively characterized in some samples using known models assuming the aggregation/agglomeration phenomena by the effective volume fraction of nanoparticles. The findings show that the nanoparticles aggregation/agglomeration significantly reduces the interfacial/interphase and tensile properties of nanocomposites via decreasing the specific surface area and effective volume fraction of nanoparticles. Additionally, Kerner and Paul models suggest the accurate predictions compared to the experimental data considering the aggregated/agglomerated nanoparticles. However, assumption of well-dispersed nanoparticles over-predicts the modulus in the reported samples.

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TL;DR: In this paper, thermal and shear deformation effects on the vibrational response of nonhomogeneous microbeams made of functionally graded (FG) materials are carried out, and the results are given together with other beam theories.
Abstract: In this paper, thermal and shear deformation effects on the vibrational response of non-homogeneous microbeams made of functionally graded (FG) materials are carried out. It is assumed that the temperature-dependent material properties of FG microbeams change smoothly and gradually throughout the height according to the classical rule of mixture. The governing differential equations and related boundary conditions are derived by implementing Hamilton's principle on the basis of hyperbolic shear deformation beam and modified couple stress theories and they are analytically solved. The results are given together with other beam theories. A detailed parametric study is performed to indicate the influences of slenderness ratio, material length scale parameter, gradient index, shear correction factors and temperature rise on natural frequencies of FG microbeams. It is revealed that the use of modified shear correction factor can provide more accurate and valid results for first-order shear deformable microbeam model.

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TL;DR: In this article, the static response of composite plates and shells reinforced by agglomerated nanoparticles made of carbon nanotubes (CNTs) is investigated in a two-parameter model.
Abstract: The static response of composite plates and shells reinforced by agglomerated nanoparticles made of Carbon Nanotubes (CNTs) is investigated in the present paper. A two-parameter agglomeration model is taken into account to describe the micromechanics of such particles, which show the tendency to agglomerate into spherical regions when scattered in a polymer matrix. From the macro mechanical point of view, the structures under consideration are characterized by a gradual variation of their mechanical properties along the thickness direction, since various distributions are employed to describe the volume fraction of the reinforcing phase. Several Higher-order Shear Deformation Theories (HSDTs) are taken into account and compared. The fundamental equations which govern the static problem in hand are solved numerically by means of the Generalized Differential Quadrature (GDQ) method. The variation of the agglomeration parameters, as well as the through-the-thickness profiles which describe the CNT volume fraction, are investigated to show the effect of the reinforcing phase on the static response of these nanocomposite plates and shells. In particular, a posteriori stress and strain recovery procedure is developed for these purposes. The current approach is validated through the comparison with the results available in the literature or obtained by a three-dimensional finite element model.

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TL;DR: In this article, a hybrid filler composed of nanodiamond (ND) nanoclusters-decorated graphene oxide (GO) was fabricated and incorporated in an epoxy matrix using a facile thermoregulatory liquid-liquid extraction method.
Abstract: Novel hybrid fillers composed of nanodiamond (ND) nanocluster-decorated graphene oxide (GO) were fabricated and incorporated in an epoxy matrix using a facile thermoregulatory liquid-liquid extraction method. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses confirmed a chemical bonding between the (3-aminopropyl)triethoxysilane-functionalized ND and (3-glycidyloxypropyl)trimethoxysilane-functionalized GO. The morphology of the hybrid filler (GN) was characterized by field-emission transmission electron microscopy. ND nanoclusters with an average diameter of 50–100 nm were uniformly grown on the GO surface. The hybrid filler provided significant enhancement of mechanical properties, such as flexural strength, flexural modulus, and fracture toughness. In particular, the epoxy composite containing 0.1 wt% of GN hybrid exhibited a stronger mechanical behavior compared to that containing 0.2 wt% of GO. As the GN loading increased, the thermal stability, the integral procedural decomposition temperature, and the activation energy increased as well. The toughening mechanism was illustrated by a microcrack theory based on the microscopic analysis of the fracture surfaces. The presence of ND nanoclusters not only hindered the aggregation of the GO sheets, but also played a crack pinning role in the polymer-matrix composites, which could significantly enhance its fracture toughness.