Showing papers in "Composites Part B-engineering in 2014"

Flax fibre and its composites – A review

Abstract: In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.

Study on mechanical and wear properties of Al 7075/Al2O3/graphite hybrid composites

Abstract: This work investigated the influence of graphite on the wear behavior of Al 7075/Al 2 O 3 /5 wt.% graphite hybrid composite. The investigation reveals the effectiveness of incorporation of graphite in the composite for gaining wear reduction. The Al 7075 (aluminium alloy 7075) reinforced with Al 2 O 3 –graphite were investigated. The composites were fabricated using liquid metallurgy route. Ceramic particles along with solid lubricating materials were incorporated into aluminium alloy matrix to accomplish reduction in both wear resistance and coefficient of friction. The Al 7075/Al 2 O 3 /graphite hybrid composite was prepared with 5 wt.% graphite particles addition and 2, 4, 6 and 8 wt.% of Al 2 O 3 . The hardness, tensile strength, flexural strength and compression strength of the Al 7075–Al 2 O 3 –graphite hybrid composites are found to be increased by increased weight percentage of ceramic phase. The wear properties of the hybrid composites containing graphite exhibited the superior wear-resistance properties.

An efficient and simple higher order shear and normal deformation theory for functionally graded material (FGM) plates

Abstract: In this paper, an efficient and simple higher order shear and normal deformation theory is presented for functionally graded material (FGM) plates. By dividing the transverse displacement into bending, shear and thickness stretching parts, the number of unknowns and governing equations for the present theory is reduced, significantly facilitating engineering analysis. Indeed, the number of unknown functions involved in the present theory is only five, as opposed to six or even greater numbers in the case of other shear and normal deformation theories. The present theory accounts for both shear deformation and thickness stretching effects by a hyperbolic variation of all displacements across the thickness, and satisfies the stress-free boundary conditions on the upper and lower surfaces of the plate without requiring any shear correction factor. Equations of motion are derived from Hamilton’s principle. Analytical solutions for the bending and free vibration analysis are obtained for simply supported plates. The obtained results are compared with 3-dimensional and quasi-3-dimensional solutions and those predicted by other plate theories. It can be concluded that the present theory is not only accurate but also simple in predicting the bending and free vibration responses of functionally graded plates.

The influence of the NaOH solution on the properties of the fly ash-based geopolymer mortar cured at different temperatures

Abstract: In this study, geopolymer mortar was produced using Class F fly ash from the thermal power plant in Kutahya Seyitomer (Turkey). The changes caused by the geopolymerization on the properties of the final product were investigated by applying curing on geopolymer mortars in different NaOH concentrations at different temperatures and for different curing times. The purpose of this process was to determine the relationship between alkali solution concentration, curing temperature and curing time. In order to determine the effect of NaOH concentration on geopolymer mortars, three different molarities of NaOH concentrations (3 M, 6 M and 9 M) were used together with sodium silicate (water glass) solution. The samples were cured at two different temperatures (65 and 85 °C). Physical properties such as porosity, bulk density, apparent density and water absorption, and mechanical properties such as flexural strength and compressive strength were determined from the 7-day geopolymer mortar samples after the curing process. As a result, this study determined that curing temperature and curing time had an effect on the physical properties of the geopolymer mortars. It was observed that NaOH concentration had a clear effect on the properties of the mortar cured at 85 °C. Compressive strength values of 21.3 MPa and 22 MPa were obtained from the mortar of 6 M concentration cured at 65 °C for 24 h and from a sample of the same mortar cured at 85 °C, respectively. Compressive strength values of the geopolymer mortars cured at 85 °C increased depending on the curing time and the increase in NaOH concentration. Given the strength values obtained, the optimal thermal curing temperature and the optimal NaOH concentration were 85 °C and 6 M, respectively.

Effect of ball milling on graphene reinforced Al6061 composite fabricated by semi-solid sintering

Abstract: A 1.0 wt.% graphene reinforced aluminum 6061 (Al6061) composite was synthesized to investigate the effects of graphene dispersion by ball milling technique. The Al6061 powder and graphene were ball milled at different milling times. The composites were then synthesized by hot compaction in the semi-solid regime of the Al6061. A three point bending test was performed to characterize the mechanical properties of the composite. The ball milled powder and the fracture surfaces of the composites were analyzed using the scanning electron microscopy. A maximum enhancement of 47% in flexural strength was observed when compared with the reference Al6061 processed at the same condition.

Material and bond properties of ultra high performance fiber reinforced concrete with micro steel fibers

Abstract: For investigating the effect of fiber content on the material and interfacial bond properties of ultra high performance fiber reinforced concrete (UHPFRC), four different volume ratios of micro steel fibers (Vf = 1%, 2%, 3%, and 4%) were used within an identical mortar matrix. Test results showed that 3% steel fiber by volume yielded the best performance in terms of compressive strength, elastic modulus, shrinkage behavior, and interfacial bond strength. These parameters improved as the fiber content was increased up to 3 vol.%. Flexural behaviors such as flexural strength, deflection, and crack mouth opening displacement at peak load had pseudo-linear relationships with the fiber content. Through inverse analysis, it was shown that fracture parameters including cohesive stress and fracture energy are significantly influenced by the fiber content: higher cohesive stress and fracture energy were achieved with higher fiber content. The analytical models for the ascending branch of bond stress-slip response suggested in the literature were considered for UHPFRC, and appropriate parameters were derived from the present test data.

Effect of stacking sequence on the flexural properties of hybrid composites reinforced with carbon and basalt fibers

Abstract: We investigated the effect of different stacking sequences of carbon and basalt fabrics on the flexural properties of hybrid composite laminates. The hybrid composites were fabricated using a vacuum-assisted resin transfer molding process. Three-point bending test was performed and the fracture surfaces were examined by scanning electron microscopy. The present results showed that the flexural strength and modulus of hybrid composite laminates were strongly dependent on the sequence of fiber reinforcement. All the stacking sequences showed a positive hybridization effect. The interply hybrid composite with carbon fiber at the compressive side exhibited higher flexural strength and modulus than when basalt fabric was placed at the compressive side. Here, the proper stacking sequence of basalt and carbon fiber layers was found to improve the balance of the mechanical properties of the hybrid composite laminate.

Effect of activator type and content on properties of alkali-activated slag mortars

Abstract: Investigation of alkali activation of Turkish slag (AAS) was carried out using sodium silicate and sodium hydroxide activators within the scope of this study. The objective of the present work is to determine the SiO 2 /Na 2 O ratios ( M S ) and Na 2 O contents of the solutions on the development of workability, setting times, mechanical properties, drying shrinkage, water absorption characteristics and microstructure of alkali activated slag cement binders. Test results showed that M S and Na 2 O contents of activator solution are of great importance on the properties of AAS. Portland cement free high performance composite with compressive strength values about 100 MPa can easily be achieved by activation of slag without heat curing. Moreover, in case of activation by optimum M S ratio, sodium silicate activated AAS mortars present higher compressive strength, lower water absorption, higher workability, lower porosity and a wide range of setting times compared to NaOH activated AAS mortars and Portland cement mortar. Consequently, it can be said that this new binder is likely to have enormous potential to become an alternative to Portland cement.

Wear and mechanical characteristics of Al 7075/graphite composites

Abstract: This work investigates 7075 aluminium alloy–graphite composites for its tribological and mechanical behaviour under dry sliding conditions. The conventional liquid casting technique was used for the fabrication of composite material and subjected to T6 heat treatment. The reinforcement content was chosen as 5, 10, 15 and 20 wt.% of graphite to identify its potential for self-lubricating property under dry sliding conditions. Wear tests were conducted by using pin on disc apparatus to evaluate the tribological behaviour of the composite and to determine the optimum content of graphite for its minimum wear rate. The wear rate decreases with addition of graphite content and reaches its minimum at 5 wt.% graphite. The wear mass loss was found to decrease with increasing sliding distance. The average coefficient of friction decreases with addition of graphite content and was found to be minimum at 5 wt.% graphite. The mechanical properties of the composites and base alloy were tested. The mechanical properties decrease with increasing graphite content as compared to base alloy. The worn surfaces were examined through SEM. The presence of 5 wt.% graphite in the composites can exhibit superior wear property as compared to base alloy.

Development of kenaf-glass reinforced unsaturated polyester hybrid composite for structural applications

Abstract: The main aim of this paper is to develop kenaf-glass (KG) fibres reinforced unsaturated polyester hybrid composite on a source of green composite using sheet moulding compound process. Unsaturated polyester resin (UPE) and KG fibres in mat form were used at a ratio of 70:30 (by volume) with treated and untreated kenaf fibre. The kenaf fibre was treated with 6% sodium hydroxide (NaOH) diluted solution for 3 h using mercerization method. The hybrid composites were tested for flexural, tensile and Izod impact strength using ASTM D790-03, ASTM D618 and ASTM D256-04 standards respectively. The highest flexural, tensile and impact strength were obtained from treated kenaf with 15/15 v/v KG fibres reinforced UPE hybrid composite in this investigation. Scanning electron microscopy fractography showed fibre cracking, debonding and fibre pulled-out as the main fracture mode of composites and kenaf treated 15/15 v/v KG reinforced hybrid composite exhibited better interfacial bonding between the matrix and reinforcement compared to other combinations.

Free vibrations of free-form doubly-curved shells made of functionally graded materials using higher-order equivalent single layer theories

Abstract: The theoretical framework of the present manuscript covers the dynamic analysis of doubly-curved shell structures using the generalized displacement field of the Carrera Unified Formulation (CUF), including the Zig-Zag (ZZ) effect given by the Murakami’s function. The partial differential system of equations is solved by using the Generalized Differential Quadrature (GDQ) method. This numerical approach has been proven to be accurate, reliable and stable in several engineering applications. The current paper focuses on Functionally Graded (FG) doubly-curved shells and panels using various higher-order equivalent single layer theories, introduced and applied for the first time by the authors to completely doubly-curved shell structures, and different through-the-thickness volume fraction distributions, such as four-parameter power law, Weibull and exponential distributions. Moreover, the classic theory of mixtures is compared to the Mori–Tanaka scheme for the calculation of the mechanical properties of the materials. In particular, the numerical applications presented in this work are related to particular FG configurations in which it is possible to model a soft-core structure using a continuous variation of the mechanical properties of the materials at hand. The natural frequencies and mode shapes of several structures are presented and compared to numerical solutions taken from the literature.

Effects of modifications of bamboo cellulose fibers on the improved mechanical properties of cellulose reinforced poly(lactic acid) composites

Abstract: Three kinds of modifications, alkali soaking or silane coupling cellulose and maleic anhydride grafting poly( l -lactic acid), were applied in the preparation of cellulose/poly( l -lactic acid) composites The effects of treatments of the cellulosic fibers on the mechanical properties of cellulose/poly( l -lactic acid) composites were comparatively investigated The results demonstrated that the alkali soaking provided the composites with highest strength and Young’s modulus, increased by 286% and 346%, respectively, than untreated samples The highest impact toughness and elongation were achieved by silane agent pretreatment, which were 115% and 62% higher than those of poly( l -lactic acid) reinforced with virgin bamboo cellulosic fibers Maleic anhydride grafting had moderate effects on both the stiffness and ductility, exhibiting best over-all properties From the scanning electron microscopy observations and Fourier transform infrared spectrum analysis, it was found that the interfacial interactions between the filler and matrix were improved after all the modifications mentioned

On the modeling of carbon nanotubes: A critical review

Abstract: A comprehensive review is conducted on the modeling and simulation of isolated carbon nanotubes (CNTs) concentrating on all mechanical, buckling, vibrational and thermal properties Three different approaches consisting of atomistic modeling, continuum modeling and nano-scale continuum modeling are firstly explained and their applications toward understanding behavior of CNTs are discussed Different investigations available in literature focusing on mentioned behaviors are reviewed and their results are compared to show the applicability and efficiency of employed/developed technique Taking into account both runtime and accuracy of modeling, advantages and disadvantages of introduced methods are nominated and analyzed

Mechanical, electrical and thermal properties of aligned carbon nanotube/polyimide composites

Abstract: Carbon nanotubes (CNTs) have high strength and modulus, large aspect ratio, and good electrical and thermal conductivities, which make them attractive for fabricating composite. The poly(biphenyl dianhydride-p-phenylenediamine) (BPDA/PDA) polyimide has good mechanical and thermal performances and is herein used as matrix in unidirectional carbon nanotube composites for the first time. The strength and modulus of the composite increase by 2.73 and 12 times over pure BPDA–PDA polyimide, while its electrical conductivity reaches to 183 S/cm, which is 1018 times over pure polyimide. The composite has excellent high temperature resistance, and its thermal conductivity is beyond what has been achieved in previous studies. The improved properties of the composites are due to the long CNT length, high level of CNT alignment, high CNT volume fraction and good CNT dispersion in polyimide matrix. The composite is promising for applications that require high strength, lightweight, or high electrical and thermal conductivities.

Drop-weight impact behaviour of woven hybrid basalt–carbon/epoxy composites

Abstract: This study addresses the effects of basalt fibre hybridization on quasi-static mechanical properties and low velocity impact behaviour of carbon/epoxy laminates. Interply hybrid specimens with two different stacking sequences (sandwich-like and intercalated) are tested at three different energies, namely 5, 12.5 and 25 J. Residual post-impact properties of the different configurations of carbon/basalt hybrid laminates are characterized by quasi static four point bending tests. Post-impact flexural tests and interlaminar shear tests are used for the mechanical characterization along with two non-destructive methods, namely acoustic emission and ultrasonic phased array, in order to get further information on both the extent of damage and failure mechanisms. Results indicate that hybrid laminates with intercalated configuration (alternating sequence of basalt and carbon fabrics) have better impact energy absorption capability and enhanced damage tolerance with respect to the all-carbon laminates, while hybrid laminates with sandwich-like configuration (seven carbon fabric layers at the centre of the laminate as core and three basalt fabric layers for each side of the composite as skins) present the most favourable flexural behaviour.

Characterization of electrical and thermal properties of carbon nanotube/epoxy composites

Abstract: The electrical and thermal conductivity of pristine, oxidized, and fluorinated single-wall/multi-wall carbon nanotube (CNT) mixtures, dispersed in epoxy, were investigated as a function of CNT concentration. The effect of fabrication parameters, such as stirring rate and degree of epoxy pre-curing, on CNT dispersion was analyzed. The electrical conductivity increased by 10 and 6 orders of magnitude for pristine and oxidized CNT composites, respectively, relative to neat epoxy, while fluorinated CNT composites showed no increase in electrical conductivity. An increase of up to 5.5% was observed in thermal conductivity for pristine CNT composites while oxidized and fluorinated CNTs provide less enhancement in thermal conductivity. A micromechanics model, based on the composite cylinders method, was implemented to study the electrical and thermal conductivity of these composites. Effects in electrical and thermal conduction, such as electron hopping and thermal interface resistance, respectively, were incorporated into the model to accurately simulate the acquired experimental results.

Use of 2D Graphene Nanoplatelets (GNP) in cement composites for structural health evaluation

Abstract: This study investigates the use of Graphene Nanoplatelets (GNP) in cement composite to quantify the material damage extent. The damage sensing capability of this new cement composite is demonstrated by experimentally measuring the electric potential across prisms with a known notch depth and comparing it with the finite element simulations. Meanwhile, the damage extent is directly related to the change in electric potential based on a mathematical analogy between the electrostatic field and the elastostatic field under anti-plane shear loading. It is shown that the fractional change in electric potential arising from damage is equivalent to the fractional change in elastic compliance, which can be exploited for structural health evaluation.

Graded conventional-auxetic Kirigami sandwich structures: Flatwise compression and edgewise loading

Abstract: The work describes the manufacturing and testing of graded conventional/auxetic honeycomb cores. The graded honeycombs are manufactured using Kevlar woven fabric/914 epoxy prepreg using Kirigami techniques, which consist in a combination of Origami and ply-cut processes. The cores are used to manufacture sandwich panels for flatwise compression and edgewise loading. The compressive modulus and compressive strength of stabilized (sandwich) honeycombs are found to be higher than those of bare honeycombs, and with density-averaged properties enhanced compared to other sandwich panels offered in the market place. The modulus and strength of graded sandwich panel under quasi-static edgewise loading vary with different failure mode mechanisms, and offer also improvements towards available panels from open literature. Edgewise impact loading shows a strong directionality of the mechanical response. When the indenter impacts the auxetic portion of the graded core, the strong localization of the damage due to the negative Poisson’s ratio effect contains significantly the maximum dynamic displacement of the sandwich panel.

Characterizing thermal and mechanical properties of graphene/epoxy nanocomposites

Abstract: This study aims to investigate the thermal and mechanical properties of graphene/epoxy nanocomposites using molecular dynamics (MD) simulation. Three different formats of graphene: graphene flakes, intercalated graphene and intercalated graphene oxide, were incorporated respectively in an epoxy matrix to form the graphene/epoxy nanocomposites. The mechanical properties of the graphene/epoxy nanocomposites, including Young’s modulus (E), glass transition temperature (Tg) and coefficient of thermal expansion (CTE), in terms of three different formats of graphene, were characterized in this study. In addition to the mechanical properties, the influences of graphene on the density distribution of epoxy polymers in the nanocomposites were also examined. The results showed that the local density in the vicinity of the graphene is relatively high, and then progressively decreases to the bulk value in regions further away from the interface. On the other hand, for the mechanical and thermal properties, the nanocomposites with intercalated graphene exhibit a higher Young’s modulus, a higher glass transition temperature and a lower thermal expansion coefficient than do those with graphene flakes. This is because the intercalated graphene can lead to a high amount of high density polymer in the nanocomposites, and thus enhance the overall properties of the nanocomposites. In addition, the interacted graphene oxide provides the best reinforcement of the three systems of nanocomposites. Based on the calculation of interaction energy, it appears that the oxide modification of the graphene surface can effectively lead to the high interaction energy, such that the graphene oxide can demonstrate a relatively high reinforcing efficiency.

In-plane and out-of-plane motion characteristics of microbeams with modal interactions

Abstract: The three-dimensional nonlinear size-dependent motion characteristics of a microbeam are investigated numerically, with special consideration to one-to-one internal resonances between the in-plane and out-of-plane transverse modes. All of the in-plane and out-of-plane displacements and inertia are taken into account and Hamilton’s principle, in conjunction with the modified couple stress theory, is employed to obtain the nonlinear partial differential equations governing the motions of the system in the in-plane and out-of-plane directions. The discretization procedure is carried out by applying the Galerkin technique to the partial differential equations of motion, yielding a set of nonlinear ordinary differential equations. A linear analysis is performed upon this set of equations so as to obtain the size-dependent natural frequencies of the system. The nonlinear analysis of the discretized equations of motion is carried out by employing the pseudo-arclength continuation technique, resulting in the resonant responses of the system. It is shown that, due to the presence of one-to-one internal resonances between the in-plane and out-of-plane transverse modes, an in-plane excitation can give rise to an out-of-plane displacement; the internal resonances also cause the occurrence of extra solution branches and new bifurcation points.

Improving the thermal and mechanical properties of polysulfone by incorporation of graphene oxide

Abstract: Nanocomposites of polysulfone (PSF)-graphene oxide (GO) were prepared by classical phase inversion method. The structural and surface features and the mechanical and thermal performances of the prepared materials were investigated in detail. TEM and X-ray diffraction analysis indicated a good compatibility and excellent dispersability with PSF matrix for the low GO content (0.25, 0.5 and 1 wt.%) composites. It was observed that GO dispersion was reasonably homogeneous for the composite with 2 wt.% GO. The mechanical properties of the prepared materials were found to be greatly enhanced by the addition of GO for some compositions. The thermogravimetrical investigation demonstrated considerable improvements in thermal stability for the composite with low GO content. This novel material offers a feasible candidate for practical membrane application.

Effect of carbon nanotube type and functionalization on the electrical, thermal, mechanical and electromechanical properties of carbon nanotube/styrene–butadiene–styrene composites for large strain sensor applications

Abstract: Thermoplastic elastomer tri-block copolymer, namely styrene–butadiene–styrene (SBS) composites filled with carbon nanotubes (CNT) are characterized with the main goal of obtaining electro-mechanical composites suitable for large deformation sensor applications. CNT/SBS composites with different filler contents and filler functionalizations are studied by morphological, thermal, mechanical and electrical analyses. It is shown that the different dispersion levels of CNT in the SBS matrix are achieved for pristine or functionalized CNT with strong influence in the electrical properties of the composites. In particular covalently functionalized CNTs show percolation thresholds higher than 8 weight percentage (wt%) whereas pristine CNT show percolation threshold smaller than 1 wt%. On the other hand, CNT functionalization does not alter the conduction mechanism which is related to hopping between the CNT for concentrations higher than the percolation threshold. Pristine single and multiwall CNT within the SBS matrix allow the preparation of composites with electro-mechanical properties appropriate for strain sensors for deformations up to 5% of strain, the gauge factor varying between 2 and 8. Composites close to the percolation threshold show larger values of the gauge factor.

The synthesis of a novel graphene-based inorganic–organic hybrid flame retardant and its application in epoxy resin

Abstract: In this paper, a novel graphene-based inorganic–organic hybrid flame retardant (GFR) was prepared via sol–gel reaction of FGO and phenyl-bis-(triethoxysilylpropyl) phosphamide (PBTP) and characterized by FT-IR, XPS, XRD, TGA and AFM. The influence of the GFR on the thermal stability and flame retardance of epoxy resin composites were characterized by TGA, LOI as well as micro-cone, which indicated that GFR brought a good effect in enhancing the residual char and flame retardance of epoxy composites. The dynamic mechanical properties and electrical properties of EP composites were also analyzed.

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

Abstract: An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.

Effect of coupling agent on natural fibre in natural fibre/polypropylene composites on mechanical and thermal behaviour

Abstract: To enhance the adhesion between the natural fibre and the thermoplastic matrix, a coupling agent of maleic anhydride grafted polypropylene MAPP is applied. In literature, there are different guidelines of the optimum percentage required of MAPP. Therefore, a systematic work is carried out to optimise the MAPP percent with respect to the type of the natural fibre. Different parameters are investigated namely; Coupling agent ratio to the fibre (0%, 6.67%, 10%, 13.3%, 16.67%), coupling agent source, fibre type (flax, hemp, sisal), and fibre content (30%, 50%). Composite is produced using a kneader and the resulting material is assessed mechanically, thermally, microscopically and for water absorption. For different MAPP source and the natural fibre type, optimum MAPP to fibre ratio is found in average to range between 10% and 13.3% according to the investigated property (stiffness, strength and impact). Increase of MAPP is found to decrease the melting temperature. The thermal behaviour is also linked to the copolymer molecular weight.

A novel process to improve yield and mechanical performance of bamboo fiber reinforced composite via mechanical treatments

Abstract: The aims of the present study are to produce bamboo fiber reinforced composite (BFRC) with high yield and to investigate the mechanical properties of BFRC comparing with those of commercial bamboo scrimber (BS) and laminated bamboo lumber (LBL). A novel process was developed for production of BFRC using oriented bamboo fiber mat (OBFM) made by a pilot machine. The yield and the mechanical properties of BFRC were investigated and analyzed in comparing with those of raw bamboo and other bamboo-based composites. The results show that the novel process produces 92.54% yield of OBFM due to without any chemical and special removing of inner and outer layer of bamboo during processing. In addition, all the mechanical properties and the variability of BFRC were significantly enhanced comparing with those of raw bamboo and other bamboo-based composites.

Fabrication and characterization of fully biodegradable natural fiber-reinforced poly(lactic acid) composites

Abstract: Polymer composites were fabricated with poly(lactic acid) (PLA) and cellulosic natural fibers combining the wet-laid fiber sheet forming method with the film stacking composite-making process. The natural fibers studied included hardwood high yield pulp, softwood high yield pulp, and bleached kraft softwood pulp fibers. Composite mechanical and thermal properties were characterized. The incorporation of pulp fibers significantly increased the composite storage moduli and elasticity, promoted the cold crystallization and recrystallization of PLA, and dramatically improved composite tensile moduli and strengths. The highest composite tensile strength achieved was 121 MPa, nearly one fold higher than that of the neat PLA. The overall fiber efficiency factors for composite tensile strengths derived from the micromechanics models were found to be much higher than that of conventional random short fiber-reinforced composites, suggesting the fiber–fiber bond also positively contributed to the composites’ strengths.

Large amplitude free vibration of nanobeams with various boundary conditions based on the nonlocal elasticity theory

Abstract: In this paper, a non-classical beam model based on the Eringen’s nonlocal elasticity theory is proposed for nonlinear vibration of nanobeams with axially immovable ends. This non-classical (nonlocal) beam model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect. The Hamilton’s principal is employed to derive the governing equations and the related boundary conditions together with Euler–Bernoulli beam theory and the von-Karman’s nonlinear strain–displacement relationships. An approximate analytical solution is obtained for the nonlinear frequency of the nanobeam by utilizing the Galerkin method and He’s variational method. In the numerical results, the ratio of nonlinear frequency to linear frequency is presented for three different boundary conditions. The effect of nonlocal parameter on the nonlinear frequency ratio is examined. Also, some illustrative examples are also presented to verify the present formulation and solutions. Good agreement is observed. These results can be used as benchmark for future studies.

Effect of hydrothermal ageing on the thermal and delamination fracture behaviour of CFRP composites

Abstract: This work investigates the hydrothermal ageing behaviour of a carbon fibre reinforced laminate and its epoxy matrix in bulk conditions. A model DGEBA epoxy is employed, and water uptake and dynamic mechanical thermal (DMTA) analyses have been performed on both the composites and bulk resin. Fracture toughness of the bulk resin has been measured, evidencing a substantially unmodified critical stress intensity factor KIC, although the evidence of plasticisation effects given by DMTA. Interlaminar Mode I fracture toughness of the composite showed a variable trend towards slight decreases or slight increases, according to the prevailing toughening or embrittling mechanisms activated by the aging conditions.

Isogeometric analysis of functionally graded plates using a refined plate theory

Abstract: We present in this paper a simple and effective approach that incorporates isogeometric finite element analysis (IGA) with a refined plate theory (RPT) for static, free vibration and buckling analysis of functionally graded material (FGM) plates. A new inverse tangent distributed function through the plate thickness is proposed. The RPT enables us to describe the non-linear distribution of shear stresses through the plate thickness without any requirement of shear correction factors (SCF). IGA utilizes basis functions namely B-splines or non-uniform rational B-splines (NURBS) which reach easily the smoothness of any arbitrary order. It hence satisfies the C1 requirement of the RPT model. The present method approximates the displacement field with four degrees of freedom per each control point allowing an efficient solution process.