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With the development of the recycling economy for waste rubber, the highvalue application of rubber powder, such as the modifier in asphalt mixture and the polyurethane foam, has attracted more and more attention. In the study, the surface characteristics of rubber powder modified by deep eutectic solvents were investigated by infrared spectroscopy, sol fraction, solid surface energy, and scanning electron microscope. The mechanical properties of modified ground tire rubber powder (M-GTR)/SBR/silica composites were studied. Meanwhile, the viscoelasticity of the composites was characterized by the Payne effect and Mullins effect. Compared with the unmodified rubber powder, the rubber powder treated at 105[degrees]C had a higher sol fraction and maximum value of solid surface energy. With the increase of the content of M-GTR, the Payne effect of the M-GTR/SBR/silica composites firstly weakened and then increased. As for the Mullins effect, the vulcanizates showed stresssoftening phenomenon in the process of uniaxial cyclic compression. The recovery ability of the Mullins effect strongly depended on temperature. Besides, the modified rubber powder could improve the dispersity of silica in the SBR matrix, and the Mullins effect of the composite contained modified rubber powder was weak, which would provide potential high-value application for rubber powder. KEYWORDS deep eutectic solvents, dispersity, ground tire rubber powder, interaction, modified, viscoelasticity, 1 | INTRODUCTION With the development of the social economy, the demand for rubber products rises from year to year, resulting in more and more waste rubber. But, due to [...]

This study investigates and predicts the tribological properties of an imidazolium ionic liquid modified graphene oxide (ILGO) with silicone rubber (QM) composite. The pin on the disc tribometer was utilized to conduct experimental tribological property analysis, with load, sliding velocity, and temperature as changing parameters. Coefficient of friction (COF) of QMILG01.5 was 42% lower than that of pure QM. Study found that ionic liquid serves as a self-lubricating layer for graphene, establishing a solid graphene-to-ionic liquid interface bond with the rubber matrix. The experimental data were utilized for training artificial neural networks (ANNs), which were then used to predict the COF of the nanocomposites for values for which the experiment was not performed. The produced composite's predictions of friction coefficient utilizing the ANN technique were quite close to experimental results. The work's fundamental goal is to buy experimentation verifies the COF of functionalized graphene oxide (ILGO) with silicone rubber composite, use the actual experimental values to train a deep neural network using Multilayer perceptron, and then use the trained network to predict the values of COF for which obtaining the values by experimentation was difficult. KEYWORDS graphene oxide, ionic liquids, multilayer perceptron, silicone rubber, tribology, 1 | INTRODUCTION Silicone rubber (QM) is a synthetic elastomer with a solid silicone-oxygen chemical structure that contributes to its excellent properties, high chemical and thermal stability, and biocompatibility. [1] [...]

Endowing waterborne polyurethane (WPU) materials with mechanically reinforced and self-healing property is a pressing issue for expanding practical applications. In this article, we proposed a simple method to give WPU with self-healing properties while improving the mechanical properties. First, furfuryl-modified silica nanoparticles (furan@Si[O.sub.2]) with high functionality and excellent dispersibility were prepared by the sol-gel method. Furan@Si[O.sub.2] was then introduced into the side-hanging maleimide WPU to form a thermally reversible inorganic-organic network (WMSPUS-x) based on the Diels-Alder reaction. The morphologies and properties of furan@Si[O.sub.2] and WMSPUS-x emulsions were analyzed by TEM and DLS, demonstrating the excellent dispersion of furan@Si[O.sub.2] and the storage stability of emulsions. The cross-linking density of the nanocomposites was varied by the furan@Si[O.sub.2] contents, and the effects of cross-linking density on mechanical and selfhealing properties were systematically investigated. In addition, the thermal stability of WMSPUS-x nanocomposites was significantly improved shown by TGA results. Finally, qualitative and quantitative studies of the self-healing process were carried out to verify that WMSPUS-x nanocomposites possess great self-healing capacity. The outcomes indicate that WMSPUS-x nanocomposites have great potential for application as a smart material. KEYWORDS inorganic organic hybrid material, mechanical property, nanocomposites, self-healing, waterborne polyurethane, 1 | INTRODUCTION Waterborne polyurethane (WPU) is a novel polymer material with excellent performance and meets environmental requirements, as no volatile organic compounds (VOCs) are released during the practical application. [...]

Cross-laminated timber (CLT) is an engineered timber composite that is finding increasing structural application in construction today. Analysis of the structural behavior of CLT can be carried out by various analytical and numerical methods. Due to the complex behavior of CLT, use of numerical modelling such as the finite element method (FEM) offers a convenient approach to analysis. In this paper, simulation of the elastic behavior of 1-way and 2-way spanning CLT panels using the FEM program ABAQUS is presented. Various modelling choices are explored numerically with the results being evaluated against those from either a 3D analytical method known as the state space approach (SSA) or existing experimental data. Among the case studies examined is a novel boundary condition for the SSA solution. In general, the optimum finite element model produced reasonable levels of accuracy with an average relative error equal to 3% in comparison to the SSA and a maximum of 10% in comparison to the experimental results. Key words: cross-laminated timber, finite element method, analytical solution, state space approach. Le bois lamelle-croise (BLC) est un composite de bois d'ingenierie qui desormais sert de plus en plus a la construction. L'analyse du comportement structurel du BLC peut etre effectuee par diverses methodes analytiques et numeriques. En raison du comportement complexe du BLC, l'utilisation de la modelisation numerique telle que la methode des elements finis (MEF) offre une approche pratique de l'analyse. Dans cet article, la simulation du comportement elastique des panneaux en BLC a une et deux directions utilisant le programme FEM ABAQUS est presentee. Divers choix de modelisation sont explores numeriquement et les resultats sont evalues par rapport a ceux d'une methode d'analyse tridimensionnelle (3D) connue sous le nom d'approche de l'espace des etats (AEE) ou de donnees experimentales existantes. Parmi les etudes de cas examinees, il y a une nouvelle condition limite pour la solution d'AEE En general, le modele optimal d'elements finis a produit des niveaux raisonnables de precision avec une erreur relative moyenne egale a 3% par rapport a l'AEU et un maximum de 10% par rapport aux resultats experimentaux. [Traduit par la Redaction] Mots-cles : bois lamelle-croise, methode des elements finis, solution analytique, approche de l'espace des etats., 1. Cross-laminated timber (CLT): background and characteristics CLT is a laminated timber composite that can be used to form structural elements including walls, floor plates, and roofs etc. It was [...]

Novel polyimide (PI) composites were designed and prepared as a frictional material for ultrasonic motors (USM). The effect of roughness and reciprocating time on the tribological properties of PI composites was specially investigated for simulating USM operating condition. These typical PI composites were designed along with the special characteristics of USM by filling proportional solid lubricants and nanoparticles, and prepared using classical hotpress sintering. The friction and wear behavior of PI composites with different surface roughness polished by SiC sandpaper and various reciprocating time was carried out on a pin-on-plate tribo-meter against GCr15 steel pin. The worn surface was observed by SEM to reveal wear mechanisms. Experimental results indicated that the coefficient of friction and specific wear rate increased with an increase of surface roughness which was detrimental for USM to prolong the service life. The coefficient of friction and wear volume will increase with an increase of reciprocating time due to fatigue wear, but specific wear rate will decrease with the minimum value of 2.1 x [10.sup.-6] [mm.sup.3] /N m. This study can provide significant guidance for USM to optimize frictional surface and running-in time., INTRODUCTION Ultrasonic motors (USM), driven by friction force between stator and rotor, are increasingly demanded in the medical apparatus, precision positioning, and aerospace engineering because of special performance, such as [...]

Siliceous earth (SE), which has a special morphology and structure, was selected as filler of natural rubber (NR) and mechanical properties of compounds were analyzed. Two processes were employed to prepare SE/NR compounds described as mechanical mixing method and latex method, respectively. Cure characteristics, mechanical properties of the vulcanizates prepared from the master-batches were compared with those prepared by mechanical mixing method. X-ray diffraction results of NR/SE vulcanizations indicated that mechanical mixing above the latex process facilitated the intercalation of NR into the galleries of SE. The results of mechanical properties show that SE has good reinforcing properties on NR both by latex or mechanical mixing process. By comparison, H samples show slightly higher crosslink density, tensile strength, 300% modulus, and lower elongation at break than M sample in same loading. But in the aspect of dynamic properties there exist obviously difference between latex and mechanical mixing process. Rubber processing analyzer (RPA) results showed that uncured M samples showed obviously higher storage modulus than that of H samples. The heat build-up of M30 is much lower than that of H30. These behaviors indicated better dynamitic properties when the masterbatches prepared by the predispersing method was utilized. POLYM. ENG. SCI., 58:1043-1052, 2018. [C] 2017 Society of Plastics Engineers, INTRODUCTION The development of the green tire push the silica increasingly applied in the tire as tread rubber [1, 2], Introduced in the 1990s, silica is one of the key [...]

This investigation aims to improve the ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene (UHMWPE) fibers by incorporating small amounts of functionalized activated nanocarbon particles with a wide range of specific surface areas (ca. 1001,400 [m.sup.2]/g) during gel spinning processes of UHMWPE fibers. The ultradrawing, ultimate tensile, orientation properties, and 'microfibril' characteristics of UHMWPE/functionalized activated nanocarbon fibers was discovered to improve considerably with the increase in specific surface areas of functionalized activated nanocarbon. An extraordinary high ultimate tensile strength at 95.8 g/d was obtained for the best prepared UHMWPE/functionalized activated nanocarbon drawn fiber. This value is the highest value ever reported for one-stage drawn UHMWPE fibers and is about 2.9 times that of the UHMWPE drawn fiber prepared in this study. In addition to thermal, ultimate tensile, and orientation factor properties of asprepared and/or drawn UHMWPE/functionalized activated nanocarbon fibers, specific surface area, Fourier transform infrared, and morphological analyses of original and functionalized activated nanocarbons were performed to comprehend the considerably improved ultradrawing, ultimate tensile properties, and microfibril characteristics of the UHMWPE/functionalized activated nanocarbon fibers. POLYM. ENG. SCI., 58:980-990, 2018. [C] 2017 Society of Plastics Engineers, INTRODUCTION Unremitting efforts were made in the exploration and development of high performance fibers with tenacity higher than 20 g/d [1]. Ultrahigh molecular weight polyethylene (UHMWPE) fibers attracted great attention [...]

Ternary nanocomposites (NCs) were obtained by meltmixing maleic anhydride-modified polypropylene (gPP) with previously prepared polyamide-12 (PA12)/organically modified montmorillonite (OMMT) NCs. During meltmixing, OMMT migrated from the PA12 phase to the gPP/ PA12 interphase. Moreover, a critical concentration of OMMT was found to saturate the interphase and, at higher contents, the excess OMMT migrated to the gPP matrix. When compared with the unfilled gPP/PA12 blends, the addition of OMMT caused a change in the microstructure. The average size of the PA12 dispersed particles in the NCs was found to be independent of the OMMT content. At OMMT contents below the critical concentration, that is, when the OMMT located at the interphase, Young's modulus remained practically unchanged and the ductile nature of the ternary NCs maintained. However, at higher OMMT contents, Young's modulus increased linearly and the NCs became brittle, due to the presence of OMMT in the gPP matrix. POLYM. ENG. SCI., 58:830-838, 2018. [C] 2017 Society of Plastics Engineers, INTRODUCTION In recent years, research on polymer nanocomposites (NCs) based on modified layered clays, usually montmorillonite (OMMT), has ranged from studying conventional polymeric matrices consisting of a single polymer to [...]

The objective of the present work is to investigate the electro-activated shape memory behavior of a polycyclooctene (PCO) based nanocomposite device. At this aim, carbon black (CB) and exfoliated graphite nanoplatelets (xGnP) were melt compounded with a PCO matrix crosslinked with a dicumylperoxide content of 2 wt% and a total filler amount of 4 wt%. Electrical resistivity measurements on bulk materials evidenced a noticeable decrease of the electrical resistivity upon CB addition, while no synergistic effects were detected mixing CB and xGnP. Nanocomposite with a CB amount of 4 wt% revealed also a noticeable heating capability through Joule effect for voltage levels higher than 100 V. The subsequent characterization of an electro active shape memory device based on this composition demonstrated how it is possible to prepare a shape memory nanocomposite material able to completely recover its original shape after 100 s with a voltage of 90 V. The retention of the shape memory behavior after several (50) programming cycles was also demonstrated., INTRODUCTION It is well known that the addition of metal and carbon based nanofillers, such as metal nanopowders, graphite nanoplatelets (GnPs), carbon black (CB), and carbon nanofibers (NFs) could significantly [...]

The present work checks on the efficiency of a grafted atactic polypropylene, with a high level of succinic anhydride-grafted groups, as an interfacial modifier in Polypropylene/Short Carbon Fiber composites (iPP/SCF) by mean of Dynamic Mechanic Analysis (DMA). Additionally, Differential Scanning Calorimetry to determine the crystalline content of the different materials comes in support of the DMA results. Hence, this work has been designed as an exploratory study for incoming works wherein recovered carbon fibers (rSCF) will be evaluated as reinforcement of thermoplastic composites. Consequently, we studied two different polypropylene-based composites with extreme amounts, 15% and 40% w/w, of a commercial sized SCF. Notwithstanding, just to notice that the main relaxation processes associated to the iPP matrix in the pristine composites appear sharply affected by the SCF amount, influencing also the crystalline content of the iPP matrix. The glass transition region of the iPP matrix shows significant variations well correlated with both the processing history of both the pristine iPP and the composites, and evidences the efficiency of the interfacial modifier (aPP-SA/ SA) revealed as a good candidate for improving the performance in PP/rSCF composites., INTRODUCTION In an overall context of sustainability and circular economy [1-3], lower operation costs combined with the high versatility and easy processability of the polyolefins, and more specifically the polypropylene [...]

In this study, carbon nanotubes reinforced polyoxymethylene with different filler loadings was joined by using linear vibration welding technique. The tensile properties of vibration welded polyoxymethylene nanocomposites with different carbon nanotube contents were studied as functions of filler loading and weld pressure. The results showed that the addition of carbon nanotubes into polyoxymethylene slightly improved the matrix tensile strength and pronounced decreased the ductility of pure polyoxymethylene. Interestingly, the weld strength of the nanocomposites was also higher than the polymer matrix strength even at high weld pressure of 2 MPa. Possible reasons for this high weld strength are discussed based on the morphological investigations., INTRODUCTION Due to their outstanding mechanical properties with low density and high thermal as well as electrical conductivity, carbon nanotubes are used as functional fillers in polymer-based composites for a [...]

The article presents research on the mechanical properties of epoxy resin modified with potassium polytitanate small additives. The influence of the surface modification of potassium polytitanate particles on their properties and interaction with epoxy resins and the mechanical properties of the resulting composite were investigated. The interactions among the dressing additives, binders and fillers were determined. The study shows the dependence of properties of composite materials on the content of dressing additives and method of filling with potassium polytitanate. This study also highlights possible reasons for variation in the mechanical properties of epoxy resin filled with potassium polytitanate particles., INTRODUCTION Potassium polytitanates (PPT) are ceramic functional materials with the common chemical formula [K.sub.2][Ti.sub.n][O.sub.2n+1]. The structure and properties of PPT strictly depend on the oxide ratio and the temperature of [...]

This paper presents the findings of an experimental research project that was conducted in two phases to study the behavior of glass fiber reinforced polymer (GFRP) sandwich panels with reinforced cores under in-plane loading conditions. The tested panels consisted of two GFRP face skins separated by a polymeric foam core. The foam core was reinforced with different configurations of through-thickness fiber insertions and through-thickness GFRP web skins. In the first phase the performance of three different types of structural connections was tested--namely, bolted, bonded, and so-called enhanced bolted connections. The findings indicate that bolted connections to thinner and more flexible panels exhibited lower strength and a higher degree of nonlinear behavior compared with the bonded connections to the same panels. In contrast, the bolted connections to thicker and stiffer panels were generally stronger and stiffer than their bonded counterparts. The findings further indicate that the ultimate strength of the connections can be increased by up to 26% by bonding a steel reinforcing plate to the face skins of the panel prior to bolting. In the second phase three full-scale sandwich panels (1400 mm x 1400 mm) with different panel configurations were tested under proportional, biaxial, in-plane loading. The applied loads were selected to simulate the in-plane loading conditions in sandwich panels that are subjected primarily to in-plane loads, such as webs of deep beams and shear walls in lightweight structures. The full-field strains and displacements of the panels were measured using a digital image correlationbased (DIC) non-contact measurement system. The findings indicate that the through-thickness core reinforcements effectively prevented localized buckling, debonding, and separation of the panels' face skins. The findings also demonstrated that slender panels exhibit shear-compression buckling failures, whereas less slender panels exhibit shear-tension rupture failures. Key words: digital imaging techniques, fastening, fiber reinforced polymer sandwich panels, shear. Cet article presente les conclusions d'un projet de recherche experimental, realise en deux phases, visant a etudier le comportement des panneaux-sandwich en polymeres renforces de fibre de verre (PRFV) munis de noyaux armes sous des conditions de chargement en plan. Les panneaux a l'essai comportaient deux revetements en PRFV separes par un noyau de mousse de polymere. Ce noyau de mousse etait arme en utilisant differentes configurations d'intersections de fibres sur toute l'epaisseur ainsi que des revetements de l'ame en PRFV sur toute l'epaisseur. Durant la premiere phase, le rendement de trois types de raccords structuraux ont ete mis a l'epreuve : boulonnes, lies et les raccords boulonnes communement appeles ameliores. Les resultats indiquent que les raccords boulonnes sur des panneaux plus minces et plus flexibles montraient une plus faible resistance et un niveau plus eleve de comportement non lineaire que les raccords lies sur les memes panneaux. A l'oppose, les raccords boulonnes sur des panneaux plus epais et plus rigides etaient generalement plus resistants et plus rigides que les raccords lies. Les resultats indiquent aussi que la resistance a la rupture des raccords peut etre augmentee jusqu'a 26 % en liant une plaque d'armature en acier aux revetements du panneau avant le boulonnage. Durant la deuxieme phase, trois panneauxsandwich a pleine echelle (1400 mm x 1400 mm) de differentes configurations de panneaux ont ete mis a l'epreuve sous chargement proportionnel, biaxial et en plan. Les charges appliquees ont ete choisies pour simuler les conditions de chargement en plan dans les panneaux-sandwich soumis principalement a des charges en plan, tels que les ames des poutres cloisons et les murs de contreventement dans les structures legeres. Le plein champ des contraintes et des deplacements des panneaux ont ete mesures en utilisant un systeme de mesure sans contact de correlation d'image numerique. Les resultats indiquent que les renforcements de noyau a pleine epaisseur previennent efficacement le flambement, le decollage et la separation localises des revetements des panneaux. Les resultats demontrent egalement que les panneaux plus elances presentent des defaillances par flambement en cisaillement/compression alors que les panneaux moins elances comportent des defaillances par rupture en cisaillement/traction. [Traduit par la Redaction] Mots-cles: techniques d'imagerie numerique, fixation, panneaux-sandwichs en polymere renforce de fibres, cisaillement., Introduction Sandwich structures typically consist of two thin, strong, and stiff face skins that are separated by a thicker, weaker, and more flexible core. The skins may be fabricated from [...]

The necessary and sufficient conditions for hygrothermal stability of laminated composites are presented. A thorough survey of hygrothermally stable families is performed to identify stacking sequences that produce maximum extension-twist coupling. This is achieved through a constrained optimization routine, where the objective function is derived from the constitutive law given in classical lamination theory and the constraints are the necessary conditions for hygrothermal stability. A representative sample of these optimized laminates are constructed and tested to demonstrate significant improvement in coupling over the previously known optima. Comparisons are made with a nonlinear model and finite element analysis. An investigation of the robustness of the optimal stacking sequences to errors in ply angle typical of hand-layup manufacturing is presented. DOI: 10.2514/1.J050596

This paper describes the structural performance of an innovative wood plastic composite (WPC) sheet piling. Tensile coupon tests were performed to determine tensile strength and modulus over a range of strain rates for both WPC and specimens cut from commercially available vinyl sheet piles. Full scale four-point bending tests were conducted up to failure on 20 sets of joined pairs of WPC Z-piles with four different span lengths. For comparison, bending and coupon-level tension tests were also conducted on commercially available vinyl Z-piles and coupons cut from them. The coupon-level tests indicated that WPC had on average a 14% greater modulus than the vinyl specimens in the initial linear range, defined as between 10 and 40% of the respective material's ultimate tensile strength. However, if the modulus is computed over the same stress range of 10-40% of the WPC ultimate tensile strength, both materials have a similar modulus. The vinyl had a tensile strength 3.6 times that of the WPC. During the bending tests, the hollow cross section WPC Z-piles failed primarily in bending-induced tension, while the solid vinyl Z-piles exhibited buckling of the compression flange. Creep rupture testing was conducted for pair of WPC Z-piles in a four-point bending setup to determine long-term load- carrying capacity. No loss of load-carrying capacity was observed during the 90-day test and creep rates generally decreased during the test. However, creep deflections were larger than what would normally be exhibited by wood structural members. While additional studies are needed to address the effects of water absorption on WPC properties, the findings show promise for wood plastic composite light duty sheet piling retaining wall structures. DOI: 10.1061/(ASCE)MT.1943-5533.0000132 CE Database subject headings: Composite materials; Composite structures; Sheet piles; Stiffness; Creep. Author keywords: Composite materials; Composite structures; Sheet piles; Stiffness; Creep.

A multifield continuum is adopted to grossly describe the dynamical behavior of composite microcracked solids. The constitutive relations for the internal and external (inertial) actions are obtained using a multiscale modeling based on the hypotheses of the classical molecular theory of elasticity and the ensuing overall elastodynamic properties allow us to take properly into account the microscopic features of these materials. Referring to a one-dimensional microcracked bar, the ability of such a continuum to reveal the presence of internal heterogeneities is investigated by analyzing the relevant dispersive wave propagation properties. Scattering of traveling waves is shown to be associated with the microcrack density in the bar. [DOI: 10.1115/1.4001639] Keywords: composite materials, multifield continua, multiscale modeling, lattice mechanics, coarse-graining, wave propagation, dispersion

A mesoscale three-dimensional finite-element model is set up to model two-dimensional triaxially braided composites. Unit cell scheme is used to take into account braiding architecture as well as mechanical behavior of fiber tows, matrix, and fiber tow interface. A 0[degrees] / [+ or -] 60[degrees] braiding configuration has been studied. A failure criterion and progressive damage evolution model taking into account fiber tow and tow interface has been applied to theoretically predict interlaminar and intralaminar failure mode. Straight- sided specimen testing has been carried out in both axial and transverse direction. Results obtained in the tests as well as finite-element approaches are discussed. This paper also discusses the main feature of the model through an extensive parameter study. Overall, by comparison of experiment and model results, the applicability of the developed model is assessed and the failure process is investigated; furthermore, conducted parameter study enhances the strength of the model, which lies in the correlation of model parameters and identification of damage modes with experimental data on the overall stress strain curves. DOI: 10.1061/(ASCE)EM.1943-7889.0000181 CE Database subject headings: Composite structures; Finite element method; Stress strain relations; Degradation; Bonding; Parameters; Damage. Author keywords: Two-dimensional triaxially braided composite; Unit cell; Progressive degradation; Interface debonding; Parameter study.

The objective of this paper is to understand through parametric studies the effect of microstructural parameters, viz., the carbon nanotube (CNT) orientation with respect to the cutting direction, CNT loading, and level of dispersion within the matrix on the machinability of aligned CNT composites. To this end, a microstructure-based finite element machining model is used to simulate microstructures containing 1.5% and 6% by weight of CNTs. Microstructures with both uniform and nonuniform dispersions of CNTs are simulated. For each of these cases, CNTs having orientations of 0 deg, 45 deg, 90 deg, and 135 deg to the cutting direction are studied. The machining simulations were conducted using a positive rake tool Chip morphology, cutting forces, surface roughness, and surface/subsurface damages are the machinability measures used for comparison. The results of the parametric studies demonstrate that the CNT orientation, loading, and level of dispersion all play a critical role in dictating the machining response of aligned composites. The results further indicate that the surface morphology of the machined surface can be harnessed to produce the next generation of microfluidic devices. This application demonstrates the feasibility of designing the microstructure of CNT composites by taking into account both their engineering functionality and machinability. [DOI: 10.1115/1.4002495] Keywords: aligned CNT composites, micromachining, FEM models

The paper deals with interface behavior of bimaterial ceramic-metal composites under dynamic time-harmonic load, The first plate is precracked with a normal crack touching the interface between the plates. It is assumed that the respective restriction for the ratio of energy release rates of the plates allowing the occurrence of an interface single delamination before the initiation of the normal crack in the second plate is satisfied. The growth of interface delamination is not considered. The used approximate shear- lag dynamic approach gives a possibility to obtain solutions in a closed form for axial and shear stresses of the structure. At an elastic- brittle interface behavior theoretical predictions for single debond length of two bimaterial structures are calculated. The parametric analysis reveals the sensitivity of the interface single debond length and shear stress to the type of bimaterial structure and to the characteristics of the dynamic load--in particular its frequency and amplitude. All results are illustrated in figures and tables and are discussed, DOI: 10.1061/(ASCE)EM.1943-7889.0000155 CE Database subject headings: Cracking; Shear lag; Bonding; Delaminating; Plates; Dynamic loads, Author keywords: Dynamics of bimaterial cracked plate; Shear lag model; Interface elastic-brittle delamination; Single debond length.

Flutter control of smart composite plates under subsonic airflow is investigated in hygrothermal environment. The active fiber composite (AFC) which is more effective and adaptive than the conventional monolithic piezoelectric material is used in the present analysis to control the undesirable response due to hygrothermal effect. The velocity and displacement feedback control algorithm are subsequently established to reduce actively the response of the plate. Numerical examples of isotropic and laminated composite plates with or without hygrothermal effect are presented. It is observed that the structures become weak in the presence of hygrothermal load in the form of reduced flutter boundary. The flutter boundary can be enhanced with the help of AFC. The parametric study is performed and it is observed that the flutter boundary can be enhanced with the help of a feedback-control system activating the AFC. Therefore, one can say that the AFC is effective to enhance the flutter boundary of the present aeroelastic structure in the hygrothermal environment. DOI: 10.1061/(ASCE)AS.1943-5525.0000046 CE Database subject headings: Aircraft; Control systems; Flutter; Composite structures; Thermal factors. Author keywords: Flutter; AFC; Hygrothermal; Actuator; Feedback; Geometric stiffness.

The coupled electrothermoelastic constitutive relations, representing the behavior of piezo materials, are shown to be nonlinear when the polarization-electric field interaction effects are properly accounted for. Under static condition, the polarization-electric field nonlinearities correspond to a distributed body force and body moment. For time varying situations, polarization-electric field interaction exhibits a hysteresis effect. Using the nonlinear constitutive relations, a layer-by-layer finite element formulation is developed for both static and dynamic analyses of smart plates including hysteresis effects. Linear and nonlinear analyses are carried out to study the effect of nonlinearity due to polarization--electric field interaction on the response of the smart plates. To validate the present formulation, the results of static analysis of a smart plate are compared with experimental data available in literature. It is observed that the P-E hysteresis effects show a friction-type damping in the dynamic response of the smart plate. DOI: 10.2514/1.J050223

In this study, we conduct a combined experimental and micromechanical investigation into the strain-rate sensitivity of concretes, with a special reference to the effect of aggregate concentration. We first measured the stress-strain relations of Type I portland cement with 0.45 water-to-cement ratio (w/c), and then those of the mortar containing sand aggregates of up to 50% volume concentration, over six orders of magnitude of strain rate, from 5 x [10.sup.-6]/s to 1 x [10.sup.-1] / s under compression. It was found that, at a given strain rate, the peak stress increases with the aggregate concentration but the peak strain tends to decrease with it. At a given aggregate concentration, the peak stress also increases with strain rate whereas the peak strain generally decreases with it. We then developed an inclusion-matrix type micromechanical model to simulate the behavior of the concrete. In this process the nonlinear viscoelastic behavior of the portland cement was modeled by a modified Burger's model with strain-rate dependent spring and dashpot elements, and the stress- strain relations of the mortar at various aggregate concentrations and strain rates were calculated from a two-phase composite model with a secant-moduli approach. It is shown that the measured data could be sufficiently well predicted by the developed micromechanics composite model. DOI: 10.1061/(ASCE)EM.1943-7889.0000153 CE Database subject headings: Strain rates; Stress strain relations; Cement; Aggregates; Micromechanics; Composite materials. Author keywords: Strain-rate sensitivity; Stress-strain behavior; Cement paste; Aggregates; Micromechanics; Cementitious composites; Peak stress and peak strain.

This paper provides a polytetrafluoroethylene (PTFE)/nano-EG solid self-lubricating composite that exhibits very low friction coefficient and wear rate. In present study, the influences of the content of expanded graphite with nanoscale lamellar structure (nanoEG) in PTFE/nano-EG composite, normal contact pressure, and sliding velocity on tribological properties were studied by using the MMU-5G friction and wear tester sliding against AISI-1045 steel. Meanwhile, the property of nano-EG was characterized by utilizing a field emission scanning electron microscope. Compared with that of pure PTFE, the addition of nano-EG into PTFE matrix effectively' improved the antifriction and wear resistance properties of PTFE/nano-EG composite. The highest wear resistance was found for the PTFE/nano-EG composite filled with 15 wt % nano-EG. The morphologies of worn surface of the ANSI-1045 steel and composites were observed using a confocal laser scanning microscopy (CLSM) and a scanning electron microscope (SEM) to examine composite microstructures and to study modes of failure. The images of CLSM and SEM indicate that the property of transfer film generated on the surface of mating pair is likely responsible for the lower wear rate observed in these experiments. [DOI: 10.1115/1.4001546] Keywords: PTFE/nano-EG composite, friction and wear, transfer film, CLSM, FESEM

Particle shape plays a crucial role in the design of novel reinforced composites. We introduce the notion of a geometrical anisotropy index A to characterize the particle shape and establish its relationship with the effective elastic constants of biphase composite materials. Our analysis identifies three distinct regions of A: (i) By using ovoidal particles with small A, the effective stiffness scales linearly with A for a given volume fraction [alpha]; (ii) for intermediate values of A, the use of prolate particles yield better elastic properties; and (iii) for large A, the use of oblate particles result in higher effective stiffness. Interestingly, the transition from (ii) to (iii) occurs at a critical anisotropy [A.sup.cr] and is independent of [alpha]. [DOI: 10.1115/1.4000928]

A finite-element model (FEM) is developed to predict the load-displacement behavior of a composite wood-concrete floor/ deck system under short-term loading. The interlayer connection was modeled with link elements dedicated for connection modeling. Results of past tests of two full-scale layered floor/deck specimens are employed to confirm the FEM model. The specimen had a layer of solid sawn lumber overlaid by concrete and interconnected to it with a pattern of notched shear key/anchor details. The FEM results agreed closely with the measured deflection data for the loadings considered. The efficiency of composite behavior achieved by each of those specimens is quantified by a conventional and three improved approaches based on the computer modeling and measured test results. The new approaches better capture the overall efficiency of the entire floor/deck. DOI: 10.1061/(ASCE)ST.1943-541X.0000117 CE Database subject headings: Composite materials; Finite element method; Floors; Decks; Wood; Concrete. Author keywords: Composite; Composite efficiency; Finite-element model; Floor/deck; Short-term loads; Wood-concrete.

This paper presents a micromechanical finite-element (FE) model for predicting the viscoelastic properties (dynamic modulus and phase angle) of asphalt mixtures, typical stone-based composites. The two-dimensional (2D) microstructure of asphalt mixtures was captured by optically scanning the surface image of sectioned specimens. FE mesh of image samples was generated within each aggregate and asphalt mastic. Along the aggregate boundary, the FEs share the nodes to connect the deformation. The micromechanical FE model was accomplished by incorporating specimen microstructure and ingredient properties (viscoelastic asphalt mastic and elastic aggregates). The generalized Maxwell model was applied for viscoelastic asphalt mastic with calibrated parameters from nonlinear regression analysis of the mastic test data on dynamic modulus and phase angle. The displacement-based FE simulations were conducted on the numerical samples under sinusoidal cyclic loading. The predicted dynamic modulus and phase angle were compared favorably with the mixture test data over a frequency range. The simulation results of the asphalt mixture samples have good correlations with the numerical calibration of asphalt mastic specimens. These results indicate that the developed micromechanical FE model can provide a computational tool for predicting the global viscoelastic properties of asphalt mixtures with captured microstructure and ingredient properties. Additionally, this study can increase the mechanistic understanding of global viscoelastic properties of asphalt mixtures by linking their microstructure. DOI: 10.1061/(ASCE)MT.1943-5533.0000062 CE Database subject headings: Micromechanics; Composites; Aggregates; Asphalts; Mixtures; Finite element method; Viscoelasticity; Microstructures. Author keywords: Micromechanics; Composites; Aggregates; Asphalts; Mixtures; Finite-element method; Viscoelasticity; Dynamic modulus; Phase angle.

A composite geomaterial (CGM) is developed using dredged soil, bottom ash, cement and air foam. The engineering properties of the CGM are characterized as a function of the content of the various admixtures and the curing time in a laboratory test program. Several series of unconfined compression tests were carried out to characterize the strength and elastic properties of the CGM. Experimental results indicate that the unconfined compressive strength and modulus of CGM are influenced by the content of each component in the mixture. The unconfined compressive strength of CGM increases with an increase in curing time due to the pozzolanic reaction of the bottom ash. The strength after 28 days of curing is found to be approximately 1.5-2.3 times the strength after 7 days of curing, regardless of mix conditions. The bottom ash materials contain nearly 50% siliceous material and 13.9% CaO. With the removal of particles larger than 4.75 mm, a larger surface area is available to react with cement. It is postulated that the increase in shear strength is caused not only by the development of friction at the interface of the mixture components, but also by bond strength is due to the pozzolanic reaction of the bottom ash. Further study is needed, however, to discern aspects related to increase in pozzolanic reaction of bottom ash with the removal of larger size particles. The secant modulus of CGM is in the range of 185-480 times the unconfined compressive strength. The observed general trend is that the stiffness of CGM is greater than that of lightweight soil not containing the bottom ash as a component. DOI: 10.1061/(ASCE)MT.1943-5533.0000052 CE Database subject headings: Composite materials; Geomaterials; Dredge spoil; Bottom ash; Recycling; Compression tests. Author keywords: Composite geomaterial; Dredged soil; Bottom ash; Recycling; Unconfined compression test.