Showing papers in "Composites Part B-engineering in 2008"
TL;DR: In this article, the effects of particle size, particle/matrix interface adhesion and particle loading on the stiffness, strength and toughness of such particulate polymer composites are reviewed.
Abstract: There have been a number of review papers on layered silicate and carbon nanotube reinforced polymer nanocomposites, in which the fillers have high aspect ratios. Particulate–polymer nanocomposites containing fillers with small aspect ratios are also an important class of polymer composites. However, they have been apparently overlooked. Thus, in this paper, detailed discussions on the effects of particle size, particle/matrix interface adhesion and particle loading on the stiffness, strength and toughness of such particulate–polymer composites are reviewed. To develop high performance particulate composites, it is necessary to have some basic understanding of the stiffening, strengthening and toughening mechanisms of these composites. A critical evaluation of published experimental results in comparison with theoretical models is given.
2,767 citations
TL;DR: In this paper, the authors investigated the stability, mechanical properties, and the microstructure of wood-plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour (Pinus radiata ) as filler.
Abstract: This paper investigated the stability, mechanical properties, and the microstructure of wood–plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour ( Pinus radiata ) as filler. The post-consumer HDPE was collected from plastics recycling plant and sawdust was obtained from a local sawmill. Composite panels were made from recycled HDPE through hot-press moulding exhibited excellent dimensional stability as compared to that made from virgin HDPE. The tensile and flexural properties of the composites based on recycled HDPE were equivalent to those based on virgin HDPE. Adding maleated polypropylene (MAPP) by 3–5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content or by addition of coupling agent. This project has shown that the composites treated with coupling agents will be desirable as building materials due to their improved stability and strength properties.
471 citations
TL;DR: In this paper, the authors developed conductive, carbon nanotube (CNT)-filled, polymer composite films that can be used as strain sensors with tailored sensitivity and measured resistivities were correlated with the applied strains to evaluate the sensitivity of the nanocomposite film sensor.
Abstract: This paper reports the development of conductive, carbon nanotube (CNT)-filled, polymer composite films that can be used as strain sensors with tailored sensitivity. The films were fabricated via either melt processing or solution casting of poly(methyl methacrylate) (PMMA) matrices containing low concentrations of multi-walled carbon nanotubes (MWNTs). The electrical resistivities of the films were measured in situ using laboratory-designed fixtures and data acquisition system. The measured resistivities were correlated with the applied strains to evaluate the sensitivity of the nanocomposite film sensor. The study suggests that conductive network formation, thus strain sensitivity of the conductive films, can be tailored by controlling nanotube loading, degree of nanotube dispersion, and film fabrication process. The developed sensors exhibited a broad range of sensitivity, the upper limit showing nearly an order of magnitude increase compared to conventional, resistance-type strain gages. A semi-empirical model that shows the relationship between CNT volume fraction and sensitivity is proposed.
338 citations
TL;DR: In this article, the free and forced vibration of a laminated functionally graded beam of variable thickness under thermally induced initial stresses is studied within the framework of Timoshenko beam theory, where the beam consists of a homogeneous substrate and two inhomogeneous functionally graded layers whose material composition follows a power law distribution in the thickness direction.
Abstract: The free and forced vibration of a laminated functionally graded beam of variable thickness under thermally induced initial stresses is studied in this paper within the framework of Timoshenko beam theory. The beam consists of a homogeneous substrate and two inhomogeneous functionally graded layers whose material composition follows a power law distribution in the thickness direction in terms of the volume fractions of the material constituents. Both the axial and rotary inertia of the beam are considered in the present analysis. It is assumed that the beam may be clamped, hinged, or free at its ends and is subjected to one-dimensional steady heat conduction in the thickness direction before undergoing dynamic deformation. To include the effect of temperature change, the initial stress state is determined through a thermo-elastic analysis before the free and forced vibration analyses. The differential quadrature method that makes use of Lagrange interpolation polynomials is employed as a numerical solution tool to solve both the thermo-elastic equilibrium equation and dynamic equation. Numerical results are presented in both tabular and graphical forms for various laminated functionally graded beams, showing that vibration frequencies, mode shapes and dynamic response are significantly influenced by the thickness variation, temperature change, slenderness ratio, volume fraction index, the thickness of the functionally graded layer, and the end support conditions.
223 citations
TL;DR: In this paper, it was shown that a proper choice of the reference surface can eliminate the coupling between the inplane and bending deformations, so that the bending of the plate is governed by the same equation of motion as that of homogeneous plates.
Abstract: In recent years many articles concerned with the mechanics of functionally graded plates have been published. Usually new analysis methods are developed to handle the continuous variation in material properties through the thickness of the plate and extensive results are presented. This article shows that no special tools are required because functionally graded plates behave like homogeneous plates. This simple result is developed using the classical plate theory and is shown to hold true when higher order plate theories or the three dimensional elasticity theory is used. The variation in material properties through the thickness of the plate introduces a coupling between the inplane and bending deformations which complicates the analysis. Here we show that by a proper choice of the reference surface, this coupling can be eliminated so that the bending of the plate is governed by the same equation of motion as that of homogeneous plates.
222 citations
TL;DR: In this paper, the effect of the length and weight content of silk fibers on the properties of poly(lactic acid) and polyamide poly(plastic acid) was investigated for tissue engineering applications.
Abstract: Poly(lactic acid) (PLA), a kind of well recognized biodegradable polymer, was reinforced by silkworm silk fibers to form a completely biodegradable and biocompatible biocomposite for tissue engineering applications. The influence on the mechanical and thermal properties of the biocomposite in relation to the length and weight content of silk fibers is studied in this paper. Through the micro-hardness test, optimized fiber length and weight content of silk fibers used to make a better strength silk fiber/PLA biocomposite was determined. Tensile property test and thermal analyses including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetry analysis (TGA) for the silk fiber/PLA biocomposite with specified fiber length and weight content were then conducted to investigate its property changes in comparison to a pristine PLA sample. Experimentally, it was found that the fiber length and weight content of silk fibers are key parameters that would substantially influence the hardness of the biocomposite samples. For microscopic observations, good wettability of the fibers inside the biocomposite was seen. The surface of the fibers was well bonded with the matrix, as observed by a SEM image of fractured sample. As a result, it was found that the use of silk fibers can be a good candidate, as reinforcements for the development of polymeric scaffolds for tissue engineering applications.
173 citations
TL;DR: In this paper, different types of debonding failure modes are described and experimental results of four-point bending tests on FRP strengthened RC beams are presented and debond failure mechanisms of strengthened beams are investigated using analytical and finite element solutions.
Abstract: In this paper, different types of debonding failure modes are described. Then, experimental results of four-point bending tests on FRP strengthened RC beams are presented and debonding failure mechanisms of strengthened beams are investigated using analytical and finite element solutions. Reasonable results could be obtained for modelling of debonding failure load of tested beams. Existing international codes and guidelines from organizations such as ACI, fib , ISIS, JSCE, SIA, TR55, etc. are presented and compared with the results from the experiments and calculations. A discrepancy of up to 250% was seen between different codes and guidelines for predicting the debonding load. Furthermore, a new recommendation for debonding control is given.
156 citations
TL;DR: In this article, the results of an experimental study on the interfacial bond strength of glass fiber reinforced polymer (GFRP) bars in high-strength concrete cube were presented.
Abstract: This paper presents the results of an experimental study on the interfacial bond strength of glass fiber reinforced polymer (GFRP) bars in high-strength concrete cube. The experimental program consisted of testing 54 concrete cube specimens prepared according to CSA S802-02 standard. Two main parameters were considered in the experimental investigation: the compressive strength of concrete (from 25.6 MPa to 92.4 MPa) and the type of rebar (steel, sand-coated GFRP, and helically wrapped GFRP). The test results showed that the interfacial bond strength of the GFRP bars increased as the compressive strength of concrete increased. However, the increasing rate of the bond strength of the GFRP bars with respect to the concrete strength was much smaller than that of the steel bars. The concrete specimens were sawn in half after the test for a closer investigation of the actual mode of bond failure. Visual examination of the specimens showed that bond failure of the steel bar was caused by concrete crushing against the face of the ribs, while bond failure of the GFRP bars occurred not only in the concrete but also in the bars by delamination of the resin-rich outer layer from the fiber core. The average area of the delaminated resin-rich layer of the GFRP bar increased with increasing compressive strength of concrete.
155 citations
TL;DR: In this paper, a series of axial compression tests on short FRP-confined circular columns with an inner void were conducted to examine the behavior of concrete in such FRPconfined annular sections.
Abstract: This paper presents and interprets the results of a series of axial compression tests on short FRP-confined circular columns with an inner void to examine the behavior of concrete in such FRP-confined annular sections. This study was motivated by the need to understand and model the behavior of concrete in a new form of double-skin tubular columns (DSTCs) composed of a steel inner tube, an FRP outer tube and a concrete infill between the two tubes. To this end, three types of specimens were tested: FRP-confined solid cylinders (FCSCs), FRP-confined hollow cylinders (FCHCs), and short DSTCs. The main parameters examined include the section configuration, the void ratio, the diameter-to-thickness ratio of the inner steel tube, and the thickness of the FRP tube. The test results show that the presence of an inner void reduces the effect of external FRP confinement, but this loss of confinement effectiveness can almost be completely compensated for through the provision of a suitable steel tube. As a result, the concrete in hybrid DSTCs is very effectively confined by the two tubes and the load–axial shortening behavior of concrete in hybrid DSTCs is very similar to that of FCSCs. For an approximate analysis of DSTCs with a suitable steel tube and a reasonable void ratio, an existing stress–strain model for FCSCs may be used.
152 citations
TL;DR: A brief overview of anchorage systems is dealt with introducing experimental tests on eight types of end fixing for reinforced polymers (FRP) sheets glued on RC elements as mentioned in this paper, which confirm that the various solutions have different performances in improving the debonding load.
Abstract: A brief overview of anchorage systems is dealt with introducing experimental tests on eight types of end fixing for reinforced polymers (FRP) sheets glued on RC elements. Particular test set-up and T-shaped specimens have been designed and realized to test mechanical fixings with steel or FRP plates glued or bolted, FRP bars or L-shaped fibers. The experimental results confirm that the various solutions have different performances in improving the debonding load. Numerical analysis confirm the reliability of debonding formulations available; furthermore a simple evaluation of anchorage effectiveness is proposed.
143 citations
TL;DR: In this paper, the uniaxial compressive responses of two polymeric foams (Divinycell H100 and H250) and balsa wood (ProBalsa LD7) have been measured over a wide range of strain rates, ranging from 10−4 s−1 to 4000 S−1.
Abstract: The uniaxial compressive responses of two polymeric foams (Divinycell H100 and H250) and balsa wood (ProBalsa LD7) have been measured over a wide range of strain rates, ranging from 10−4 s−1 to 4000 s−1. These materials are widely used as cores for composite sandwich structures. The high strain rate compression tests were performed using a Split-Hopkinson Pressure Bar made from AZM magnesium alloy, with semi-conductor strain gauges used to measure the low levels of stress in the specimens. The experimental data for compressive strength as a function of strain rate are adequately approximated by power-law fits. The compressive yield strength of the H250 PVC foam and balsa wood doubles when the strain rate is increased from quasi-static rates (10−4 s−1) to rates on the order of 103 s−1. In contrast, the H100 PVC foam displays only a small elevation in uniaxial compressive strength (about 30%) for the same increase in strain rate.
TL;DR: In this paper, the failure of polymer matrix composites upon exposure to the environment has been assessed in order to investigate the combined action of temperature, humidity and UV radiation on polymers and composites, an environmental ageing chamber has been constructed and tested.
Abstract: The failure of polymer matrix composites upon exposure to the environment has been assessed in the present study. In order to investigate the combined action of temperature, humidity and UV radiation on polymers and composites, an environmental ageing chamber has been constructed and tested. The accelerated environmental ageing was based on two kinds of alternating cycles, which provided humidity, temperature and ultraviolet radiation. The materials examined were isophthalic polyester and isophthalic polyester reinforced with a glass fiber random mat onto which glass fibers were knitted at 0°/90° (GFRPC) at a total volume fraction of approximately 20%. Dynamic mechanical analysis, for a range of temperatures and frequencies under tensile and three-point bending loadings, revealed that the aged materials gained in stiffness, whereas a small deterioration in strength was found. Scanning electron microscopy studies performed before and after environmental chamber conditioning revealed that some microcracks had occurred on the surface of the specimens. Nevertheless, the length of these microcracks was less than the critical value of 0.1 mm, required for crack propagation.
TL;DR: In this paper, two different fiber materials, namely, E-glass and carbon, with different architecture are chosen, and subjected to quasi-static and high strain rates of loading utilizing different testing methodologies.
Abstract: Fiber based composites have found extensive applications in various fields. In this study, two different fiber materials, namely, E-glass and carbon, with different architecture are chosen. Polymer (vinyl ester) based composites were designed using these fibers and were fabricated using VARTM process. These composites were subjected to quasi-static and high strain rates of loading utilizing different testing methodologies. In quasi-static testing, the tensile, compressive and shear properties were studied using existing ASTM standard testing procedures and the results are reported. The carbon composite showed higher tensile and compressive modulus. In-plane shear properties of both the composites were comparable and inter laminar shear properties of E-glass composites were observed to be better than the carbon composite because of the better nesting between the E-glass fabric layers. A shock tube and a controlled explosion tube were utilized in the study of dynamic damage behavior of these composite materials. Based on the experimental study, it is observed that the carbon fiber composites tend to achieve sudden destructive damage whereas E-glass fiber composites tend to sustain progressive damage, under dynamic loading.
TL;DR: In this article, the reinforcing fibers were constructed with three different geometries, i.e., embossed, straight, and crimped, from waste polyethylene terephthalate (PET) bottles and used them to control plastic shrinkage cracking in cement-based composites.
Abstract: In this study, the reinforcing fibers were constructed with three different geometries, i.e., embossed, straight, and crimped, from waste polyethylene terephthalate (PET) bottles and used them to control plastic shrinkage cracking in cement-based composites. Pullout tests evaluated how the fiber geometry and fraction by volume (0.1–1.00%) affected the rate of moisture loss and controlled the plastic shrinkage cracking characteristics. The fiber geometry and fraction by volume did not affect the total moisture loss or moisture loss per hour; the moisture loss per hour exceeded 0.5 kg/m2/h in 5 h after casting, causing plastic shrinkage cracking. However, increased fractions of recycled PET fiber resulted in improved control of the plastic shrinkage cracking. At a fraction of 0.25%, the plastic shrinkage was reduced, but no further improvements were observed when the fraction of fiber was increased to 0.5%. Fiber geometry also affected the control of plastic shrinkage cracking up to a fiber fraction of 0.25%.
TL;DR: In this article, a new three node element is proposed which is made up of warp and weft fibres, the tensile and in plane shear energy of which are considered.
Abstract: Continuous and discrete approaches for forming simulations of textile performs both involve difficulties and drawbacks The semi-discrete method is an alternative based on a meso-macro approach It is based on specific finite elements made of a discrete number of the components of the textile at lower scale Their strain energy in the interpolated displacement field leads to the nodal interior loads of the element In this paper a new three node element is proposed It is made up of warp and weft fibres, the tensile and in plane shear energy of which are considered The directions of the warp and weft yarns are arbitrary with regard to the element sides That is very important in case of simultaneous multiply draping simulations and when using remeshing The determination of the material data necessary to the simulation from standard tensile and bias tests is straightforward A set of elementary tests and mono and multi-ply draping shows the efficiency of the approach
TL;DR: In this paper, a simply supported, sandwich plate with FGM face sheets and a simple power law distribution in terms of the volume fractions of the constituents is presented for compressive postbuckling under thermal environments.
Abstract: Compressive postbuckling under thermal environments and thermal postbuckling due to heat conduction are presented for a simply supported, sandwich plate with FGM face sheets. The material properties of FGM face sheets are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM face sheets and homogeneous substrate are assumed to be temperature-dependent. The governing equations are based on a higher order shear deformation plate theory that includes thermal effects. The initial geometric imperfection of the plate is taken into account. A two-step perturbation technique is employed to determine buckling loads (temperature) and postbuckling equilibrium paths. The numerical illustrations concern the compressive and thermal postbuckling behavior of perfect and imperfect, sandwich plate with FGM face sheets under different thermal environmental conditions. The results reveal that the temperature changes, the volume fraction distribution of FGM face sheets, and the substrate-to-face sheet thickness ratio have a significant effect on the buckling load and postbuckling behavior of sandwich plates. The results also confirm that for the case of heat conduction, the postbuckling path is no longer of the bifurcation type.
TL;DR: In this article, carbon nanotubes were employed to reinforce the interfaces between polymer particles, enhancing composite stiffness as well as structural damping, and the results showed that CNT-reinforced samples have advanced impact strength and vibration damping properties over a wide temperature range.
Abstract: The focus in this paper is directed toward to thermal spraying fabrication and experimental validation of carbon nanotube-reinforced composite structures, providing processing route and design concepts. Sandwiched metal–polymer–ceramics coatings and moulded UHMW-PE polymer composites with carbon nanotubes were investigated at flexural tests and thermal cycling between +200 °C and −80 °C temperature. Carbon nanotubes were employed to reinforce the interfaces between polymer particles, enhancing composite stiffness as well as structural damping. Results on damping behavior and impact toughness of the composite sandwiches showed that CNT-reinforced samples have advanced impact strength and vibration damping properties over a wide temperature range. Experiments conducted using a vibrating clamped beam with the composite layers indicated up to 200% increase in the inherent damping level and 30% increase in the stiffness with some decrease (20–30%) in density of the composite. The cross-links between nanotubes and composite layers also served to improve load transfer within the network resulting in improved stiffness properties. The results are targeted for the application in aerospace and naval engineering.
TL;DR: In this paper, an analytical approach is developed for the prediction of failure under general in-plane loading including the variability of strength, stiffness and the thermal expansion coefficients, and a direct comparison is also presented for failure locii at a specific reliability level as derived by the various probabilistic approaches.
Abstract: Results are presented from an experimental study for the modeling of stochastic behavior of a unidirectional Glass/Polyester composite. An analytical approach is developed for the prediction of failure under general in-plane loading including the variability of strength, stiffness and the thermal expansion coefficients. Monte Carlo simulation and the first-order reliability method are used for comparison and the new method is proved to be in good agreement. Following international design codes, a direct comparison is also presented for failure locii at a specific reliability level as derived by the various probabilistic approaches. Results reveal that a serious overestimation of the reliability of the composite structure is being made when the stochastic nature of the material elastic properties is not taken into account.
TL;DR: In this article, the impact resistance of all-polypropylene composite laminates based on these highly oriented co-extruded PP tapes, and the temperature and velocity of impact are investigated.
Abstract: Highly oriented polypropylene (PP) tapes, with high tensile strength and stiffness achieved by molecular orientation during solid state drawing, are consolidated to create fully recyclable, high performance “all-polypropylene” (all-PP) composites. These composites possess a large processing temperature window (>30 °C) and a high volume fraction of highly oriented PP reinforcement phase (>90%). This large processing window is achieved by using co-extruded, highly drawn PP tapes. This paper investigates the relationship between the impact resistance of all-PP composite laminates based on these highly oriented co-extruded PP tapes, and the temperature and velocity of impact. Unlike isotropic PP, the highly oriented nature of all-PP composites means that a significant influence of glass transition temperature is not observed and so all-PP composites retain high impact energy absorption even at low temperatures. Finally, the ballistic impact resistance of all-PP composites is investigated and compared with current commercial anti-ballistic materials.
TL;DR: In this paper, the behavior of strengthened masonry infilled reinforced concrete (RC) frames using diagonal CFRP strips under cyclic loads was investigated and the effect of width and arrangement type on the lateral strength and stiffness of masonry-infilled walls was investigated.
Abstract: The purpose of this study was to investigate experimentally the behavior of strengthened masonry infilled reinforced concrete (RC) frames using diagonal CFRP strips under cyclic loads. Ten test specimens were constructed and tested under cyclic lateral loading. Specimens were constructed as 1/3 scale, one-bay, one-storey perforated clay brick-infilled nonductile RC frames. The aspect ratio (lw/hw, where lw is the infill length and hw is the infill height) of masonry-infilled wall was 1.73. CFRP strips were applied with different widths and with three different arrangements such as on both sides (i.e. symmetrically) and on the interior side or the exterior side of the masonry walls. This experimental study investigated the effects of CFRP strips’ width and arrangement type on specimens’ behavior. Strength, stiffness and storey drifts of the test specimens were measured. Test results indicated that, CFRP strips significantly increased the lateral strength and stiffness of perforated clay brick infilled nonductile RC frames. Specimens receiving symmetrical strengthening showed higher lateral strength and stiffness. Specimens at which CFRP strips of the same width were applied to one of the interior or exterior surface of the infill wall showed similar lateral strength and stiffness.
TL;DR: In this article, a simplified biaxial tensile model is proposed to give the tension response for all warp and weft strains with very fast computations, based on a consistent description of the fabric geometry.
Abstract: The knowledge of the mechanical behaviour of woven composite reinforcements is necessary to analyse and simulate the forming processes of these composites. Tensile rigidities of fabrics are large compared to others and they mainly drive the deformation. The tensile behaviour of woven reinforcements is specific because the undulations due to weaving lead to strong non-linearities at the beginning of the loading. These undulations in both directions lead to a biaxial phenomenon. In the present paper, a simplified biaxial tensile model gives the tension response for all warp and weft strains with very fast computations. It can be used to carry out optimization of the parameters of the woven reinforcement. This model is based on a consistent description of the fabric geometry. Contrary to most others models it strictly avoids spurious voids and interpenetrations of the yarns due to geometrical assumptions. The geometrical model remains nevertheless simple and requires three or six dimensional parameters according to whether the fabric is balanced or not. The simplified mechanical model based on this geometrical description is a truss type model. From the local equilibrium equations of woven yarns, it relates the tensions in the warp and weft directions to the axial strains in these two directions. The tensile surfaces are obtained very quickly and are in good agreement with results of experimental biaxial tests.
TL;DR: In this article, the authors investigated the tensile strength and interfacial shear strength between Jute fibers and polypropylene (PP) composites by micromechanical test combined with the wettability and non-destructive acoustic emission (AE).
Abstract: Interfacial evaluation and the durability of alkaline and silane treated Jute fibers/polypropylene (PP) composites were investigated by micromechanical test combined with the wettability and nondestructive acoustic emission (AE). After boiling water test, tensile strength and interfacial shear strength (IFSS) between Jute fibers and PP matrix decreased due to the deterioration of swelled fibrils by water infiltration and microfailure. The IFSS decrement of the untreated and treated Jute fibers/PP composites was different from each other, respectively. IFSS between silane treated Jute fiber and PP matrix was higher than the untreated or even alkaline treated cases. From the dynamic contact angle results, micromechanical IFSS was not always consistent with thermodynamic work of adhesion, Wa in the interface. Since hemicellulose and lignin could be removed from Jute fiber after boiling water test, Jute fiber surface became more hydrophilic and surface roughness increased. With water present, the work of adhesion did not only decrease but they were negative, which indicates the instability of the interfacial system. Microfailure pattern of boiled Jute fiber was obviously different from the untreated case based on monitored AE parameters. AE energy increased for the alkaline and silane treated Jute fibers/PP composites, whereas AE energy for all three cases decreased distinctly after boiling water test.
TL;DR: In this article, an analysis of the damping of unidirectional fiber composites, orthotropic composites and laminates is presented using a finite element analysis which evaluated the different energies dissipated in the material directions of the layers.
Abstract: The paper presents an analysis of the damping of unidirectional fibre composites, orthotropic composites and laminates. Damping parameters are investigated using beam test specimens and an impulse technique. Damping modelling is developed using a finite element analysis which evaluated the different energies dissipated in the material directions of the layers. The results obtained show that this analysis describes fairly well the experimental results. The finite element analysis can be applied to complex shape structures.
TL;DR: In this paper, a nanocomposite (NC) hydrogel was prepared by incorporating the nanoclay (Laponite (Lap) XLS) into a poly(acrylamide) (PAAm)-based PAAm/Lap NC by the in situ polymerization method without any organic crosslinker.
Abstract: A nanocomposite (NC) hydrogel was prepared by incorporating the nanoclay (Laponite (Lap) XLS) into a poly(acrylamide) (PAAm) hydrogel by the in situ polymerization method without any organic cross-linker. The parameters pertaining to the swelling (Q) and diffusion (D) of water for the PAAm/Lap NC hydrogels were estimated. The crystal violet (CV) dye adsorption properties of the PAAm/Lap NC hydrogels were investigated. The adsorption of CV dye by the hydrogel increases as the concentration of the dye increases. The cationic dye adsorption ability of the NC hydrogel increased with increasing clay content in the NC hydrogel. The NC hydrogels containing CV dye were characterized by FT-IR. A sigmoidal type of adsorption isotherm was observed for the CV-NC hydrogels. The effects of heat treatment on the dye adsorption behavior of the NC hydrogels were studied.
TL;DR: In this paper, a method for the assessment and calibration of the elastoplastic behavior of FRP confined concrete is presented based on the evaluation of permanent deformations from observed experimental deformations and theoretical elastic response of confined concrete.
Abstract: A method is presented for the assessment and calibration of the elastoplastic behaviour of FRP confined concrete. The method is based on the evaluation of permanent deformations from observed experimental deformations and theoretical elastic response of confined concrete. The inelastic response of concrete and the parameters of its mathematical modelling are investigated. Closed form expressions are produced to relate the model parameters to the mechanical properties of the material. A strain-hardening Drucker–Prager model is developed which simulates both the hardening and softening material response with reasonable agreement to the experimental observations. The predictive ability of the model is verified through comparisons to numerous published experimental data and analytical models.
TL;DR: In this article, the meshless local Petrov-Galerkin (MLPG) method with radial basis functions (RBFs), and the higher order shear and normal deformable plate theory (HOSNDPT) are used to analyze static infinitesimal deformations of thick laminated composite elastic plates under different boundary conditions.
Abstract: The meshless local Petrov–Galerkin (MLPG) method with radial basis functions (RBFs), and the higher order shear and normal deformable plate theory (HOSNDPT) are used to analyze static infinitesimal deformations of thick laminated composite elastic plates under different boundary conditions. Two types of RBFs, namely, multiquadrics (MQ) and thin plate splines (TPS), are employed for constructing trial functions while a fourth order spline function is used as the test function. Computed results for different lamination schemes are found to match well with those obtained by other researchers. A benefit of using RBFs over those generated by the moving least squares approximation is that no special treatment is needed to impose essential boundary conditions, which substantially reduces the computational cost. Furthermore, the MLPG method does not require nodal connectivity which reduces the time required to prepare the input data.
TL;DR: In this paper, the effects of synthetic and steel fibers on the bond properties of high-strength concrete and fiber-reinforced polymer (FRP) reinforcing bars were evaluated.
Abstract: This study evaluated the effects of synthetic and steel fibers on the bond properties of high-strength concrete and fiber-reinforced polymer (FRP) reinforcing bars. Direct bond tests were performed to evaluate the bond performance of 9-mm-∅ carbon fiber-reinforced polymer (CFRP) and 13-mm-∅ glass fiber-reinforced polymer (GFRP) reinforcing bars in three types of high-strength concrete with varying amounts of steel (20 and 40 kg/m 3 ) or synthetic (4.55 and 9.1 kg/m 3 ) fiber. The bond strength increased with the compressive strength of the high-strength concrete. The type and amount of fiber also affected the bond strength. The specimens with 40 kg/m 3 steel fiber had the highest bond strength. The larger FRP bars tended to have stronger bonds, regardless of the strength of the concrete and type or amount of fiber. The relative bond strength was determined to analyze the effect of the type and amount of fiber; it increased as more fiber was added. Overall, the specimens with 40 kg/m 3 steel fiber had the best bond performance.
TL;DR: In this article, a preliminary study has been conducted to investigate the ballistic behavior of a model lattice and to explore the effect of filling the lattices void spaces with polymers and ceramics.
Abstract: Sandwich panels with lattice cores have attracted significant interest as multifunctional structures. The lattices consist of 3D repeating unit cells constructed from plates or trusses oriented to efficiently support applied stresses. These systems show promise for supporting structural loads and mitigating the blast effects of explosions. Here, a preliminary study has been conducted to investigate the ballistic behavior of a model lattice and to explore the effect of filling the lattices void spaces with polymers and ceramics. A sheet folding and brazing method has been used to fabricate pyramidal lattice truss structures from 304 stainless steel. The impact response of the various panels was assessed after impact by spherical, 12 mm diameter, 6.9 g projectiles with an incident, zero obliquity velocity of ∼600 m/s. Empty lattice sandwich panels with an areal density of 27.7 kg m−2 do not prevent the perforation of the sandwich panel. The impact with proximal face sheet reduced the projectile velocity to ∼450 m/s (by about 25%). Interactions with the lattice trusses and the distal face sheet further slowed the projectile resulting in an exit velocity at the distal face sheet of ∼360 m/s. The projectiles energy was dissipated by face sheet plastic dishing and fracture by petaling, and by truss plastic deformation. Infiltration of the lattice with polyurethane elastomers further reduced the projectile exit velocity. The strength of the effect depended upon the modulus of the polymer (and therefore its glass transition temperature, Tg). Only high modulus (high Tg) elastomers fully arrested the projectile. The energy of the projectile in this case was dissipated by a combination of face sheet stretching and polymer deformation and fracture. Low modulus elastomers reduced the projectile exit velocity by about 45% (to ∼250 m/s) and also resulted in resealing of the projectile path within the sandwich panel core. The incorporation of ballistic fabric within the polymer infiltrated systems had little effect on the ballistic resistance. A hybrid sample containing metal encased Al2O3 prism inserts provided the greatest resistance to penetration. In this case the projectiles were arrested within a sphere diameter of the sample front surface. Several of these hybrid systems offer promise as multifunctional, ballistic resistant, load-bearing structures.
TL;DR: In this paper, the tensile properties of kenaf bast fibers bundle (KBFB) and KBFB-reinforced epoxy strands were evaluated statistically using large sample sets and the elastic modulus, tensile strength, as well as failure strains of KBFBs displayed large scatter statistically ranging from 10% to 30%.
Abstract: This paper presents extensive experiments and micromechanics-based modeling to evaluate systematically the tensile properties of kenaf bast fibers bundle (KBFB) and kenaf bast fiber-reinforced epoxy strands. Uniaxial tension behaviors of KBFBs and KBFB-reinforced epoxy strands were evaluated statistically using large sample sets. The elastic modulus, tensile strength, as well as failure strains of KBFBs, displayed large scatter statistically ranging from 10% to 30%. The loading rate-dependency was evaluated at three strain rates ranging from approximately 10−4 ∼ 10−2/s. The tensile strength increases gradually as the loading rate increases, while the tensile modulus almost remains the same as the loading rate increases until the loading rate reaches 10−2/s, at which a much higher modulus was presented. The high temperatures (170–180 °C), possibly subjected during fiber processing and composite fabrication, do not impose significant effects on the tensile properties of KBFBs if the duration is less than 1-h. The tensile properties of KBFB were not affected by the conditioning at 130 °C for 24-h, which mimics the severe service temperature of automotive front-end components. KBFB-epoxy composite strands were further evaluated at various loading rates. A micromechanics-based Mori–Tanaka model was implemented to predict the anisotropic elastic moduli of KBFB and KBFB-epoxy composite strands based on the microstructural compositions.
TL;DR: In this article, a micromechanical model was proposed to predict the dynamic modulus of hot-mix asphalt mixtures, where the mastic-coated aggregate particles were embedded into the equivalent medium of HMA mixtures.
Abstract: Hot-mix asphalt (HMA) mixtures are widely used in the surface layer of flexible pavements. HMA mixtures are a kind of polymer matrix composite composed of polymeric asphalt mastic with the inclusion of particulate-filled media and air voids. Nowadays, more and more petroleum-based polymers (epoxy, resin) have been widely used in the HMA mixtures, in which the polymer matrix accounts for around 10–20% by volume. The properties of polymer matrix play a key role in the performance of flexible pavements. Dynamic modulus (∣E∗∣) of HMA mixtures is one of the fundamental engineering properties measured by the simple performance tester (SPT) and has been incorporated as a basic input in the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical Design Guide for flexible pavements. Although direct laboratory testing and empirical equations (such as the Witczak model and the Hirsch model) provide two ways to obtain the values of dynamic modulus of HMA mixtures, a predictive model based on the microstructure of HMA mixtures is more desirable. This paper presents a micromechanical model to predict the dynamic modulus of HMA mixtures. In this model, HMA mixtures are treated as a composite by embedding the mastic-coated aggregate particles into the equivalent medium of HMA mixtures. Based on the proposed model, closed-form equations were derived to predict the dynamic modulus value of HMA mixtures. The equations were able to take into account aggregate gradation and air void size distribution. In addition, laboratory experiments were conducted to verify the developed model. The dynamic modulus values of mastics and HMA mixtures were obtained through direct laboratory testing. The dynamic modulus of mastic was then used to predict the dynamic modulus of laboratory-prepared HMA mixtures with the newly developed model. It was found that the predicted dynamic moduli agreed reasonably well with the measured ones at high frequencies. The reasons for the discrepancy between measured and predicted dynamic moduli and the factors affecting the dynamic modulus were also explored in the paper.