Showing papers in "Composites Part B-engineering in 2007"

Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures

Abstract: Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is one of the latest and most promising strengthening techniques for reinforced concrete (RC) structures. Research on this topic started only a few years ago but has by now attracted worldwide attention. Issues raised by the use of NSM FRP reinforcement include the optimization of construction details, models for the bond behaviour between NSM FRP and concrete, reliable design methods for flexural and shear strengthening, and the maximization of the advantages of this technique. This paper provides a critical review of existing research in this area, identifies gaps of knowledge, and outlines directions for further research.

A critical review on polymer-based bio-engineered materials for scaffold development

Abstract: Since the last decade, tissue engineering has shown a sensational promise in providing more viable alternatives to surgical procedures for harvested tissues, implants and prostheses. Due to the fast development on biomaterial technologies, it is now possible for doctors to use patients’ cells to repair orthopedic defects such as focal articular cartilage lesions. In order to support the three-dimensional tissue formation, scaffolds made by biocompatible and bioresorbable polymers and composite materials, for providing temporary support of damaged body and cell structures have been developed recently. Although ceramic and metallic materials have been widely accepted for the development of implants, its non-resorbability and necessity of second surgical operation, which induces extra for the patients, limit their wide applications. This review article aims at introducing (i) concept of cartilage tissue engineering, (ii) common types of bio-engineered materials and (iii) future development of biomaterial scaffolds.

Stress-strain model for concrete confined by FRP composites

Abstract: In this paper, a stress–strain model for concrete confined by fiber reinforced polymer (FRP) composites is developed. The model is based on the results of a comprehensive experimental program including large-scale circular, square and rectangular short columns confined by carbon/epoxy and E-glass/epoxy jackets providing a wide range of confinement ratios. Ultimate stress, rupture strain, jacket parameters, and cross-sectional geometry were found to be significant factors affecting the stress–strain behavior of FRP-confined concrete. Such parameters were analyzed statistically based on the experimental data, and equations to theoretically predict these parameters are presented. Experimental results from this study were compared to the proposed semi-empirical model as well as others from the literature.

Blast resistance of FRP composites and polymer strengthened concrete and masonry structures - A state-of-the-art review

Abstract: Recent world events such as bombings in London, Madrid and Istanbul have highlighted the susceptibility of many civilian structures to terrorist attack. Explosives directed towards vulnerable structures may cause considerable damage and loss of life. As a result, there is now a desire to increase the blast resistance of many types of existing structures. This has led to experimental and finite element (FE) research in retrofitting concrete and masonry structures with fibre reinforced polymer (FRP) composites for blast protection. This paper presents a review of the publicly available literature and highlights areas where research is lacking.

Spider and mulberry silkworm silks as compatible biomaterials

Abstract: Silks are a diverse family of natural materials with extraordinary mechanical properties such as high tensile strength and extensibility, as well as reported biological compatibility. In recent years, the reported exceptional nature of silk lead to increased interest in silk for biomedical applications. The aim of this review is to assess the potential and compatibility of silk fibres and silk-based materials for biomedical purposes. It will do so by reviewing silk properties, structure and formation, with special focus on spider and mulberry silkworm silk fibres, as well as the application of silk in the biomedical field. The review will begin by introducing the general characteristics of silk, and a consideration of properties of particular relevance to the use of silk in biomedical applications: degradation and tensile properties. Subsequently, the formation of silk in vivo will be outlined, as well as the current understanding of silk structure. A comparison of the structural differences between spider and silkworm silks will follow. Some of the different types of silk produced by orb weaving spiders, their main functions and structural features will be described. This will be followed by an introduction to ‘supercontraction’, a phenomenon that has only been observed in spider silks, and is considered to be one of the major obstacles to the use of native spider silk for medical applications. Finally, there will be an account of previous biomedical applications of silk. It is the intention of this review to point out the wide range of excellent and valuable properties observed in different silk types, and to propose that silk’s versatility is possibly its strongest advantage. However, in the context of biomedical research and development, there are still major limitations and difficulties with native silk fibres. It is suggested in this review that an artificially produced silk or silk-like material formed to possess specific desired properties will allow the overcoming of present limitations.

Dynamic mechanical analysis of carbon/epoxy composites for structural pipeline repair

Abstract: The viscoelastic behavior of a carbon fiber/epoxy matrix composite material system used for pipeline repair has been evaluated though dynamic mechanical analysis. The effects of the heating rate, frequency, and measurement method on the glass transition temperature ( T g ) were studied. The increase in T g with frequency was related to the activation energy of the glass transition relaxation. The activation energy can be used for prediction of long term performance. The measured tan delta peak T g ’s of room temperature cured and post-cured composite specimens ranged from 60 to 129 °C. Analysis of T g data at various cure states was used to determine use temperature limits for the composite repair system.

The effect of silane treated-and untreated-talc on the mechanical and physico-mechanical properties of poly(lactic acid)/newspaper fibers/talc hybrid composites

Abstract: This paper evaluates the effect of the addition of silane treated- and untreated- talc as the fillers on the mechanical and physico-mechanical properties of poly(lactic acid) (PLA)/recycled newspaper cellulose fibers (RNCF)/talc hybrid composites. For this purpose, 10 wt% of a talc with and without silane treatment were incorporated into PLA/RNCF (60 wt%/30 wt%) composites that were processed by a micro-compounding and molding system. PLA is utilized is a bio-based polymer that made from dextrose, a derivative of corn. Talc is also a natural product. The RNCF and talc hybrid reinforcements of PLA polymer matrix were targeted to design and engineer bio-based composites of balanced properties with added advantages of cost benefits besides the eco-friendliness of all the components in the composites. In this work, the flexural and impact properties of PLA/RNCF composites improved significantly with the addition of 10 wt% talc. The flexural and impact strength of these hybrid composites were found to be significantly higher than that made from either PLA/RNCF. The hybrid composites showed improved properties such as flexural strength of 132 MPa and flexural modulus of 15.3 GPa, while the unhybridized PLA/RNCF based composites exhibited flexural strength and modulus values of 77 MPa and 6.7 GPa, respectively. The DMA storage modulus and the loss modulus of the PLA/RNCF hybrid composites were found to increase, whereas the mechanical loss factor (tan delta) was found to decrease. The storage modulus increased with the addition of talc, because the talc generated a stiffer interface in the polymer matrix. Differential scanning calorimetry (DSC) thermograms of neat PLA and of the hybrid composites showed nearly the similar glass transition temperatures and melting temperatures. Scanning electron microscopy (SEM) micrographs of the fracture surface of Notched Izod impact specimen of 10 wt% talc filled PLA/RNCF composite showed well filler particle dispersion in the matrix and no large aggregates are present. The comparison data of mechanical properties among samples filled with silane-treated- and untreated- talc fillers showed that the hybrid composites filled with silane treated talc displayed the better mechanical prosperities relative to the other hybrid composites. Talc-filled RNCF-reinforced polypropylene (PP) hybrid composites were also made in the same way that of PLA hybrid composites for a comparison. The PLA hybrid bio-based composites showed much improvement in mechanical properties as compared to PP-based hybrid counterparts. This suggests that these PLA hybrid bio-based composites have a potential to replace glass fibers in many applications that do not require very high load bearing capabilities and these recycled newspaper cellulose fibers could be a good candidate reinforcement fiber of high performance hybrid biocomposites.

Influence of edge sharpness on the strength of square concrete columns confined with FRP composite laminates

Abstract: This paper presents the experimental and analytical results of the study carried out to investigate the influence of the radius of the cross-sectional corners (edges) on the strength of small scale square concrete column specimens confined with FRP composite laminates. The experimental part of the study was achieved by testing 20 specimens under uniaxial compression. Depending on the selected radius of the edges, the section varied from square to circular. Intermediate radii were about 1/6, 1/4, and 1/3 of the side dimension. The sharpest square specimens had a corner radius of 5 mm to make composite application easier and to avoid a premature rupture of the composite. The results show that smoothening the edges of square cross-section plays a significant role in delaying the rupture of the FRP composite at these edges, and the efficiency of FRP confinement is directly related to the radius of the cross-section edges. A modified analytical model is presented to predict the strength of FRP-confined square as well as circular sections. The predicted results are found to be in excellent agreement with the measured ones.

Influence of processing methods and fiber length on physical properties of kenaf fiber reinforced soy based biocomposites

Abstract: Biocomposites from kenaf fiber and soy based bioplastic were fabricated by extrusion, followed by injection or compression molding. The impact of fiber length and the processing method on the thermal and mechanical properties of the composites were characterized with dynamic mechanical analysis (DMA) and mechanical properties measurements. The morphology was studied with optical and electron microscopy. Compression molded specimens have a similar modulus to injection molded specimens at room temperature, but exhibit a higher heat deflection temperature (HDT) and notched Izod impact strength. The improved HDT and impact strength are derived from an increase in modulus at high temperature and fiber bridging effects, respectively. The modulus, impact strength and HDT of kenaf fiber reinforced soy based biocomposites increase with increases in fiber length, fiber content and fiber orientation. Through microscopy observations, it was found that the fractured fiber length on the impact fracture surface increased with increasing fiber length and fiber content. This indicates that the role of fiber bridging effects is predominant on impact strength of the biocomposites.

Dynamical-mechanical and thermal analysis of polymeric composites reinforced with keratin biofibers from chicken feathers

Abstract: Keratin fibers from chicken feathers were used as short-fiber reinforcement for a poly(methyl methacrylate) matrix. The composites were evaluated via thermal and dynamical–mechanical analysis. The thermal stability and transition temperature were found to be higher than standard PMMA. The storage modulus at room temperature increased with 1% and 2% weight of keratin biofibers and, at high temperature, the reinforcement provides higher stability, as reflected in the modulus behavior. Keratin fibers within the rigid polymer reduces tan δ peak, indication of a strong interface, as optical images confirm.

In-plane shear performance of masonry panels strengthened with FRP

Abstract: The opportunities provided by the use of Fiber Reinforced Polymers (FRPs) composites for the shear strengthening of tuff masonry structures were assessed on full-scale panels subjected to in-plane shear-compression tests at the ENEL HYDRO S.p.A. laboratory, ITALY. Tuff masonry specimens have been arranged in order to simulate both mechanical and textural properties typical of buildings located in South-Central Italian historical centres. In this paper, the outcomes of the experimental tests are presented. The monotonic shear-compression tests were performed under displacement control and experimental data have provided information about in-plane behaviour of as-built and FRP strengthened tuff masonry walls. Failure modes, shear strength, displacement capacity and post-peak performance are discussed.

Blast loading response of reinforced concrete panels reinforced with externally bonded GFRP laminates

Abstract: The behavior of reinforced concrete panels, or slabs, retrofitted with glass fiber reinforced polymer (GFRP) composite, and subjected to blast load is investigated. Eight 1000 × 1000 × 70 mm panels were made of 40 MPa concrete and reinforced with top and bottom steel meshes. Five of the panels were used as control while the remaining four were retrofitted with adhesively bonded 500 mm wide GFRP laminate strips on both faces, one in each direction parallel to the panel edges. The panels were subjected to blast loads generated by the detonation of either 22.4 kg or 33.4 kg ANFO explosive charge located at a 3-m standoff. Blast wave characteristics, including incident and reflected pressures and impulses, as well as panel central deflection and strain in steel and on concrete/FRP surfaces were measured. The post-blast damage and mode of failure of each panel was observed, and those panels that were not completely damaged by the blast were subsequently statically tested to find their residual strength. It was determined that overall the GFRP retrofitted panels performed better than the companion control panels while one retrofitted panel experienced severe damage and could not be tested statically after the blast. The latter finding is consistent with previous reports which have shown that at relatively close range the blast pressure due to nominally similar charges and standoff distance can vary significantly, thus producing different levels of damage.

Dynamic mechanical and thermal analysis of aligned vapor grown carbon nanofiber reinforced polyethylene

Abstract: Dynamic mechanical and thermal analysis of aligned vapor grown carbon-nanofibers (VGCNFs)-reinforced high-density polyethylene (HDPE) was performed. High-shear mixing was used to disperse and distribute the nanofibers. Extensional flow was used to obtain anisotropic nanoreinforced composite tapes. Dynamic mechanical analysis showed dual increase of storage modulus and loss modulus with different draw ratios. The modulus and complex viscosities of the drawn samples converged to that of pure PE at high temperatures, indicating that in the melt, the behavior is dominated by the semicrystalline matrix. Additionally, an increase in thermal stability was observed for the composites compared to PE matrix. Differential scanning calorimetry analysis showed that the inclusion of nanofibers hindered the structure evolution of PE upon drawing.

Experimental and nonlinear finite element studies of RC beams strengthened with FRP plates

Abstract: This paper presents a joint experimental–analytical investigation aimed at studying the brittle failure modes of RC members strengthened in flexure by FRP plates. Both midspan and plate end failure modes are studied. The finite element analyses are based on nonlinear fracture mechanics. The model considered the actual crack pattern observed in the tests by using a smeared and an interface crack model. This paper shows how concrete cracking, adhesive behavior, plate length, width and stiffness affect the failure mechanisms. The numerical and experimental results show that debonding and concrete cover splitting failure modes occur always by crack propagation inside the concrete.

Behavior of normal and high-strength concrete cylinders confined with E-glass/epoxy composite laminates

Abstract: This paper is aimed at studying the behavior of concrete cylinders with varying compressive strength wrapped with E-glass/epoxy fiber reinforced polymer (GFRP) jackets and subjected to uniaxial compressive loads. A comprehensive experimental program which involves 54 plain concrete cylinders was conducted in this study. The cylinders evaluated in this study, were divided into six groups, and each group contain a control cylinder without confinement to quantify the amount of gain obtained using the GFRP laminates. Experimental results indicated that the use of GFRP jackets substantially increases both the compressive strength and ductility of unreinforced concrete cylinders. In this paper, the influences of two parameters influencing the behavior of the GFRP confined cylinder is investigated. These parameters are: the number of composite plies (i.e. composite thickness) and concrete compressive strength. The results of this study showed that: (i) compressive strength and ductility of the concrete cylinders increases with number of composite layers; and (ii) effect of confinement is substantial for normal strength concrete and marginal for high-strength concrete. A semi-empirical theoretical model is also presented in order to predict stress–strain relationship of GFRP confined concrete cylinders. The model results showed an excellent agreement with experimental values.

Design factors, reliability, and durability prediction of wet layup carbon/epoxy used in external strengthening

Abstract: Although fiber reinforced polymer composites are increasingly used through the wet layup process for the rehabilitation of deteriorating and understrength concrete structures, there is very little validated information regarding performance over extended time periods. This has resulted in the use of excessively conservative factors in design in some cases, and unconservative estimates, or complete disregard of degradation effects on some characteristics, in others. In this paper two commonly used predictive approaches are used to provide estimates of long-term deterioration for a range of material characteristics which are compared to experimental data obtained over a 3 years period of exposure. It is shown that although predicted durability of tensile characteristics is extremely good for thin sections used conventionally, the rates of deterioration increase significantly with increase in the number of reinforcing layers used. In addition there is deterioration of other characteristics, especially related to interlaminar and intralaminar properties, that need to be considered. It is noted that both methods are unable to accurately account for effects of initial post-cure seen in ambient cured carbon/epoxy systems, although the conventional Arrhenius predictions provide good correlation with experiments once this mechanism has ceased. A methodology that is capable of accounting for temperature variation during exposure is also outlined. The predictions are compared with safety factors prescribed by ACI-440 and TR-55 and some inherent disadvantages of such approaches is highlighted. The basis for the estimation of safety factors based on a reliability approach using Weibull parameters is presented and typical results are shown, emphasizing some weaknesses in current design methodologies in the area of FRP rehabilitation of concrete.

Out-of-plane flexural behavior of unreinforced red brick walls strengthened with FRP composites

Abstract: This paper presents the results of a study focused on evaluating the out-of-plane flexural behavior of two fiber reinforced polymer (FRP) composite systems for strengthening unreinforced red brick masonry walls. The full-scale tests followed the International Code Council Evaluation Service (ICC-ES) AC 125 procedure. In the experimental program, a total of four full-scale destructive tests were conducted on UMR red brick walls. One wall specimen was used as control (as-built) specimen without composites, and the remaining three wall specimens were strengthened with either E-glass/epoxy or carbon/epoxy composite systems with different fiber architecture. The effect of applying a cross-ply laminate on the ultimate failure mode has been investigated. Full-scale experimental results confirmed the effectiveness of the FRP composite strengthening systems in upgrading the out-of-plane flexural structural performance of URM walls. In addition, an analytical model was developed to predict the ultimate load capacity of the retrofitted walls. The analytical modeling is based on deformation compatibility and force equilibrium using simple section analysis procedure. A good agreement between the experimental and theoretical results was obtained.

The effect of non-symmetric distribution of fiber orientation and aspect ratio on elastic properties of composites

Abstract: A composite’s microstructure significantly influences its overall properties. Orientation and aspect ratio of the fiber are two key parameters that describe the microstructures of a composite with straight short fibers. This paper discusses the effects of fiber orientation and aspect ratio distribution on the overall elastic properties of composites using the Mori–Tanaka’s method in this paper. The results show that using an average aspect ratio of the fibers to estimate overall elastic properties is not appropriate under some conditions. When the aspect ratio of the fibers does not follow a symmetric distribution, the overall elastic properties obtained by the average aspect ratio of the fibers may differ by more than 30% from those obtained by the method considering the aspect ratio distribution. This paper presents a model used to predict the properties of nanotube-reinforced composites. The results obtained by the model were compared with experimental results.

Improving the blast resistance capacity of RC slabs with innovative composite materials

Abstract: This paper examines the feasibility of using innovative composite materials to improve the blast resistance capacity of one-way reinforced concrete slabs. In order to achieve this objective, five slabs were tested under real blast loads. One of the slabs was used as the control unit to establish a baseline for comparison of the other four slabs. These four slabs were strengthened with carbon fiber and steel fiber reinforced polymers, comprising of two slabs retrofitted on a single side and two slabs retrofitted on both sides. Test results indicate that there was no significant increase in blast resistance when the slabs were retrofitted on a single side; however, slabs retrofitted on both sides displayed a significant increase in blast resistance. This result can be attributed to the negative moments that develop under the dynamics of blast loads. Another objective of this research program was to study the feasibility of using a modified displacement based methodology to predict the explosive charges weight and standoff distances required to impose a given damage level. Test results showed that for the most part the blast loads were effectively estimated using this method and the damage levels observed from the field tests correlated well with the predicted levels. This paper discusses the analytical steps used to predict the charges weight and standoff distances along with the relevant experimental results.

Application of FRP composites for underwater piles repair

Abstract: The lightweight, high strength and corrosion resistance of fiber reinforced polymers (FRP) make them ideally suited for quick and effective structural repairs. As a result, they have been favoured for conducting emergency bridge repairs where speed is of essence. The availability of resins that can cure under water has made it possible to similarly extend its application to substructure elements such as partially submerged damaged piles. Such repairs can be carried out using the same strategies that were successfully used in recent demonstration projects in which FRP was used to repair and rehabilitate corrosion-damaged piles. In the projects two disparate FRP systems – a pre-preg and a wet layup – were used and both carbon and glass evaluated. Access to the piles in the deep waters was provided by a custom-designed, lightweight modular scaffolding system that was assembled around the piles. An overview of the project is provided with particular emphasis on changes that would allow its adoption for emergency repairs. � 2006 Elsevier Ltd. All rights reserved.

Inherent sensing and interfacial evaluation of carbon nanofiber and nanotube/epoxy composites using electrical resistance measurement and micromechanical technique

Abstract: Inherent sensing of load, micro-damage and stress transferring effects were evaluated for carbon nanotube (CNT) and carbon nanofiber (CNF)/epoxy composites (with various added contents) by an electro-micromechanical technique, using the four-point probe method. Carbon black (CB)/epoxy composites, with conventional nanosize material added, were used for the comparison with CNT and CNF composites. Subsequent fracture of the carbon fiber in the dual matrix composites (DMC) was detected by acoustic emission (AE) and by the change in electrical resistance, ΔR due to electrical contacts of neighboring CNMs. Stress/strain sensing of the nanocomposites was detected by an electro-pullout test under uniform cyclic loading/subsequent unloading. CNT/epoxy composites showed the best sensitivity to fiber fracture, matrix deformation and stress/strain sensing, whereas CB/epoxy composite exhibited poorer sensitivity. From the apparent modulus (as a result of matrix modulus and interfacial adhesion), the stress transferring effects reinforced by CNT was highest among three CNMs. The thermodynamic work of adhesion, Wa as found by dynamic contact angle measurements of the CNT/epoxy composite as a function of added CNT content was correlated and found to be consistent with the apparent mechanical modulus. Uniform dispersion and interfacial adhesion appear to be key factors for improving both sensing and mechanical performance of nanocomposite. Thermally treated-CNF composites exhibited a slightly higher apparent modulus, whereas higher testing temperatures appeared to lower the apparent modulus.

Shear enhancement of reinforced concrete beams strengthened with FRP composite laminates

Abstract: This paper presents the results of an experimental investigation on shear strength enhancement of reinforced concrete beams externally reinforced with fiber-reinforced polymer (FRP) composites. A total of nine full-scale beam specimens of three different classes, as-built (unstrengthened), repaired and retrofitted were tested in the experimental evaluation program. Three composite systems namely carbon/epoxy wet layup, E-glass/epoxy wet layup and carbon/epoxy precured strips were used for retrofit and repair evaluation. Experimental results indicated that the composite systems provided substantial increase in ultimate strength of repaired and strengthened beams as compared to the pre-cracked and as-built beam specimens. A comparative study of the experimental results with published analytical models, including the ACI 440 model, was also conducted in order to evaluate the different analytical models and identify the influencing factors on the shear behavior of FRP strengthened reinforced concrete beams. Comparison indicated that the shear span-to-depth ratio (a/d) is an important factor that actively controls the shear failure mode of beam and consequently influences on the shear strength enhancement.

40-Year-old full-scale concrete bridge girder strengthened with prestressed CFRP plates anchored using gradient method

Abstract: A 17 m long internally prestressed concrete girder taken from a bridge in southern Switzerland was strengthened flexurally using prestressed CFRP plates and then tested to failure The prestressing level in the plates was 32% of their nominal tensile strength The load carrying behaviour of this test girder was compared to a reference girder and a girder strengthened using non-prestressed plates For the anchorage of the prestressed CFRP plates, a method developed at Empa was used In this method, the force in the CFRP plate is reduced to zero at the plate ends and permanent anchorage system is not required The experiments proved the feasibility of anchoring CFRP plates using the gradient method Repeated loading showed stable tensile strains in the plates and shear stresses between the plates and concrete Furthermore, prestressing resulted in decreased deflections and strains and a 45% increase in maximum recorded load

Optimal design of composite wing structures with blended laminates

Abstract: In this paper we formulate the problem of wing box design optimization using composite laminates with blending constraints. The use of composite laminates necessitates the inclusion of fiber orientation angle of the layers as well as total thickness of the laminate as design variables in the design optimization problem. The wing box design problem is decomposed into several independent local panel design problems. In general such an approach results in a nonblended solution with no continuity of laminate lay ups across the panels, which may not only increase the lay up cost but may also be structurally unsafe due to discontinuities. The need for a blended solution increases the complexity of the problem many fold. In this paper we impose the blending constraints globally by using a guide based design methodology within the genetic algorithm optimization scheme and compare the results with the published ones. Two different blending schemes – outer and inner blending are presented. The result shows that the optimum design obtained using the current methodology has better continuity of laminate lay ups and also the reported weight of the composite wing box is on the lower side. Finally, a parametric study of the effect of global deflection constraint on the total weight of the optimum design is presented.

Characterization of carbon nanotube/nanofiber-reinforced polymer composites using an instrumented indentation technique

Abstract: An instrumented indentation technique was tested on three types of carbon nanotube/nanofiber-reinforced composites to investigate its applicability for measuring mechanical properties (elastic modulus and hardness). There was good agreement in the measured elastic modulus between the instrumented indentation and uniaxial tension tests for the case of a nanocomposite with a harder epoxy matrix material. In contrast, there was a considerable difference in elastic modulus between the two tests for the case of a nanocomposite with a softer polystyrene matrix material. A modified area function was then developed for the nanocomposite with the softer polystyrene matrix material, and this eliminated the difference in elastic modulus between the two test techniques. Thus, the instrumented indentation technique can be used for evaluating the mechanical properties of polymer matrix nanocomposites with an added advantage that a small sample size can be used. The instrumented indentation test was also utilized in the case of a patterned nanotube array-reinforced epoxy matrix composite. This clearly showed the modulus of the array nanocomposite improved considerably compared to that of the neat epoxy resin.

Nonlinear thermal bending response of FGM plates due to heat conduction

Abstract: Nonlinear thermal bending analysis is presented for a simply supported, shear deformable functionally graded plate without or with piezoelectric actuators subjected to the combined action of thermal and electrical loads Heat conduction and temperature-dependent material properties are both taken into account The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction and the electric field considered only has non-zero-valued component E Z The material properties of functionally graded materials (FGMs) 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 and piezoelectric layers are assumed to be temperature-dependent The governing equations of an FGM plate are based on a higher order shear deformation plate theory that includes thermo-piezoelectric effects A two step perturbation technique is employed to determine the thermal load–deflection and thermal load–bending moment curves The numerical illustrations concern nonlinear bending response of FGM plates without or with surface bonded piezoelectric actuators due to heat conduction and under different sets of electric loading conditions The results reveal that for the case of heat conduction the nonlinear thermal bending responses are quite different to those of FGM plates subjected to transverse mechanical loads, and the temperature-dependency of FGMs could not be neglected in the thermal bending analysis

Discrete models of woven structures. Macroscopic approach

Abstract: A discrete model of a woven fabric structure has been established, whereby nodes endowed with a mass and a rotational rigidity are connected by extensible bars to form a two-dimensional truss. The set of four bars that delineate a quadrilateral element—the unit cell of the micromechanical analysis—is further endowed with a torsion deformation mode. The equilibrium shape of the structure is obtained as the minimum of its total potential energy versus the set of kinematic translational and rotational variables, accounting for eventual kinematic constraints due to contact with a rigid surface. A linearized stability analysis is performed, and the potentiality of the model is illustrated by fabric draping simulations.

High strength and bioactive hydroxyapatite nano-particles reinforced ultrahigh molecular weight polyethylene

Abstract: Nano-sized hydroxyapatite (HA) particles reinforced UHMWPE composite was developed for biomedical applications. The biocomposite with HA volume fraction of 0.5 was successfully processed by combined swelling/twin-screw extrusion, compression molding, and then hot drawing. SEM and EDAX characterization revealed that HA nano-particles were homogeneously dispersed in UHMWPE. WAXD showed that hot drawing effectively oriented the UHMWPE chains along the drawing direction. The composite exhibited tensile strength of 100 ± 22 MPa after hot drawing, which was comparable to that of cortical bone. The composite also exhibited great ability of inducing calcium phosphate precipitates on its surface in simulated body fluid, which was widely accepted as an indication of bioactivity.

Investigation into nanocellulosics versus acacia reinforced acrylic films

Abstract: Three closely related cellulosic acrylic latex films were prepared employing acacia pulp fibers, cellulose whiskers and nanocellulose balls and their respective strength properties were determined. Cellulose whisker reinforced composites had enhanced strength properties compared to the acacia pulp and nanoball composites. AFM analysis indicated that the cellulose whisker reinforced composite exhibited decreased surface roughness.

Response of fiber reinforced composites to underwater explosive loads

Abstract: An in-house developed, verified and fully validated three-dimensional finite element code, with rate dependent damage evolution equations for anisotropic bodies, is used to numerically ascertain the damage developed in a fiber-reinforced composite due to shock loads representative of those produced by an underwater explosion. Three internal variables characterize damage due to fiber/matrix debonding, fiber breakage, and matrix cracking. The delamination and relative sliding of adjoining layers has been simulated by the nodal release technique. The interaction among the four failure modes, and the possibility of their initiating concurrently at one or more points in the composite is considered. The effect of different parameters on the damage development and propagation, and energy absorbed in each one of the four failure modes has been examined. These results give preliminary information on composite structure’s design for maximizing the energy absorption and hence increasing structure’s resistance to blast loads. The paper is a sequel to Hassan and Batra’s paper [Composites B, 2007] wherein details of the damage model, verification of the code, and the validation of the mathematical model are given.