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WOS: 000464636400034, Including fibers in concretes improves their mechanical properties such as flexural strength, impact load resistance and limited crack propagation. The dispersion, orientation and types of the fibers placed in the concretes affect these mechanical properties. The aim of the study is to propose a standard and a novel prediction method for determining the dispersion and orientation of the concretes in which fibers are reinforced in microwave frequency range. This study demonstrates that determination of both orientation and dispersion of the fibers regardless of the fiber types in concretes is possible by extracting electromagnetic properties of the structures in microwave regime as a nondestructive method. The measurement technique requires sample under test (SUT) and two wideband linearly polarized antennas placed in the front and backside of material under the free space condition. Although there are some studies investigated the fiber content of concrete samples through certain electromagnetic techniques, the proposed novel approach concentrates on the electromagnetic behavior of the fiber reinforced concretes in a very wideband range from 3 GHz to 17 GHz. Unlike the other studies, open space measurement with the help of a vector network analyzer which is capable of measuring up to 43 GHz along with two high gain horn antennas was carried out in the laboratory environment. Time required for exact measurement of dielectric constant and loss factor of the concrete between antennas is less than a minute. A simple and confidential model is carried out to determine both orientation and dispersion of fibers in concrete by observing the changes of dielectric constant and loss factor. The determination of electromagnetic properties of concretes with fibers has potential applications for future nondestructive sensors. In addition, observation of negative dielectric constant and some other electrical properties such as low loss factor and impedance match with free space presented in the study for particular frequency intervals gives a chance for future radome applications in harsh environmental conditions. (C) 2019 Elsevier Ltd. All rights reserved.

A reinforcement of the interface between the fiber and polymer matrix using reactive polymer colloids were investigated by the acoustic emission (AE) method. The correspondence between the fracture mechanisms, fracture types and AE signals parameters during tensile loading of composites using the discrete wavelet transform (DWT) and the energy criterion for identification of fracture type based on the continuous wavelet transform (CWT) of AE signals were established. The investigated composites were ranked by the estimation of the initial and final fracture stress, AE activity, energy parameter of AE signals, and distribution of the different fracture types.

Objective of the present study is the definition and implementation of a constitutive creep model for fiber reinforced thermoplastics. Both, unidirectionally as well as discontinuously long fiber reinforced materials are considered. Assuming that creep deformation is restricted to the thermoplastic matrix, a three term Kelvin–Voigt formulation is employed as a base material model. For continuously unidirectionally fiber reinforced materials, the thermoplastic matrix is superimposed with a standard linear elastic model. For discontinuously long fiber reinforced thermoplastics, an anisotropic generalization of the original, isotropic Kelvin-Voigt model is proposed. Both models are implemented into a finite element program and validated against an experimental data base consisting of tensile creep experiments on neat matrix material, unidirectionally fiber reinforced material as well as discontinuously long fiber reinforced material with different fiber volume fractions. Different fiber orientations as well as different temperatures are considered. As a structural example for further validation, creep experiments on loading points for hybrid thermoplastic sandwich structures are performed and simulated numerically. In all cases, the experimental results and the numerical prediction are found in a good agreement.

In this study, epoxy-based composite materials reinforced with unidirectional glass fiber (GFRP) fabric were manufactured by adding nanosized multi-walled carbon nanotube (MWCNT) and nanoclay to epoxy resin during production process. The effects of those additives on fatigue strength of the composite materials were investigated experimentally. In this context, both nanoparticles by adding 0.5 wt% of epoxy resin were mixed with ultrasonic homogenization mixer. To examine the contribution of nanoparticles, composite plates were produced as MWCNT and nanoclay filled and unfilled. Mechanical properties and fatigue behavior (S-N diagram) were obtained and the results were compared with each other. From the results obtained, fatigue and tensile strength of composite specimens with MWCNT filled were found higher than unfilled specimens. © 2018 Polish Academy of Sciences Institute of Physics. All rights reserved.

In recent years, there has been a great deal of interest in lightweight vehicle design due to regulations about reducing fuel consumption and emissions. Lightweight design of vehicle components is one of the most important research topics in vehicle design. Developing the optimum structure in the early stages of design process is very important for minimizing the vehicle weight and production costs. In this paper, an automobile hinge component has been developed using PA66 GF60 glass fiber-reinforced polyamide composite materials instead of conventional steel. The automobile hinge component has been conceived using computer aided design software. Topology optimization was made under specific loadings subject to the constraints of finite element method analysis. As a result of this study, optimum dimensions of the component have been obtained and the weight of the component has been reduced via structural topology optimization techniques while satisfying displacement and stress conditions. The results show that composite materials are an important alterative in lightweight vehicle design.

Pultruded FRP (fibre reinforced polymer) materials have attracted the attention of civil engineers with their high strength weight ratio and environmentally friendly production and use. Mechanical analysis of pultruded FRP profiles is complex since the material is anisotropic and becomes more complex when thin FRP dedicated hollow cross sections are involved. This is particularly relevant with square or rectangular construction forms where the corners of the material are suspected to produce weak points under compressive loading. FRPs are also believed to behave contrarily when subjected to heat and thermal duress. This research investigates problems in predicting their behaviour under compression (hollow square pultruded FRP sample) using different analytical and modelling approaches. The mechanical behaviour of the material is investigated under different thermal conditions through finite element simulation and the results are then compared with previously conducted laboratory research analysis. The large deformation in anisotropic materials is simulated to provide better prediction regarding the failure mechanism of this material. Finite element simulation is then used to estimate the performance of similar and often competitive construction materials to GFRP (i.e.: wood, concrete and steel) under similar thermal and compressive duress.

Despite cheap and sustainable in nature, the use of natural fiber composites is limited due to their high moisture absorption, poor fiber-matrix interface, and lack of data on evolution of properties when subjected to environmental factor such as temperature and humidity. The aim of this research is to study the interdependence of moisture regain, hydrophobic treatment, and the mechanical properties of jute fiber-reinforced composite materials. Composite samples made from treated and untreated jute fiber-reinforced composites were exposed to humid environment and their moisture regain, mechanical properties and fiber-matrix interface was tested at given time intervals until four weeks. The composites produced with hydrophobic treated reinforcement showed lesser moisture regain and improvement in the tensile and flexural strengths compared to untreated fabric composite. A clear improvement in fiber-resin interface was observed by scanning electronic microscopy. The dynamic mechanical analysis of treated and untreated composites was conducted in a temperature range 20-140 degrees C. An increase in the storage modulus of treated composite materials was noted as compared to untreated ones. Furthermore, it was concluded that developed composite loss their mechanical properties linearly with immersion time. However, this aging was slow in treated fabric composites especially hybrid fluorocarbon and fluorocarbon. Higher Education Commission of Pakistan - NRPU 4239

The application of additive manufacturing technologies to the construction industry has a wide range of advantages from the economic, social and design flexibility point of view. However, most of up to date research studies have been performed using ordinary Portland cement (OPC)-based mortars and concretes. Therefore, the objective of this article is to explore the development of an eco-friendly earth composite reinforced with natural sisal fibers and chemically stabilized with a hydraulic binder. Analysis of the workability by shear vane tests was performed on fresh earth samples to find the optimum water content in sisal fiber-reinforced earth stabilized with OPC. Afterward, the effect of the addition of OPC on the hardening process was evaluated through shear vane and Vicat needle tests from 0 to 180 min after mixing. The results indicate that water content, fiber addition and OPC replacement have a strong influence on the shear yield strength. Furthermore, the presence of chemical stabilizers as OPC accelerates the hardening process allowing a faster layer-by-layer deposition. This low cost and eco-friendly preliminary earth-based composite can be used for 3D printing applications in the construction industry.

Presently, fiber reinforced materials are used for many industrial applications. Laser transmission welding (LTW) is a suitable method to join these materials. For multiple thermoplastics, the weld seam quality is affected by the amount of moisture content in the joining members. For LTW, heat is applied to the welding members and water in the composite changes phase from liquid to gas. Increasing the gas content can lead to detrimental cavities in the weld seam. Therefore, experiments were performed to investigate the influence of the laser focal geometry on the generation of cavities. Different focal geometries lead to different levels of process heat generation which affects the amount of vaporization. The experiments were conducted with endless glass fiber reinforced polyetherimide and endless carbon fiber reinforced polyetherimide. These samples were tested for their weld seam strength and the results were correlated to the moisture content and laser beam geometry. © 2016 The Authors.

WOS; International audience; Delamination is one of the most critical damage mechanisms in laminated composites. A fracture test, referenced in the following as Tensile Flexure test on Notched Specimen, is proposed in this work to characterize the propagation of delamination. After the description of the experimental procedure, experimental results on carbon/epoxy specimens are presented to describe the capabilities and advantages of the test to characterize delamination. Then, a new propagation law is proposed to describe the evolution of the fracture toughness. Finally, a non-deterministic analysis is performed to determine the influence of the measured parameters on the toughness identification.

WOS: 000385154900022, This study presents the mechanical and transport properties of milled cut steel fiber reinforced concretes (MCSFRC). Properties studied include unit weight, workability, compressive strength, flexural strength, splitting tensile strength, bond strength, water absorption, water porosity, water sorptivity, rapid chloride ion permeability and drying shrinkage of concrete. Mixtures with a waterbinder ratio of 0.40, total binder content of 500 kg/m(3) and milled cut steel fiber content of 0, 0.25, 0.50 and 1.00% by concrete volume were produced and tested. The laboratory results showed a slight reduction in compressive strength with the use of milled cut steel fiber. On the other hand milled cut steel fibers significantly improved the tensile strength and decreased the drying shrinkage. Although no significant increase was observed in the absorption, porosity and sorptivity, chloride ion permeability increased drastically with the increase of milled cut steel fiber content.

In this study novel multifunctional composites consisting of glass fibre/epoxy/microencapsulated phase change materials (micro-PCMs) were prepared and their thermophysical properties have been investigated. Test results showed that the phase change properties of micro-PCMs are not affected after incorporating these materials in fibre reinforced plastic composites. Results obtained from DSC demonstrated that the enthalpy (heat of fusion/crystallisation) is linearly proportional to the mass fraction of microcapsules incorporated into the composites. In addition, it was found that the thermal and dimensional stability of the multifunctional composites are significantly affected by increasing micro-PCMs concentration. The thermal decomposition temperature of the multifunctional composites was reduced while their coefficient of thermal expansion was increased due to the inclusion of micro-PCMs. Understanding the thermophysical properties of these composites pave the path for the development of new material systems that can simultaneously exhibit loading bearing and thermal storage capabilities. Scopus

In the present work the effects of micro-crack initiation and evolution under mixed mode loading conditions on the macroscopic response of elastic periodic composite materials, are investigated. To this end an innovative micro-mechanical approach based on homogenization techniques and adopting stress based failure criteria in conjunction with fracture mechanics concepts is presented, taking into account also the influence of unilateral frictionless contact between crack faces. The crack propagation process, including also the competition between progressive interface cracking and kinking out of the interface, is driven by the maximum energy release rate criterion adopted to predict incremental changes in crack path, whereas a generalized coupled stress–energy criterion is adopted to predict crack initiation under mixed mode conditions. A novel strategy for quasi-automatic simulation of arbitrary crack initiation and propagation in 2D finite element models has been implemented, accounting for mixed mode loading conditions and taking advantage of a generalized J-integral formulation. Numerical applications are developed with reference to a 2D model of a fiber-reinforced composite material with an initially undamaged inclusion/matrix interface. The capability of the proposed approach is shown by computing the composite nonlinear macroscopic response for prescribed uniaxial and shear macro-strain paths, assuming a crack initiation at the fiber/matrix interface. The effects of loading in the transverse fiber direction, inclusion size and fiber volume fraction, are also examined.

The energy absorbing capability of FRP composite cylindrical tubes used as energy absorbers, by destroying itself progressively, depends on the way in which the tube material is crushed i.e., trend of petalling. This paper investigates the influence of fibre orientation and stacking sequence on the petal formation and specific energy absorption (SEA) of four and six-ply, 0�/90� glass/polyester composite cylindrical shells under axial compression. Number of petals formed and the trend of petalling are changed with proportion of axial (0�) and circumferential (90�) fibre content and stacking sequence in the tubes. In the tubes undergo petalling, presence of axial fibres close to inner surface and the proper proportion of circumferential fibres close to outer surface of the tube wall lead to higher energy dissipation. The axial fibres placed nearer to outer surface leads to more number of petal formation, leading to a stable crushing mechanism. The contribution of mode I strain energy release rate (GIc) to the energy dissipation in the form of circumferential delamination is also studied with double cantilever beam (DCB) tests. Analytical model which considers petalling is developed, and used to predict the mean crush load and SEA of cylindrical composite shells under axial compression. Results from the analytical model agree well with experimental results and are presented. � 2007 Elsevier Ltd. All rights reserved.

In this study, a failure analysis was carried out to determine bearing strengths of mechanically fastened joints with single bolt in glass—epoxy laminated composite plates. Two different geometrical parameters that were the edge distance-to-hole diameter ratio (E/D) and plate width-to-hole diameter ratio (W/D) were investigated. For that reason, E/D ratio was selected from 1 to 5, whereas W/D ratio was chosen from 2 to 5. Tensile tests were subjected to composite bolted joints for four different ply orientations such as angle-ply [0/30]s, [0/45]s, [0/60]s, and cross-ply [0/90]s. The major focus of this study was to observe the failure mechanisms of bolted joints under various preload moments as 0, 2.5, and 5 Nm. The experimental results showed that the magnitudes of bearing strengths in bolted joints were strictly influenced from increasing value of applied preload moments, changing of W/D and E/D ratios, and also ply orientations of laminated composite plates.

This paper reports a Genetic Algorithm (GA) based reconstruction procedure to determine the elastic constants of an orthotropic plate from ultrasonic velocity data. Phase velocity measurements are carried out using ultrasonic back-reflection technique on laminated unidirectional graphite-epoxy (0)16 and quasi-isotropic graphite-epoxy (+45, -45, 0, 90)7s fiber reinforced composite plates. A forward model to generate the slowness curves from elastic constants has been used to verify the quality of the reconstruction. The sensitivity of the chosen GA parameters is studied. As expected, out of 9 orthotropic elastic constants to be determined, the C23 and C44 found to be insensitive. The GA based reconstruction using data obtained from multiple planes were evaluated and it is shown that the single plane reconstruction at a non-symmetric plane was sufficient for the computation of the seven elastic constants. � 2006 Elsevier Ltd. All rights reserved.

This paper presents work from a comprehensive study on the development of a flexural design framework for concrete reinforced with steel fibres that are recovered from used tyres. The experimental flexural behaviour of notched concrete prisms reinforced with these fibres is initially presented. For comparison purposes, prisms reinforced with industrially produced fibres are also considered. An attempt to adopt an existing RILEM design framework to derive appropriate tensile stress-strain blocks is made, but problems are identified with key parameters of the framework. The influence of crack propagation and location of neutral axis depth on the tensile stress distribution is examined. Following an analytical study, it is concluded that the uniaxial stress-strain model, proposed by RILEM overestimates the load-carrying capacity and should be modified by utilising more advanced analytical techniques. © RILEM 2006.

Injection molded polymer composite gears are being used in many power and or motion transmission applications. In order to widen the utilization of reinforced polymers for precision motion transmission and noise less applications, the accuracy of molded gears should be increased. Since the injection molded gear accuracy is significantly influenced by the material shrinkage behaviour, there is a need to understand the influence of fiber orientation and gate location on part shrinkage behaviour and hence the gear accuracy. Unreinforced and 20% short glass fiber reinforced Nylon 6/6 spur gears were injection molded in the laboratory and computer aided simulations of gear manufacturing was also carried out. Results of the mold flow simulation of gear manufacturing were correlated with the actual fiber orientation and measured major geometrical parameters of the molded gears. Actual orientation of the fibers near the tooth profile, weld line region and injection points of molded gears were observed using optical microscope and correlated with predicted fiber orientation. � Springer Science+Business Media B.V. 2006.

The anisotropy of fiber-reinforced plastics (FRP) affects the chip formation and thrust force during drilling. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce good quality holes with high efficiency by conventional drilling method. This research concerning drilling of polymeric composites aims to establish a technology that would ensure minimum defects and longer tool life. Specifically, the authors conceived a new drilling method that imparts a low-frequency, high amplitude vibration to the workpiece in the feed direction during drilling. Using high-speed steel (HSS) drill, a series of vibratory drilling and conventional drilling experiments were conducted on glass fiber-reinforced plastics composites to assess thrust force, flank wear and delamination factor. In addition, the process-status during vibratory drilling was also assessed by monitoring acoustic emission from the workpiece. From the drilling experiments, it was found that vibratory drilling method is a promising machining technique that uses the regeneration effect to produce axial chatter, facilitating chip breaking and reduction in thrust force. � 2005 Elsevier Ltd. All rights reserved.

A computational analysis of the longitudinal deformation of continuous fibre reinforced metals is presented. Elastic and elastic-plastic matrix behaviour are considered. Analytical approaches are confronted with finite element analyses (FEA) for varying fibre distributions, ranging from single fibre unit cells to complex cells. Analysis of microfields shows that the main cause for deviation from the equistrain rule of mixtures is a stiffening effect of matrix confinement when surrounded by touching fibres arranged as "rings". Comparison with FEA shows that Hill's [J. Mech. Phys. Solids 12 (1964) 199, 213] bounds, although best possible in terms of volume fraction, are of limited value in so far as Hill's upper bound lies far above any practical limit for a fibre reinforced material, whereas Hill's lower bound loses its bounding property when extended to non-linear behaviour via an incremental scheme. This latter effect can be corrected by changing slightly Hill's derivation in a way that preserves the bounding property. Finally, implications are given for the derivation of in situ matrix flow stress curves from, experimental tensile curves on fibre reinforced composites. It is suggested that linear three-point bounds can in practice be used for this purpose. (C) 2004 Elsevier Ltd. All rights reserved.

Aluminum metal matrix composites (MMCs) reinforced with ceramic constituents have been increasingly used in engineering applications because of their improved properties over those of nonreinforced alloys. The full application of such MMCs is, however, cost sensitive because rapid tool wear during machining leads to high machining costs. In this paper, the machinability of LM.13 Al alloy reinforced with 25% by volume fraction of aluminosilicate fibers using multicoated carbides having different restricted contact (RC) type rake faces and polycrystalline cubic boron nitride (PCBN) tools is presented. A quantitative description of the mode of action of RC tools is given based on a simple model for cutting. The two tool materials were compared with respect to number of response parameters. The results show that PCBN outperforms the multicoated carbides in machining these materials. The plethora of advantages offered by RC tools is not realized in machining MMC material as they are heterogeneous in nature.

Fibre armatures have been studied both dynamically and statically to gain insight in their electrothermal and mechanical behaviour. In the first part of this paper, the results of launch experiments with single and multi-segment copper and molybdenum fibre armatures integrated in carbon-fibre reinforced launch packages are discussed. The launch experiments with Cu fibre armatures showed an improved reproducibility and a higher transition velocity. The poor results of the launch experiments with the Mo fibre armatures thus far, are explained with results of armature compliance and resistance measurements. In the second part, results are presented which are obtained from static experiments in an armature test bed. Using miniature B-dot probes and Rogowski coils, the magnetic field diffusion into monobloc and fibre armatures with identical geometry has been studied. The results show a significant difference in diffusion behaviour between the two types of armatures. It appears that the magnetic field diffuses faster into the fibre armature. The experimental data are compared with the results of calculations of the magnetic field distribution in both armatures based on 2D- and 3Dfinite element computer simulations. The results of the ID-simulations appear to confirm the measured results for monobloc and fibre armatures only qualitatively. The experimental results obtained with monobloc armatures agree with the results of the 3D-simulations in a quantitative sense. © 1997 IEEE.

International audience; This article presents the implementation of a new inelastic damage model able to carry out simulation of initiation and evolution of damage in the Z-pinned laminated composite structures with friction effects. The classical elastic damage model is modified to an inelastic model with friction effects obeying the simple Coulomb friction criterion. The main idea is the modification of strain energy parameter by introducing sliding and friction parameters. The simulations of single Z-fiber pull tests highlight the effectiveness of the proposed model for micro-scale predictions.

Composite sandwich structures have extensive applications due to their high strength and structural efficiency. Skew fibre-reinforced composite laminates are used as important structural elements in modern structural design, particularly in the aerospace industry. Natural frequency of these skew laminates is of primary significance to structural designers. The present article studies the free vibration and damping characteristics of sandwich skew plates consisting of composite stiff layers with viscoelastic (VEL) or electrorheological fluid (ER) core, using finite element method. The vibration behavior of these core materials is critically compared. Detailed analysis was conducted by varying the boundary conditions, core to stiff layer thickness ratios and stacking sequence. The inherent composite damping and the damping due to VEL (or ER fluid) core are investigated. The influence of electric field on the frequency and loss factor were also examined. � 2006 Elsevier Ltd. All rights reserved.

Near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminate strips are used to increase the load-carrying capacity of concrete structures by inserting them into slits made in the concrete cover of the elements to be strengthened and gluing them to the concrete with an epoxy adhesive. In several cases the NSM technique has substantial advantages when compared with externally bonded laminates. In order to assess the bond behavior between the CFRP and concrete under monotonic and cyclic loading, an experimental program, based on a series of pullout bending tests, was carried out. The influence of the bond length and loading history on the bond behavior was investigated. In this work the details of the tests are described, and the obtained results are discussed. Using the experimental data and an analytical-numerical strategy, a local bond stress-slip relationship was determined. A finite element analysis was performed to evaluate the influence of the adhesive on the global response observed in the pullout bending tests., The first author wishes to acknowledge the grant SFRH/BD/3259/2000 provided by FCT (Portuguese Foundation for Science and Technology) and FSE (European Social Fund). The tests were performed at the Structural Technology Laboratory of the Technical University of Catalonia, Spain, with the help of Miguel Angel Martín and Ernesto Diaz. The authors wish to acknowledge the support provided by S&P and Bettor MBT who supplied the material used in the study.

Steel fiber-reinforced concrete (SFRC) uses fibers as shear reinforcement, a successful approach to coping with the brittle nature of shear failure. This article reports on a study undertaken to characterize the failure and toughness of SFRC subjected to direct shear loading at the material level. The study used a push-off test on a double-notched prism to quantify the shear stress-displacement behavior of SFRC. The shear stress-slip response (obtained experimentally) can be used to calculate toughness-based parameters, which can be employed in structural design. The authors note that the test can be performed in a stable manner for steel fiber-reinforced concrete, permitting the determination of the pre- and post-peak responses and, consequently, characterizing the shear stress that can be transferred across an open crack. The authors conclude that significant improvements in the ductility of concrete during shear failure and some increase in the shear strength are achieved through the incorporation of steel fibers in both normal- and high-strength concretes.

In this study, an elastic-plastic stress analysis is carried out on a steel fiber-reinforced thermoplastic composite disc under uniform thermal distribution. The composite disc is reinforced by steel fibers curvilinearly. Its mechanical properties are obtained by strain gauges and Instron test machine. The modulus of elasticity in the tangential direction is measured by fitting a solid disc to the composite disc, exactly. However, other material properties are found approximately. The material is assumed to be non work hardening. Stresses are determined for uniform temperature distribution. The magnitude of the tangential stress component in polar coordinates is the highest at the inner points of the disc. Plastic solution is performed numerically. Plastic region beg-ins at the inner surface of the disc. The residual stress component of the tangential stress is the highest at the inner surface of the disc. C1 Dokuz Eylul Univ, Dept Mech Engn, TR-35100 Izmir, Turkey. Pamukkale Univ, Dept Mech Engn, Camlik, Denizli, Turkey.

This paper deals with the elastic-plastic stress analysis of a thin aluminum metal-matrix composite disk under internal pressure. An analytical solution is performed for satisfying the elastic-plastic stress-strain relations and boundary conditions for small plastic deformations. The Tsai-Hill Criterion is used as a yield criterion, and an elastic-perfectly-plastic material is assumed. Elastic-plastic and residual stress distributions are obtained from inner radius to outer radius, and they are presented in the tables and figures. All radial stresses, σr, are compressive, and they are highest where the plastic deformation begins. All tangential stresses, σ θ, are tensile, and they are highest at the inner radius. Magnitude of the tangential residual stresses is higher than that of the radial residual stresses, and it is changing from negative sign to positive.

Alumina-zirconia fibres were prepared by sol-gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride, respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contains 10 wt.% ZrO 2. Fibres were drawn from the gel using an extruder and dried at room temperature and subsequently sintered at 1200, 1400 and 1600 �C. Differential thermal analysis showed that �-Al 2O 3 phase transition occurs at 1290 �C. The phases present in the sintered fibres were �-Al 2O 3, t-ZrO 2 and m-ZrO 2. Scanning electron microscope revealed dense microstructure is formed at 1600 �C. Tensile strength was found to be the highest for fibres sintered at 1600 �C. ? 2005 Elsevier B.V. All rights reserved.

The conventional design philosophy for reinforced concrete (RC) relies heavily on the ductile properties of steel. These ductile properties are used as a "fuse" and conceal the large uncertainty in the determination of modes of failure caused directly by concrete. Current design guidelines for fiber reinforced polymer (FRP) RC structures have inappropriately adopted the same design philosophy used for steel RC, leading either to the adoption of conservative safety factors or reduced structural reliability. A reliability-based analysis of FRP RC beams shows that the current, very conservative partial safety factors for FRP reinforcement on their own do not influence the structural safety of overreinforced concrete elements. Proposals are made for the modification of the material partial safety factors to achieve target safety levels.

The use of fiber-reinforced polymers (FRPs) for the strengthening and repair of existing concrete structures is a field with tremendous potential. The materials are very durable and, hence, ideally suited for use as external reinforcement. Although extensive work has been carried out investigating the use of FRPs for flexural strengthening, a fairly recent development is the use of these materials for the shear strength enhancement of concrete. The current system investigates the use of posttensioned, nonlaminated, carbon fiber-reinforced polymer (CFRP) straps as external shear reinforcement for concrete. Experiments were carried out on an unstrengthened control beam and beams strengthened with external CFRP straps. It was found that the ultimate load capacity of the strengthened beams was significantly higher than that of the control specimen. Existing design codes and analysis methods were found to underestimate the ultimate resistance of the control specimen and the strengthened beams. Nevertheless, the modified compression field theory provided insight into possible failure mechanisms and the influence of the strap prestress level on the structural behavior. It is concluded that the use of these novel stressed elements could represent a viable and durable means of strengthening existing concrete infrastructure.

The scope of this paper is to present a possible methodology for the calibration of partial safety factors for the design of strengthening measures of reinforced-concrete (RC) members using fiber-reinforced plastic (FRP). The methodology is general and can be used for any type of strengthening measure, e.g., in flexure, shear, ductility, or for the design of anchorage zones. The approach considers the problem of strengthening an RC member from a current unsafe situation, where all involved quantities are known from assessment, though only in probabilistic terms, to a target safe one, of which only the desired reliability is known. All relevant random variables are attributed a predefined probability distribution, based on a statistical survey separately conducted on geometrical and mechanical characteristics of old-style components. A first-order reliability method-based optimization procedure is used to seek the solution of such a problem so that the target reliability is attained with the optimal FRP quantity, the appropriate collapse mechanism of the strengthened member, and the FRP design strength, with the associated partial safety factor. From Monte Carlo design simulations, the partial safety factor is probabilistically characterized, thus allowing one to select an appropriate fractile value for it.

Orthotropic cylindrical shells with discontinuity in the thickness and subjected to axisymmetric loading have been analysed. A higher order finite element based on the thick shell theory is used for the analysis. The material used is a glass/epoxy composite with 0° and 90° fibre orientation with respect to the axial direction of the cylinder. The loadings considered are uniform internal pressure and circular ring load at the mid-section. Numerical results are presented for various end conditions and step-ratios in the thickness. The weight of the shell is kept constant for various step-ratios. It has been shown that 90° fibre orientation gives less deformation and stress for axisymmetric loading than 0° fibre orientation. The variation in the thickness reduces the maximum stresses for some cases of loading and end conditions presented in this paper.

For steady-state heat conduction, a new variational functional for a unit cell of composites with periodic microstructures is constructed by considering the quasi-periodicity of the temperature field and in the periodicity of the heat flux fields. Then by combining with the eigenfunction expansion of complex potential which satisfies the fiber-matrix interface conditions, an eigenfunction expansion-variational method(EEVM) based on a unit cell is developed. The effective transverse thermal conductivities of doubly-periodic fiber reinforced composites are calculated, and the first-order approximation formula for the square and hexagonal arrays is presented, which is convenient for engineering application. The numerical results show a good convergency of the presented method, even though the fiber volume fraction is relatively high. Comparisons with the existing analytical and experimental results are made to demonstrate the accuracy and validity of the first-order approximation formula for the hexagonal array.

Conference Name: 7th Cirp Conference on High Performance Cutting Date on Conference: May 31st - June 2nd 2016 Carbon fiber reinforced polymers (CFRPs) are widely used in the aerospace industry due to their light weight, high strength, and low thermal conductivity. Drilling is a critical process that affects the quality of CFRP parts. This work studies the influence of process parameters on delamination and tool wear. Polycrystalline diamond helical drills are used in the experiments. It has been shown that drilling energy calculations can be used to set appropriate feed and speed parameters and for increasing drilling performance of CFRPs. The results also indicate the importance of thermal modeling of CFRP laminate for better understanding of the drilling process. © 2016 The Authors.

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-Surface Mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete (Steel Fiber Reinforced Concrete - SFRC), the post cracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed.