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Two new aspects related to analysis of Carbon Nanotubes Reinforced Materials (CNTRM) are emphasized in this work. First, a modeling methodology allowing for presence of interphases is proposed. Second, the physically expected dominance of the axial stiffness of Carbon nanotubes (CNT) on the effective properties of CNTRM is demonstrated by purposefully selected numerical experiments. In the proposed model the Gutrin-Murdoch theory is applied to a hollow cylinder of finite thickness and combined with the notion of energy equivalence to replace CNT with an equivalent solid cylinder. The interphase – modeled as a spring layer – is subsequently added to obtain another equivalent solid cylinder. Effective properties of CNRTM are evaluated using the Method of Conditional Moments. [ABSTRACT FROM AUTHOR]

The development of new materials based on industrial wastes has been the focus of much research for a sustainable world. The growing demand for tyres has been every year exacerbating environmental problems due to indiscriminate disposal in the nature, making a potentially harmful waste to public health. The incorporation of rubber particles from scrap tyres into polymeric composites has achieved high toughness and moderate mechanical properties. This work investigates the geometric effects (thickness, width and internal cell angle) of auxetic structures made of recycled rubber composites based on experimental and numerical data. The response surface models integrated with the swarm intelligence and finite element analysis were proposed in order to obtain a range of solutions that provides useful information to the user during the selection of geometric parameters for reentrant cells. The results revealed the cell thickness ranges from 39-40 mm and 5.98-6 mm, and the cell angle range from -0.01 to -0.06º maximize the ultimate strength. The same parameters were able to optimize the modulus of elasticity of rubber auxetic structures, excepting for the angle factor which must be set between -30º and 27.7º. The optimal Poisson's ratio was found when the cell angle ranged from -30º to -28.5º, cell width ranged from 5-5.6 mm and 2 mm in thickness.

A recently developed framework to quantify variability of common textile reinforcements of unit cell size is extended to allow for a stochastic description of complex three-dimensional (3-D) textile architectures spanning multiple unit cells. The reinforcement geometry is characterised from synchrotron micro-tomography images in terms of centroid coordinates and tow cross-section. The statistical information includes an average trend, standard deviation and correlation information. A general representation of correlation information is proposed to account for the different tow correlations depending on the location inside the 3-D architecture. The methodology is applied to the characterisation of a 3-D carbon fabric considered for NASA’s Adaptive Deployable Entry Placement Technology (ADEPT) system. Determining geometrical variability in the weave is of importance during the process of setting design margins and risk analysis. Statistical analysis demonstrates strong dependency on the crossover positions for the average trends and correlation data, with a substantially higher variation for the Z-interconnecting tows. [ABSTRACT FROM AUTHOR]

Tow-Based Discontinuous Composites (TBDCs, composed by chopped carbon-fibre tows embedded in polymer) combine high performance with manufacturability; the random orientation and large dimensions of the tows generates significant variability of properties, which governs the response of TBDC structures. This paper proposes the concept of characteristic length-scale as the intrinsic property of a TBDC governing its spatial variability (i.e. how properties are distributed in space). A new methodology to experimentally measure a TBDC's characteristic length-scale, based on the triangulation of peaks and troughs in elastic strain fields of unnotched specimens, is developed; this is complemented by another methodology based on the cross-correlation of strain fields. A meso-scale Finite Element (FE) methodology (based on an explicit representation of the tows) reveals that a TBDC's characteristic length-scale can be approximated as the harmonic mean of the tow length and width. A new macro-scale FE methodology, based on generating stochastic equivalent laminates at discrete points (separated by the TBDC's characteristic length-scale) and interpolating their orientation tensors into continuously smooth stochastic fields, is proposed and validated against experiments; this methodology is mesh-objective and does not require explicit representations of the tows, making it computationally-efficient and suitable to complex geometries. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) reinforcements are taken as an alternative solution for the deterioration of civil infrastructures. GFRP bars have received increasing attention due to low cost compared to carbon fiber-reinforced polymer (CFRP) bars. Bond characteristic of GFRP bars in concrete is the most critical parameter for implementation of the material to the corrosion-free concrete structures. Unlike steel reinforcement, GFRP materials behave anisotropic, non-homogeneous and linear elastic properties, which may result in different force transfer mechanism between reinforcement and concrete. With the purpose of covering the most valuable contributions regarding bond mechanism in the past work, a comprehensive review focusing on the failure mode and bond strength is carried out in this paper. A database consisted of 682 pullout-test specimens was created to observe the factors affecting bond behavior. Basic relationship between bond strength/slip and factors was analyzed accordingly. In addition, the development of bond degradation under environmental conditions, such as freezing-thawing cycling, wet-dry cycling, alkaline solutions and high temperature was presented thereafter. These environmental influences need to be further investigated. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composite materials offer light-weight solutions to many structural challenges. In the development of high-performance composite structures, a thorough understanding is required of the composite materials themselves as well as methods for the analysis and failure prediction of the relevant composite structures. However, the mechanical properties required for the complete constitutive definition of a composite material can be difficult to determine through experimentation. Therefore, efficient methods are necessary that can be used to determine which properties are relevant to the analysis of a specific structure and to establish a structure's response to a material parameter that can only be defined through estimation. The objectives of this study deal with demonstrating the potential value of sensitivity and uncertainty quantification techniques during the failure analysis of loaded composite structures; and the proposed methods are applied to the simulation of the four-point flexural characterization of a carbon fiber composite material. Utilizing a recently implemented, phenomenological orthotropic material model that is capable of predicting progressive composite damage and failure, a sensitivity analysis is completed to establish which material parameters are truly relevant to a simulation's outcome. Then, a parameter study is completed to determine the effect of the relevant material properties' expected variations on the simulated four-point flexural behavior as well as to determine the value of an unknown material property. This process demonstrates the ability to formulate accurate predictions in the absence of a rigorous material characterization effort. The presented results indicate that a sensitivity analysis and parameter study can be used to streamline the material definition process as the described flexural characterization was used for model validation. [ABSTRACT FROM AUTHOR]

Flax fibers are superior to E-glass fibers in terms of specific Young modulus. Many researchers have recently tried to exploit this feature and use flax fibers in polymeric composites to compete with glass fiber composites. In this work, a new type of unidirectional flax/paper reinforcement obtained after resin transfer molding with epoxy is investigated. Reinforcement's parameters (paper ply and flax ply surface densities) and manufacturing parameters (forming pressure and drying temperature) are optimized to obtain the best possible composite strength and modulus. Internal bond strength between flax and paper layers is also investigated. Results show that at equivalent V f the new flax/paper/epoxy composite is superior, in both specific strength and modulus, to another flax/epoxy composite (without the paper layer). It also surpasses the specific stiffness of a unidirectional E-glass/epoxy composite and the specific strength of a commercially available similar reinforcement. [ABSTRACT FROM AUTHOR]

Unidirectional carbon fiber reinforced polymer (CFRP) composites fabricated by Vacuum Assisted Resin Transfer Molding (VARTM) are tested at four initial strain rates (25, 50, 100 and 200 s −1 ) and six temperatures (−25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate the effects of strain rate and temperature on their tensile properties and failure behaviors. A high speed digital camera is used to capture the deformation and failure behavior of the CFRP composites at a sampling rate of 20,000 fps with resolution of 256 × 256 pixels. In order to illuminate corresponding strain rate effect mechanism, carbon yarn samples are complementally tested under dynamic tensile loading at four different strain rates (40, 80, 120 and 160 s −1 ) utilizing an Instron drop-weight impact system. The stress–strain responses at these strain rates are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications. The non-uniform strain and displacement fields as well as the damage process are characterized by digital image correlation (DIC) method. [ABSTRACT FROM AUTHOR]

Anchorage is of critical importance in the glass fibre-reinforced polymer (GFRP) bar reinforced concrete structures to allow reinforcing GFRP bars to provide sufficient bond to concrete. This study presents a new strategy for anchorage reliability assessment of GFRP bars to concrete by integrating superiorities of artificial neural network (ANN) and genetic algorithm (GA). The new methodology harnesses not only the strong nonlinear mapping ability in the ANN to approximate the performance function (PF) and solve its partial derivatives in terms of the design variables, but also global searching ability in the GA to explore the optimal initial weights and biases of the ANN to avoid falling into local minima during the network training. The ANN-based first order second moment (FOSM) method and Monte Carlo simulation (MCS) method were first derived. Implementation of the proposed hybrid ANN-GA procedures for GFRP bar anchorage reliability analysis were then achieved by the targeted reliability index and development length. Both the ANN-based FOSM and MCS methods were utilized for determining the reliability index and probability of failure of GFRP bar anchorage. The further implementation of the proposed strategy was achieved by a graphical user interface toolbox in Matlab environment for practical use. [ABSTRACT FROM AUTHOR]

A new approach is presented for generating random distribution of fibres in the representative volume element (RVE) of fibre reinforced composite laminates. The approach is based on discrete element method (DEM) and experimental data of fibre diameter distribution. It overcomes the jamming limit appeared in previous methods and is capable of generating high volume fractions of fibres with random distributions and any specified inter-fibre distances. Statistical analysis is then carried out on the fibre distributions generated within the RVEs, which show good agreement with experiments in all statistics analysed. The effective elastic properties of the generated RVEs are finally analysed by finite element method, which results show more reasonable agreement with the experimental results than previous methods. [ABSTRACT FROM AUTHOR]

This paper proposes design models for insulated concrete sandwich wall panels (SWPs) with GFRP grids against a flexural failure. The design models are developed by considering both ultimate and serviceability limit states. First, mean-prediction models for evaluating ultimate moments and cracking moments of SWPs are proposed, and second, they are further developed into design models by adding capacity factors (or safety factors). The capacity factors are statistically determined using the method provided in Eurocode 1990: 2002 [1]; this method considers the random distribution of resistance defined by evaluating both modeling and parametric uncertainties. Two capacity factors are calibrated for an ultimate limit state function and a serviceability limit state function. For a more convenient design process, a unified capacity factor is determined by combining both factors into a function of a nominal ultimate moment. The unified factor can be applied to achieve the ultimate limit state requirement, and at the same time it automatically achieves the serviceability requirement. [ABSTRACT FROM AUTHOR]

The isotropy of different numerical simulations of fiber reinforced elastomers has been explored by explicitly applying stretch in different loading directions, in models with representative volume elements (RVEs) spanning a wide range of fiber volume fractions and system sizes. The results show that the homogenized response is not the same for all loading directions, and that the corresponding dependance takes the form of a sine. The anisotropy decreases with the RVE size, and so it can be used to asses if the scales can be separated in a given model. Considering the average response over all loading directions greatly reduces the variation between different RVEs, which can be used to improve the accuracy of the simulations in a way that is significantly more efficient than increasing the size of the RVE. The simulations have also shown a good correlation between the isotropy of each representative volume element at low and high values of the applied stretch. The result of linear simulations can therefore be used as an efficient indication of the anisotropy expected at high deformations. [ABSTRACT FROM AUTHOR]

A statistical multiscale homogenization strategy of polymer nanocomposites is proposed to account for the inherent uncertainties of molecular dynamics (MD) simulations. The proposed statistical multiscale homogenization scheme includes a discrete MD simulation system, a continuum theory of micromechanics of Eshelby's solution and two-scale homogenization, and Monte-Carlo simulations. The means and standard deviations of the elastic properties of the nanocomposites are quantified and discussed through statistical analyses that show the interphase effect. The elastic properties of the matrix, interphase, and composites are assumed to follow a lognormal distribution. An iterative inverse algorithm for obtaining the probability density distribution of the interphase is proposed and validated. [ABSTRACT FROM AUTHOR]

To evaluate the risk of complex structures such as a 2.5D/SiC composites turbine blade, Response Surface Methodology is applied to investigate the reliability due to its high efficiency. In this paper, the Response Surface is based on Support Vector Machines (SVM), and new sample strategies are proposed to assess the failure domain and probability as well as reliability index with less computational cost and higher accuracy. 2.5D/SiC composites are defined by 5 geometric parameters to represent their architecture. Using the finite element method, we establish the structure of 2.5D/SiC composites and predict the mechanical properties with double scale models. The stochastic behaviors of load, material strength and microstructure of 2.5D/SiC composites are considered to analyze the reliability of a turbine blade in an aircraft engine. The methodology in this paper provides an accurate and effective way to value the risk of turbine blade design. [ABSTRACT FROM AUTHOR]

This paper concerns the shear behavior of reinforced concrete beams externally strengthened with composite materials. The study gathers numerous experiments on concrete beams, strengthened in shear with FRPs, from the international literature and develops an experimental database. The database is utilized to assess the predictive accuracy of significant existing design recommendations, with respect to the vertical load capacity of the tested beams. The crucial parameters for predicting the shear capacity of FRP strengthened beams are identified. Some of these parameters are disregarded in the reported results of several experimental programs or are difficult to measure. The research utilizes the available full load-deformation curves for numerous tests as well as the predictive accuracy and easy to apply modified compression field theory (MCFT). Reverse MCFT analysis of beams may provide significant information concerning the angle of main shear crack, the average crack width of concrete and the average effective deformation of the FRP and of internal steel, given the failure load. Thus, a hybrid approach is followed to enrich the experimental database with analytically derived significant parameters towards an advanced database. The hybrid experimental–analytical database is further elaborated and recent studies on shear behavior of concrete members are taken into account. The study explores the influence of different crucial parameters and proposes suitable modifications of existing design equations towards remarkably improved shear force resistance predictions. [ABSTRACT FROM AUTHOR]

Several researchers have shown how sisal fibres possess remarkable tensile properties that yield them good candidates as reinforcement in biocomposite materials. This work aims to evaluate the effect of an eco-friendly and cost effective surface treatment method based on the use of commercial sodium bicarbonate (i.e. baking soda) on properties of sisal fibre and its epoxy composites. In particular, raw sisal fibres were treated with a 10%w/w of sodium bicarbonate solution for different periods (24, 120 and 240 h), at room temperature. Changes occurring in sisal fibres were characterized through scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis and helium pycnometer analysis. The mechanical characterization of sisal fibre was carried out through single fibre tensile tests and a reliability analysis of the experimental data was performed. A mathematical model was also applied to investigate the relation between the transverse dimension of the fibres and their tensile properties. Interfacial adhesion of sisal fibre with an epoxy matrix was investigated using single fibre pull out technique. Moreover, to deeper investigate the effect of the proposed treatment, epoxy based composites reinforced with short randomly oriented sisal fibres were manufactured and characterized by means of quasi-static flexural tests. The experimental results showed that 120 h is the optimum time for treating sisal fibre to achieve highest interfacial adhesion and mechanical properties with epoxy matrix. [ABSTRACT FROM AUTHOR]

The object of this work is to study the mechanical properties of ternary nano-composites based on polypropylene/linear low density polyethylene/nano-titanium dioxide (PP/LLDPE/TiO 2 ) using the response surface methodology (RSM). Experiments were designed according to a Box–Behnken method, to quantify the effects of linear low density polyethylene (LLDPE), styrene–ethylene–butylene–styrene (SEBS as a compatibilizer), and titanium dioxide (TiO 2 ) nano-particles. Three levels were chosen for the considered parameters as follows: LLDPE (20–60 wt%), TiO 2 (0–4 wt%), and SEBS (0–6 wt%). In addition, RSM models were used to develop the desirability function. Finally, the morphology and thermal properties of the samples were evaluated by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). It was found that the LLDPE content had the main role in mechanical properties and morphology of the nano-composite. The optimal values of the nano-particle were predicted to be 24.85 wt% for LLDPE, 3.02 wt% for TiO 2 , and 6 wt% for SEBS. The obtained R 2 values and normal probability plots indicated a good agreement between the experimental results and those predicted by the model (above 0.95 for all the responses). [ABSTRACT FROM AUTHOR]

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal cooling capacity of all channels (which directly minimizes the amount of coolant needed). In the first step, available uncertainties in the constituent material properties, the applied mechanical load, the heat flux and the heat convection coefficient are considered. Using the Reliability Based Design Optimization (RBDO) approach, the probabilistic constraints ensure the failure due to excessive temperature and deflection will not happen. The deterministic constraints restrict the capacity of any arbitrary cooling channel between two extreme limits. A “series system” reliability concept is adopted as a union of mechanical and thermal failure subsets. Having the results of the first step for CMC with uniformly distributed carbon (C-) fibers, the algorithm presents the optimal layout for distribution of the C-fibers inside the ceramic matrix in order to enhance the target reliability of the component. A sequential approach and B-spline finite elements have overcome the cumbersome computational burden. Numerical results demonstrate that if the mechanical loading dominates the thermal loading, C-fibers distribution can play a considerable role towards increasing the reliability of the design. [ABSTRACT FROM AUTHOR]

The propagation of thermal uncertainty in composite structures has significant computational challenges. This paper presents the thermal, ply-level and material uncertainty propagation in frequency responses of laminated composite plates by employing surrogate model which is capable of dealing with both correlated and uncorrelated input parameters. The present approach introduces the generalized high dimensional model representation (GHDMR) wherein diffeomorphic modulation under observable response preserving homotopy (D-MORPH) regression is utilized to ensure the hierarchical orthogonality of high dimensional model representation component functions. The stochastic range of thermal field includes elevated temperatures up to 375 K and sub-zero temperatures up to cryogenic range of 125 K. Statistical analysis of the first three natural frequencies is presented to illustrate the results and its performance. [ABSTRACT FROM AUTHOR]

Talc is broadly used in the ceramic materials industry, either as a basic raw material, or as filler, due to its chemical inertia, fragmentation proneness, thermal stability, and refractoriness. The mechanical activation is frequently employed in the direct enhancement of talc properties, and thereby in the design of talc based composites with advanced performances. The differences in the set of the process parameters measured before and after talc activation via ultra-centrifugal mill Retsch ZM-1, and their influence on the grain-size distribution related characteristics have been investigated. The mechanical treatments are energetically unsustainable procedures, therefore the talc activation was optimized on basis of assessment of the process variables (number of rotor revolutions, current intensity, activation period, circumferential rotor speed and mill capacity) effect on the final quality of product parameters (mesh sizes, cumulative oversizes, average grain size, level of micronization kinetics, mesh size appropriate to 95% micronized product cumulative undersize and specific surface area). The activated product parameters in all experimental sequences were obtained by the analytical procedure based on Rosin-Rammler-Sperling equation. Response surface method, standard score analysis and principal component analysis were used as a means of the optimization. Developed models showed r 2 values in the range of 0.714–0.908 and they were able to accurately predict quality parameters in a wide range of process parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 120 μm set of processing parameters (SS = 1.0). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of talc samples inherent properties on the final score and improve the activation procedure energetic and economic sustainability. [ABSTRACT FROM AUTHOR]

In composite materials, accurate characterisation of damage using NDT techniques is vital. Techniques which are well developed in homogeneous materials do not translate easily to composites due to their complex and anisotropic properties. This is especially true in acoustic emission (AE) where propagation behaviour significantly affects the signal data. This paper describes a novel solution to enable AE parameters to be “corrected” to account for the material properties and the geometry of the structure. The ‘‘Parameter Correction Technique (PCT)’’ derives an empirical relationship between signal parameters and varying source amplitude from a number of locations, across a structure. This method does not require knowledge of the sensor location or wave velocity. A five-step description of the process is provided and practical results from an initial trial are presented. Results from the initial trial demonstrate a considerable improvement over the conventional parameters. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment–curvature ( M – χ ) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M – χ points that characterize the flexural behavior of CFRP strengthened beams. Two additional M – χ points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force–deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements. [ABSTRACT FROM AUTHOR]

The probabilistic impact responses of single layer greige and scoured plain-weave Kevlar KM2 fabrics are experimentally studied. Single-layer, 101 cm × 101 cm fabric targets are mounted in a novel equilateral octagon (EO) fixture that leaves the principal yarns unclamped. A probabilistic velocity response (PVR) curve, which describes the probability of fabric penetration as a function of projectile impact velocity, is generated through a series of thirty impact tests using a spherical steel projectile impacted at velocities between 69 and 113 m/s. Additional experiments are conducted by impacting targets repeatedly at identical velocities, and comparing the resulting residual velocities of the penetrating projectiles. Fabric penetration in all cases is entirely accommodated by yarn pull-out and windowing, without any principal yarn failure at the impact site. The results indicate that frictional yarn sliding and pull-out are the primary energy dissipating mechanisms during these impact conditions. Controlled yarn pull-out experiments are conducted on the same greige and scoured fabrics to statistically characterize the yarn pull-out loads. Variability in pull-out forces in the greige fabrics are measurably higher than the variability in pull-out forces for the scoured fabrics, which correlates well with variability trends in the PVR and residual velocity ballistic experiments. Additional factors, such as yarn-projectile friction and differences in filament packing efficiency, are hypothesized to also contribute to the observed differences in the greige and scoured fabric impact responses. [ABSTRACT FROM AUTHOR]

This paper experimentally analyzes the influence of temperature and type of matrix on the delamination process of two composites subjected to fatigue loading through the study of their fracture under mode I behavior. The materials were manufactured with the same AS4 unidirectional carbon reinforcement and two epoxy matrices with different fracture behavior. The chosen temperatures for the experiments were 20 (room temperature), 50 and 90 °C. The experimental study carried out under dynamic loading enabled the authors to determine the influence that temperature has on the onset of delamination for the entire range of fatigue life of the material, from the low number of cycles zone to the high number of cycles zone. That is, it enabled the plotting of fatigue curves, represented as G Imax – N (number of cycles required for the onset of delamination given a certain energy release rate) for an asymmetry coefficient of 0.2 (the ratio between the maximum and minimum fracture energies applied during the dynamic tests). The experimental data obtained were treated with a probabilistic model based on a Weibull distribution which allowed the identification of relevant aspects of the fatigue behavior of the materials such as the estimation of fatigue strength for periods greater than the tested values and the analysis of the reliability of the results. [ABSTRACT FROM AUTHOR]

In this work, kenaf fibers were pre-treated in a NaOH solution (6% in weight) at room temperature for two different periods (48 and 144 h). The chemical treatment of kenaf fibers for 48 h allowed to clean their surface removing each impurity whereas 144 h of immersion time had detrimental effect on the fibers surface and, consequently, on their mechanical properties. Untreated and NaOH treated kenaf fibers (i.e. for 48 h) were also used as reinforcing agent of epoxy resin composites. The effect of the stacking sequence (i.e. using unidirectional long fibers or randomly oriented short fibers) and the chemical treatment on the static mechanical properties was evaluated showing that the composites exhibit higher moduli in comparison to the neat resin. As regards the strength properties, only the composites reinforced with unidirectional layers show higher strength than the neat resin. Moreover, the alkali treatment increased the mechanical properties of the composites, due to the improvement of fiber–matrix compatibility. The dynamic mechanical analysis showed that the storage and the loss moduli are mainly influenced by the alkali treatment above the glass transition temperature. Moreover, the alkali treatment led to a notable reduction of tan δ peaks in addition to significant shifts of tan δ peaks to higher temperatures whereas the stacking sequence did not influence the trends of storage modulus, loss modulus and damping of the composites. [ABSTRACT FROM AUTHOR]

The paper describes from a statistical perspective the diameter-dependence tensile strength and Young’s modulus in 40 sisal fibres samples. The fibres tensile properties depend significantly upon their diameter, which has been determined using optical and SEM microscope techniques. Further characterisation of the sisal fibres has been carried out using FT-IR and DSC techniques. The fibres’ ultimate tensile strength and Young’s modulus have been evaluated using four different estimation methods from two and three-parameter Weibull distribution statistics. We show the significant sensitivity of the Weibull predictions versus the number of fibres samples used in the distributions, with the Weibull modulus m σ obtained from our results being 10% smaller compared to what is reported in open literature. The scatter of the mechanical properties of the sisal fibres shown in this work is also compared to analogous distributions present in other works. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) and wool composite sheets were fabricated by continuous extrusion. Increases in mechanical properties of the composites, such as tensile modulus and strength, were achieved by adding wool and a suitable compatibiliser. Significant manufacturing parameters and desired formulations of the wool–PP composites to achieve the best possible mechanical properties were determined by Taguchi analysis. Wool characteristics within the extruded composites, namely fibre length, orientation and fracture behaviour, were also investigated by image analysis to find out their influence on the improvement of mechanical properties. Furthermore, positive effect of wool on improving fire retardancy of the composite has been identified by some preliminary flammability tests. [ABSTRACT FROM AUTHOR]

This study describes a control system designed for real-time monitoring of damage in materials that employs methods and models that account for uncertainties in experimental data and parameters in continuum damage mechanics models. The methodology involves (1) developing an experimental set-up for direct and indirect measurements of damage in materials; (2) modeling damage mechanics based constitutive equations for continuum models; and (3) implementation of a Bayesian framework for statistical calibration of model with quantification of uncertainties. To provide information for real-time monitoring of damage, indirect measurement of damage is made feasible using an embedded carbon nanotube (CNT) network to perform as sensor for detecting the local damage. A software infrastructure is developed and implemented in order to integrate the various constituents, such as finite element approximation of the continuum damage models, generated experimental data, and Bayesian-based methods for model calibration and validation. The outcomes of the statistical calibration and dynamic validation of damage models are presented. The experimental program designed to provide observational data is discussed. [ABSTRACT FROM AUTHOR]

FRP reinforcement for concrete has been developed to replace steel in several applications, particularly in corrosion-prone RC structures. FRP rebars, generally, have a lower modulus of elasticity compared to steel, which leads to wider cracks and larger deflections. Furthermore, the FRP rebars have a low transverse stiffness and strength which are usually neglected. Consequently, the effectiveness of concrete contribution to shear capacity in terms of aggregate interlock and dowel action of the longitudinal rebars is lower for FRP-RC members respect to steel. Eurocode-like design equations for predicting the shear strength of FRP-RC members are herein suggested. Based on a database containing 129 flexural tests on RC beams strengthened with FRP stirrups performed in different research institutions across the world, a statistical calibration of Eurocode-like design equations for the shear capacity of RC beams with FRP shear reinforcement has been performed according to two alternative regression-based proposals and the EN 1990-procedure that is used as a benchmark. [ABSTRACT FROM AUTHOR]

The work describes the manufacturing and tensile static behaviour of natural fibres produced with novel extraction techniques. The fibres are extracted using two new methods, one consisting of immersing the blades of the Agave leaves in water for 10-13 days in a container, and another sustainable extraction process during which the Agave leaves are buried in earth for 90 days. Single fibre tensile tests have been performed at four gauge lengths to assess the effect of the gauge length over the tensile strength and Young's modulus. The results have been analysed through a two-parameter Weibull distribution to quantify the degree of variability in fibre strength and Young's modulus at different gauge lengths for the two extraction methods. Strong sensitivity of the mechanical properties of the fibres has been observed based on the production methods used. [ABSTRACT FROM AUTHOR]

A previously developed statistical model for transverse cracking in cross ply laminates is extended to oblique cracking in multidirectional laminates. The oblique cracks are assumed to form in a ply when the local in-plane tensile stress normal to fibers exceeds the transverse strength of the ply. This strength is assumed to have a statistical distribution given by a two-parameter Weibull function. The model is applied to a glass–epoxy [0/60 2 /0/−60 2 ] s laminate in which cracking evolution of the four −60° plies in the middle of the laminate is examined. The local stress field in the cracked −60° plies is calculated by a three-dimensional finite element method based on a unit cell construction developed by Li et al. [1] . The measured crack density is found to agree well with that calculated by the statistical model. [ABSTRACT FROM AUTHOR]

Abstract: Degradation of composite materials subject to cyclic loading is a multi-step process involving micro-cracks formation and progression until failure occurs. In this paper, the signatures of acoustic emission (AE) response emanating from composite specimens subjected to fully-reversed bending fatigue are studied. The composite is glass/epoxy (G10/FR4) laminates and the experiments cover different frequencies and displacement amplitudes. Results are presented for AE energy, counts and amplitudes. It is shown that the distribution of the cumulative AE amplitude can be described by a power law. Further, examination of the evolution of the probability density function (PDF) of the AE energy (counts) reveals two scaling zones wherein the transition from the low energy (count) to high energy (count) regime is identified. The low-energy phase represents very low damage or damage-free state of the laminate characterized by a power law with an exponent of αE =1.8 ± 0.05. In these series of experiments, AE energy release and AE counts follow the statistics and power laws that do not depend on the operational conditions. [Copyright &y& Elsevier]

Abstract: The use of fibre reinforced polymers (FRPs) to strengthen reinforced concrete (RC) structures has gained a wide popularity in the last decades. Although many experimental and analytical studies are available in literature, some issues are still under discussion in the research communities. Since the typical failure mode of FRP–concrete joints is reported to be debonding of the composite from the concrete substrate [1], the estimation of the bond strength between FRP and concrete substrate represents a key issue for the proper use of this technology. For this reason, several analytical models for the evaluation of the FRP–concrete bond strength and few models for the estimation of the effective bond length were proposed (some of them are included in design codes/recommendations/guidelines); however they were not assessed by means of an appropriate experimental database. This work shows an assessment of twenty analytical models for the evaluation of the FRP–concrete bond strength. The assessment is based on the analysis of a wide experimental database collected from the literature. The results are provided distinguishing between the test setup adopted (single or double shear test, bending test) and the material used (post impregnated sheets or pre impregnated laminates). The accuracy of each model was evaluated by means of a simplified statistical analysis. The influence of the test setup and basic material on the accuracy of the model used was analysed as well. Lastly, the accuracy of twelve available models in providing an estimation of the effective bond length was also assessed. [Copyright &y& Elsevier]

Abstract: This paper presents test results of six concrete beams reinforced with longitudinal carbon fiber reinforced polymer (CFRP) bars and without vertical shear reinforcement. All beams were tested under a two-point loading system to investigate shear behavior of CFRP reinforced concrete beams. Beam depth and amount of CFRP reinforcement were the main parameters investigated. All beams failed due to a sudden diagonal shear crack at almost 45°. A simplified, empirical expression for the shear capacity of FRP reinforced concrete members accounting for most influential parameters is developed based on the design-by-testing approach using a large database of 134 specimens collected from the literature including the beams tested in this study. The equations of six existing design standards for shear capacity of FRP reinforced concrete beams have also been evaluated using the large database collected. The existing shear design methods for FRP reinforced concrete beams give either conservative or unsafe predictions for many specimens in the database and their accuracy are mostly dependent on the effective depth and type of FRP reinforcement. On the other hand, the proposed equation provides reasonably accurate shear capacity predictions for a wide range of FRP reinforced concrete beams. [Copyright &y& Elsevier]

Abstract: The objective of this paper was to evaluate the effect of injection molding parameters, particularly melt temperature and injection pressure, and strain rate on the mechanical properties of polypropylene (PP) filled with different contents of multi-wall carbon nanotubes (MWCNTs). Tensile specimens with 1, 3 and 5wt.% MWCNTs were manufactured using the injection molding method and mechanical properties, such as Young’s modulus, the yield strength and yield strain, the stress at break and strain at break, were measured at three different strain rates. The effects of the process variables on these mechanical properties were investigated using a set of metamodeling techniques including the Taguchi method and the analysis of variance (ANOVA). The experimental results have shown that the incorporation of MWCNTs could effectively enhance the above mentioned mechanical properties of the injection molded PP/MWCNTs nanocomposites, the reinforcing effect of MWCNTs being more pronounced at higher injection pressure. The yield strength, stress at break and Young’s modulus of the PP/MWCNTs nanocomposite increased with the increase of the MWCNTs content and strain rate, while an opposite trend was found in the yield strain and strain at break. The effect of crystallinity is secondary with respect to the effect of carbon nanotubes. [Copyright &y& Elsevier]

Abstract: This paper establishes a set of criteria to check two microstructures in fiber-reinforced composites for geometrical equivalence. The criteria are based on a combination of a point process, one-point and two-point probability functions; convergence of microstructure size; and equality of fiber radius distribution. The criteria were shown to distinguish different microstructures and identify similar ones. Also, a reconstruction technique is proposed that can efficiently reconstruct a microstructure while satisfying the criteria. Results show the reconstruction technique exceeded the 5% tolerances set by multiple samples of an experimental observation. [Copyright &y& Elsevier]

Abstract: The decay and termite resistance and effects of a robust leaching process on the efficacy of zinc borate-incorporated particleboard were examined. Particleboards (300×300×15mm) prepared from particles of mixed wood species generated from demolished construction materials were incorporated with zinc borate at target retentions of 0%, 1%, 1.5% and 2% of the particle weight. An in-line treatment method was utilized to introduce the powdered chemical during the blending stage. ICP analysis indicated that the amount of zinc borate was not lost during manufacturing. Standard static bending tests demonstrated that there was no significant loss in mechanical properties. The decay and termite tests indicated that the efficacy of zinc borate at a higher retention was enough to suppress the biological activity, even after application of a robust leaching process. [Copyright &y& Elsevier]

Abstract: This paper presents the closing step of a synthesis process aiming at deriving, from a previously developed more complex model, a simple design formula to evaluate the shear strength contribution provided by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips to a Reinforced Concrete (RC) beam. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by the two previous and more sophisticated versions of the same modeling strategy. Monte Carlo simulations are carried out in order to appraise the sensitivity of the NSM shear strength contribution prediction to the value assumed by the input parameters. [Copyright &y& Elsevier]

Abstract: Subset Simulation, which is a promising and efficient technique to qualify probabilistic uncertainties propagation, is utilized to perform a probabilistic analysis on the bearing strength of a composite pin joint. A two-dimensional (2D) finite element (FE) analysis is utilized for the deterministic progressive damage analysis. Three groups of failure criteria, three sets of degradation rules and two kinds of shear relationship are employed for progressive damage analysis to predict mean, coefficient of variation (COV) and cumulative distribution function (CDF) of its bearing strength. The computational results have been validated by comparison with experimental data available in the literature. [Copyright &y& Elsevier]

Abstract: This paper reports a two-step modeling approach for predicting the effective mechanical properties of polymeric nanocomposites modified with single walled carbon nanotube (SWNT). In step one, the nano-heterostructures of the nanocomposites were represented by 3-D nanoscale cylindrical, square, or hexagonal prismatic representative volume elements (RVEs). Each RVE contained a long or a short carbon nanotube (CNT) and consisted of three phases, i.e., CNT, matrix, and interphase. The mechanical properties of each RVE were extracted from the modeling results of the RVE undergone three load tests, i.e., uniaxial tensile test, lateral expansion test, and axial torsional test, using appropriately derived formulae. The effects of the volume fraction of CNTs on the mechanical properties of the RVEs were studied. The equivalent mechanical properties of the nano-heterostructures were obtained by averaging the mechanical properties extracted from each RVE. In step two, micro/macroscale nanocomposites were represented by a 3-D microscale unit cell which was discretized into cubic elements. Using Monte Carlo method, each element was assigned the averaged mechanical properties of the RVEs with random CNT orientation and length type. The overall effective mechanical properties of the nanocomposites were predicted by a tensile test on the unit cell. The modeling results by this proposed approach was compared with and validated by the experimental data of the SWNT modified epoxy nanocomposites. [Copyright &y& Elsevier]

Abstract: A mixture design was used in experiments, to determine the optimal mixture for composites of rubberwood flour (RWF) and reinforced recycled polypropylene (rPP). The mixed materials were extruded into panels. Effects were determined of the mixture components rPP, RWF, maleic anhydride-grafted polypropylene (MAPP), and ultraviolet (UV) stabilizer, on the mechanical properties. The overall composition significantly affected flexural, compressive, and tensile properties. The fractions of recycled polypropylene and rubberwood flour increased all the mechanical material properties; however, increasing one fraction must be balanced by decreasing the other, and the rubberwood flour fraction had a higher effect size. The fraction of MAPP was best kept in mid-range of the fractions tested, while the UV stabilizer fraction overall degraded the mechanical properties. Our results suggest that the fraction of UV stabilizer should be as small as possible to minimize its negative influences. The models fitted were used for optimization of a desirability score, substituting for the multiple objectives modeled. The optimal formulation found was 50.3wt% rPP, 44.5wt% RWF, 3.9wt% MAPP, 0.2wt% UV stabilizer, and 1.0wt% lubricant; the composite made with this formulation had good mechanical properties that closely matched the model predictions. [Copyright &y& Elsevier]

Abstract: The reinforced plastic materials have been widely used to manufacture several machine parts due to their lightweight and superior specific strength/modulus compared to the metallic materials. This paper investigates the use of Taguchi’s method in order to identify the best drilling setup of glass reinforced polyamide. Experimental study on PA6 and PA66GF30 composites was conducted using three carbide drills (K20) with different geometries. The effect of tool geometry, spindle speed and feed rate factors on the thrust force, hole mean diameter and circularity error were analyzed. The results revealed the quality of the holes can be improved by proper selection of cutting parameters. [Copyright &y& Elsevier]

Abstract: Strengthening of reinforced concrete (RC) members by means of fibre reinforced polymers (FRP) has gained increasing importance in the last few decades. On the other hand the necessity of skilled labour, high costs and particularly the weak response under high temperature conditions represent critical issues for the effective application of this technique. The use of fibre reinforced cementitious matrix (FRCM) composites applied to RC members seems to be a promising technique since it combines cost economy and high performance. Despite the fact that a number of experimental investigations on strengthening of RC elements by means of fibre reinforced polymers (FRP) composites are available in the literature, very little information is available about fibre reinforced cementitious matrix composite (FRCM). Hence, the use of cementitious composites in strengthening of RC structures is strongly limited by the lack of design models, guidelines, and recommendations and by the few available experimental investigations. This work aims to better understand the behaviour of FRCM strengthened RC full-scale elements through experimental tests on precast prestressed double-T beams. In addition to investigating the experimental behaviour of an innovative and promising strengthening system, a further element of novelty of the work is that the tested beams belong to an actual existing industrial building, since the few experimental tests available in the literature are mostly related to small-scale and cast-in-place RC elements. [Copyright &y& Elsevier]

Abstract: This paper presents the wear behaviour of Al6061-T6 discontinuously reinforced with silicon carbide (SiC) and aluminium oxide (Al2O3) composite. The test specimens are prepared and tested as per ASTM standard. The experiments are conducted by using a pin on disc wear tester. Empirical relation is established to estimate the wear using statistical regression analysis and analysis of variance (ANOVA). The results indicated that the wear resistance of the 15% hybrid composite is better than that of the 5% composite. The fracture surface of composites shows the ductile tear ridges and cracked SiC and Al2O3 particles indicating both ductile and brittle fracture mechanism. [Copyright &y& Elsevier]

Abstract: Six different formulations of wood–plastic composites (WPC) fabricated from wood and polypropylene (PP) were tested in the laboratory against decay and termites and in a protected above-ground field test in southern Japan. Variables examined included comparisons of untreated and zinc borate (ZnB) incorporated formulations, wood content ratio, wood particle size and increased surface area via surface grooves (channels) to promote moisture infusion. A standard method originally designed to test durability of solid wood was modified for testing WPC. Wood decay fungi and Formosan subterranean termite activity in laboratory and field tests resulted in different mass losses, post-decay moisture contents and field test ratings depending on their wood and ZnB content. The results show that as wood content increased, mass losses also increased. Addition of ZnB at 1% (w/w) retention level significantly decreased mass losses of wood–plastic composite when exposed to laboratory decay and termite tests. The effects of surface grooves and wood particle size were less important, compared to wood particle content. All WPC tested were highly resistant to fungal decay under protected above-ground field conditions during 36months. Termite attack, on the other hand, started at earlier stage reducing mean ratings 1year after the installation. [Copyright &y& Elsevier]

Abstract: Metal matrix composites (MMCs) are difficult to machine due to their abrasive properties. With the projected widespread application of MMCs, it is necessary to develop an appropriate technology for their effective machining. The present investigation focuses on finding the optimal machining parameters setting in drilling of hybrid aluminium metal matrix composites using the grey-fuzzy algorithm. This proposed algorithm, coupling the grey relational analysis with the fuzzy logic, obtains a grey-fuzzy reasoning grade to evaluate the multiple performance characteristics according to the grey relational coefficient of each performance characteristics. The Taguchi method of experimental design is a widely accepted technique used for producing high quality products at low cost, therefore a L27 3-level orthogonal array is used for the experiments. The optimisation of multiple responses in complex processes is common; therefore, to reduce the degree of uncertainty during the decision making, fuzzy rule-based reasoning is integrated with the Taguchi’s method. The response table, response graph and analysis of variance (ANOVA) are used to find the optimal setting and the influence of machining parameters on the multiple performance characteristics. Experimental results have shown that the required performance characteristics in the drilling process are improved by using this approach. [Copyright &y& Elsevier]

Abstract: This research focuses on the behavior of the tensile and flexural modulus of polypropylene/hemps strands composites. The intrinsic tensile modulus of the hemp strands was computed using Hirsch model and experimental data of the tensile modulus of the polypropylene composites at the 20–50 wt.% hemp strands content. The modified rule of mixtures was used to evaluate the efficiency factor. Square packing distribution was assumed and the length factor was fixed by Cox–Krenchel’s model. The mean value of the orientation efficiency factor was found to be 0.55. Tensile and flexural modulus were compared concluding that its value was independent of the manner the composite was loaded. Finally the Tsai–Pagano model was applied to predict the behavior of the composite’s tensile modulus. [Copyright &y& Elsevier]