Search

A novel preforming process was developed for non-crimp fabric (NCF) materials that generated in-plane tension through discontinuous blank boundary conditions. The method employed magnetic clamps and was designed to be both flexible and scalable, with clear routes to industrialisation. The capability of the process was explored in physical trials for a hemispherical and a cubic geometry. Characterisation of a biaxial veiled NCF showed the veil had a dominant effect on the bending mechanics. Subsequently a macroscale finite element model was developed to include an efficient bending idealisation and non-orthogonal in-plane material behaviour. Finally, global process optimisation of the preforming process was demonstrated. The optimisation approach used Gaussian process modelling with a periodic kernel to estimate the wrinkle size for untested clamping arrangements and then deployed Bayesian optimisation to find the optimal configuration. Results indicated that distributed magnetic clamping was effective and amenable to surrogate modelling.

Made available in DSpace on 2022-04-28T19:43:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 The dynamic mechanical behavior (storage modulus, loss modulus, and tan δ) of hybrid sisal/glass composites was investigated in the temperature range of 30–210 °C, for two different volume percentages of reinforcement along with the different ratios of sisal and glass fibers. Based on the experimental outcome, an artificial neural network (ANN) approach was used to predict the dynamic mechanical properties followed by a surface response methodology (SRM). The ANN analysis showed an excellent fit with the storage modulus, loss modulus, and tan δ experimental data. In addition, the fitted curves with the ANN approach were used to propose equations based on SRM. The simulation result has shown that the ANN is a potential mathematical tool for the structure–property correlation for polymer composites and may help researchers in the development and application of their data, reducing the need for long experimental campaigns. Federal University for Latin American Integration (UNILA) Department of Materials and Technology School of Engineering São Paulo State University (Unesp) Postgraduate Program in Mining Metallurgical and Materials Engineering (PPGE3M) Federal University of Rio Grande do Sul (UFRGS) Postgraduate Program in Engineering of Processes and Technologies (PGEPROTEC) University of Caxias do Sul (UCS) Department of Materials and Technology School of Engineering São Paulo State University (Unesp)

In this study, the morphological, physical, and tensile properties of flax were experimentally investigated at three different scales (single fiber, yarn and unidirectional fabric). The cross-sectional area was determined directly using microscopic image and indirectly via linear density with gravimetric and vibroscopic methods. All specimens were tested in tension until failure. The results showed that measured properties and their variability were scale-dependent. The tensile strength and modulus of elasticity were gradually decreasing with the scale and the variabilities were decreasing when going from fibers to yarns and fabric. This difference in the properties should be considered for any multi-scale analysis of the flax reinforcement. The average failure strains of single fiber, yarn and fabric were 2% (±30%), 1.7% (±12%) and 1.7% (±2.8%), respectively. Due to the consistency of failure strain at different material scales, it can be recommended as design criterion. The results of this study can be used for better design and preparation of plant-based natural fiber reinforced polymer composites.

This paper highlights the amount of risk taken when a deterministic approach is used in designing composite structures without consideration of stochastic effects. The study treats all material and geometric parameters of the composite laminated plates under investigation as stochastic. Monte Carlo simulation is employed to investigate the stochastic effects of material properties, ply thickness, and ply orientation on the failure of laminated composite plates under static loads. Classical lamination theory is used to calculate the strength ratios using maximum stress, Tsai-Hill, and Tsai-Wu failure criteria for plates of three different materials in various stacking sequences. Variation in the failure ply distributions are shown to increase with coefficient of variation of the input variables. A positive linear trend between the coefficients of variation of the strength ratio and input variables is found, whose slope increases as randomness is considered for more input variables. Probability of failure and failure ply distributions are shown to be heavily dependent on the combination of laminate stacking sequence, material, and failure probability. In particular, while the empirical failure probability for cross-ply laminates is highest for the ply predicted by a deterministic analysis, this probability decreases rapidly with increasing variation in input parameters. Further, the failure of unexpected plies for cross-ply laminates is shown to be related to the stiffness ratios of the plies. The general significance of considering ply thickness and ultimate strength as random variables is also demonstrated, as well as the significance of randomness in ply orientation for balanced and angle ply laminates.

International audience; This study aims to assess the viability of nanocomposites in fused filament fabrication. Polylactide/organo-modified layered silicate materials have been studied in terms of structure and properties evolution through the whole manufacturing chain, and for thermomechanical optimisation. The method included the optimisation by the composite formulation and by the additive manufacturing process by experimental designs. A competition between flow thinning of the molten composite and stiffness of the input filament with the addition of filler allows an enhanced printability at intermediate loadings. The method provides an optimisation of the final parts, enabling similar or greater tensile properties, while providing better thermal stability, with additively manufactured nanocomposite materials compared to conventionally manufactured polymers.

WOS: 000428487200012 Several formulations of wood-plastic composites and a particleboard were fabricated with combining zinc borate biocide at different retention levels during the manufacturing process. The treated specimens were exposed to a field test under protected above ground conditions for 7 years in southern Japan. During biannual inspections, the specimens were visually inspected and graded for decay and Formosan subterranean termite damage. While zinc borate retention levels tested were able to protect the particleboards from decay activity for 7 years, their efficacy was lower against termite attack. The retention levels tested up to 2% (w/w) helped to reduce termite damage noticeably but failed from full protection (e.g. rating 10) indicating higher zinc borate loadings are required in particleboards if they will be utilized in southern Japan climatic conditions. Wood-plastic composites were also more durable against fungal damage during the 7 years exposure period but this condition seems changed last 18 months since some lower decay ratings were recorded even for zinc borate embedded formulations. While termite destruction diminished significantly with zinc borate integrated formulations, higher retentions might be recommended as threshold for full protection in wood-polypropylene composites.

International audience; Composite processing strongly affects the size of lignocellulosic fibers, and consequently the mechanical properties of the final product. Using a reliable method for the analysis of fiber length and diameter distributions is thus crucial for the understanding of fiber behavior during processing. In this study, three different techniques, X-ray microtomography, 2D scanning and automated fiber analyzer, were compared in terms of their reliability for the characterization of dimensions of two kinds of lignocellulosic fibers, hemp and miscanthus, in polymer-natural fiber composites. Statistical analysis was employed to interpret fiber size distributions. The study confirmed that interpreting the dimensions of natural fiber is still a difficult task. The inherent limitations of the measuring methods make each technique complementary to the others in terms of length scale. The choice of the technique is, therefore, strictly dependent on fiber dimensions and the aim of the work.

Injection molded short fiber reinforced composites (SFRC) have different local fiber orientation distribution (FOD) at every point. SN curves of short fiber reinforced composites are known to depend on the fiber orientation distribution. Such materials also suffer from continuous loss of stiffness during cyclic loading. It is not known whether the loss of stiffness is different for SFRC with different FOD. A statistical analysis of the loss of stiffness curves is presented in this paper. Tension-tension fatigue experiments are performed and loss of stiffness is collected for every data point in the SN curve. A systematic method for comparing the loss of stiffness is developed. It is concluded that the difference in loss of stiffness curves for coupons of SFRC with different FOD is not statistically significant. (C) 2016 Elsevier Ltd. All rights reserved.

This paper concerns the homogenization of the dynamic response of Euler Bernoulli'sbeam with random Young's modulus. Considering the eigenvalue problem, specialattention is dedicated to the homogenization residuals (correctors) analysis, i.e. thedfference between the random heterogeneous solution and the homogenized solution.Several correlation (mixing) laws of the Young's modulus are considered anda dimensionless characteristic scale length, based on the correlation length, is introduced. The effects of the mixing law on the residuals are analyzed using numericalapproaches both for sampling the random Young' modulus and for examining thebeam eigenvalue problem. Two measurements are introduced to estimate the residualsbetween apparent and effective solution: the normalized difference of Young'smodulus and the normalized difference of modes' shape. The effect of the mode'sorder is also highlighted with reference to forced vibrations.

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 r2 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.

WOS: 000333506500068, 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 degrees. 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. (C) 2013 Elsevier Ltd. All rights reserved.

WOS: 000328801200006 The decay and termite resistance and effects of a robust leaching process on the efficacy of zinc borate-incorporated particleboard were examined. Particleboards (300 x 300 x 15 mm) 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. (C) 2013 Elsevier Ltd. All rights reserved. Japan Society for the Promotion of Science (JSPS)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of Science [P07171]; RISH, Kyoto University The first author extends his appreciation to Japan Society for the Promotion of Science (JSPS) for supporting this study through a post-doctoral fellowship grant (P07171), to RISH, Kyoto University, for support under the Visiting Professor program between April 1 and June 30, 2012, and to the late Dr. Kunio Tsunoda (who passed away on October 5th, 2011) for moral support at the initiation of the project and Ms. Nuriye Peachy for English proof readings of the manuscript.

Composites manufacturing involves many sources of uncertainty associated with material properties variation and boundary conditions variability. In this study, experimental and numerical results concerning the statistical characterisation and the influence of inputs variability on the main steps of composites manufacturing including process-induced defects are presented and analysed. Each of the steps of composite manufacturing introduces variability to the subsequent processes, creating strong interdependencies between the process parameters and properties of the final part. The development and implementation of stochastic simulation tools is imperative to quantify process output variabilities and develop optimal process designs in composites manufacturing.

Local variations in the random filament arrangement in carbon fibre bundles were determined by optical microscopy and automated image analysis. Successive steps of abrading, polishing and acquiring micrographs of the sample surface made it feasible to analyse the micro-structure over a series of cross-sections along the fibre bundle path. Random and systematic changes in local filament arrangements were determined. Systematic changes were related to the interaction of a fibre bundle with an intersecting binder thread leading to a local increase of the fibre volume fraction at the interface. Random clustering of filaments in areas of high or low fibre volume fractions within the fibre bundles were found to be unaffected by the relative position of the bundle.

In the recent past, experimental results of bond tests performed by several researchers on the performances of Fiber Reinforced Polymer (FRP) applied according to Near Surface Mounted (NSM) strengthening technique showed that mechanical properties of materials and surface properties of FRP reinforcement as well as the grooves geometry and the test set up can affect the bond of this strengthening system. An experimental program aimed to compare the bond behavior of different types of FRP materials applied on concrete blocks according to Externally Bonded Reinforcement (EBR) and NSM strengthening techniques has been presented and discussed in a previous paper, showing that the NSM technique could represent a sound alternative to EBR systems since it allows the FRP tensile strength to be better exploited. Herein the results of bond tests on different types of NSM reinforcement are analyzed in terms of bond-slip relationships in order to show the appropriateness of using simplified bilinear relationships. Moreover, further experimental results of bond tests available in literature and characterized by different types of bond failures have been selected and joined to those widely analyzed in this paper in order to provide an experimentally calibrated relationship predicting the maximum debonding strain in the FRP NSM reinforcement. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; Using high resolution optical microscopy coupled with image analysis software and statistical methods, fibre length and aspect ratio distributions in polypropylene composites were characterized. Three types of fibres, flax, sisal and wheat straw, were studied. Number and surface weighted distributions were used to demonstrate the presence and amount of elementary fibres, fibre bundles and particles. A large number of small particles that are usually not taken into account were found. The obtained fibre length and aspect ratio distributions were successfully fitted by a two-parameter Weibull model. No significant effect of fibre concentration on the length and aspect ratio distributions was detected for 20% and 40% flax-based composite. Fibre type was found to be a very important parameter influencing size and shape distributions: flax is broken into long elementary fibres, sisal-based composite contains non-dispatched bundles and elementary fibres and wheat straw-based composite has bundles and large and small particles.

Natural fibres are studied as alternatives for man-made fibres to reinforce composites while keeping the weight lower. The assessment of the value of some commonly available tropical fibres for the composite industry starts with the determination of the strength, E-modulus and strain to failure through single fibre tensile tests. The mean strength and standard deviation is calculated following the normal and Weibull distribution resulting in the questionable benefit of applying the Weibull distribution. Furthermore, a correction method assesses the real fibre elongation from the measured clamp displacement. This procedure seems to be useful for strong, brittle fibres to produce more reliable results for the E-modulus and strain to failure.

Synchrotron radiation computed tomography has been used to analyse fibre break accumulation in unidirectional composites loaded in tension. The data are compared to model predictions. The model only slightly overestimated the composite failure strain, but predictions of fibre break density were too high, which can be mainly attributed to errors in the Weibull distribution. Both the number and percentage of interacting fibre break clusters were under-predicted by the model. This was attributed to an underestimation of stress concentrations in the model. While the experimental observations revealed mainly co-planar clusters, the model predicted mainly diffuse clusters. The experiments showed that the clusters did grow any further after their formation, while the model predicted a gradual development. Both local and dynamic stress concentrations were hypothesised to be key features for further exploration. The discrepancies identified, inform suggestions for directions advancing the state-of-the-art strength models of UD composites. publisher: Elsevier articletitle: Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional fibre-reinforced composites journaltitle: Composites Part A: Applied Science and Manufacturing articlelink: http://dx.doi.org/10.1016/j.compositesa.2015.06.018 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: Composites A, Applied Science and Manufacturing vol:77 pages:106-113 status: published

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., The study reported in this paper is part of the project "PreLami - Performance of reinforced concrete structures strengthened in flexural with an innovative system using prestressed NSM CFRP laminates", with the reference PTDC/ECM/114945/2009. The third author also wishes to acknowledge the scholarship granted by FT (SFRH/BD/61756/2009). The authors would also like to acknowledge the support provided by S&P, for supplying the adhesives and the laminates, and Casais and CiviTest for the preparation of the beams.

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., Fundação para a Ciência e a Tecnologia (FCT)

WOS: 000320294200022 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 36 months. Termite attack, on the other hand, started at earlier stage reducing mean ratings 1 year after the installation. (C) 2013 Elsevier Ltd. All rights reserved. Japan Society for the Promotion of Science (JSPS)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of Science [P07171] The first author extends his appreciation to Japan Society for the Promotion of Science (JSPS) for supporting this study through a post-doctoral fellowship Grant (P07171) and RISH, Kyoto University for invitation under the Visiting Professor program between April 1 and July 29, 2012 and to the late Dr. Kunio Tsunoda for initiation of the project, to Mr. Akio Adachi for assistance with field work and to Mr. Masami Kato from Misawa Homes Co. Ltd. for fabrication of WPC composites.

The aim of this paper is to fabricate novel glass matrix composites reinforced by means of celsian particulate. In fact, the attractive features of celsian, such as chemical stability and high mechanical resistance, can be favourably exploited in order to obtain enhanced-performance composites with respect to bulk glass. A design of experiments (DOE ) procedure has been utilized to optimise the fabrication route of glass–celsian composites. This method allowed the determination of the optimal processing conditions for the obtainment of a fully dense material with a good particulate dispersion.

Birgoren, Burak/0000-0001-9045-6092 WOS: 000220303300008 Estimating confidence lower bound for fracture strength of composites is a key concern in design and manufacture, and the Weibull distribution has been widely used for this purpose. Previous simulation-based studies presented computational tools for these bounds involving tables or parametric equations, which lack generality and may contain simulation and curve-fitting errors. An alternative approach is to present a fast and effective simulation tool that can be directly used by the end-user. Such a tool is developed in this study for estimating the bounds using the Weibull distribution based on maximum likelihood estimation. This is a more versatile approach in that it allows the user to input any desired confidence level, failure probability, and simulation-run number. The tool is demonstrated by using fracture strength data obtained from ASTM D3039 tension tests of 19 identical carbon-epoxy composite specimens. The results are compared with those obtained from previously developed approaches. (C) 2004 Elsevier Ltd. All rights reserved.