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Temperature and moisture are important environmental conditions governing the usage of carbon fiber‐reinforced plastics (CFRP). In this study, tensile, compression, and shear tests of woven CFRP composites were conducted in four composite environments: cold‐temperature dry state, room‐temperature dry state, elevated‐temperature dry state, and elevated‐temperature wet state. Fourier transform infrared (FTIR) spectroscopy was used to analyze the molecular composition and structure under these environments. The fracture morphology was also analyzed using scanning electron microscopy (SEM) to understand the deterioration mechanism of the material properties at the macro and micro scales. Finally, a two‐parameter Weibull statistical model was used to evaluate the scattering of the composites. The results demonstrate that the tensile, compressive, and shear properties of the material decrease under harsh conditions, and the degradation effect on the ultimate strength is much greater than that of the modulus. Cold‐temperature dry and elevated‐temperature wet conditions are particularly severe. Composite environments significantly affect the macroscopic failure process and ultimate failure mode of materials. In general, the temperature and humidity of the matrix system acts at the core of the deterioration mechanism of composites, affecting the properties of the fiber/matrix and orthogonal woven fiber interfaces, and eventually resulting in a loss of their constitutive strength and bearing capacity. The theoretical ultimate strength were consistent with the experimental values. Highlights: Comprehensive mechanical property testing in multiple composite environments.Degradation mechanisms were revealed from multiscale morphology analysis.Scattering of composites were evaluated using statistical analyses.Cold temperature dry and elevated temperature wet were the worst states.Deterioration effect of environment on matrix and interface is the core failure mechanism. [ABSTRACT FROM AUTHOR]

Corrugated packaging models and theories are well-established under static load conditions, however, very few studies can be found in the literature dealing with the behaviour of corrugated boards under impact conditions, which is critical in e-commerce distribution. Packaging capacity of energy absorption and the acceleration peak provoked during the drop or shock event are the key factors to assure the impact does not cause damage to the products. This study describes cushioning properties of corrugated boards in edge crush disposition and proposes a predictive model, experimental methods, and tools to assess its dynamic properties. The proposed model is based on static edge crush test theory adapted to impact conditions through relations with static properties of paper. This novel model will allow the estimation of energy absorption for packaging solutions that rely on this deformation mode.

In this paper, 400 flax fibers with 10 different lengths (40 fibers at each length) are experimentally characterized (quasi-static tensile behavior) and then the results are statistically analyzed. The quasi-static tensile test results appeared to have a large dispersion, which makes it possible to measure the degree of variability in the ultimate tensile strength (UTS), failure strain, and the Young’s modulus of the fiber, at different gage lengths (10 mm to 500 mm). The variation in mechanical properties at each fiber length is established using two and three Weibull statistics based on maximum likelihood estimation (ML) and least square estimation (LS). Finally, all 10 groups for each tensile property are analyzed by one-way (ANOVA).

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. [ABSTRACT FROM AUTHOR]

In this work, a novel algorithm is proposed to generate three-dimensional random spatial distribution representative volume elements (RVEs) of composite materials. The approach is based on the bionic optimization technology of Cuckoo search algorithm. It addresses the problem of jamming limitation in the previous approaches and is able to generate nonuniformly dispersed microstructures with high fiber volume fractions and any specified inter-fiber distances. Statistical analysis is implemented to evaluate the nonuniform distributions of the generated RVEs and the results agree well with the experimental data in all statistical distributions. Furthermore, finite element method and volume homogenization are conducted to predict the elastic properties of the generated RVEs. The predictions are close to the experimental data in the literatures and the expected transversal isotropy in the 2–3 plane of the microstructures is confirmed. In addition, the effective elastic properties of glass/epoxy composites with fiber volume fractions of 30–70% are calculated by using the generated microstructures and compared with the theoretical models. The agreement of the numerical and analytical results provides further validation for the proposed algorithm to generate RVEs of composite materials. This method also can be easily used in the exploration of particle-reinforced composites.

Copyright of Journal of Natural Fibers is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

This work describes a novel hybrid polymer composite made from sugarcane bagasse and discarded rubber particles. A 25 full factorial design is performed to identify the effects of bagasse fibres and rubber particles on the physical and mechanical properties of the composites. The mechanical properties are evaluated by tensile and compression tests, and the physical properties by apparent porosity, water absorption and bulk density. The mechanical and physical properties are substantially affected by the amount and size of the rubber particles. The length and treatment of bagasse fibres affect the stiffness and strength of the composites with less contribution. The presence of sugarcane bagasse increases the compressive toughness of hybrid composites. [ABSTRACT FROM AUTHOR]

Currently, the manufacture of composite structures often requires material removal operations using a cutting tool. Indeed, since biocomposites are generally materials that do not conduct electricity, electro-erosion cannot be utilized. As a result, the processes that can be used not only the unconventional method of abrasive water jet but also conventional machining, such as drilling. Delamination factors (Fd) are widely recognized for controlling the damaged area (delamination) induced by drilling in industry. As discussed in the literature, several approaches are available to evaluate and quantify the delamination surrounding a hole. In this context, the objective of this study is to compare the three Fd evaluation methods that have been most frequently used in previous investigations. To this end, three spindle and feed speeds and three Brad and Spur drills (BSD) tool diameters were selected (L27) for drilling 155-g/m2 density jute fabric–reinforced polyester biocomposites. The desirability function (DF) was further made to optimize the drilling parameters. The response surface methodology (RSM) and artificial neural networks (ANNs) were applied to validate the results obtained experimentally as well as to predict the behavior of the structure depending on the cutting conditions. [ABSTRACT FROM AUTHOR]

The integration of repurposed and recycled carbon fibers into high-performance composites is essential to the adoption of composites for automotive structures due to their low-cost, high formability, and reduced environmental impact. When high areal density nonwovens of these fibers are infused with a semi-crystalline thermoplastic resin, organosheets offering competitive mechanical properties can be produced. This study examined the optimization of such composites through multiscale material characterization and post-process annealing. Single fiber tensile tests were used to characterize repurposed and recycled fiber formats. The thermomechanical properties of the polyphenylene sulfide matrix and resulting composites subjected to different post-process annealing conditions were characterized using differential scanning calorimetry, dynamic mechanical analysis, and nano-indentation. Single fiber push-in testing was conducted to evaluate the fiber–matrix interface as a function of annealing. It was shown that statistical methods based on the bootstrap principle successfully identify the effects of post-process annealing, which are otherwise masked by material inhomogeneity. Post-process annealing was shown to be an effective method of improving the resulting mechanical properties of repurposed and recycled carbon fiber organosheet composites, thereby optimizing their properties for use as a high-performance automotive structural material. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative approach for the efficient analysis of composites manufacturing processes and phenomena. The method combines low- and high-fidelity simulation schemes with limited amounts of experimental data to train surrogate machine learning (ML) models. Guided by a novel approach, Spatially Weighted Gaussian Process Regression (SWGPR), a predictive model is efficiently constructed and calibrated by assigning datapoint-dependent noise levels to simulation points, establishing a multi-scale data-driven uncertainty structure. This study demonstrates the effectiveness of the method in accurately predicting process-induced deformations (PIDs) for L-shaped cross-ply laminates using minimal experimental efforts. The presented method aims to provide a cost-effective and broadly applicable framework for understanding and improving the design, development, and manufacturing of composites. [ABSTRACT FROM AUTHOR]

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.

A prediction method is proposed for the probabilistic failure of composite multi-bolt double-lap joints based on a single-parameter spring-based method, a failure envelope method and Monte Carlo simulation. In this method, the effects of the randomness of the laminate bearing and open-hole strength, laminate's properties, geometric parameters, clearances, tightening torques and bolt bearing chord stiffness are considered. And the application of failure envelope method leads to an advantage of a very small amount of calculation. To validate the proposed method, composite two-bolt and three-bolt double-lap joints were designed and tested to determine the stochastic failure load. Following the testing of all the necessary parameters, satisfactory agreement between the numerical and experimental stochastic failure loads of the multi-bolt joints was found. Furthermore, the sensitivities of the probabilistic failure load of multi-bolt joints were investigated. It follows that the randomness of the laminate open-hole tensile and bearing strengths have the most significant influences on the failure load, while the influences of the randomness of the other parameters are slight, which affect bolt load distribution directly, and indirectly affect the failure load through influencing the bolt load distribution. [ABSTRACT FROM AUTHOR]

Abstract This paper concerns the homogenization of the dynamic response of Euler Bernoulli's beam with random Young's modulus. Considering the eigenvalue problem, special attention is dedicated to the homogenization residuals (correctors) analysis, i.e. the difference between the random heterogeneous solution and the homogenized solution. Several correlation (mixing) laws of the Young's modulus are considered and a dimensionless characteristic scale length, based on the correlation length, is introduced. The effects of the mixing law on the residuals are analyzed using numerical approaches both for sampling the random Young' modulus and for examining the beam eigenvalue problem. Two measurements are introduced to estimate the residuals between apparent and effective solution: the normalized difference of the Young's modulus and the normalized difference of the modes' shape. The effect of the mode's order is also highlighted with reference to forced vibrations. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental study to assess the effects of food chemicals and temperature on the mechanical performance of glass fiber reinforced bio-based polyamide. The diffusion of food chemicals was mainly driven by thermal energy, following Arrhenius law in all tested environments. Degradation of mechanical properties and decrease in reliability were assessed, due to the plasticization of polymer matrix. Secondary but not negligible effect on flexural strength degradation is given by the different chemical interaction between polymeric chains and molecules of food chemicals. Colour change was measured and resulted to be positively correlated to diffusion. [ABSTRACT FROM AUTHOR]

The results of time‐variant reliability analysis of shear‐strengthened reinforced concrete (RC) beams with externally bonded fiber‐reinforced polymer (FRP) are presented with an emphasis on the effects of environmental harshness and effective design parameters. The effects of chloride‐induced pitting corrosion and FRP degradation are considered using Monte Carlo simulation to assess the influence of environmental deterioration on the fib 2001 limit states instead of applying design reduction factors. For the defined worked example, the proposed method specifies the remaining lifetime of the strengthened beam by considering a reasonable value for the target reliability index. With regard to the reliability index profiles, it is shown that chloride‐induced pitting corrosion has a greater effect on the shear capacity of strengthened beams than the degradation of the FRP. It was found that the FRP reinforcement ratio has a considerable effect on the governing failure mode; hence, it is important to calibrate the proposed safety verifications of fib bulletin 14 using sufficient experimental data for the relevant random variables in a reliability‐based context. [ABSTRACT FROM AUTHOR]

Knowledge of the stochastic nature of fatigue life of composite materials can be modeled by the failure time with the Weibull distribution. This task becomes complex when the samples are small and scattered. In this way, it is necessary to know and to improve robust models of estimation of the parameters of the distribution of Weibull. The aim of this work is to compare the performance of least squares, least squares weighted, maximum likelihood estimator and momentum method and to suggest a method that obtains better performance in life behavior to fatigue with small samples. Monte Carlo simulations were performed to estimate the distribution parameters with different sample sizes and an application with real fatigue data that compares performance using goodness-of-fit. The results of the simulations showed that the weighted least squares estimation was able to generate more reliable estimators for fatigue behavior during its useful life. In this way, it is possible to conclude that small samples make the real representation of life difficult to the material fatigue, but using the weighted least squares estimation method, it is possible to obtain more estimates. [ABSTRACT FROM AUTHOR]

Continuous basalt fibers present a unique combination of good mechanical and functional properties at an attractive cost level. These characteristics can be useful in high performance polymer matrix composites where cost orientation and function integration are becoming priority objectives. The present work examines a currently unresolved problem of basalt fibers regarding high performance applications: the variation of fiber structural and mechanical properties due to inhomogeneity of the natural raw material and the spinning process. Commercial basalt fibers from seven different manufacturers were investigated regarding their fiber chemistry, diameter distribution and occurrence of defects and crystallites. In a second step, structure-property relations on different scales were established with single fiber, impregnated roving and composite tensile test results. [ABSTRACT FROM AUTHOR]

Resin transfer moulding is one of several processes available for manufacturing fibre-reinforced composites from dry fibre reinforcement. Recently, dry reinforcements made with Automated Dry Fibre Placement have been introduced into the aerospace industry. Typically, the permeability of the reinforcement is assumed to be constant throughout the dry preform geometry, whereas in reality, it possesses inevitable uncertainty due to variability in geometry. This uncertainty propagates to the uncertainty of the mould filling and the fill time, one of the important variables in resin injection. It makes characterisation of the permeability and its variability an important task for design of the resin transfer moulding process. In this study, variability of the geometry of a reinforcement manufactured using Automated Dry Fibre Placement is studied. Permeability of the manufactured preforms is measured experimentally and compared to stochastic simulations based on an analytical model and a stochastic geometry model. The simulations showed that difference between the actual geometry and the designed geometry can result in 50% reduction of the permeability. The stochastic geometry model predicts results within 20% of the experimental values. [ABSTRACT FROM AUTHOR]

Process-induced residual stresses occur in composite structures composed of dissimilar materials. As these residual stresses could result in fracture, their consideration when designing composite parts is necessary. However, the experimental determination of residual stresses in prototype parts can be time and cost prohibitive. Alternatively, it is possible for computational tools to predict potential residual stresses. Therefore, the objectives of the presented work are to demonstrate an efficient method for simulating residual stresses in composite parts, as well as the potential value of statistical methods during analyses for which material properties are unknown. Specifically, a simplified residual stress modeling approach is implemented within Sandia National Laboratories’ SIERRA/SolidMechanics code. Concurrent with the model development, bi-material composite structures are designed and manufactured to exhibit significant residual stresses. Then, the presented modeling approach is rigorously verified and validated through simulations of the bi-material composite structures’ manufacturing processes, including a mesh convergence study, sensitivity analysis, and uncertainty quantification. The simulations’ final results show adequate agreement with the experimental measurements, indicating the validity of a simple modeling approach, as well as a necessity for the inclusion of material parameter uncertainty in the final residual stress predictions. [ABSTRACT FROM AUTHOR]

The strength of metal matrix composites shows wide scatter on account of variability in the strengths of individual fibres. The relationship between the strength distribution of the fibres, and that of the composite is also affected by the non-linear matrix and fibre/matrix interfacial responses. The present study aims to describe the strength distribution of 2D and 3D commercial Ti/SiC composites. This is accomplished by performing Monte Carlo failure simulations of these composites, comprised of up to 128 fibres. A detailed deformation theory based model, developed and validated against experimental data in previous work, is used to calculate load redistribution in the course of each simulation. The empirical composite strength distribution obtained from the simulations follows weakest-link scaling. A stochastic model for the clustered propagation of fibre breaks, akin to a model proposed for polymer matrix composites in the literature, captures the empirical weakest-link strength distribution. A scaling relationship is derived between the composite strength and composite size for a number of reliability levels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Randomly oriented strand composites are promising materials for complex-shaped parts, especially in the aerospace and automotive industries. However, test data from small specimens tend to have a high level of scatter as these materials contain several centimetres of chopped carbon fibre strands. In this study, we investigated the mechanical properties of ultra-thin chopped carbon fibre tape reinforced thermoplastics (UT-CTT), which contain chopped thermoplastic thin-ply prepreg tapes produced using a paper-making technique. We propose a model for accurately evaluating the flexural modulus and its scatter, which was verified by comparison with experimental data. The predictions of the model showed excellent agreement with the experimental results. This method makes it possible to quantify the scatter of the flexural modulus and is useful for designing geometries of, not only standard test specimens, but also complex parts for actual applications. [ABSTRACT FROM AUTHOR]

Void consolidation of high-performance thermoplastic composites strongly depends not only on average void content but also on the distributions of void size, shape, and location within the prepreg materials. High-resolution 3-D X-ray microcomputed tomography shows that voids in carbon/poly(ether ether ketone) (AS4/APC2) prepreg are rodlike with major axis along the fiber axial direction. In order to accurately characterize the void microstructure, a detailed study was conducted to quantify the statistical distribution of void content, void length, equivalent void diameter, and void aspect ratio. Resolution of 1.48 μm/pixel provided a balance of measurement accuracy and inspection time. Suitable statistical distribution functions were found to describe the void length, diameter, and aspect ratio. For each void property, a sub-statistical representative volume element (SRVE) was determined. The SRVE of the overall void microstructure is defined as the maximum dimensions of the sub-SRVEs. In case of AS4/APC2 tape, the SRVE was found to be 6.1 mm in length (fiber direction), 27 mm in width (transverse to fiber direction), and 0.18 mm of full prepreg thickness. [ABSTRACT FROM AUTHOR]

This study set out to investigate the applicability of data assimilation to the monitoring of the flow of non-planar 3D shapes through the integration of visual observations with a stochastic numerical simulation of the resin flow in a vacuum-assisted resin-transfer molding process. First, we investigated the effect of the image resolution on the flow-monitoring estimation performance. By means of numerical experiments using images of various resolutions, we verified the applicable range of the image resolution in the proposed technique. Furthermore, the proposed technique was applied to 3D structures such as curved surfaces or ribbed structures. Using the visual observation values, the impregnation distances obtained from the image data were calculated in combination with the shape of the molding. The results confirmed that our proposed method is capable of successfully estimating the 3D impregnation behavior and permeability fields. [ABSTRACT FROM AUTHOR]

Enhancing the fatigue performance of scarf adhesive joints (SAJs) in carbon fiber-reinforced epoxy (CFRE) composite structures via incorporation of nanofillers into the epoxy adhesive has not yet been fully investigated and is the subject of this study. The optimum weight percentages of multi-walled carbon nanotubes (MWCNTs), SiC and Al2O3 nanofillers were ultrasonically dispersed in Epocast 50-A1/946 epoxy. The nanophased matrices were used to fabricate the SAJs with 5° scarf angle. Fatigue tests were conducted at constant-load amplitude, frequency of 10 Hz and stress ratio of 0.1. Result from fatigue tests showed that the gain/loss in the fatigue lives of the modified SAJs with MWCNTs, SiC and Al 2 O 3 are respectively 19%, 52% and −22% at fatigue limit of 36 MPa. The load-displacement hysteresis loops of the nano-modified SAJs showed higher fatigue stiffness compared to neat epoxy-SAJ. The stiffness of the SAJs was increased with increasing number of cycles up to about N/Nf = 0.01. As the number of cycles increases the damage level is increased and thus the slope of the hysteresis loop (stiffness) is decreased and the hysteresis loop area becomes wider. The highest penalty paid to gain safe lives was observed for Al2O3-SAJs, which has highest scatter in the fatigue lives. [ABSTRACT FROM AUTHOR]

In this paper, the interest is in estimating the fatigue life distribution of highly reliable structural components from data obtained via accelerated life tests. These tests consist in subjecting the products of interest to stress levels more severe than those encountered in normal use. This forces the considered products to fail more quickly and allows collecting failure data in a reasonably short amount of time. Estimates of the product's reliability at normal use conditions are then extrapolated from accelerated failure data by adopting proper models. The model proposed in this paper generalizes a model which is widely applied in literature to analyze accelerated fatigue life data. In fact, as the abovementioned standard model it relies on two very classical assumptions, namely: a) the test conditions affect the lifetime distribution parameters, and not its form, and b) the fatigue life at each considered stress level follows a Birnbaum-Saunders distribution. On the other side, differently from the standard model, in which only the scale parameter depends on the stress conditions, the proposed model assumes that both the parameters of the Birnbaum-Saunders distribution possibly depend on the stress. The model is applied to a real set of accelerated fatigue failure data. Model parameters are estimated via the maximum likelihood method. The estimate of the reliability function at normal use conditions is extrapolated from the accelerated data. It is shown that the proposed Birnbaum-Saunders based model, in which both scale and shape parameters depend on the stress conditions, fits the considered data better than the model usually adopted in the literature. Differences among results provided by the two considered alternative models are highlighted and discussed. Finally two graphical strategies are proposed that allow judging the goodness of fit of the proposed model in absolute terms. [ABSTRACT FROM AUTHOR]

In the current research a statistical micromechanical approach for the determination of the mechanical properties of composite materials is proposed. The proposed method is mainly based on the well-known periodic homogenization scheme. The methodology implements multi-step multiscale approach to calculate the mechanical properties of composite materials where the statistical characteristics (e.g. size, aspect ratio, orientation) of the reinforcing phase are known as probability distribution functions (PDF). The calculations start from Unit Cell I which resembles the microstructure of material at the lowest length scale and continue until the largest fiber is considered in the final unit cell setting. The results of the presented theory are compared with experimental data on composite materials which show that good estimates of the elastic moduli can be achieved by using statistical multi step homogenization technique. [ABSTRACT FROM AUTHOR]

Synthetic and artificial fiber fabrics are commonly used as masonry structures reinforcement, both for seismic retrofitting of historical buildings and for realization of new constructions in seismic areas. Correspondingly, natural fiber fabrics are appropriate to earth buildings reinforcement, being compatible from the point of view of environmental sustainability. In this paper the results of tensile tests on jute yarns are reported, organized and statistically analyzed in order to interpret the basic laws of size effects involved. The great variability of yarns behavior and the difficulties in controlling the boundary conditions induced to perform numerical tensile tests on statistical samples of jute fabric, generated in compliance with the statistical distribution of yarns mechanical properties. The comparison between laboratory and numerical tests permits to make some considerations on the difficulties involved in the experimental analysis, in order to define a reliable experimental technique to determine the properties necessary to the successive design. [ABSTRACT FROM AUTHOR]

The mechanical properties of Kevlar® 29 single filaments and yarns with different gage lengths were investigated by utilizing an MTI miniature tester and an MTS load frame. Single yarns of 25 mm were also tested over four different strain rates using a drop-weight impact system. The experimental results showed that the mechanical properties of Kevlar® 29 are sensitive to gage length, structural size scale, and strain rate. The tensile strength decreased with increasing gage length and the structural scale from fiber to yarn, and increased with increasing strain rate. Weibull analysis was conducted to quantify the degree of variability in tensile strength. The obtained Weibull parameters were then used in an analytical model to simulate the stress–strain response of single yarn. Finally, Weibull parameters of single filaments with other gage lengths and strain rates were also obtained by fitting the stress–strain curves of single yarns with corresponding testing conditions. [ABSTRACT FROM AUTHOR]

In recent years, many researchers have studied the exploitation of vegetable fibres as reinforcement in composite materials. The biodegradable nature of natural fibres makes them friendly to the environment which can lead to the preservation of nature and human wellbeing. With low cost and good performance, vegetable fibres are generating an economic interest for various industries. The objective of this work is the determination of the mechanical properties of the vegetable sisal yarns, with a twist angle equal to 13° and a linear density of 232 tex, subjected to tensile quasi-static loading. A test program consisting of 150 samples is performed. Due to the variability of natural yarns, more than 30 samples were tested for each gauge length (GL). Five different GLs are used: 50, 100, 150, 200 and 300 mm. The acquired results are then analysed by the statistical two and three parameter Weibull distribution for different probability index and estimation by Least Square (LS) and Maximum Likelihood Estimation (ML). Finally, all five groups for each tensile property are analysed by one-way (ANOVA). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Automated image analysis of textile surfaces allowed determination and quantification of intrinsic yarn path variabilities in a 2/2 twill weave during the lay-up process. The yarn paths were described in terms of waves and it was found that the frequencies are similar in warp and weft directions and hardly affected by introduced yarn path deformations. The most significant source of fabric variability was introduced during handling before cutting. These resulting systematic deformations will need to be considered when designing or analysing a composite component. An automated method for three dimensional reconstruction of the analysed lay-up was implemented in TexGen which will allow virtual testing of components in the future. [ABSTRACT FROM AUTHOR]

There is no complete consensus of researchers on the problem of evaluating tension stiffening phenomena in cracked flexural glass fibre-reinforced polymer reinforced concrete members and, therefore, various empirical correction factors are used in the existing weighted averaging techniques for obtaining consistent estimates of experimental deflection of traditional steel bars reinforced concrete cross-sections. This paper presents an alternative method for deformational analysis of cracked GFRP RC flexural members based on constitutive modeling, taking into account the direct or inverse approach to evaluating the post-cracking stress-strain response of concrete in tension. The effect of tension stiffening is defined analytically by the derived formula for the effective moment of inertia, omitting the empirical correction of the moments of inertia of the uncracked or fully cracked RC cross-sections. Analytical formulae are also proposed to derive the parameters of tension stiffening based on the test data of GFRP RC beams subjected to bending. The relative systematic and random errors of the method are considered in the statistical analysis, involving the experimental sample of deflections for 42 beams. The case studies of manual calculation of the mid-span deflection of the beams by using the proposed technique and the inverse analysis for deriving tension stiffening parameters based on of the experimental data are also provided. [ABSTRACT FROM AUTHOR]

A constitutive model for carbon nanotube (CNT) reinforced rubbers is proposed on the basis of the polymer chain length statistics. Rubbers both with conventional fillers like silica or carbon black (hybrid system) and without them are considered. The reinforcement by CNTs is explained by additional cross-linking which influences the probability density function of polymer chain lengths. The change in the probability density function is statistically reasoned and incorporated into a full network model based on the numerical integration over the unit sphere. This full network model is able to describe typical inelastic effects of filled rubbers as for example the Mullins effect, strain induced anisotropy and permanent set. The so obtained model demonstrates good agreement with experimental data on CNT blended rubbers available in literature. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of moisture propagation in fibre reinforced polymer (FRP) materials with spatial tortuosity. An algorithm for creation of microstructures with clustered fibre architecture is presented. Several controls for different characteristics of the clusters are described. Different statistical descriptors of geometry are used to quantify the clustering. A Fickian diffusion process has been modelled. The effect of clustering on moisture diffusion through the FRP is reported. It is observed that microstructures greatly affect the diffusion behaviour of the FRP. Correlation between moisture diffusion and the statistical descriptors has been examined. The statistical measures that depict the global characteristics of the microstructure are found to have a better correlation with time to saturate the representative volume element. The results should help in prediction of macroscopic response and durability of FRPs. [ABSTRACT FROM AUTHOR]

Algae blooms represent a worldwide contamination problem, 55% of the water bodies in the U.S. are in poor condition mainly because of algae. A second source of algae waste is the co-product of the algae biofuel process. There is potentially an abundant source of algae fiber; however, little is known about the utilization of algae as reinforcement for natural fiber composites (NFC). The purpose of this work is to study the morphology and mechanical properties of the blue-green algae Lyngbya as a natural fiber reinforcement for biocomposite materials according to the Standards ASTM-D792-00 and ASTM C1557-03. Lyngbya were sourced and by conducting a sequence of chemical treatments on the algae the fiber that was extracted. The average properties of Lyngbya fiber are: density 1.06 g/cm 3 , width 60 μm, tensile strength of 215 MPa, and tensile modulus of 24 GPa. Lyngbya fiber properties are comparable to jute and sisal fibers. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced composite (GFRP) samples were tested at different strain rates from quasi-static up to 160 s −1 and temperatures from −25 to 100 °C to investigate any possible effects on their mechanical properties and failure patterns. The experimental results show that the tensile strength, maximum strain and toughness increase with increasing strain rates at room temperature, and the Young’s modulus, tensile strength and toughness decrease with increasing temperatures at the strain rate of 40 s −1 . Weibull statistics were used to quantify the degree of variability in the tensile strength and obtain Weibull parameters for numerical simulations and engineering applications. [ABSTRACT FROM AUTHOR]

In the present study, the effect of fiber and (5% wt) coconut shell powder (CSP) loading on the tensile properties of randomly oriented roselle fiber reinforced vinyl ester (RV) composites was carried out. Composite specimens were fabricated using the hand lay-up technique. It was observed that tensile properties of vinyl ester composites increase upon reinforcement with roselle fibers and CSP particles. The reinforcement of roselle fibers has significant effects on the tensile strength and modulus of the composite. The fractographic study was carried out on the surface of fractured composite specimens using scanning electron microscopy. A better interfacial adhesion, fiber dispersion and less fiber pull out on the surface of fractured composite specimens were identified. The tensile strength of RV composites has also been statistically analyzed by two-parameter Weibull distribution. Twenty-five tension tests were carried out. The results obtained varied between 37.89 MPa and 45.07 MPa. Furthermore, the inspection of the developed distribution was examined by the Kolmogorov-Smirnov (KS) test. The results show that the gained two-parameter Weibull distribution can be used to express the tensile strength and predict its values accurately. [ABSTRACT FROM AUTHOR]

Applications of artificial intelligence in engineering disciplines have become widespread and have provided alternative solutions to engineering problems. Image processing technology (IPT) and artificial neural networks (ANNs) are types of artificial intelligence methods. However, IPT and ANN have been used together in extremely few studies. In this study, these two methods were used to determine the compressive strength of concrete, a complex material whose mechanical features are difficult to predict. Sixty cube-shaped specimens were manufactured, and images of specific features of the specimens were taken before they were tested to determine their compressive strengths. An ANN model was constituted as a result of the process of digitizing the images. In this way, the two different artificial intelligence methods were used together to carry out the analysis. The compressive strength values of the concrete obtained via analytical modeling were compared with the test results. The results of the comparison (R2 = 0:9837-0:9961) indicate that the combination of these two artificial intelligence methods is highly capable of predicting the compressive strengths of the specimens. The model's predictive capability was also evaluated in terms of several statistical parameters using a set of statistical methods during the digitization of the images constituting the artificial neural network. [ABSTRACT FROM AUTHOR]

The paper presents a comparison of the test results for the fiber volume fraction, static bending and Charpy impact strength of glass fiber reinforced polymer laminates reinforced by 0/90 fabric and chopped strand mat, produced by the hand lay-up and the vacuum-assisted resin infusion (VARI) method. The laminates were produced under equivalent conditions, with polyester matrix and lay-up areal mass 2100 g/m2. In the comparison of the obtained measurement results, similar mechanical performance was stated in the case of the hand lay-up and the VARI production. However, significantly smaller scatter of results and better uniformity of the reinforcement in the matrix with smaller amount of local structure defects was observed for the samples obtained by VARI method. The laminates obtained by VARI method show a much more advantageous coefficient of variation than that of the hand lay-up method, especially in the case of the mat reinforcement. [ABSTRACT FROM AUTHOR]

The objectives of this paper include identifying important architectural parameters that describe the SiC/SiC five-harness satin weave composite and characterizing the statistical distributions and correlations of those parameters from photomicrographs of various cross sections. In addition, realistic artificial cross sections of a 2D representative volume element (RVE) are generated reflecting the variability found in the photomicrographs and include explicitly modeled voids (something not routinely done for woven CMCs). These models are used to make preliminary observation of the effects of architectural variability on the thermo-mechanical properties (material constants). Lastly, information is obtained on the sensitivity of linear thermo-mechanical properties to architectural variations. Two-dimensional finite element analysis is used in combination with a response surface and it is shown that the present method is effective in determining the effects of architectural variability on thermo-mechanical properties and their variability. [ABSTRACT FROM AUTHOR]