Properties Of Short Fiber Composites Research Articles

Extrusion Parameters Optimization and Mechanical Properties of Bio-Polyamide 11-Based Biocomposites Reinforced with Short Basalt Fibers.

The increasing demand for sustainable materials in high-value applications, particularly in the automotive industry, has prompted the development of biocomposites based on renewable or recyclable matrices and natural fibers as reinforcements. In this context, this paper aimed to produce composites with improved mechanical and thermal properties (tensile, flexural, and heat deflection temperature) through an optimized process pathway using a biobased polyamide reinforced with short basalt fibers. This study emphasizes the critical impact of fiber length, matrix adhesion, and the variation in matrix properties with increasing fiber content. These factors influence the properties of short-fiber composites produced via primary processing using extrusion and shaped through injection molding. The aim of this work was to optimize extrusion conditions using a 1D simulation software to minimize excessive fiber fragmentation during the extrusion process. The predictive model's capacity to forecast fiber degradation and the extent of additional fiber breakage during extrusion was evaluated. Furthermore, the impact of injection molding on these conditions was investigated. Moreover, a comprehensive thermomechanical characterization of the composites, comprising 10%, 20%, and 30% fiber content, was carried out, focusing on the correlation with morphology and processing using SEM and micro-CT analyses. In particular, how the extrusion process parameters adopted can influence fiber breakage and how injection molding can influence the fiber orientation were investigated, highlighting their influence in determining the final mechanical properties of short fiber composites. By optimizing the process parameters, an increment with respect to bio-PA11 in the tensile strength of 38%, stiffness of 140%, and HDT of 77% compared to the matrix were obtained.

Recycled Carbon Fibre Composites in Automotive Manufacturing

Article Recycled Carbon Fibre Composites in Automotive Manufacturing Jean-Baptiste R. G. Souppez 1, * , and Geethanjali S. Pavar 2 1 Department of Mechanical, Biomedical and Design Engineering, School of Engineering and Technology, College of Engineering and Physical Sciences, Aston University, Birmingham B4 7ET, UK. 2 Institute for Energy Systems, School of Engineering, University of Edinburgh, Edinburgh EH9 3JW, UK. * Correspondence: j.souppez@aston.ac.uk Received: 9 January 2023 Accepted: 22 February 2023 Published: 6 March 2023 Abstract: The contemporary need for lightweight and sustainable materials in automotive manufacturing has made recycled carbon fibre an attractive option. Yet, aspects such as the mechanical properties of short fibre composites need to be characterised to fully identify the capabilities and opportunities for recycled carbon fibre in the automotive industry. Consequently, this paper aims to ascertain the potential of recycled carbon fibre materials for automotive manufacturing by considering mechanical properties, design implications, and resulting costs and sustainability. Destructive testing is employed to characterise the mechanical properties of virgin carbon fibre (VCF), recycled carbon fibre (RCF) using pyrolysis, and blended recycled carbon fibre (BRCF) comprising 50% polypropylene fibre. Here we quantify (i) the reduction in mechanical properties, namely the tensile modulus and breaking strength, (ii) the resulting increase in required thickness and therefore mass for manufactured parts and (iii) the reduction in cost and embodied energy achieved for RCF and BRCF compared to VCF, based on both a stiffness- and a strength-driven design criterion. Furthermore, we present a decision-making methodology revealing BRCF as the most cost-effective solution, while RCF proves to be the most sustainable alternative. These results provide a novel quantitative assessment of recycled carbon fibre for automotive manufacturing and may contribute to future developments in sustainable composite manufacturing in the automotive industry.

Closed-form analytical solutions for predicting stress transfers and thermo-elastic properties of short fiber composites

Novel analytical solutions with closed-form expressions for the stress and displacement fields of short fiber reinforced composites (SFRCs) and analytical prediction of their effective thermo-elastic properties are presented. The cylindrical SFRC unit-cells with periodic boundary conditions are subjected to axial and transverse stresses as well as thermally induced residual stresses. By comparison with available numerical and analytical solutions, it is revealed that the present closed-form solutions provide accurate stress field variations as well as accurate predictions for the effective thermo-elastic properties of SFRCs in a split second, and thus, the developed model is much more computationally efficient than numerical methods.

A micromechanics-based artificial neural networks model for elastic properties of short fiber composites

There are a wide variety of microstructural parameters which affect the macro-mechanical response of short fiber reinforced composites. Effects of these parameters could be captured using different micromechanics-based models. However, in some cases, it is very challenging and computationally expensive. In this study, a micromechanics-based Artificial Neural Networks (ANN) model is developed to predict the elastic properties of these materials, accurately and quickly. The required data for training and validating the model is created using a two-step approach, combining Finite Element Analysis and Orientation Averaging. The capability of the model for fair predictions is proven, not only by using the validation data, but also by comparisons to experimental results taken from literature.

The effect of micromechanics models on mechanical property predictions for short fiber composites

The Tandon-Weng (T-W), the Halpin-Tsai (H-T) micromechanical models and a novel numerical implementation of asymptotic homogenization method (NIAH) for determining the stiffness of unidirectional orientation short fiber composites are compared. Based on rigorous mathematical theory, NIAH can be easily implemented using commercial software as a black box as representative volume approaches. Representative volume element (RVE) models were generated using random sequential adsorption technique (RSA) based on the optimal Latin hypercube sampling method. For arbitrary fiber orientation, the NIAH approach was compared with orientation averaging with the T-W and the H-T micromechanical models. Agreement between the three approaches in predicting the effective properties of short fiber composites was found to be excellent. Finally, the results calculated with the three approaches were compared with experimental values. It is shown that the three approaches in this paper are in quite good agreement with measured values. However, for random oriented short fiber composites with fiber length and fiber diameter distribution, the NIAH method still can provide calculated results with sufficient prediction accuracy, and the other two methods are not any more effective.

A Comparative Study of Analytical and Numerical Evaluation of Elastic Properties of Short Fiber Composites

Unlike the case of continuous fiber composites, the prediction of elastic properties of short fiber composites using the corresponding elastic properties of constituents is not a straight forward task. Many authors have attempted to predict the properties using completely either by analytical or by experimental methods or a combination of both leading to empirical solutions. The current trend is to use the well known numerical solution Finite element method (FEM) to model the short fiber composite to predict their properties. In this paper, a RVE (Representative Volume Element) approach is used to model, with appropriate boundary and loading conditions and application of homogenization process to estimate elastic properties. The present values are compared with the available experimental and analytical solutions. The methods that best match with the current FE solutions are highlighted.

Coupling of injection molding process to mechanical properties of short fiber composites: A through process modeling approach

Fiber-reinforced plastics are a cost efficient solution for many structural applications as they offer sufficient stiffness and a large freedom of shapes provided by injection molding. These materials are increasingly being used for making structural components, which are subjected to complex and repeated mechanical loads. Therefore, the need for a method to predict the mechanical behavior of such materials is important. In this work, a through process modeling methodology suitable for coupling the microstructure and the macroscopic response of composites considering plastic injection molding process for different injection modes is presented. The key tasks discussed in this work are (1) simulation of the whole manufacturing process in order to obtain the fiber orientation distribution at each point of the part; (2) estimation of local effective properties using the orientation tensor obtained by performing a two-step homogenization and (3) prediction of the mechanical response as a function of a local anisotropy using a mean-field homogenization technique which is based on assumed relationships between average values of strain and stress fields in each phase. The scheme suggested allows to analyze the influence of processing conditions on elastic properties of composites. By changing these conditions, for example, the injection mode (central or linear), the cavity thickness, the fiber volume fraction, the microstructure and hence the local elastic properties of the material can be tailored. Thus, for desired structural response of composites, the optimum filling parameters can be chosen even at the stage of design.

Thermal Properties of Short Fibre Composites Modeled by Meshless Method

Computational model using continuous source functions along the fibre axis is presented for simulation of temperature/heat flux in composites reinforced by short fibres with large aspect ratio. The aspect ratio of short fibres reinforcing composite material is often as large as 103 : 1–106 : 1, or even larger. 1D continuous source functions enable simulating the interaction of each fibre with the matrix and also with other fibres. The developed method of continuous source functions is a boundary meshless method reducing the problem considerably comparing to other methods like FEM, BEM, meshless methods, or fast multipole BEM formulation.

Carbon and glass hierarchical fibers: Influence of carbon nanotubes on tensile, flexural and impact properties of short fiber reinforced composites

Dense carbon nanotubes (CNTs) were grown uniformly on the surface of carbon fibers and glass fibers to create hierarchical fibers by use of floating catalyst chemical vapor deposition. Morphologies of the CNTs were investigated using scanning electronic microscope (SEM) and transmission electron microscope (TEM). Larger diameter dimension and distinct growing mechanism of nanotubes on glass fiber were revealed. Short carbon and glass fiber reinforced polypropylene composites were fabricated using the hierarchical fibers and compared with composites made using neat fibers. Tensile, flexural and impact properties of the composites were measured, which showed evident enhancement in all mechanical properties compared to neat short fiber composites. SEM micrographs of composite fracture surface demonstrated improved adhesion between CNT-coated fiber and the matrix. The enhanced mechanical properties of short fiber composites was attributed to the synergistic effects of CNTs in improving fiber–matrix interfacial properties as well as the CNTs acting as supplemental reinforcement in short fiber-composites.

Modelling the elastic and thermoelastic properties of short fibre composites with anisotropic phases

An analytical procedure is proposed and validated for predicting the elastic anisotropy and thermal expansion behaviour of a short fibre polymer composite, where both the fibre and the polymer matrix possess anisotropic material properties. The modelling strategy is to consider the fibre composite as an aggregate of units of structure, with an averaging scheme which takes into account the state of orientation. Validation of this strategy required the accurate determination of the unit properties and a satisfactory orientation averaging procedure. First, the unit properties were determined for very highly aligned samples with either an isotropic or an anisotropic fibre (glass or carbon) and either an isotropic or an anisotropic matrix (Nylon or liquid crystalline polymer). The fibre orientation and length distribution were determined by image analysis together with measurements of their elastic and thermoelastic properties. In combination with finite element calculations developed by Gusev, these results provided the basis for validation of appropriate analytical schemes to predict the unit properties. The orientation averaging procedures were validated by measurements on a model ribbed box component manufactured from a carbon fibre filled liquid crystalline polymer (anisotropic fibre and anisotropic matrix). Measurements of Young’s modulus and the coefficient of thermal expansion were combined with the determination of fibre orientation by image analysis. The key result was that if the fibre orientation level was high, the best prediction was to assume that the matrix orientation was identical to that of the fibres. For a lower degree of alignment, a better prediction was obtained by assuming that the matrix was isotropic.

Study of Fiber Breakage and Length Distribution During Compounding Glass-NBR-Phenolic Composites

: One of the main criteria in preparation of short fiber composites in fiber length retention and distribution during compounding. This is because the mechanical properties of short fiber composites depend strongly on the fiber length and distribution. In this study, 50 mm glass fibers were used to make a glass-nitrile rubber (NBR)-Phenolic composite on a two-roll mill. Fiber breakage during the manufacturing process was investigated and a fiber length distribution was obtained at various mixing times. A reduction in fiber length was observed as mixing proceeded and an average fiber length was determined for different mixing times. It was concluded that for a particular matrix processing, conditions must be optimized in order to achieve the maximum reinforcing effect of the fiber.

On the possibility of reduced variable predictions for the thermoelastic properties of short fibre composites

Computer aided design offers the potential for the rapid development of new advanced structures from short fibre reinforced composites. The advantage of a validated numerical simulation is clear, as it allows a large number of the potential structure's solutions to be studied before proceeding to a manufacturing stage, reducing cost and risk accordingly. In our recent work we have demonstrated that the direct finite-element-based procedure of Gusev could be reliably employed for the prediction of thermoelastic properties of laboratory injection moulded samples, on the basis of Monte Carlo multi-fibre computer models built based on the measured fibre orientation distribution functions. Most injection moulded or extruded structures however, exhibit non-uniform fibre orientation states across the final parts, with a diverging variety of different local fibre orientation states. It would be impractical to characterize all the possible orientation states by their full distribution functions, and it would be equally impractical to attempt direct numerical property predictions for all the various orientation states. Here we show that real injection moulded and extruded materials show fibre orientation states close to a maximum entropy prediction (i.e. most random) and that local thermomechanical properties can be excellently predicted based on the second order orientation moments and a constant strain assumption between the phases. Our results landmark a practical possibility of computer aided design of advanced structural parts from short fibre reinforced composites.

Stiffness and Thermal Expansion of Short Fiber Composites with Fully Aligned Fibers

Predicting the overall, effective properties of short fiber composites with fully aligned fibers from the properties of the individual phases and the composite’s morphology has attracted a great deal of attention during the last decades. In this work, the authors focus on the overall elastic constants and use the finite‐element‐based numerical procedure developed by them to assess the adequacy of two of the most widely used micromechanics‐based models.

Direct numerical predictions for the elastic and thermoelastic properties of short fibre composites

In this paper we compare the predictions of the thermoelastic properties of misaligned short glass fibre reinforced composites, calculated using the finite-element-based numerical approach of Gusev, with experimental measurements. Characterisation of the microstructure of the two injection moulded materials chosen for examination, in particular the fibre length and fibre orientation distributions, were used to ensure that the computer models were built with the same microstructure as the ‘real’ materials. Agreement between the measurements, in particular for the longitudinal Young's modulus E 11 and the longitudinal and transverse thermal expansion coefficients, α 1 and α 2, and the numerical predictions was found to be excellent. A comparison was also made with the most commonly used micromechanical models available from the literature. The approaches of Tandon and Weng, Takao and Taya and McCullough [Polym Comp 5 (1984) 327; J Comp Mater 21 (1987) 140] were found to give good agreement with both the numerical and measured values, although only the numerical approach showed the same relationship between α 1 and the degree of orientation as shown by the real materials.

Numerical simulation of the effects of volume fraction, aspect ratio and fibre length distribution on the elastic and thermoelastic properties of short fibre composites

In this paper a new numerical procedure by Gusev, for predicting the elastic and thermoelastic properties of short fibre reinforced composites, is described. Computer models, comprising 100 non-overlapping aligned spherocylinders, were generated using a Monte Carlo procedure to produce a random morphology. Periodic boundary conditions were used for all the generated structures. Where necessary, the generated microstructures were based on measurements of real materials: for example a measured fibre length distribution was used to seed the Monte Carlo generator to produce a computer model with an equivalent fibre length distribution (FLD). The generated morphologies were meshed using an intelligent 3 dimensional meshing technique, allowing the elastic and thermo-elastic properties of the microstructures to be calculated. The numerical predictions were compared with those from three commonly used micromechanical models, namely those attributed to Halpin/Tsai, Tandon/Weng and Cox (shear lag). Firstly, the effect of volume fraction and aspect ratio were investigated, and the numerical results were compared and contrasted with those of the chosen models. Secondly, the numerical approach was used to investigate what effect a distribution of fibre lengths, as seen in real materials, would have on the predicted mechanical properties. The results were compared with simulations carried out using a monodispersed fibre length, to ascertain if the distribution of lengths could be replaced with a single length, and whether this length corresponded to a particular characteristic of the distribution, for example the first moment or average length.

Prediction on tribological properties of short fibre composites using artificial neural networks

Using a multiple-layer feed-forward artificial neural network (ANN), the specific wear rate and frictional coefficient have been predicted based on a measured database for short fibre reinforced polyamide 4.6 (PA4.6) composites. The results show that the predicted data are well acceptable when comparing them to the real test values. The predictive quality of the ANN can be further improved by enlarging the training datasets and by optimising the network construction. A well-trained ANN is expected to be very helpful for an optimum design of composite materials, for a particular tribological application and for systematic parameter studies.

Evaluation of Two-Roll Mill Method for Preparing Short Glass Fibre Reinforced Nbr-Phenolic Composites

Mechanical properties of short fibre composites depend strongly on the fibre length. Therefore, in preparing short fibre composites, processing conditions are of great importance as they affect the final fibre length. In this study 50 mm glass fibres were used to prepare acrylonitrile butadiene rubber (NBR) phenolic-glass fibre composites by two-roll mill method. Fibre breakage during processing was studied and the fibre critical length was calculated. On the basis of the critical length, the usefulness of the two-roll mill method for preparing glass-NBR-phenolic composites with the specified formulation was assessed.

Tensile properties of short fiber composites with fiber strength distribution

The influence of fiber rupture, fiber pull-out and fiber tensile strength distribution on the post-cracking behavior of short-randomly-distributed fiber reinforced brittle-matrix composites has been analyzed using an approach based on the Weibull weakest-link statistics. The analysis led to the development of a predicting model for the composite bridging stress-crack opening displacement (σc − δ) law—a fundamental material property necessary for the analysis of steady-state cracking in the composites. The proposed σc − δ relationship can be used to relate the composite tensile and fracture properties to the microstructural parameters. The model revealed the importance of fiber strength distribution as described by the Weibull weakest-link statistics in governing the post-cracking response of the composite. The proposed model was able to reproduce the results of an earlier model for a limiting case where fiber tensile rupture was accounted for assuming a deterministic fiber tensile rupture strength. Model-predicted post-peak σc − δ curve was also in close agreement with those obtained from uniaxial tensile tests of a Kevlar fiber reinforced cementitious composite where fiber tensile rupture was reported. The model provided physical insights as to the micro-mechanisms controlling the post-cracking response of short-fiber reinforced brittle-matrix composites where fibers have a tensile strength distribution described by the Weibull weakest-link statistics.

A model to predict the strength of short fiber composites

AbstractThe material properties of short fiber composites, such as modulus, strength and thermal expansion, are greatly dependent on the fiber orientation state in the composite. Although the orientation pattern is often quite complex, models that allow its prediction have been successfully applied in combination with micromechanical models to calculate moduli and thermal properties. This paper describes the derivation of a model to predict the strength of short fiber composites with arbitrary fiber orientation and fiber length distribution based on classical (micro‐) mechanical theories. The predictions are in good agreement with data measured on short fiber composites with different fiber contents.

A 3-D numerical simulation of AC electrical properties of short fiber composites

The relation between microstructure and electrical properties of polymer reinforced by electrically conducting nanofibers is investigated using a RC type simulation. Real and imaginary parts of the conductivity vs. the frequency and the filler fraction are presented both for two- and three-dimensional systems. In the latter case, resistor and capacitor values are deduced from a random microstructure and the measured macroscopic properties of each component. These results are compared with experimental data obtained on a nanocomposite material composed of electrically conductive fillers dispersed in an insulating matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 805–814, 1999