Unidirectional Fiber-reinforced Composites Research Articles

Generation of unidirectional fiber random distribution structures based on an artificial fish swarm algorithm with random deletion after fiber filling

This study proposes a random distribution method for generating high-content volume fractions of fibers in their cross-sectional area. This approach is referred to as the artificial fish swarm algorithm (AFSA) with random deletion after fiber filling (RDAFF_AFSA). Initial fibers were first generated using AFSA, followed by fiber filling the matrix-rich region with a hard-core model. The desired representative volume element (RVE) was ultimately obtained by random deletion. The proposed method can generate RVEs with high-content volume fractions (up to 67%) of fibers. The generated RVEs were statistically analyzed and compared with the completely spatial random (CSR) pattern and experiment data. The results showed that RDAFF_AFSA exhibited a high degree of consistency with the CSR and experimental data. The elastic constants of the carbon fiber-reinforced plastic composites were predicted by finite element analysis. The predicted results are very reasonable compared to the experimental results. The proposed method can provide a highly valuable alternative for micromechanical and multiscale analyses of unidirectional fiber-reinforced composites.

Influence of interphase characteristics on the elastic modulus of unidirectional glass-reinforced epoxy composites: a computational micromechanics study

Abstract This article briefly discusses the role of interphase in the elastic moduli of unidirectional fiber-reinforced polymer composite materials. For this unidirectional glass fiber was chosen as reinforcement, and epoxy was selected as the matrix. A hexagonally packed representative volume element is used for the micromechanical analysis. Experimental validation was initially used to verify the accuracy of the established equations of the rule of mixing, Composite Cylinder Assemblage, Chamis, Halpin and Tsai, and Puck. The Chamis equation was found to be the most reasonable. Then the finite element approach in which interphase has been included was used to estimate the elastic moduli. The finite element model without interphase and the experimental result were taken as a reference. The influence of interface ratio and property of interphase on the homogenised elastic properties of the unidirectional fiber-reinforced polymer composites is analysed. A micromechanics plugin in Abaqus software was used to estimate the density and Young’s modulus of the unidirectional fiber-reinforced polymer composites. The interphase properties are varied, having 6.25%, 12.5%, 25% and 50% influence of the fiber phase and the remaining influence of the matrix phase with interface ratios of 0.1, 0.2 and 0.3. The interface ratio of 0.3, having 6.25% fiber phase influence, gave the most reasonable moduli values (with an error <10%) compared to the mean experimental moduli. The study showed interface ratio and interphase properties to critically influence the overall elastic property of the unidirectional fiber-reinforced polymer composites.

Effects of fiber surface modification on mechanical properties of short pineapple leaf fiber-carbon black reinforced natural rubber hybrid composites

At present, the world is focusing on the circular economy by turning waste into production resources again, reducing waste generation, and making it circulate in the system. This research focuses on using agricultural waste, which is pineapple leaves abundant in Thailand, to be processed into pineapple leaf fibers (PALF) and used to reinforce natural rubber. PALF has relatively high strength when compared to other natural fibers. On the other hand, the challenge of using PALF to reinforce natural rubber is the difference in the polarity of the fibers and rubber matrix. Thus, surface modification of PALF was studied to enhance the adhesion between the fiber surface and the matrix. Four systems were compared, i.e., untreated PALF, alkaline-treated, silane69-treated, and aminosilane-treated PALF. A unidirectional fiber-reinforced natural rubber composites were prepared with fixed fiber and carbon black contents of 10 and 30 phr, respectively. Mechanical properties of the composites were determined by tensile test and morphology was observed by scanning electron microscope (SEM). It was found that silane69-treated and aminosilane-treated PALF could reinforce the rubber matrix over the entire strain. However, silane69-treated and aminosilane-treated PALF had lesser reinforcement effect than alkaline-treated PALF at low strains. Despite a clear change in mechanical behavior, SEM could not tell the difference or changes that occur at the interface. Fiber surface modifications with silane69 and aminosilane have the potential to be further developed to improve properties of natural rubber composites and will, hopefully, increase the value of rubber products for Thailand industry.

Integrated digital image correlation for micro-mechanical parameter identification in multiscale experiments

Micromechanical constitutive parameters are important for many engineering materials, typically in microelectronic applications and material design. Their accurate identification poses a three-fold experimental challenge: (i) deformation of the microstructure is observable only at small scales, requiring SEM or other microscopy techniques; (ii) external loadings are applied at a (larger) engineering or device scale; and (iii) material parameters typically depend on the applied manufacturing process, necessitating measurements on material produced with the same process. In this paper, micromechanical parameter identification in heterogeneous solids is addressed through multiscale experiments combined with Integrated Digital Image Correlation (IDIC) in conjunction with various possible computational homogenization schemes. To this end, some basic concepts underlying multiscale approaches available in the literature are first reviewed, discussing their respective advantages and disadvantages from the computational as well as experimental point of view. A link is made with recently introduced uncoupled methods, which allow for identification of material parameter ratios at the microscale, still lacking a proper normalization. Two multiscale methods are analysed, allowing to bridge the gap between microstructural kinematics and macroscopically measured forces, providing the required normalization. It is shown that an integrated experimental--computational scheme provides relaxed requirements on scale separation. The accuracy and performance of the discussed techniques are analysed by means of virtual experimentation under plane strain and large strain assumptions for unidirectional fibre-reinforced composites. The robustness against image noise is also assessed.

A direct method for wave propagation in elastic fiber composites

A direct method is proposed to study wave dispersion in stiff unidirectional fiber-reinforced elastic random composites. The present model is featured by a modified form of classical elastodynamic equations supplied with a simple differential relation between the displacement field of the composite and the displacement field of the mass center of representative cell. Explicit formulas are derived for the attenuation coefficient and effective phase velocity of in-plane P-waves, SV-waves, and anti-plane SH-waves, respectively. The efficiency and accuracy of the model are demonstrated by comparing predicted results (on the frequency for the maximum attenuation and effective phase velocity at frequencies below the bandgap) with a large group of known data reported in past decades. The proposed model offers a novel general method for dynamics of stiff unidirectional fiber-reinforced elastic random composites.

Efficient generation of random fiber distributions in fiber reinforced composites

This paper proposes a new algorithm to generate representative volume elements (RVEs) with random fiber distribution in fiber reinforced composites (FRC). The proposed algorithm is straightforward and easy to implement based on judging the maximum and minimum distances between a new fiber and existing fibers. The generation results demonstrate that the maximum fiber volume fraction gradually increases and oscillates violently before reaching 78.54% as the fiber radius rises. Moreover, with the increase of RVE size, the maximum fiber volume fraction changes gently when the fiber radius does not exceed 6.5 μm, but it changes dramatically at other fiber radii. Then, the fiber distributions of the generated RVEs are evaluated using the nearest neighbor distance, Ripley’s K function, and pair distribution function. The evaluation results indicate that the fiber distributions present randomness. Lastly, the effective elastic properties of the Carbon/Epoxy unidirectional FRC are predicted using the RVEs generated by the proposed algorithm, the RVEs generated by regularization, and the Mori–Tanaka method. It is found that the prediction using the RVEs generated by the proposed algorithm is more accurate than the regularization, compared with the Mori–Tanaka and experiment results. The proposed algorithm contributes to microstructure modeling in computational micromechanics.

A review on micromechanical modelling of progressive failure in unidirectional fibre-reinforced composites

The recent decades have seen various attempts at the numerical modelling of fibre-reinforced polymer (FRP) composites in the aerospace, auto and marine sectors due to their excellent mechanical properties. However, it is still challenging to accurately predict the failure of the composites because of their anisotropic and inhomogeneous characteristics, multiple failure modes and their interaction, especially under multiaxial loading conditions. Micromechanics-based numerical models, such as representative volume elements (RVEs), were developed to understand the progressive failure mechanisms of composites, and assessing existing failure criteria. To this aim, this review paper summarises the development of micromechanics-based RVE modelling of unidirectional (UD) FRP composites reported in the literature, with a focus on those models developed using finite element (FE) and discrete element (DE) methods. The generation of fibre spatial distribution, constitutive models of material constituents as well as periodic boundary conditions are briefly introduced. The progressive failure mechanisms of UD FRP composites simulated by RVEs under various loadings are discussed and the comparison of failure envelopes predicted by numerical results and classical failure criteria are reviewed.

Modelling the Non-linear fibre and matrix dominated compressive behaviour in unidirectional Fibre-reinforced composites

The mechanical behaviour of unidirectional fibre-reinforced composites is typically assumed to be linear elastic before failure. However, these materials exhibit nonlinear responses while being loaded in the matrix and fibre dominated directions that are generally disregarded. This research explores alternative physically-inspired finite element based modelling approaches that are formulated after the mechanisms behind such nonlinearities. The effect of fibre waviness/misalignment on the elastic modulus corresponding to the fibre direction has been investigated developing a phenomenological model based on the fibre micro-buckling theory. This model has been combined with the localisation plane plasticity, which deals with the matrix-dominated nonlinear deformation, for a complete description of the material’s mechanical behaviour. The proposed combined approach in a single model has shown to be capable of predicting the compressive stress-strain fibre- and matrix-dominated responses of IM7/8552 coupons at various loading rates.

Modeling Study of the Creep Behavior of Carbon-Fiber-Reinforced Composites: A Review.

The aim of this paper is to present some important practical cases in the analysis of the creep response of unidirectional fiber-reinforced composites. Some of the currently used models are described: the micromechanical model, homogenization technics, the Mori-Tanaka method, and the finite element method (FEM). Each method was analyzed to determine its advantages and disadvantages. Regarding the accuracy of the obtained results, comparisons are made with experimental tests. The methods presented here are applied to carbon-fiber-reinforced composites, but these considerations can also be applied to other types of composite materials.

Machine learning-assisted modelling of stress concentration factor of unidirectional fiber composites for predicting their tensile strength

Significant variations in the tensile strength of unidirectional (UD) fiber-reinforced composites are frequently observed due to randomness in the fiber arrays. Herein, we propose a novel method for predicting tensile strength capable of quantifying uncertainty based on a new recurrence relation for fiber fracture propagation and a determination algorithm for the fracture sequence for random fiber arrays (RFAs). We performed finite element simulations, calculating the stress concentration factor (SCF) for UD composites with various RFAs. Then, we trained an artificial neural network with the obtained SCF data and used it to predict the SCF for composites with an arbitrary RFA. The tensile strength of UD composites was predicted over a range of values, demonstrating that accuracy was superior to conventional prediction methods.

The Effect of Glass Fiber Storage Time on the Mechanical Response of Polymer Composite.

The growing demand for polymer composites and their widespread use is inevitably accompanied by the need to know their degradation behavior over a sufficiently long period of time. This study focuses on commercial glass fiber rovings, which were stored in the indoor environment for up to 11 years. Fibers with different storage times, from fresh up to the oldest, were used to produce unidirectional fiber-reinforced polyester composites that were characterized to determine their shear and flexural properties dependent on fiber storage time. A significant decrease in shear strength was observed throughout the aging of the fibers, down to a decrease of 33% for the oldest fibers. An important finding, however, was that the significant decrease in shear strength was only partially reflected in the flexural strength, which corresponded to a decrease of 18% for the oldest fibers at consistent flexural modulus.

Predictions of macroscopic mechanical properties and microscopic cracks of unidirectional fibre-reinforced polymer composites using deep neural network (DNN)

Fibre-reinforced polymer (FRP) composites have been widely used in different engineering sectors due to their excellent physical and mechanical properties. Therefore, fast, convenient and accurate prediction tools for both macroscopic mechanical properties and failure of the composites are highly demanded by industry and interested by academia. In this study, two back-propagation deep neural network (DNN) models are developed. The first model is a regression model for predicting macroscopic transverse mechanical properties of FRP laminae, which is based on a data set generated by Discrete Element Method (DEM) simulations of 2000 Representative Volume Element (RVE) with 200 different sets of fibre volume fractions and fibre radii. The second model, which is a classification model based on the results of 1600 DEM simulations of RVEs with a fixed 45 % fibre volume fraction and 3.3μm fibre radius, is developed for predicting microscopic crack patterns of the FRP laminae. The results show that the two developed DNN models are able to predict both the macroscopic transverse mechanical properties and the microscopic cracks of the RVE accurately.

Micromechanical analysis of fiber-reinforced ceramic matrix composites by a hierarchical quadrature element method

This work performed stress predictions of unidirectional fiber-reinforced ceramic matrix composites (CMCs) subjected to longitudinal tension using a hierarchical quadrature element method (HQEM). The HQEM is a p-version finite element method that can present highly accurate results using only a few sampling points. Parametric analysis was conducted to investigate the sensitivity of the HQEM model to interface properties and the detailed process of determining the optimal interface parameters for micromechanical analysis of damaged CMCs has been elaborated. By comparison with the analytical results based on the classical shear-lag model which is commonly adopted to analyze the stress distributions of the damaged fiber-reinforced CMCs, the HQEM estimates of fiber and matrix stress distributions were validated. For uniformly loaded SiCf/SiC composites with a single matrix crack, the micromechanical behaviors of three typical cases during failure process, namely, interface perfectly bonded, interface debonding and fiber failure were analyzed, illustrating the characteristics of CMC failure and providing insight into the mechanisms relating the microstructural behavior to global failure. The present work offers the foundations of the extension of a promising approach for highly accurate and efficient fracture analysis of CMCs.

Microbuckling behavior of unidirectional fiber-reinforced shape memory polymer composite undergoing compressive deformation

The microbuckling mechanics of unidirectional fiber-reinforced shape memory polymer composite (SMPC) with low fiber volume fraction were investigated, and the mechanical models were formulated considering the attenuation of shear strain in the resin matrix near the buckled fibers. We deduced the analytical expression of the attenuation function and the key parameters during the microbuckling process of SMPC, including the critical buckling wavelength and strain. The values determined by finite element analysis verified the accuracy of the above theoretical predictions. The nonlinear stress–strain relationship during the post-buckling process was also investigated. Additionally, the classical elastic–viscoelastic correspondence principle was established to determine the dynamic buckling behaviors of SMPC at different temperatures. The viscoelastic parameters of shape memory polymer (SMP) were obtained from the isothermal stress relaxation experiments, and then the variation of buckling wavelength with time at different temperatures was evaluated.

Peridynamic modeling of toughening enhancement in unidirectional fiber-reinforced composites with micro-cracks

The matrix component of composite structures is generally brittle. In any damage occurrence, fracture propagates rapidly through the structure. This study proposes a novel toughening enhancement model for unidirectional (UD) composites to overcome these damage-propagation issues. The toughening mechanism is established by introducing the so-called micro defects/cracks for increasing the toughness of the matrix constituent of the composite structure. Mechanical simulations are performed utilizing a non-local continuum formulation known as Peridynamics (PD). The PD formulation facilitates modeling material discontinuities such as complex crack/defect formations with arbitrary size, orientation, and location features in composite structures. Here, the toughening enhancement models are established by allocating various micro-crack formations in three different fiber orientations (0°, 45°, 90°) of UD composite plates. The toughening effects of micro-crack clusters are thoroughly analyzed by making comprehensive comparisons of the propagation speed of an initially introduced macro-crack and its tip strain energy density. As a result, various micro-crack distributions are established to provide an augmented toughness to the brittle composite materials, and their key features are assessed in detail.

An anisotropic localizing gradient damage approach for failure analysis of fiber reinforced composites

This article presents an anisotropic gradient-enhanced continuum damage model developed within the finite element method framework to address complex fracture phenomena in anisotropic layered materials with unidirectional fiber-reinforced composites as the primary material examples. The main objective of the work is to model damage anisotropy due to progressive intra-laminar fracture at mesoscale in transversally isotropic composite laminae using distinct damage variables associated with different in-plane failure modes. Departing from the conventional gradient enhancements, the model adopts an improved spatial nonlocal description to ensure correct localized damage bandwidths using a single internal length scale. The coupled system of equations is decoupled using an operator-split (staggered) methodology to ensure a robust and straightforward computational implementation without compromising accuracy using lower order finite elements. The proposed damage model is tested on experimental results of fracture response in a single-edge notched tension, center notched tension, and open-hole tension fiber-reinforced composite laminae, where the numerical results were consistent with experimental observations.

A direction-dependent smoothing gradient damage model for anisotropic brittle fracture

We present a novel smeared gradient-enhanced damage model which takes into account direction-dependent damage evolution in two-dimensional brittle materials (e.g., uniaxial fiber-reinforced composites and polycrystalline materials). The recently developed smoothing gradient damage model for isotropic localized failure analysis is revisited by introducing a new damage evolution equation towards anisotropic fracture. To this end, the evolving anisotropic gradient interaction parameter existed in the damage evolution law is redefined by associating with a second-order structural tensor, aiming to possibly drive the directional fracture properties. This structural tensor restrains the crack growth in the direction of predefined fracture plane. In this circumstance, all cleavage or family of cleavage in a grain (for instance in polycrystalline materials) are assumed to be described by a single cleavage plane (or fiber plane) where the resistance of materials is considered to be weakest. Consequently, the directional dependency of cleavage fracture and transgranular fracture are captured precisely. This new definition utilized solely a scalar damage variable is in contrast to most other existing gradient damage models which usually employ multiple damage variables or higher-order gradient terms. Here, we also introduce an effective staggered algorithm aiming to reduce the computational cost, and its desirable features are demonstrated in the numerical experiments for transversely isotropic materials. The predicted crack paths in unidirectional fiber-reinforced composites and polycrystalline materials are in good agreement with reference results derived from other numerical methods.

A frictional cohesive zone model for characterizing transverse compression responses of unidirectional fiber-reinforced polymer composites

The Coulomb friction law is incorporated into the traction separation law, so a friction cohesive zone model (FCZM) combining sliding friction, interfacial debonding, and the coupling of the debonding and friction is developed. The proposed interface model is used to describe the interfacial mechanical responses of fiber/resin composite. To verify this model, the finite element model of microdroplet is built, then the calculated results of the finite element model are compared with the microdroplet test. To analyze the effect of interface friction on the macroscopic strength and stiffness of unidirectional composites, the FCZM is applied to representative volume element (RVE), and the mechanical behaviors of composites is simulated by finite element analysis of RVE, then the results are compared with the test in reference [1, 2]. It is found that the interfacial debonding is accelerated and the macroscopic strength is reduced due to the friction.

Influence of non-uniformity in inter-fibre distance on strength distribution of unidirectional fibre-reinforced polymer composites

Unidirectional fibre-reinforced polymer (UDFRP) composites exhibit statistical variations in the material properties. It is essential to acknowledge these variations and use a statistics-based strength property for designing composite structures. In this work, the effect of non-uniformity in inter-fibre distance on the statistics of strength distribution of UDFRP composite is studied through computational micromechanics. Micromechanics-based realisations of the UDFRP composite are developed with a quantified measure of non-uniformity (MoN) in fibre distribution through an algorithm. Several realisations of these models are created for each non-uniform fibre distribution. External stress is applied to each realisation in the transverse direction till failure initiates in the matrix. The modified Drucker–Prager failure criteria are implemented for matrix failure. This externally applied stress is termed as the failure initiation strength. Statistical distribution of failure initiation strength is obtained for each fibre distribution. Variations of mean value, standard deviation and B-basis of failure initiation strength with the measure of non-uniformity in fibre distribution are studied for the fibre volume fractions of 0.5 and 0.6. In addition to the mean value, non-uniformity in fibre distribution also significantly influences the standard deviation and B-basis of strength distribution.

Experimental characterization and micro-modeling of transverse tension behavior for unidirectional glass fibre-reinforced composite

The mechanical behaviour of unidirectional fibre-reinforced polymer composites under transverse tension was studied using micromechanical computation and macroscopic experimentation. The representative volume element (RVE) of a composite with random fibre distribution was built by the proposed algorithm, which can effectively solve the jamming-limit problems for the hard-core-based model. The progressive damage process of the interface and matrix was simulated using the cohesive zone model and the extended Drucker–Prager model. The solutions of the mechanical loading case and the thermal mechanics loading case were compared to illustrate the effect of thermal residual stress. According to parametric studies, the failure models were mainly divided into two categories: interface-dominated and matrix-dominated damage, which rely on the interface strength, interface fracture energy, and matrix plastic deformation.