Continuous Fiber-reinforced Composites Research Articles

Improvement in dynamic properties of laminated MWCNT-polystyrene composite beams via an integrated numerical–experimental approach

A new concept for the optimization of dynamic behavior of laminated nanocomposites is introduced where fiber orientation factor in continuous fiber-reinforced composites is replaced by different wt.% of carbon nanotubes (CNTs) in each layer. First, at a design concept level, an optimum distribution of multi-walled CNTs (MWCNTs) through the thickness of a typical cantilever beam is sought to achieve its highest fundamental natural frequency for a given weight percent of MWCNTs. This is done using a finite element (FE) model in ABAQUS along with a user-defined Python code. Next, based on the obtained optimum distribution, actual laminated MWCNT/polystyrene (PS) composite beams were fabricated and their effective stiffness, fundamental natural frequencies and damping ratios were measured through static deflection and free vibration tests. It was found that the optimum distribution of MWCNTs resulted in an increase of 21.9% and 10.4% in the effective Young’s modulus and the fundamental damped natural frequency values, respectively, which were almost two-fold higher than those of a beam with a uniform MWCNT distribution. In addition, compared to a pure polymer beam, 38.9% and 27.8% improvements in the damping ratio of the uniformly and optimally distributed MWCNT polymer composite beams were achieved.

Numerical simulation of microscopic damage and strength of fiber-reinforced plastic composites

Discontinuous fiber-reinforced composites have better productivity and formability than continuous fiber-reinforced composites. However, their strength is remarkably low. Thus, there is an urgent need to improve the strength of discontinuous fiber-reinforced plastic composites. In this study, we utilized a unit-cell model that considers microscopic damage including matrix cracking and fiber breaking, and incorporates constitutive laws of thermosetting resin or thermoplastic resin for the matrix. The tensile damage and strength of the composite were investigated for various fiber lengths and/or matrix properties. We compared the simulated strengths with experiments for carbon fiber-reinforced polypropylene. The effect of deformation rate on mechanical behavior was also investigated.

Experimental fabrication and characterization of out-of-plane fiber waviness in continuous fiber-reinforced composites

This study presents the development of fabrication techniques and experimental measurements of out-of-plane fiber waviness in a continuous fiber-reinforced polymer composite. Literature on characterization and fabrication techniques was briefly reviewed. Three fabrication methods were developed: the transverse-strip method, ply-drop method, and constant-thickness ply-drop method. Experimental characterization demonstrated that specimens with a range of waviness parameters can be easily manufactured. The most important features of the techniques are ease of fabrication and simplicity of experimental setup. An industrial part was characterized optically to validate the techniques, showing a maximum misalignment angle of 5.3°.

Study of Thermal Stress of Iron-Boron Alloy Casing

The outer casing of heater made of iron-boron alloy is brittle fractured easily. It is a an effective way to add continuous fibers in brittleness material to improve the mechanical properties of composites. Temperature and thermal stress distribution of iron-boron alloy casing and the influence of thickness on the thermal stress of the casing is computed with finite element method, and the thermal stress distribution and influence of fiber volume fraction of continuous fiber-reinforced composites is studied. The result indicates that the external surface is in tensile stressed condition, and the internal surface is in compression stressed condition; the thermal stress increases with the thickness. The compression stress of the matrix decreases and the tensile stress increases with the increasing of the fiber volume fraction.

Impact behavior of short and continuous fiber-reinforced polyester composites

In this study, the impact strengths of E-glass, coir, oil palm as well as E-glass/coir and E-glass/oil palm hybrid polyester composites were studied. All types of composites were reinforced with fiber volume fractions of 30%, 40%, and 50% and fiber lengths 3, 7, and 10 mm. Composite laminates reinforced with longitudinal and transverse coir fiber mats were also studied. The number of fiber mats varied from 1, 2, 3, and 4 layers for non-spaced fiber mats and 2, 3, and 4 layers for 1.5 mm spaced fiber mats. Besides, coir—polyester composite with addition of sand filler was studied as well, with 40%, 50%, and 60% of volume fractions and fiber lengths of 3, 7, and 10 mm. Results show that impact strength improves with fiber content and fiber length. In addition, longitudinal fiber mats always exhibit better impact toughness compared to transverse fiber mats. Impact strength is improved with the number of fiber layers but worsened by the fiber spacing. As for coir/polyester concrete, low fiber content and fiber length improve the impact strength. The fractured surfaces were inspected under scanning electron microscope to investigate the fracture mechanisms in each type of composites.

Micromechanical effective elastic moduli of continuous fiber-reinforced composites with near-field fiber interactions

A higher-order micromechanical framework is presented to predict the overall elastic deformation behavior of continuous fiber-reinforced composites with high-volume fractions and random-fiber distributions. By taking advantage of the probabilistic pair-wise near-field interaction solution, the interacting eigenstrain is analytically derived. Subsequently, by making use of the Eshelby equivalence principle, the perturbed strain within a continuous circular fiber is accounted for. Further, based on the general micromechanical field equations, effective elastic moduli of continuous fiber-reinforced composites are constructed. An advantage of the present framework is that the higher-order effective elastic moduli of composites can be analytically predicted with relative simplicity, requiring only material properties of the matrix and fibers, the fiber–volume fraction and the microstructural parameter γ. Moreover, no Monte Carlo simulation is needed for the proposed methodology. A series of comparisons between the analytical predictions and the available experimental data for isotropic and anisotropic fiber reinforced composites illustrate the predictive capability of the proposed framework.

Modeling of Damage Evolution and Failure in Fiber-Reinforced Ductile Composites Under Thermomechanical Fatigue Loading

In this article, a methodology based upon micromechanical analysis of multiple damage-plasticity events is developed to predict nonlinear cyclic stress-strain response and fatigue failure of continuous fiber-reinforced metal matrix composites under cyclical thermomechanical loading. Microscopic damage-plasticity events in composite are described by fiber fracture, local cyclic plasticity of matrix and interface as well as interfacial debonding. A superposition method under the framework of shear-lag arguments is developed to analyze cyclic stress and deformation in the composites. A simulation scheme coupled with Monte-Carlo method is proposed to investigate evolution of damage-plasticity, cyclic behavior, and fatigue life of the composites. The statistic variations in fiber strength, local thermoplasticity of matrix properties, and interface characters between fiber and matrix have been taken into account. The model can predict the crossover behavior of the S-N curves observed in experiments for the in-phase and out-of-phase thermomechanical fatigue loads. The underlying mechanisms controlling the cross-over behavior have been revealed by the simulation.

Effect of imperfect interfaces on Elastothermodynamic Damping of fibre-reinforced MMCs

Elastothermodynamic Damping (ETD) is a source of damping present in all thermoelastic materials. Most of the works related to the evaluation of ETD in fibre-reinforced Metal-Matrix Composites (MMCs) assume perfect interfaces between reinforcement and matrix. On the contrary, composite materials do have imperfect interfaces because of debonding between the reinforcement and matrix. In recent years, the effect of imperfect interfaces on ETD of particulate MMCs has been analysed. In this work, imperfect interface model for the particulate composites has been extended to a continuous unidirectional fibre-reinforced composite. The investigations of imperfect mechanical and thermal interface on the ETD capacity have been carried out.

Modeling of Progressive Failure in Ductile Matrix Composites Including Local Matrix Yielding

In this article a theoretical model based upon micromechanical analysis of damage is developed to predict nonlinear stress-strain response and progressive failure of continuous fiber-reinforced metal matrix composites (MMCf). A micromechanically analytical model using an influence function superimposition technique is developed to derive stress profiles for any configuration of breaks in MMCf under tensile loading, by considering local matrix tensile yield and interface yield (or sliding). Several hundred Monte Carlo simulations including these failure mechanisms have been executed to simulate failure process and determine statistically the ultimate strength distributions of the composites. Site discretization, material sizes and shape parameter in Weibull distribution are studied to investigate the dependence of ultimate strength on these factors. It is shown that the size dependence of composite ultimate strength is dominated by fiber strength statistics and stress redistribution due to progressive microdamage.

3D-Damage Model for Fiber-Reinforced Brittle Composites with Microcracks and Imperfect Interfaces

A three-dimensional (3D) micromechanics-based evolutionary damage model is proposed to predict the effective elastic behavior of continuous fiber-reinforced brittle matrix composites with microcracks and imperfect interfaces. Eshelby’s tensor for a circular cylindrical inclusion with slightly weakened interface is adopted to model continuous fibers with imperfect interfaces. The nucleation of microcracks is simulated by employing the continuum damage model. A multilevel damage modeling process in accordance with Weibull’s probabilistic function is incorporated into the micromechanical framework to describe the sequential evolution of imperfect interfaces in the composites. Numerical examples corresponding to uniaxial loadings in the longitudinal and transverse directions are solved to illustrate the potential of the proposed damage model. Furthermore, the present prediction is compared with available experimental data in the literature to highlight the applicability of the proposed model.

Effects of laminate sequencing on thermoforming of thermoplastic matrix composites

Continuous fiber-reinforced thermoplastic composites are promising materials for light-weight structural components. Their medium to high processing and temperature-dependent properties, and the complex deformation mechanisms that occur within the composite sheet during the forming, are main problems in the practical production of parts. Thermoforming is an effective fabrication method due to the reversible solid–liquid phase transformation of thermoplastic materials. Deep drawing of these materials involves heating the composite to its melt/softening temperature and then applying suitable force to form the composite to the required shape. In the present study the influence of essential processing parameters on the forming behavior and quality of the profiles was examined experimentally. The base material was polypropylene and unidirectional glass fibers were used as reinforcement. The appropriate processing temperature, pressure and heating time for producing and deep drawing of thermoplastic composite sheet obtained. In order to study the process analytically, finite element ABAQUS software package has been employed. In this investigation, fiber properties gained from experiments were considered. Finally, apparent deformation of fibers and logarithmic axial strain are compared between ABAQUS and experimental results and these comparisons are represented graphically. Consequently these comparisons lead to optimum film stacking among selected lay-ups to prevent wrinkling in deep drawing process.

Materials Characterization in Continuous Fiber-Reinforced Ceramic Composites Served in Simulating Environment

Materials characterization is a crucial issue in the development and application of new materials. Materials characterization aims to mine and acquire characteristic information and their evolution in the materials. It mainly includes three important topics which are microstructural characterization, properties characterization, and environmental degradation. In this paper, characterization techniques about these topics were discussed for C/SiC composites and a characterization system was preliminarily established. All these characterization research and their results further the better understanding of the relationship between microstructure and properties and of the failure mechanisms in the C/SiC composites.

Longitudinal Compressive Strength of Continuous Fiber Composites

The in-plane longitudinal compressive strength of continuous fiber-reinforced composites is significantly less than their tensile strength, a phenomenon that is still not well understood. Dow and Rosen attempted in 1965 to explain this phenomenon through a fiber microbuckling model, in which each fiber was modeled as a beam-on-an-elastic-foundation. The model, however, grossly overestimates the compressive strength; researchers have since focused on introducing factors that reduce the predicted compressive strength to fit experimentally observed values. These include initial fiber waviness, fiber and matrix properties, the interfacial strength, and interphase properties. While empirical results have demonstrated the influences of some of these factors, an analytical model that can accurately predict the strength while taking into account the underlying failure mechanism is still lacking. The present study treats the compressive strength prediction of continuous fiber-reinforced composites using a different approach. Here, the matrix surrounding the fiber is not assumed to be homogeneous, but is divided into a discrete interphase region adjacent to the fiber and bulk matrix phase beyond the interphase. The three-phase model is shown to provide a more accurate prediction of the compressive strength of typical high-performance composites, such as glass and carbon fiber-reinforced epoxy. The present model's prediction agrees well with the trends shown in the experimental database available in the literature.

Application of the Spectral Methods of Microstructure Design to Continuous Fiber-reinforced Composites

A new mathematical framework called microstructure-sensitive design (MSD) has recently been developed to facilitate solutions to inverse problems in microstructure design, where the goal is to identify the complete set of relevant microstructures that are theoretically predicted to satisfy a set of designer-specified criteria on effective properties or performance. This methodology has been applied previously to a few design-related case studies, mainly involving polycrystalline metals. This article describes the first application of MSD methodology to customized design of continuous fiber-reinforced composites for specified combinations of performance criteria. The main contribution of this study is that it presents a novel but simple mathematical framework for the application of first-order MSD to the design problems involving continuous fiber-reinforced composites. In the examples presented in this article, elementary first-order theories spanning two length scales have been selected to obtain effective properties of continuous fiber-reinforced composite material systems. Having selected these first-order theories, the authors proceed to demonstrate the viability of applying the first-order MSD framework to design the case studies in continuous fiber-reinforced composites.

Commingled Hybrid Yarn Diameter Ratio in Continuous Fiber-reinforced Thermoplastic Composites

Manufacturing of lightweight structures from fiber-reinforced thermoplastic composites is of great benefit. Among various manufacturing methods the usage of semi-finished products is in high demand. To improve the mechanical properties and increase the productivity, the commingled hybrid yarn was developed recently. Among many parameters the fiber volume fraction and was diameters of reinforcement filaments and thermoplastic filaments in hybrid yarn are investigated in this study. The target is to improve the impregnation of reinforcement by molten thermoplastic polymer. Two hybrid yarn samples are illustrated (a) high performance thermoplastic PEEK/CF and (b) standard thermoplastic/glass fibers polypropylene (PP)/GF. The unidirectional (UD) composite samples, manufactured using thinner filaments, show little improvement of mechanical properties within the investigated region. In this study, a new technological approach will be introduced to increase the homogeneity of PP/GF commingled yarns by online hybrid spinning.

Elastic–plastic thermomechanical response of composite co-axial cylinders

A new method is developed in this paper to deal with the thermomechanical response of continuous fiber-reinforced composites. Treating the matrix as an elastic-perfectly plastic solid, the analytical formulae of the deformations and stresses of the matrix are obtained from the plasticity theory, axisymmetric equilibrium equation, and stress–strain and strain–displacement relations. The fiber is taken to be an anisotropic, elastic material, and the formulae calculating its deformations and stresses are also presented. The boundary conditions and the consistence of deformations and stresses between the fiber and matrix, and between elastic and plastic regions of the matrix are employed to determine the unknown constants in the analytical formulae. With the developed method, the thermomechanical stress distributions in composites reinforced with circumferentially orthotropic, radially orthotropic and transversely isotropic fibers are investigated, and how the elastic-perfectly plastic property and different materials of the matrix affect the thermomechanical response of the composites is discussed. For the thermomechanical loads and composite systems given in this paper, the elastic-perfectly plastic property of the matrix can reduce the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix. A strong matrix can raise the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix.

Kinetics and mechanism of interfacial reaction in SCS-6 SiC continuous fiber-reinforced Ti-Al intermetallic matrix composites

Abstract SCS-6 SiC continuous fiber-reinforced Ti-Al intermetallics-matrix composites were fabricated by HIP method and then heat-treated in vacuum under different conditions. The interfacial reaction kinetics and mechanism were studied by using SEM, EDS and XRD. The results show that the content fluctuation of reactive elements such as C, Ti and Si appears in interfacial reaction layers, and multi-layer interfacial reaction compounds form. Alloying element Nb in matrix remarkably diffuses into interfacial reaction zone and changes the activation energy for the interfacial reaction layer growth following a role of parabolic rate. The activation energy (Q k) and (k 0) of SCS-6 SiC/super α 2 and SCS-6 SiC/Ti 2AlNb are 317.664 kJ/mol, 175.709 kJ/mol and 5.4438 x 10 −2 m/s 1/2, 1.44 x 10 −5 m/s 1/2; respectively, and the diffusion coefficient ( D c) is about 10 −18–10 −20 m 2/s. It is confirmed that the SCS-6 SiC/Ti-Al intermetallic composites have higher interface compatibility and stability. Furthermore, compared with SCS-6 SiC/super α 2, the interface compatibility and stability of SCS-6 SiC/Ti 2AlNb are even higher.

The effect of fiber orientation on the polymerization shrinkage strain of fiber-reinforced composites

The aim of this study was to characterize the linear polymerization shrinkage strain of glass fiber-reinforced composite (FRC) according to the fiber orientation. Test specimens (n=5) (10.0 x 10.0 x 1.5mm) were prepared from different brands of photopolymerizable resin-preimpregnated FRC; unidirectional continuous FRC, experimental random-oriented FRC, and bidirectional continuous FRC. As control materials, particulate filler composite resin and unfilled dimethacrylate monomer resin were used. Two uniaxial strain gages (gage length 2mm) were used to measure shrinkage strains in two directions: longitudinally and transversally to the fiber direction. The uncured composite or resin was placed on top of the strain gages, covered with a separating sheet and a glass plate, and irradiated for 40s with a light-curing unit. The shrinkage strain was monitored for 300 s. ANOVA and Tukey's posthoc test were used at a significance level of 0.05. ANOVA revealed that orientation of fiber and brand of material had a significant effect (P<0.05) on shrinkage strain. The unidirectional FRC revealed no shrinkage longitudinally to the fiber direction, whereas the shrinkage occurred transversally to the fiber direction. Particulate filler composite resin and unfilled resin revealed equal shrinkage strain in both of the measured directions. Anisotropic nature of FRC exists with regard to polymerization shrinkage strain. The variation of polymerization shrinkage strains of FRC compared to those of particulate filler composites and unfilled resin might be important for future clinical applications.

Finite-element analysis of the hot-pressing consolidation of continuous Al2O3fibers-reinforced NiAl composites

Abstract The finite-element method was used to model the consolidation process of continuous Al2O3 fiber-reinforced NiAl composites. Actual creep behavior of NiAl was accounted for including the instantaneous strain and primary creep behavior. Primary creep played a very important role in the consolidation process at high temperatures and high pressures. Various processing parameters were investigated to evaluate the effects of temperature and hot-pressing stress on the consolidation behavior. It was found that the effect of pressure on consolidation was more significant at high temperatures due to its strong influence on the creep rate during power-law creep. The effects of fiber volume fraction and the arrangement of the matrix-coated fibers were also analysed. The simulations recommend an optimal fiber volume fraction in the range of 30%–50 %. Fully dense composites were fabricated according to the predicted processing conditions, and good agreement between simulation and experiment was achieved.

Intraply shear characterisation of a fibre reinforced thermoplastic composite

Abstract Thermoforming, a commonly used method to manufacture components from fibre reinforced thermoplastic laminates, involves heating the composite to its melt/softening temperature and then applying suitable forces to mould the composite to the required shape. Acquiring complex curvature shapes involves flow phenomena such as interply slip, intraply shear and squeeze flow. To date, the intraply shear mechanism is the least well understood. Approaches have been made to determine both longitudinal and transverse steady intraply shear viscosities of molten unidirectional continuous fibre-reinforced composites in the past but with conflicting results. No truly comprehensive characterisation has been carried out on these materials under a steady shear rate deformation mode. The present study concentrated on experimentally establishing the intraply shear behaviour of carbon fibre reinforced polyetheretherketone (APC-2). Two basic orientations were considered, one where the fibres in the lay-up were parallel to the pull-out direction and the other where the fibres were perpendicular to the pull-out direction. Values of longitudinal and transverse shear viscosities were determined for shear rates between 0.002 and 0.02 s −1 . The viscosity was highly shear-rate dependent, and was best modelled using a ‘power-law’. At a rate of 0.01 s −1 the longitudinal viscosity was in the 1 MPa s range, and approximately 2.5 times the transverse value. These values are several orders of magnitude greater than those determined using more traditional means, such as torsional rheometry, but agree with results obtained using a picture frame test method.