Fiber Polymer Matrix Research Articles

Strain fields induced by kink band propagation in Cu-Nb nanolaminate composites

Kink band formation is a common deformation mode for anisotropic materials and has been observed in polymer matrix fiber composites, single crystals, geological formations, and recently in metallic nanolaminates. While numerous studies have been devoted to kink band formation, the majority do not consider the often rapid and unstable process of kink band propagation. Here we take advantage of stable kink band formation in Cu-Nb nanolaminates to quantitatively map the local strain fields surrounding a propagating kink band during uniaxial compression. Kink bands are observed to initiate at specimen edges, propagate across the sample during a rising global stress, and induce extended strain fields in the non-kinked material surrounding the propagating kink band. It is proposed that these stress/strain fields significantly contribute to the total energy dissipated during kinking and, analogous to crack tip stress/strain fields, influence the direction of kink propagation and therefore the kink band inclination angle.

Modeling the Failure Behavior of CFRP Laminates Subjected to Combined Thermal and Mechanical Loadings

This paper proposes a theoretical approach to predict the failure behavior of laminated carbon fiber reinforced polymer (CFRP) under combined thermal and mechanical loadings. Two types of CFRP Laminates, i.e., CCF300/BA9916 and T700/BA9916, are investigated, and TGA tests in both nitrogen and oxidation environments at different heating rates are carried out to obtain the thermal decomposition kinetic parameters of polymer matrix and carbon fiber. Based on the thermal decomposition behavior and a multi-level structure model, the thermal physical properties, mechanical properties and thermal deformations of the laminated composites at high temperatures are obtained. Then substituting thermally degraded properties into constitutive equations of composite materials as macroscopic defects, the damage mode and failure strength of the laminated composite under thermo-mechanical loadings is obtained. Predicted elastic properties and failure strength are compared with experimental results as well as previous models. Effects of heating rates and heating environments through rigorous physical model are considered in the present work. It is found that the heating rate significantly affects the thermal and mechanical properties, the higher the heating rate, the less degraded are the thermo-mechanical properties and failure strength at a given temperature. Young’s modulus and failure strength of T700/BA9916 are higher than those of CCF300/BA9916 at high temperatures, due to the higher volume fraction of carbon fibers, which are less weakened in thermal environment.

Absorção de água e propriedades mecânicas de compósitos poliméricos utilizando resíduos de MDF

Resumo Apresenta-se o estudo de viabilidade de utilização, como reforço em materiais compósitos poliméricos, de resíduos originados da manufatura dos painéis de MDF (Medium Density Fiberboard), avaliando seu potencial como alternativa em substituição a cargas minerais para aplicação industrial. A escolha da resina poliéster ortoftálica foi motivada pelas suas propriedades e principalmente pelo seu baixo custo e facilidade de aquisição. Diferentes frações mássicas (m) de adição de resíduo em resina poliéster ortoftálica foram estudadas: 0, 10, 15 e 20%. As propriedades analisadas foram: resistência mecânica, absorção de água e grau de cristalinidade. Os resultados mostram a diminuição das propriedades mecânicas em até 53%, no índice de cristalinidade em até 18% e aumento no índice de absorção de água em quase cinco vezes para o compósito de maior adição de resíduo (C20).

Comparative assessment of the explosive blast performance of carbon and glass fibre-polymer composites used in naval ship structures

An experimental investigation is presented into the explosive blast response of fibre-reinforced polymer laminates used in naval ship structures. Blast tests using plastic explosive charges were performed in air on square target plates made of carbon-polyester, glass-polyester, carbon-vinyl ester or glass-vinyl ester laminates, which are composite materials used in naval ships. The laminates were dynamically loaded by shock waves of increasing pressure and impulse, and the deformation, damage and residual mechanical properties were determined. The amount of blast-induced damage and the post-blast mechanical properties depend on both the fibre reinforcement and polymer matrix. E-glass laminates have higher resistance to blast-induced delamination cracking and tow rupture than carbon fibre composites. Furthermore, glass or carbon fibre laminates with a vinyl ester matrix have superior blast damage resistance compared to composites with a polyester matrix. The higher damage resistance is attributed to the higher flexural strain energy capacity and interlaminar fracture toughness properties of laminates containing glass fibres or vinyl ester matrix.

Reinforced thermoplastic composites with interfacial microarchitectural anchoring: Computational study

Reinforcing potential of fibers is limited for a number of thermoplastic polymers due to the inherently weak interfacial bonding between the non-polar/non-reactive polymer matrix and fiber surface. To this end, the concept of enhancing the interfacial strength in thermoplastic composites via controlled mechanical interlocking between fiber surface and polymer matrix is explored. Specifically, infiltration of the thermoplastic polymer into the anchoring sites around the microstructures located on the fiber surface provided an efficient mechanical interlocking. A computational study has been performed for several different surface morphologies for a glass/polyethylene material system. The strength calculations addressed both material failure and detachment of the matrix material from the anchoring sites. The results obtained, which focused on shear loading, indicated that the surface morphology has a significant effect on the interfacial bonding strength. The computational analysis results showed that even without any interfacial friction or adhesion, the interface strength could achieve 50% of the theoretical strength of perfect matrix-fiber bonding for a plane interface. An optimal geometry and density of the microarchitectured features on the surface was identified for many cases in a parametric study. Friction at the interface between polymer matrix and fiber surface was shown to provide a significant increase in interfacial strength for cases where the frictionless case detached, but not for cases of material failure, which shows the promise of anchoring when friction and adhesion cannot be relied on. It was therefore demonstrated that the precise surface morphology modification is an effective approach to improve the interfacial bonding in fiber reinforced thermoplastic composites.

Compressive softening and failure of basalt fibre composites in fire: Modelling and experimentation

In this study, the fire structural properties of a basalt fibre reinforced polymer laminate under compressive loading were investigated analytically and experimentally, and compared against an E-glass fibre composite with the same fibre content, ply orientation and polymer matrix. A thermal-mechanical model was used to compute the softening rate and failure stress of basalt fibre laminates which collapse, when loaded in compression, by either global buckling or material failure when exposed to fire. Fire structural measurements involving one-sided radiant heating with axial compressive loading were also performed. The measurements revealed that the softening behaviour and failure stress of the basalt fibre laminate were inferior to those of the glass fibre composite. Furthermore, the fire reaction properties, such as heat release rate and smoke density, were also less favourable for the basalt laminate. This appears to be mainly due to the thermal absorptivity of the basalt fibre laminate being higher, which causes it to heat up at a faster rate and reach higher temperatures when exposed to a radiant heat flux.

Effect of thermo-oxidative aging on compressive behavior of carbon fiber polymer matrix composites

The effects of reinforcement architecture on the compressive behaviors of carbon fiber polymer matrix composites (CF-PMCs) under thermo-oxidative aging conditions were investigated. Samples of three-dimensional and four-directional braided carbon fiber/epoxy composites (BC) and laminated plain woven carbon fiber/epoxy composites (LC) were subjected to isothermal aging at 80℃, 100℃, 120℃ and 140℃ in air circulating ovens for various durations up to 1200 h. The process resulted in progressive deterioration of the matrix reins and fiber/matrix interfaces, in the form of chain scissions, weight loss and fiber/matrix debonding, which significantly led to the decrease of the compressive strength. In addition, the compressive strength retention rates of BC were higher than those of LC at the same aging conditions due to the differences of their reinforcement architecture. On the one hand, LC lost more weight than BC because the percentage of exposure of fiber ends to air in the LC samples was five times more than that in the BC samples. Moreover, the BC samples could resist the compressive load as an integral structure and did not show delamination damage as in the case of LC samples, although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging. Therefore, adopting the three-dimensional and four-directional braided preform as the reinforcement of CF-PMCs is an effective way to improve their compressive strength under thermo-oxidative aging conditions.

Approaches to understand and predict the influence of rapid heat-up on degradation and strength of carbon fibre polymer matrix composites

This study focuses on understanding and prediction of short-term thermal degradation of polymer matrix composites. One sided irradiation of two commercial composites (HexPly® 8552/IM7 and M18-1/G939) is carried out on specimens of various thickness (2, 4, 6 mm) at different heat fluxes (50 and 80 kW/m2) for various exposure times prior to ignition. The aim is to correlate the amount of the applied thermal energy with the heat damage and the residual mechanical strength. Among the two primary components of each matrix the epoxy resin is observed to degrade faster than the thermoplastic under thermal load, as measured by IR spectroscopy. A correlation is achieved between the interlaminar shear strengths and the relative amount of the residual matrix components. The interlaminar shear strengths and degradation processes are assessed in dependence of the applied energy per volume. The derived relationships and a chemometric analysis of IR spectra, can be used to rapidly estimate mechanical properties, as well as other properties of specimens with unknown thermal preload. Degradation processes are discussed in detail.

Zaawansowana analiza wytrzymałościowa wypraski z kompozytu WPC z uwzględnieniem powtryskowej orientacji włókien w osnowie polimerowej

Zaawansowana analiza wytrzymałościowa wypraski z kompozytu WPC z uwzględnieniem powtryskowej orientacji włókien w osnowie polimerowej

Continuous carbon fiber polymer–matrix composites in unprecedented antiferroelectric coupling providing exceptionally high through-thickness electric permittivity

Continuous carbon fiber polymer–matrix composites in unprecedented antiferroelectric coupling, as enabled by stacking composites with positive value (up to 400) and negative value (down to −600) of the electric permittivity, provide exceptionally high through-thickness permittivity up to 78,000 (≤2.0 MHz), corresponding to a capacitance of 370 μF/m2. The high capacitance is consistent with the equation for negative and positive capacitors in series. The permittivity tailoring of the composites involves dielectric cellulosic tissue paper interlaminar interlayers. Negative permittivity (not previously reported for carbon fiber composites) requires the paper to be wet with tap water (resistivity 1.5 kΩ cm) during incorporation in the composite, though the water evaporates and leaves ions at very low concentrations during composite fabrication, and also requires optimum through-thickness resistivity (e.g., 1 kΩ cm, as given by paper thickness 35 μm); it is probably due to interactions between the functional groups on the carbon fiber surface and the residual ions (mainly chloride) left after tap water evaporation.

Estudo de propriedades dinâmico-mecânicas de um compósito aeronáutico de CFRP com fios de ligas com memória de forma embebidos

Resumo Este trabalho trata-se de um estudo experimental do comportamento de propriedades termomecânicas de um compósito ativo, obtido através da introdução de diferentes frações volumétricas de fios de uma liga NiTi com efeito de memoria de forma em uma matriz polimérica reforçada com fibras de carbono (CFRP). Para tal estudo, inicialmente fez-se uma análise do módulo elástico de um pré preg de CFRP aeronáutico com diferentes posições de ângulo de fibras de carbono, a fim de determinar a matriz mais adequada para a introdução de fios de NiTi para obter compósito ativo. Verificou-se que a matriz com fibras alinhadas a 15º apresenta-se como uma boa opção para a obtenção de compósitos ativos, sendo utilizada para a fabricação de amostras de CFRP/NiTi. As amostras tiveram seu potencial de ativação avaliado através da análise da variação do módulo de elasticidade com o aumento da temperatura usando a técnica de Análise Dinâmico-Mecânica (DMA). Através dos resultados obtidos, verificou-se a capacidade de ativação dos compósitos CFRP/NiTi, os quais apresentam variação positiva de módulo de elasticidade ao serem aquecidos acima da temperatura de transformação dos fios NiTi.

Mechanical, Morphological, and Thermal Properties of Nutshell and Microcrystalline Cellulose Filled High-Density Polyethylene Composites

Effects of nutshell fiber loadings of 30 wt.% and MCC loadings up to 15 wt.% on some properties of high-density polyethylene composites (HDPE) were investigated. The composites were manufactured by a single screw extruder and injection molding. The experimental composite samples were tested for their mechanical performance including tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength. Thermal and morphological properties of the composites were tested by differential scanning calorimetry-DSC and scanning electron microscopy (SEM), respectively. The maximum tensile strength was obtained from the MCC-filled composites, whereas the maximum flexural strength was achieved with the MCC-nutshell filled composites. The tensile and flexural moduli of the composites were significantly improved with increasing MCC content and the presence of nutshell fibers in polymer matrix. Impact strength decreased using MCC and nutshell fiber in the polymer matrix. Based on the DSC results, there was no remarkable change in the melting point for all composites. The results showed that the incorporation of nutshell fibers and MCC in the polymer matrix had brought about some positive effect on mechanical properties of HDPE composites.

Cellulose kraft pulp reinforced polylactic acid (PLA) composites: effect of fibre moisture content

PLA offers a competitive and CO 2 neutral matrix to commonly used polyolefin polymer based composites. Moreover, the use of PLA reduces dependency on oil when producing composite materials. However, PLA has a tendency of hydrolytic degradation under melt processing conditions in the presence of moisture, which remains a challenge when processing PLA reinforced natural fibre composites. Natural fibres such as cellulose fibres are hygroscopic with 6–10 wt% moisture content at 50–70% relative humidity conditions. These fibres are sensitive to melt processing conditions and fibre breakage (cutting) also occur during processing. The degradation of PLA, moisture absorption of natural fibres together with fibre cutting and uneven dispersion of fibres in polymer matrix, deteriorates the overall properties of the composite. In the given research paper, bleached softwood kraft pulp (BSKP) reinforced PLA compounds were successfully melt processed using BSKP with relatively high moisture contents. The effect of moist BSKP on the molecular weight of PLA, fibre length and the mechanical properties of the composites were investigated. By using moist never-dried kraft pulp fibres for feeding, the fibre cutting was decreased during the melt compounding. Even though PLA degradation occurred during the melt processing, the final damage to the PLA was moderate and thus did not deteriorate the mechanical properties of the composites. However, comprehensive moisture removal is required during the compounding in order to achieve optimal overall performance of the PLA/BSKP composites. The economic benefit gained from using moist BSKP is that the expensive and time consuming drying process steps of the kraft pulp fibres prior to processing can be minimized.

Numerical Modeling of Non-destructive Testing of Composites

Low-velocity strikes are considered as one of the most dangerous load types for composites, especially in aviation. They do not lead to an immediate destruction of a whole detail, but inner damage, provoking a delamination between layers or between fiber and matrix, lowers the material strength and may cause a destruction during the flight. This inner damage can only be noticed via complex study, which increases an exploitation cost. Numerical modeling can help to interpret the results obtained from common portable devices, which are currently used for metals. The modification of known methodology can be reliably used for composites. In this research, a hybrid grid-characteristic method of 1-2 order on irregular tetrahedral grid is used. A carbon fiber polymer matrix of unidirectional composite is modeled as a homogeneous orthotropic media with a single distinguished direction along the fiber. As a result, the one-dimensional graphics, which correspond to A-scans in real devices, were obtained. The detailed analysis of received data confirms a rationality of proposed methodoly.

Virtual manufacturing of composite aerostructures

ABSTRACTThe past century has witnessed the rise and maturity of the flying machine, starting with the Wright brothers flyer to today’s modern passenger aircrafts and warfighters. At the start of this century, yet another achievement in flying vehicle technology was seen with the launch of the Boeing 787 aircraft, which has a significant portion by weight of polymer matrix fibre composites. This paper, therefore, addresses the effects of the manufacturing process of fibre reinforced polymer matrix composites on mechanical performance. Computations are carried out using the Finite Element (FE) method at the microscale where Representative Volume Elements (RVEs) are analysed with Periodic Boundary Conditions (PBCs). Straight fibre pre-preg-based composites and textile composites are considered. The commercial code ABAQUS is used as the solver for the FE equations, supplemented by user-written subroutines. The transition from a continuum to damage/failure is effected by using the Bažant-Oh crack band model, which preserves mesh objectivity. Results are presented for RVEs that are first subjected to curing and subsequently to mechanical loading. The effect of the fibre packing randomness on the microstructure is examined by considering multifibre RVEs where fibre volume fraction is held constant but with random packing of fibres. Plain weave textile composites are also cured first and then subjected to mechanical loads. The possibility of failure is accommodated throughout the analysis – failure can take place during the curing process even prior to the application of in-service mechanical loads. The analysis shows the differences in both the cured RVE strength and stiffness, when cure-induced damage has and has not been taken into account.

Through-thickness thermal conduction in glass fiber polymer–matrix composites and its enhancement by composite modification

Continuous glass fiber polymer–matrix composites are electrically insulating and used for printed wiring boards, but their thermal conductivity needs to be increased without sacrificing the electrical insulation ability. The through-thickness thermal conductivity of these epoxy–matrix composite laminates with in-plane fibers is found to be effectively modeled using the Rule of Mixtures with fibers and matrix mainly in parallel in the through-thickness direction, in contrast to the series model that is effective for previously studied carbon fiber composites. For the glass fiber composites, the through-thickness conductivity is similar to the in-plane conductivity. The conductivity for woven fiber composites is increased by up to 80 % by curing pressure increase (from 0.69 to 4.0 MPa), up to 50 % by solvent (toluene or ethanol) treatment of the prepreg for partial surface resin removal, and up to 90 % by boron nitride nanotube (BNNT) incorporation along with solvent treatment. The highest through-thickness thermal conductivity reached is 1.2 W/(m K), which is higher than those of all prior reports on glass fiber composites. The interlaminar interfaces are negligible in through-thickness thermal resistance compared to the laminae, as for previously studied carbon fiber composites. The fiber contribution dominates the lamina resistance. The fiber–fiber interface contribution to the lamina resistance decreases significantly with curing pressure increase or composite modification involving BNNT incorporation or solvent treatment of the prepreg.

Multi-scale modelling of moisture diffusion coupled with stress distribution in CFRP laminated composites

Laminated composite structures operating in a marine environment are subject to moisture ingress. Due to the slow diffusion process of moisture, the distribution of moisture is not uniform so that the laminates can develop hygrothermal stresses. An accurate prediction of the moisture concentration and the associated hygrothermal stress is vital to the understanding of the effect of marine environment on failure initiation. The present paper investigates the time-dependent moisture diffusion and the stress distribution in carbon fibre reinforced polymeric (CFRP) composites by means of experimental study and Finite Element Analysis (FEA). Samples were made from CFRP pre-preg autoclave-cured, and then immersed in fresh water and sea water at a constant 50°C for accelerated moisture diffusion. Laminates with [0]16, [90]16, [±45]4s lay-up sequences were investigated. A multiscale 3D FEA model was developed to evaluate the interfacial stresses between polymer matrix and carbon fibre and the stress distribution in the composite laminates. The analysis revealed that both the stress distribution and stress level are time-dependent due to moisture diffusion, and the interphase between fibres and matrix plays an important role in both the process of moisture diffusion and the stress/strain transfer. The interlaminar shear stresses of the laminates induced by hygrothermal expansion exhibited a significant specimen edge effect. This is correlated with the experimental observations of the flexural failure of laminates.

Mechanical properties of sisal fibre-reinforced polymer composites: a review

There has been a growing interest in the utilization of sisal fibres as reinforcement in the production of polymeric composite materials. Natural fibres have gained recognition as reinforcements in fibre polymer–matrix composites because of their mechanical properties and environmental friendliness. The mechanical properties of sisal fibre-reinforced polymer composites have been studied by many researchers and a few of them are discussed in this article. Various fibre treatments, which are carried out in order to improve adhesion, leading to improved mechanical properties, are also discussed in this review paper. This review also focuses on the influence of fibre content and fabrication methods, which can significantly affect the mechanical properties of sisal fibre-reinforced polymer composites.

Improved interfacial properties between glass fibers and tetra-functional epoxy resins modified with silica nanoparticles

The interfacial properties between fiber bundle and polymer matrix play a crucial role in determining the final performance of fiber-reinforced polymer composites. Epoxy modified with nanofillers as new “matrix” for the composites has been shown to be a possibility to enhance the interfacial properties between fiber bundle and “matrix”. Herein, we synthesized silica nanoparticles with an average diameter of ~80 nm through using the sol-gel technique and achieved a good dispersion of silica in tetra-functional epoxy matrix after intensively mechanical mixing procedure. The results revealed that incorporation of silica nanoparticles into epoxy increased its stiffness, strength and toughness simultaneously. Such silica/epoxy composite as new “matrix” showed a good impregnation in the fiber bundles, and thus produced improved interfacial properties between glass fiber bundle and new “matrix”. For example, the presence of 15.0 wt% silica nanoparticles was found to produce ~15 %, 22 % and ~34 % in the elastic modulus, tensile strength and critical stress intensity factor of epoxy, respectively; and the interfacial strength between fiber bundle and the “matrix” was also enhanced by ~58.3 %. Based on the fracture surface analysis, several possible mechanisms were proposed and discussed to understand the improved interfacial properties between glass fiber bundle and tetra-functional epoxy modified with silica nanoparticles.

High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites

An experimentally validated micro-scale analysis of the visco-thermo-mechanical behavior of polymer matrix composites under different loads is proposed. A new constitutive law for the matrix material is developed taking into account the pressure dependence of the material as well as strain-rate and temperature dependence. Capturing the matrix behavior under multi-axial stress states is concluded to be essential to accurately predict the composite material behavior, even when considering simple load cases such as transverse compression and/or shear. Without any calibration procedure at the composite level, good agreement with the experimental data is observed for different loading conditions, including strain-rate dependency.Using this validated micro-scale model, a three-dimensional simulation of the formation of a kink band under longitudinal compression of the composite is conducted. A new evidence at micro-scale is found supporting the hypothesis that shear stresses transferred between fibers and matrix are particularly important in the formation of the kink band.