Effect of fiber arrangement on mechanical properties of short fiber reinforced composites

The present paper developed a three-dimensional (3D) “tension–shear chain” theoretical model to predict the mechanical properties of unidirectional short fiber reinforced composites, and especially to investigate the distribution effect of short fibers. The accuracy of its predictions on effective modulus, strength, failure strain and energy storage capacity of composites with different distributions of fibers are validated by simulations of finite element method (FEM). It is found that besides the volume fraction, shape, and orientation of the reinforcements, the distribution of fibers also plays a significant role in the mechanical properties of unidirectional composites. Two stiffness distribution factors and two strength distribution factors are identified to completely characterize this influence. It is also noted that stairwise staggering (including regular staggering), which is adopted by the nature, could achieve overall excellent performance. The proposed 3D tension–shear chain model may provide guidance to the design of short fiber reinforced composites.     

Interlaminar properties of carbon fiber composites with halloysite nanotube-toughened epoxy matrix

Halloysite nanotubes (HNTs), which are geometrically similar to multi-walled carbon nanotubes, can improve the impact strength of epoxy substantially, according to our previous work [1]. Using a HNT-toughened epoxy as the matrix, a set of hybrid composites was prepared with carbon fiber-woven fabrics. The interlaminar properties of the composites were investigated by a short-beam shear test, a double-cantilever-beam test and an end-notched flexure test. The results showed that the addition of HNTs to the composites improved the interlaminar shear strength and the fracture resistance under Mode I and Mode II loadings greatly. The morphological study of the hybrid composites revealed that HNTs were non-uniformly dispersed in the epoxy matrix, forming a unique microstructure with a large number of HNT-rich composite particles enveloped by a continuous epoxy-rich phase. A study of the fracture mechanism uncovered the important role of this special morphology during the fracturing of the hybrid composites.     

Fabrication and mechanical properties of carbon short fiber reinforced barium aluminosilicate glass–ceramic matrix composites

Dense BaSi₂Al₂O₈ (BAS) and Ba_0.75Sr_0.25Si₂Al₂O₈ (BSAS) glass–ceramic matrix composites reinforced with carbon short fibers (C_sf) were fabricated by hot pressing technique. The microstructure, mechanical properties and fracture behavior of the composites were investigated by X-ray diffraction, scanning and transmission electron microscopies, and three-point bend tests. The carbon fibers had a good chemical compatibility with the glass–ceramic matrices and can effectively reinforce the BAS (or BSAS) glass–ceramic because of associated toughening mechanisms such as crack deflection, fiber bridging and pullout effects. Doping of BAS with 25 mol% SrSi₂Al₂O₈ (SAS) can accelerate the hexacelsian to celsian transformation and result in the formation of pure monoclinic celsian in C_sf/BSAS composites, which can avoid the undesirable reversible hexacelsian to orthorhombic transformation at 300 °C and reduce the thermal expansion mismatch between the fiber and matrix.     

Multiscale fiber reinforced composites based on a carbon nanofiber/epoxy nanophased polymer matrix: Synthesis, mechanical, and thermomechanical behavior

Vacuum assisted resin infusion molding (VARIM) was used to produce multiscale fiber reinforced composites (M-FRCs) based on carbon nanofibers dispersed in an epoxy resin. Flexural, interlaminar shear strength (ILSS) and thermomechanical tests are presented for the 0.1 wt% and 1 wt% M-FRCs and compared with the neat fiber reinforced composites (FRCs). Flexural strength and modulus increased (16–20%) and (23–26%), respectively for the 0.1 wt% and 1 wt% M-FRCs when compared to the neat FRCs. ILSS properties increased (6% and 25%) for the 0.1 wt% and 1 wt% M-FRCs, respectively when compared to neat FRCs. The glass transition temperatures (T_g) of both M-FRC samples were 25 °C higher than the neat FRC. Coefficients of thermal expansion (CTE) of the M-FRC samples improved compared to the neat FRC. The improved T_g and CTE properties in the M-FRC samples are attributed to synergistic interactions between the CNF/PNC matrix and glass fibers.     

Aligned ramie fiber reinforced arylated soy protein composites with improved properties

To enhance the strength, ramie fibers aligned in vertical (V), horizontal (H) as well as both vertical and horizontal (X) directions were used to reinforce soy protein materials (SC), coded as VSC, HSC and XSC. The soy protein isolate was arylated with 2,2-diphenyl-2-hydroxyethanoic acid through the process of “dip-coating”, coded as SC-B. The SC and SC-B composite films were characterized by Fourier transform infrared spectra, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. Substantial improvement in the water uptake (from 100% to 25%) and the increased modulus (from 125 to 942 MPa) of the VSC-B composite were observed. This could be attributed to the formation of phase separation induced hydrophobic microparticles of DPHM on the surface of the SC-B films upon arylation, leading to the hydrophobicity. The thermal stability of the arylated composites increased compared to non-arylated ones. The VSC-B materials exhibited the highest water resistance and mechanical properties compared to HSC-B and XSC-B. Therefore, the arylation of SPI and alignment of the ramie fibers in the composites played an important role in the improvement of mechanical properties. This work provided a novel idea to improve the water resistance and modulus by reinforcing the protein matrix with natural fibers.     

Tensile and thermomechanical properties of short carbon fiber reinforced polyamide 6 composites

In this study, carbon fiber (CF) reinforced polyamide 6 (PA6) composites were prepared by using melt mixing method. Effects of fiber length and content, on the mechanical, thermal and morphological properties of CF reinforced PA6 composites were investigated. Fiber length distributions of composites were also determined by using an image analyzing program. It was seen that the maximum number of fibers were observed in the range of 0–50 μm. Mechanical test results showed that, increasing CF content increased the tensile strength, modulus and hardness values but decreased strain at break values of composites. DSC results showed that T_g and T_m values of composites were not changed significantly with increasing CF content and length. However, heat of fusion and the relative degree of crystallinity values of composites decreased with ascending CF content. DMA results revealed that storage modulus and loss modulus values of composites increased with increasing CF content.     

Maya Blue as natural coloring fillers in a multi-scale polymer-clay nanocomposite

The purpose of this article is to understand the underlying mechanisms of the potential of nanohybrids. Two types of fillers were dispersed in a biocompatible organic matrix, poly-(hydroxyethyl acrylate) (PHEA): either a natural fibrous clay (pristine sepiolite), or a natural nanopigment (Maya Blue). In comparison with the pure polymer, the mechanical properties of the composites have been already greatly improved with the addition a small amount of Maya Blue. However the PHEA/pristine sepiolite nanohybrid gives better results than the PHEA/Maya Blue for the same ratio of fillers. The stress-strain curves (with unloading and reloading) show that the presence of indigo modifies the interactions between the filler and the matrix. These analyses demonstrate that there is a direct correlation between the filler/matrix local interactions, the dispersion of the fillers and some macroscopical mechanical properties.     

Stress-dependence and time-dependence of the post-fatigue tensile behavior of carbon fiber reinforced SiC matrix composites

The major objective of this paper is to phenomenally report the stress-dependence and time-dependence of fatigue damage to C/SiC composites, and to tentatively discuss the effects of the fatigue stress levels and the fatigue cycles on the post-fatigue tensile behavior. Results show that compared with the virgin strength of the as-received C/SiC specimens, the tensile strengths of the as-fatigued specimens after 86,400 cycles were increased by 8.47% at the stresses of 90 ± 30 MPa, 23.47% at 120 ± 40 MPa, and 9.8% at 160 ± 53 MPa. As cycles continued, however, the post-fatigue strength of the composites gradually decreased after the peak of 23.47%, at which the optimal strength enhancement was obtained because the mean fatigue stress of 120 MPa was the closest to thermal residual stress (TRS), and caused TRS relieve largely during the fatigue. Most interestingly, there was a general inflexion appeared on the post-fatigue tensile stress-strain curves, which was just equal to the historic maximum fatigue stress acted upon the as-fatigued specimens. Below this inflexion stress the tensile curves revealed the apparent linear behavior with little AE response, and above that nonlinearity with new damage immediately emitted highly increase rate of AE activities. This ‘stress memory’ characteristic was strongly relevant to damaged microstructures of the as-fatigued composites in the form of the coating/matrix cracks, interface debonding/wear, and fiber breaking, which resulted undoubtedly in reduction of modulus but in proper increase of strength via TRS relief.     

Soybean oil-based thermosets with N-vinyl-2-pyrrolidone as crosslinking agent for hemp fiber composites

Soybean oil-based thermosets from acrylated epoxidized soybean oil (AESO) with a highly reactive vinyl monomer, N-vinyl-2-pyrrolidone (NVP), as crosslinking agent to replace styrene (St) were formulated for the fabrication of hemp fiber composites. The theoretical miscibility of NVP–AESO and St–AESO systems were discussed based on the group contribution method. The AESO resin with 30 wt% NVP exhibited a slightly higher viscosity than the counterpart with St, while the maximum curing temperature of the former was considerably lower than that of the latter. The composites from 20 wt% NVP resin gained comparable mechanical properties and higher glass transition temperature (T_g) to the composites with 30 wt% St. Further increase in NVP usage to 40 wt% resulted in the composites with higher tensile strength, tensile modulus, flexural strength, flexural modulus, storage modulus, and T_g of 29.6%, 22.4%, 22.5%, 20.6%, 21.6%, and 47.2%, respectively, when compared to those of the St-based composites.     

Enhanced tensile properties of aluminium matrix composites reinforced with graphene encapsulated SiC nanoparticles

Due to a high propensity of nano-particles to agglomerate, making aluminium matrix composites with a uniform dispersion of the nano-particles using liquid routes is an exceptionally difficult task. In this study, an innovative approach was utilised to prevent agglomeration of nano-particle by encapsulating SiC nano-particles using graphene sheets during ball milling. Subsequently, the milled mixture was incorporated into A356 molten alloy using non-contact ultrasonic vibration method. Two different shapes for graphene sheets were characterised using HRTEM, including onion-like shells encapsulating SiC particles and disk-shaped graphene nanosheets. This resulted in 45% and 84% improvement in yield strength and tensile ductility, respectively. The former was ascribed to the Orowan strengthening mechanism, while the latter is due primarily to the fiber pull-out mechanism, brought about by the alteration of the solidification mechanism from particle pushing to particle engulfment during solidification as a consequence of high thermal conductive graphene sheets encapsulating SiC particles.     

Electrical properties of short sisal fiber reinforced polyester composites fabricated by resin transfer molding

The electrical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with special reference to fiber loading, frequency and temperature. The dielectric constant (ε′), loss factor (ε″), dissipation factor (tan δ) and conductivity increases with fiber content for the entire range of frequencies. The values are high for the composites having fiber content of 50 vol.%. This increment is high at low frequencies, low at medium frequencies, and very small at high frequencies. The volume resistivity varies with fiber loading at lower frequency and merges together at higher frequency. When temperature increases the dielectric constant values increases followed by a decrease after the glass transition temperature. This variation depends upon the fiber content. Finally an attempt is made to correlate the experimental value of the dielectric constant with theoretical predictions.     

Electromagnetic interference shielding of composites consisting of a polyester matrix and carbon nanotube-coated fiber reinforcement

We investigated the electromagnetic interference shielding effectiveness (EMI SE) of composites consisting of an unsaturated polyester matrix containing woven glass or carbon fibers that had been coated with multiwalled carbon nanotubes (MWCNTs). Composite panels consisting of fiber fabrics with various combinations of fabric type and stacking sequence were fabricated. Their EMI SE was measured in the frequency range of 30 MHz–1.5 GHz. The underlying physics governing the EMI shielding mechanisms of the materials, namely, absorption, reflection, and multiple reflections, was investigated and used in analytical models to predict the EMI SE. Simulation and experimental results showed that the contributions of reflection and absorption to EMI shielding is enhanced by sufficient impedance mismatching, while multiple reflections have a negative effect. For a given amount of MWCNTs in the glass-fiber–reinforced composite, coating the outermost, instead of intermediate, glass fiber plies with MWCNTs was found to maximize the conductivity and SE.     

An enhanced FEM model for particle size dependent flow strengthening and interface damage in particle reinforced metal matrix composites

By incorporating the dislocation punched zone model, the Taylor-based nonlocal theory of plasticity, and the cohesive zone model into the axisymmetric unit cell model, an enhanced FEM model is proposed in this paper to investigate the particle size dependent flow strengthening and interface damage in the particle reinforced metal matrix composites. The dislocation punched zone around a particle in the composite matrix is defined to consider the effect of geometrically necessary dislocations developed through a mismatch in the coefficients of the thermal expansion. The Taylor-based nonlocal theory of plasticity is applied to account for the effect of plastic strain gradient which produces geometrically necessary dislocations due to the geometrical mismatch between the matrix and the particle. The cohesive zone model is used to consider the effect of interfacial debonding. Lloyd’s experimental data are used to verify this enhanced FEM model. In order to demonstrate flow strengthening mechanisms of the present model, we present the computational results of other different models and evaluate the strengthening effects of those models by comparison. Finally, the limitations of present model are pointed out for further development.     

Hybrid 3D-textile reinforced composites with tailored property profiles for crash and impact applications

Novel 3D-textile reinforced composites with a stretched fibre arrangement have very good specific mechanical properties and outstanding energy absorption capabilities. With respect to the specific technical requirements, 3D-textile preforms can be adjusted with regard to stiffness, strength and crash-worthiness by the intelligent combination of different fibre materials in the textile preform. Thus, hybrid 3D-textile preforms with tailored property profiles are excellent candidates for the use in impact and crash components of innovative lightweight structures for the aircraft and vehicle industry as well as for mechanical engineering applications.     

Study on the mechanical properties and thermal properties of jute and banana fiber reinforced epoxy hybrid composites

The aim of the present study is to investigate and compare the mechanical and thermal properties of raw jute and banana fiber reinforced epoxy hybrid composites. To improve the mechanical properties, jute fiber was hybridized with banana fiber. The jute and banana fibers were prepared with various weight ratios (100/0, 75/25, 50/50, 25/75 and 0/100) and then incorporated into the epoxy matrix by moulding technique to form composites. The tensile, flexural, impact, thermal and water absorption tests were carried out using hybrid composite samples. This study shows that addition of banana fiber in jute/epoxy composites of up to 50% by weight results in increasing the mechanical and thermal properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behavior and fiber pull-out of the samples using scanning electron microscope.     

Mechanical behavior of Kevlar/basalt reinforced polypropylene composites

In this study, mechanical behavior of thermoplastic composites reinforced with two-dimensional plain woven homogeneous and hybrid fabrics of Kevlar/basalt yarns was studied. Five types (two homogeneous and three hybrids) of composite laminates were manufactured using compression molding technique with polypropylene (PP) resin. Static tensile and in-plane compression tests were carried out to evaluate the mechanical properties of the laminates. The tension and in-plane compression tests had shown that the composites with the combination of Kevlar and basalt yarns present better tensile and in-plane compressive behavior as compared to their base composites. Improvement in the properties such as elastic modulus, strength and failure strain in both tension and in-plane compression was observed due to the hybridization. Numerical simulations were performed in ABAQUS/Standard by implementing a user-defined material subroutine (VUMAT) based on Chang-Chang criteria. Good agreement between the experimental and numerical simulations was achieved in terms of damage patterns.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.     

Preparation, morphology and properties of acylchloride-grafted multiwall carbon nanotubes/fluorinated polyimide composites

A fluorinated polyimide (PI) was synthesized by a two-step reaction from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride and 2,2′-bis(trifluoromethyl)-4,4′diaminobiphenyl. A series of PI composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by either an in situ polymerization or blending process. To increase the chemical compatibility of carbon nanotubes with the PI matrix, MWNTs were treated with an acid mixture and sulfoxide chloride by turns. Results show that the dispersion of the MWNTs is highly improved in the PI by modification. The modified MWNTs are dispersed homogeneously in the matrix, while the structures of the PI and MWNTs are stable in the preparation process. The thermal stability of the nanocomposites is slightly lower than that of the pure PI. With incorporating MWNTs, the storage modulus and glass transition temperature of the composite films enhanced comparing to that of PI matrix. The dielectric constants of the composites increase sharply, which is favorable to their practical use in anti-static materials and embedded capacitors.     

Investigation of structure,mechanical and tribological properties of short carbon fiber reinforced UHMWPE-matrix composites

Structural, mechanical and tribological properties of composite materials based on ultra-high molecular weight polyethylene reinforced with carbon fibers were investigated. The effect of surface modification of carbon fibers on the interaction at the fiber–matrix interface in UHMWPE based composites was studied. It was found that the thermal oxidation of carbon fibers by air oxygen at 500 °C can significantly enhance the interfacial interaction between the polymer matrix and carbon fibers. This allowed us to form composite materials with improved mechanical and tribological properties.     

The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.