Band 25, Heft 6

The inherent properties of bio-composites such as biodegradability, environment friendly, low cost of production, high strength and durability make them a suitable replacement to traditional materials such as glass and nylon. Bio-polymers are finding wide applications due to their intrinsic properties such as low density, low thermal conductivity, corrosion resistance and ease of manufacturing complex shapes. This paper aims toward a comprehensive study on polymer bio-composites. The review mainly focuses on types of reinforcements such as natural fibers, seed shells, animal fibers, cellulose, bio-polymers, bio-chemicals and bioceramics which enhance the mechanical properties, such as tensile strength, compressive strength, flexural strength, Young’s modulus and creep behavior, of the composites. The pertinent study carried out in this review explores an enormous potentiality of the composites toward a wide variety of applications.

Graphene (graphene) is a new type of two-dimensional inorganic nanomaterial developed in recent years. It can be used as an ideal inorganic nanofiller for the preparation of polymer nanocomposites because of its high mechanical strength, excellent electrical conductivity and plentiful availability (from graphite). In this review, the preparation methods of graphene/polymer nanocomposites, including solution blending, melt blending and in situ polymerization, are introduced in order to study the relationship between these methods and the final characteristics and properties. Each method has an influence on the final characteristics and properties of the nanocomposites. The advantages and disadvantages of these methods are discussed. In addition, a variety of nanocomposites with different properties, such as mechanical properties, electronic conductivity, thermal conductivity and thermal properties, are summarized comprehensively. The potential applications of these nanocomposites in conductive materials, electromagnetic shielding materials, photocatalytic materials and so on, are briefly presented. This review demonstrates that polymer/graphene nanocomposites exhibit superior comprehensive performance and will be applied in the fields of new materials and novel devices. Future research directions of the nanocomposites are also presented.

In this work, we report on the structural design of a 5-m-long composite blade intended for use in a horizontal-axis tidal turbine. The blade geometry is constructed through an optimization process to obtain the maximum power coefficient at the desired tip speed ratio of 4.5 by applying the blade element-momentum theory (BEMT). The blade is primarily designed using a NACA 63-424 hydrofoil. The blade structure is designed by using the BEMT to compute the loading conditions at various inflow velocities. Two parallel spars were chosen to produce the blade structure grid, and the preliminary lay-up structure of the composite blade was determined according to the thickness distribution identified using the twisted beam theory under the assumption that the two spars plus the upper and lower skins mostly contribute to the flap-wise bending stiffness while withstanding an external load. Then, high-strength unidirectional and double-bias fiber glass/epoxy materials were chosen to fabricate the blade. The final blade structure was then analyzed in ANSYS Workbench using the finite element method. The results show that the blade structure can withstand the applied load with failure indices <0.4.

The effects of adding Al 2 O 3 nanoparticles on the microstructure, tribological, magnetic, and corrosion properties of CuFe-Al 2 O 3 nanocomposites were investigated in this work. The mixture of Cu-25 wt.% Fe powder with 5 vol.% Al 2 O 3 was mechanically milled. X-ray diffraction results revealed that after 60 h of mechanical alloying, CuFe solid solution was formed. Magnetic hysteresis loops of the mechanically alloyed powders were extracted at room temperature. The morphology and elemental analysis of the sintered specimens were studied by field emission scanning electron microscope (SEM). It was observed that uniform distribution and embedding of Al 2 O 3 nanoparticles in the CuFe alloy matrix in nanocomposites were achieved, which exhibited excellent performances. Tribological properties were evaluated through a pin-on-disk wear test, and it was found that by the addition of Al 2 O 3 nanoparticles to CuFe alloy, the weight loss rate was reduced by 30%. The existence of Al 2 O 3 nanoparticles in the matrix of CuFe alloy causes the wear mechanism change from adhesive to abrasive, which means a considerable wear resistance was obtained in nanocomposites. The corrosion properties of the sintered samples in a solution of 3.5% NaCl were studied by potentiodynamic polarization. With the addition of Al 2 O 3 nanoparticles, the corrosion rate of the alloy was reduced by 75%.

The purpose of this paper is to investigate the mechanisms of cracking and failure in fiber metal laminates (FMLs) subjected to 3-point bending. Two types of laminates, based on the glass/epoxy and carbon/epoxy composites, were selected for the study. The paper presents the failures of matrix and fibers as well as the effects of different thicknesses of metal layers on the tested laminates. The mechanisms of failure observed for the two tested types of fibers with uniform thickness of aluminum sheets seem similar. The results demonstrate that the tested laminates exhibit the following failure modes: fiber breakage, matrix cracking, fiber/matrix debonding, delamination, and anodic layer failure. Given the behavior of aluminum under the compressive and tensile stresses, the aluminum layer acts as a barrier preventing FML failure during bending. In addition to aluminum layer thickness, the fiber type and composite layer directions are also important factors to be considered.

Contradictions of strength and thermal insulation of silica aerogel (SA) are of wide concern. In this research, the mesoporous structure of SA was grafted with the polymers to increase the strength of SA and decrease the thermal conductivity of composites. The composites were characterized and analyzed using field emission scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, the thermal gravimetric analyzer (TGA), multi-assay gel permeation chromatography (GPC), a microcomputer control electronic universal testing machine and so on. The results indicated that amino-capped polydivinylsiloxane (AP) was successfully grafted on the SA surface and polymerized with methyl methacrylate (MMA) to form an AP high thermal insulation phase interface between the SA phase and poly(methyl methacrylate) (PMMA) phase. The SA-AP/PMMA composite with a covalent bonding high thermal insulation phase interface had better mechanical properties and compressive strength than those of SA/PMMA. The obtained composite was an excellent thermal insulation material with lower thermal conductivity [0.045 W/(m·K)].

The feasibility of fabricating Mg alloy degradable composites with fly ash cenospheres (FACs) using stir casting has been demonstrated. The effects of FAC addition (mass fraction: 0, 2, 4, 6, 8 and 10 wt.%) on the microstructure, mechanical properties and corrosion behavior were investigated using optical microscope, scanning electron microscope, X-ray diffraction, density tests, compression tests, immersion tests and electrochemical measurements. The result shows that the degradable composites are mainly composed of α-Mg, β-Mg 17 Al 12 , Mg 2 Si and MgO phase, and FAC can refine the grain size. The average measured densities of the FAC/Mg alloy composites are higher than the theoretical values due to the formation of the Mg 2 Si phase, which are in the range of 1.8843–2.0526 g/cm 3 . The compressive strength of the degradable composites dramatically enhances with the addition of FAC, and the maximum strength is 375 MPa with the 8-wt.% mass fraction, which can be attributed to the refined grains and the formation of massive Mg 2 Si phase. Furthermore, the corrosion rate of the degradable composites with 10 wt.% FACs shows the highest value of 5.02 g/h in 3 wt.% potassium chloride solution at 80°C, which is three times higher than the corrosion rate of composites without FAC. With the increase in FAC content, more Mg 2 Si phases formed; thus, micro-galvanic corrosion works well in the composites.

In this paper, the flexural performance of fiber-reinforced polymer (FRP) bars reinforced concrete (RC) beams after conditioning in a simulated seawater wet-dry cycling environment for 6, 9 and 12 months is experimentally investigated. Two types of FRP bars, i.e. basalt FRP (BFRP) bars and steel-FRP composite bars (SFCBs), are adopted. Steel bars are employed for comparison. During the conditioning, a constant load is coupled to the beams. A total of 24 simply supported beams are tested. In addition, microscopic damage to the conditioned BFRP bars is detected by scanning electron microscopy (SEM). The test results indicated that total corrosion was observed at the surface of the bottom longitudinal steel bars after a maximum exposure of 12 months. However, the degradation of the macro-mechanical properties of the steel bars RC beam was not distinct. The ultimate load of the BFRP bars RC beams after 6 months, 9 months and 12 months was reduced by 22%, 33% and 42%, respectively. The yield load and ultimate load of the SFCBs RC beams were reduced by a maximum of 18% and 38%, respectively. The SEM observations revealed that there were distinct damages at the outer layer of the BFRP bars after 12-month conditioning.

The lattice truss panel structure (LTPS), which is a high strength material with high efficiency of heat transfer, has a good potential to be used as compact heat exchanger. The core of LTPS is a periodic porous structure, and the effective elastic modulus (EEM) will be different from the base material. It is essential to calculate the EEM for the design of this type of heat exchanger. This paper presents a study on the EEM of X-type LTPS by homogenization method, which has been verified by finite element method (FEM). It reveals that the effects of seven geometrical parameters of the X-type LTPS on EEM are not identical, and the relationship between the seven parameters and EEM has been established. Results calculated by homogenization method and FEM show a good agreement. The EEM decreases with the increase of truss length, stamping angle, shearing angle and node length, while it increases with the increase of truss width, truss thickness and face sheet thickness. Unlike the conventional foam material, there is no clear correlation between the EEM and the relative density, and a formula has been fitted to calculate the EEM of LTPS.

Carbon fiber-reinforced polymer material has been widely used in space/aerospace industries for manufacturing of spacecraft structures, satellite panels and antennas. In space, composites can be subjected to periodic thermal cycling (TC) in which temperature ranges from −196°C to 180°C, depending on the operational condition. The effect of TC on the properties of flat laminates made of unidirectional (UD) and fabric out-of-autoclave (OOA) material will be presented. Flat laminates were made using the recommended cure cycle by the material supplier. Then, the samples were cut and subjected to the thermal cycle. To do so, the samples were dipped into liquid nitrogen (−196°C) and then transferred to the oven (140°C). After different numbers of cycles (30, 60, 100, 150 and 200), the cross section of the specimens was examined under a microscope for microcrack detection. Other mechanical and physical properties including interlaminar shear strength, storage modulus and coefficient of thermal expansion (CTE) were measured. It was identified that TC can affect the examined properties by two competing factors: (i) more cross-linking in the polymer chain due to post-curing at high temperature during TC and (ii) microcrack formation due to the induced thermal stresses as a result of the matrix/fiber CTE mismatch. It was found that TC can cause microcrack formation and propagation around the voids in the laminate and affect its properties. Depending on the size and shape of the void, microcracks can form at different stages of TC.

This work focuses on identifying the thermal conductivity of composites loaded with phase-change materials (PCMs). Three configurations are studied: (1) the PCMs are divided into identical spherical inclusions arranged in one plane, (2) the PCMs are inserted into the matrix as a plate on the level of the same plane of arrangement, and (3) the PCMs are divided into identical spherical inclusions arranged periodically in the whole matrix. The percentage PCM/matrix is fixed for all cases. A comparison among the various situations is made for the first time, thus providing a new idea on how to insert PCMs into composite matrices. The results show that the composite conductivity is the most important consideration in the first case, precisely when the arrangement plane is parallel with the flux and diagonal to the entry face. In the present work, we are interested in exploring the solid-solid PCMs. The PCM polyurethane and a wood matrix are particularly studied.

Composite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance.

This paper investigates the structure-property-processing correlations of electrically conductive polypropylene (PP) nanocomposites. The process parameters and fabrication techniques of PP-based composite materials were studied. Various structures of carbon allotrope-based materials, including synthetic graphite (SG), exfoliated graphene nanoplatelets (xGnP), multi-walled carbon nanotubes (MWCNTs) and carbon black (CB), were used to fabricate the PP-based nanocomposites. The nanocomposites were prepared by either direct melt mixing using an internal mixer or by ball milling of components before the melt mixing process. The electrical and flexural properties were measured. In order to understand the conductivity behavior, both in-plane and through-plane electrical conductivities were measured. The results showed that the incorporation of the xGnP into PP/60 wt.% SG composites resulted in a slight increase of the in-plane conductivities and had a minimal effect on the through-plane conductivities. The addition of MWCNTs and CB to the PP/SG/xGnP composites had a significant effect on the electrical properties and was more pronounced in the case of MWCNTs. The flexural properties of all samples were much lower than those of pure PP. The interface between the filler and the PP matrix and the morphology of the composite materials were observed from the fracture surfaces of the composites using scanning electron microscopy (SEM). In addition, SEM was employed to observe adhesion, microstructural homogeneity, orientation of the xGnP platelets and agglomeration in the composites.

In this paper, an inert gas assisted electromagnetic stir casting process is adapted for manufacturing a cast hybrid metal matrix composite (MMC) using Al 2 O 3 and SiC particulates as a hard phase reinforcement in Al 7075 alloy metal matrix. Four different samples containing 5, 10, 15 and 20 wt% of Al 2 O 3 and SiC with Al 7075 alloy composites were fabricated. The characterizations for all the samples were carried out through optical microstructure, scanning electron microscopy (SEM) fractograph, X-ray diffraction (XRD) analysis, differential thermal analysis (DTA) analysis and mechanical properties. The results revealed that the particles are uniformly distributed in the matrix. No peaks of Al 4 C 3 were found. There is negligible loss of material in the composite. The tensile strength and microhardness of the hybrid composite are higher by 65.7% and 13.5%, respectively, when compared to its cast metal matrix Al 7075 alloy.

The comparison of one- and three-dimensional cure simulation of thick thermoset matrix laminates was conducted in this study. The applicable conditions of one-dimensional cure simulation were investigated. The transient heat conduction equation coupled to the cure kinetics was solved numerically using one- and three-dimensional finite element analysis. The evolution of temperature and degree of cure of the laminates during the curing process obtained by the simulation agreed well with the published experimental results. The results indicate that a wider one-dimensional analysis applicable region around the center point will be obtained in the laminate with a higher span-to-thickness ratio and in a less anisotropic material system. In the applicable region, the accuracy of the one-dimensional cure simulation can satisfy the engineering request and save the computational cost. While beyond the region, there is a steep increase in deviation of the one- and three-dimensional simulation results.

The drilling process of carbon fiber reinforced plastics (CFRP) is the main secondary processing in the entire production cycle. However, there is no standard theory that could be used to estimate the hole quality and to quantify the assessment. Therefore, in this article, several influential factors of drilling quality, such as drilling parameters and materials, were utilized to establish the classification tree model. A comprehensive evaluation model [three-dimensional (3D) evaluation factor] was presented to measure and quantify the quality of the hole. Then a series of experiments were designed based on existing conditions. Further, a mathematical software (Origin) was used to fit and analyze the relationships of the drilling parameters and the 3D evaluation factor. Then a user-friendly drilling database system of CFRP was established based on the historical data of drilling experiments and the fitting function. In addition, in order to contrast the optimization results of the fitting function, the drilling experiments have been conducted, and the results have verified that the drilling database system could optimally predict the drilling schemes with a minor error.

The main objective of the present work was to establish a friction-stir-welding process to weld dissimilar metal joints on AA6082 and AA6066 aluminum alloy plates. Joints were made while varying tool rotation speed at a constant traveling speed and at the same time adding oxygen-free copper reinforcement inside the weld nugget for the purpose of analyzing the microstructural evolution and mechanical properties of the joint. Results showed that the morphology of the microstructure in the weld nugget changed significantly with rotation speed. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy analyses revealed that oxygen-free copper particles could be uniformly dispersed into the weld nugget because of higher rotation speeds. Because of the presence of reinforcement particles homogenously distributed inside the nugget zone, the mechanical properties, such as ultimate tensile strength and hardness of weld joint, were greatly improved.

This article presents a numerical method for determining the dosage of pre-embedded capsules in self-healing materials with complex crack patterns. The crack distribution on the surface of materials is simplified into a two-dimensional (2D) multi-shaped geometrical structure composed of triangles, rhombuses, and hexagons with specified area fractions, and further decomposed into three separate mono-shaped crack systems. Then, the dosage of capsules required to heal the cracks in each mono-shaped crack system is computed. According to the area fraction of each mono-shaped polygon in the whole system, the integrated models of crack-hitting probability by the capsules and the capsule dosage for the multi-shaped crack system are derived. The analytical results reveal that the dosage of capsules significantly depends on the spatial distribution of the cracks and the ratio of the capsule length to the crack size. For a certain fixed crack pattern, the size and dosage of capsules will strongly affect crack healing efficiency.