نشریه علوم و فناوری کامپوزیت
سال ششم شماره 2 (پیاپی 20، تابستان 1398)

Crack creation in composites is one of the most common failure reasons of those materials. Engineers were inspired by self-healing action in biological systems and used this innovation for the healing of different kinds of materials such as composites. In this study, using the self-healing approaches, micro-crack and damage healing of a epoxy-glass fibers composite were under consideration. So one series of hollow glass fibers were used to fabricate self-healing mechanism. These hollow fibers were filled by one self-healing agent which is one two-part epoxy resin. After the creation of undetectable micro-cracks and damages and also their encounter with hollow fibers’ walls, these hollow glass fibers will crack and the self-healing agent in them would flow into damage area that after some time it repairs the damage. The ain of the present study was to investigate the effect of heating cycles over time is restored in the composite. So consecutive temperature cycles (1, 3 and 5 cycle) in temperature were implemented in the range of 25-70 °C after damage creation in the sample. The results of bending tests show that a 74% healing efficiency can be gained after 7 days almost with 5 cycles of heat in mentioned temperature range only after one day.

In this study, we employ first-order shear deformation theory to calculate maximum deformation and critical buckling load of moderately thick viscoelastic composite plates. These quantities are calculated over time under in-plane and out of plane loadings. The mechanical properties of the viscoelastic material are assumed linearly by expressing the modulus of relaxation in the form of the Prony series. Constitutive equations are expressed as polynomials in the Laplace-Carson domain. Also, the Illyushin’s approximation and inverse Laplace-Carson methods have been used for calculating the response of these relations in the time domain. Finally, the method of generalized exponential basis functions is used to solve the governing equations for different values of time. Finally, the method of generalized exponential basis functions is used to solve the governing equations for different time values. The time-history of maximum deflection and critical buckling load are presented for the plates with different boundary conditions. The results of bending and buckling of the simply-supported plates are compared with the existing literature. Plates with two edges simply-supported and other edges fixed as well as those with all edges fixed are considered under transverse and in-plane loading, to investigate the effect of changing boundary conditions. Several problems with different boundary conditions are considered which many other analytical and semi analytical methods are unable to handle. In all cases the proposed method has been able to outperform the other methods.

There is possibility of impact loading on composite tubes while they are being placed or operated. Impact loads can be caused by the objects falls and they are able to make considerable internal damages that decrease residual resistance of layers in composite tubes. In the present study, effective parameters such as tube thickness, impact energy and inner diameter on single-wall tubes behavior under impacting and its consequent damages have been studied numerically, using LS-dyna software. Therefore, composite tubes have been modeled using 3D Solid 164 element and CODAM material model and they have been impact loaded with low velocity. In order to validate the numerical results and modeling, some of the numerical results have been compared with experimental data. An experimental sample of F205 hardener, Epon 828 resin and 400 g/m2 glass fiber was used to make the test sample. There is a reasonable good agreement between experimental and numerical results. Result discussion showed that there are no changes in diagram slope with increase in inner diameter. In other words sample strength and its resistance to impact are increased with growing in inner diameter. Furthermore, mean force level of force-displacement diagram goes up with increase in number of layers in composite sample structure which indicates an increase in sample resistance to impact.

This study is investigated the forced vibration analysis of a moderately thick rectangular plate under moving load, which are composed of functionally graded materials and floating on incompressible fluid. The governing equations of the plate are analytically derived based on First-order Shear Deformation Theory (FSDT) with consideration of rotational inertial effects and transverse shear stresses. In order to obtaining the applied pressure on the free surface plate, the method of added mass is used. At first, the natural frequencies and shape modes of the rectangular plate with two parallel simply-supported edges are determined by decoupling and solving the motion equations system. Then, the forced vibration of the plate is investigated by shape mode expansions. Finally, the results of this study are compared and validated with results of other works and the effects of the different geometrical parameters such as the length to width ratio, the height to length ratio, fluid density, fluid depth and index of volume fraction on the dynamic response of the plate are investigated.

In this study, a FeAl powder synthesized by mechanical alloying and annealing process was used as a binder to produce WC-FeAl composite. The powders of WC and FeAl were blended with composition of WC-25 vol% FeAl and sintered by spark plasma sintering at 1150℃. The hardness, fracture toughness and wear behavior of sintered WC-FeAl sample was investigated and compared with a commercial WC-Co. Structural evaluation of mixed powder was showed a homogeneous distribution of WC and FeAl which related to particle size of FeAl to be in the range of 50-800 nm. FeAl nanoparticles were able to diffuse faster between WC particles and occupy interparticle spaces among larger particles in the sintering condition; thus resulted to formation of an almost homogeneous structure with densification to near theoretical density. The hardness and fracture toughness of WC-FeAl was 17.90 GPa and 9.1 MPa√m, respectively that this hardness was higher than that of WC-Co (15.7 GPa) and fracture toughness was lower slightly. The results for wear test showed that the specific wear rate of both samples was enhanced with increasing the test temperature from room temperature to 500℃. Furthermore, WC-FeAl showed higher wear resistance than WC-Co at both room and 500℃ temperatures.

The antenna radomes have been developed to protect antenna systems against harsh environmental conditions, with the most electromagnetic transparency. The wind speed of 220 km/h, -40 to 65 degrees Celsius of temperature deviations, 90 % of relative humidity (RH), protection for UV radiation and finally, one way electromagnetic loss of less than 0.3 dB along with the maximum difference between vertical and horizontal polarizations of 0.05 dB are the main requirements of the weather radar radomes. In this paper, engineering design and experimental studies of some samples of the first sandwich panel radome of C – band weather radar, including manufacturing process, buckling and electromagnetic experimental tests, have been briefly explained. In the material selection process the environmental requirement have been considered. Evaluation of mechanical stability of the radome under wind pressure has been studied in experimental buckle tests and finite element analysis with ABAQUS 6.12. Insertion loss test in anechoic chamber was done to evaluate the transparency of the sandwich panel samples. Buckling tests show that the manufactured sandwich panel can oppose safely with 190 N buckling load. According to the electromagnetic insertion loss tests of the manufactured panels show that the one way insertion loss and the difference between the vertical and horizontal polarizations, are in the range of the required limitations.

The modification of Mg2Si is considered as a key parameter to improve the mechanical properties of Al-Mg2Si composites. In the present work, the effect of erbium (Er) on the microstructural charactristics and compressive behavior of cast Al-15 wt.% Mg2Si in situ metal matrix composite was studied. Microstructural examination was conducted using optical and scanning electron microscopy (SEM). The results showed that the size of the primary Mg2Si phase was reduced from 14 to 8.5 μm with the addition of 0.6 wt.% Er and the its morphology was modified from a coarse dendritic shape to a polyhedral shape. Through the addition of Er, the morphology of eutectic Mg2Si was also altered from coarse flake-like to a fine fibrous form. Besides, it was found that some Al3Er compound were formed during solidification. Compression test indicated that Er addition enhanced the compressive strength of the composite. The highest compressive strength was obtained for the 0.6 wt.% of Er-modified composite with 32% increase.

Polymer matrix composite materials are widely used in transportation, marine, civil, martial and aero-space industries. Resins used in composite laminates have time-dependent properties making the investigation of this property on composite laminates inevitable. In this paper, the effect of fiber orientation on viscoelastic behavior of composite laminates reinforced with long fibers is studied and a subroutine code is developed for orthotropic materials with viscoelastic behavior in Abaqus. Both experimental and numerical methods are used and the obtained results show good agreement. In experimental tests stress relaxation tests are applied for three fiber orientations of 0, 45 and 90 degree. Results show that ignoring viscoelastic behavior in numerical simulation lead to erroneous, with maximum and minimum values at 90 and 0 degree, respectively. Also results show that decreasing of relaxation modulus in 150 minutes for 0, 45 and 90 degree fiber orientation are 5, 16 and 18 percentage of initial value, respectively.

In this paper an extensive analysis have been performed on the buckling and post buckling response of unidirectional delaminated composite panels with the different curvatures (zero and 60 degrees of arc’s angle) by means of finite element method. Adjacent plies debonding is simulated by traction–separation law for the geometries containing one and two delaminations through the width and the influence of them on the response of the structure to the compressive loading is investigated. The effect of intact geometry and defective geometry containing delaminations with and without growth capability have been investigated. The complex contribution between nonlinear geometry, material non linearity, and large deformation is considered. Comparing the present results with other literatures in the special case of flat plates, indicates an excellent accuracy. The differences between the global and local buckling response, stable and unstable delamination growth of structures containing one and two delaminations in flat and saddles geometries is compared.

In this paper, the ballistic performance of two and four-layer composite plates made of Kevlar fabric and epoxy has been investigated. Composite samples were made by hand-laying method and ballistic tests were conducted. The ballistic limit and absorbed energy were evaluated as a criteria of the ballistic performance of composite plates. Experiments were carried out using a hemispherical projectile in a velocity range of 20-120 m/s. Damage and failure of composites was evaluated. Also, using the LS-DYNA software, high velocity impact simulation on composite plates was performed. So, a precise model of projectile and target was prepared. The composite layers are individually modeled and connected to each other by appropriate constraints. This numerical model can accurately determine the ballistic limit of composite targets. Maximum error was 6 and 10% for 2 and 4 layer composites respectively. In order to investigate the effect of the projectile shape on the ballistic performance of the Kevlar/Epoxy composite, simulation was carried out using a hemispherical and blunt projectile at different velocities and ballistic limit and absorbed energy for two types of projectiles were compared. The ballistic limit for 4 and four-layer composites under impact of blunt projectile is 32.5 and 43.7 m/s, which is 14 and 16% higher than the hemispherical projectile.

In this study, tensile properties of nanocomposites based on polypropylene/ Carboxylated Nitrile Rubber /Silica nano powder (PP/XNBR/Sic) were studied by using response surface methodology(RSM). The design of the experiment was carried out using Box-Behnken of the RSM method. The samples were produced using a co-rotating twin screw extruder including 0,2,4 Wt.% of nano particles, 0, 5, 10 Wt.% of carboxylated Nitrile Rubber and 0,3,6 Wt.% of Polypropylene-g-glycidyl Methacrylate (PP-gMA) as comptabilizer. tensile test was carried out to obtain tensile strength, elastic modulus and elongation at break of nano composites. The results showed that elastic modulus and tensile strength of nanocomposites were increased with addition of nano silica powder by 45% and 9% respectively. Also, the presence of XNBR was increased elongation at break by 39% and increasing the comptabilizer factor (PP-gMA) has slightly increased the tensile strength. In addition, it was found that XNBR has the greatest effect on tensile strength and elongation at break and silica nano powder has the greatest effect on elastic modulus. Finally, a regression model was obtained for tensile strength, elastic modulus and elongation at break, respectively

This contribution concerns preparation and characterization of low-density polyethylene (LDPE) melt-mixed blends in the presence of organically-modified montmorillonite nanoclays and silane-modified nano perlite. Dispersion state of hybrid nanofillers was observed by scanning electron microscopy (SEM) technique. A significant increase in average roughness of fracture surface of polyethylene with addition of hybrid nanofillers and intensive ridges and valleys are observed in the samples. Crystallization and melting characteristics of LDPE nanocomposites reinforced by hybrid nanoclay/nanoperlite were studied by differential scanning calorimetry (DSC) in isothermal mode. Hybrid nanofiller incorporation increased crystallization and melting temperature which can be related to high interaction between polymeric chains and hybrid nanofillers. The results of mechanical investigation revealed that Young’s modulus and tensile strength of LDPE are improved with introduction of hybrid nanofiller. Six constitutive models, Yeoh, Arruda-Boyce, Mooney-Rivilen, polynomial, Van der Waals, and Odgen were applied to investigate the stress-strain behavior of LDPE/nano clay/nano perlite nanocomposites. It was concluded that the ability of these models to predict the true behavior of the nanocomposite samples directly depends on the amount of hybrid nanofiller. Results showed that Arruda-Boyce, Vander-Waals, Yeoh and Mooney-Rivlin models show more deviation from experimental data in all nanohybrid filler content, whereas the others, Ogden, polynomial (2), can be used for all samples.

The existence of organosulfur compounds such as dibenzothiophene (DBT) in transportation fuels is not only a major source of acid rain, but also the reason many serious diseases of human respiratory system, such as lung cancer. Accordingly, efficient removal of DBT is very important. In the present work, magnetic nanoparticles were synthesis by co-precipitation method and then, these nanoparticles were covered with thin layer of polyaniline by chemical oxidation polymerization method in micellar medium using sodium dodecyl sulfate as surfactant. The synthetic product was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Langmuir and Freundlich isotherm models were used to fit equilibrium data for magnetic nanocomposite. Adsorption process could be well described by the Langmuir model (0.9899). The magnetic adsorbent afforded a maximum adsorption capacity of 118.42 mg g-1 at the optimized conditions (adsorbent dose, 0.01g; contact time, 15 min and pH, 9.3).

Water absorption tests were performed on unidirectional glass/polymer composite materials used in high voltage composite (nonceramic) insulators. The composites were based on E-glass fibers with polyester resin. The composites were exposed to distilled water at room temperature and their resistance to moisture absorption in terms of the rate of moisture absorption, maximum moisture content and apparent diffusivity was determined. In particular, the effects of specimen geometry (the edge effect) on moisture absorption by the composites were evaluated. It was found that changes in moisture content have a special effect on the mechanical and electrical properties of the composite material. The tensile test was conducted to determine the mechanical properties, breakdown voltage and the leakage current were measured to determine the electrical properties and scanning electron microscopy was used to observe the morphological property of Glass Fiber Reinforced Polymer (GFRP) samples. A reduction in both module and tensile strength was observed with water aging. Furthermore, Water absorbed by composite samples had a detrimental influence on the breakdown voltage and leakage current of composite specimens that could be an indicator of degradation.

The use of Textile Reinforced Concrete (TRC) materials have been developed in the construction industry due to their superior mechanical properties as well as corrosion-resistant and light weight concrete with high load-bearing capacity. Fine grained concrete penetrated within the bundle of fibers (rovings) partially. This fact reduce the load bearing capacity of fibers and enhance ductility after the first cracks. The fibers efficiency is the key aspect in the bending behavior of TRCs. The purpose of this study was to increase the fibers efficiency of TRCs. In this research, the influence of weft insertion wrap knitted fabrics by different number of carbon rovings on the flexural strength, ductility, toughness and failure mode under four points bending test evaluated experimentally. Furthermore, the fibers efficiency was improved by partially impregnated fabrics with spotted epoxy. This technique causes increased fiber efficiency in comparison with the fabric without epoxy upper fifty present and improving bending properties of TRCs.

Nowadays increasing application of Sandwich panels in various structures as like as aerospace and ship is due to excellent high strength to weight ratio, sound insulation and thermal properties. The study of failure mechanism in composites and especially sandwich panels are investigated as cutting edge. In this research, the acoustic emission data of low velocity impact tests has been used to study the impact strength and various defects created in glass / polyester-polyurthane foam composite sandwich panels with 3 different types of Lay-up technique. The analysis of the acoustic data and the study of the force-displacement diagrams and the visual images of the specimens after the various impacts of 20, 38 and 60 J have been studied. For this purpose, the obtained force-displacement diagrams and acoustic energy in each frequency range during the impact tests are interpreted and their relation to the types of failure mechanism, such as matrix cracking, fiber breakage and debonding in this type of sandwich panel has been extracted. Also, by studying the force-displacement diagrams and investigating the maximum reaction force and elastic return strength, acoustic events in signals has been verified. The results showed that the impact resistance of the cross-ply lay-up was30 to 40% higher than other specimens in the all impact tests.