نشریه علوم و فناوری کامپوزیت
سال ششم شماره 3 (پیاپی 21، پاییز 1398)

Functionally graded materials (FGM) are a new type of composites with non-homogenous microstructure, which their physical and mechanical properties vary in the thickness direction continuously. Many researches in the field of property estimation, structural and thermal analysis of materials have been targeted. Different mechanical, physical and thermo-dynamical properties can be expected from these materials by changing the containing materials volume fraction. In this research, five layered Cu-Fe FGM specimens were fabricated with changing stepwise in the layers composition between pure copper and pure iron by powder metallurgy method. First the metal powders were compressed by press in high pressures and then the green specimens were sintered in a proper furnace was used to improve the layers connection and to increase the strength of the specimens. Two press systems containing uniaxial press and cold iso-static press were used in the fabrication of specimens to compare the results. Optical microscope was used to observe the microstructure and the combination of FGM layers. The results of microscopic investigations showed fine connectivity of the layers and powders and low density of pores in each layer. The produced Cu-Fe FGM specimens were tested in bending and tension to achieve their mechanical properties. The obtained stress-strain curves of these specimens showed enhancement in flexural and tensile strength of Cu-Fe FGM compared with the existing curves for pure copper and iron made by powder metallurgy method. Also cold iso-static press was highly more effective than uniaxial press in increasing the strength of specimens.

In the presen study, the effect of carbonate calcium (CaCO3) loading and CaCO3 modification on the interlaminar shear strength (ILSS) and flexural properties of carbon fiber/epoxy composite was investigated. Firstly, CaCO3 was functionalized with 3-glycidoxypropyltrimetoxysilane (3-GPTMS), which was confirmed by Fourier transform infrared (FTIR) spectroscopy. The CaCO3 nanoparticles were infused into carbon fiber/epoxy composite at various contents (0.5, 1, 3, and 5 wt.% with respect to the matrix) using ultrasonication and standard mixing routes. The results of mechanical tests showed that adding 3 wt.% silanized-CaCO3 improved the ILSS, flexural modulus, and flexural strength of the carbon fiber/epoxy composite by 25%, 36%, and 27%, respectively. Micrographs of fracture surface analysis confirmed that the carbon fiber/matrix interfacial bonding can be improved significantly by incorporating the silanized CaCO3 nanoparticles. The ILSS, flexural modulus, and flexural strength of the silanized CaCO3/carbon fiber/epoxy composite were greater than that of unmodified CaCO3/carbon fiber/epoxy composite. These results indicated that the silane-modified CaCO3 dispersion within the matrix of fibrous composites plays a key role to achieve high performance composites.

Sandwich panels have become popular in various industries like aerospace, marine and automotive as a lightweight structure that has high stiffness and strength to weight ratio. Since many of composite structures that been used in these industries has curvature, there is a desire to investigate the effect of curvature on flexural behavior of these structures. Composite Sandwich panel with lattice core are made from thin composite shell connected to both sides of a series of composite ribs. In this research, the flexural behavior of curved composite sandwich panels under three point bending, has been investigated experimentally and numerically. For this purpose, two types of sandwich panels with core of square and isogrid ribs were considered. Grids are fabricated by filament winding method. Samples were subjected to three point bending test. The test has been numerically simulated by FEM in Abaqus. Tension tests are conducted on grids and shells in order to obtain mechanical property of them. Also, structure failure were predicted for numerical simulations. Good correlation between experimental and FEM analysis was obtained. Results show that sandwich panel with isogrid shape of core has 7% more bending stiffness compared to square-shaped core sandwich panel. Results also indicate that the ultimate strength of sandwich panel with isogrid core is 7.5% higher than the sandwich panel with square shape of core.

In this article, in-situ formed hybrid surface composite of Al 3003/Al3Zr + Al3Ti was fabricated by friction stir processing (FSP). A rolled Al 3003-H14 aluminum alloy sheet and zirconium and titanium metal powders were used as reinforcements and six passes of FSP were applied. Then, FSPed samples were subjected to annealing heat treatment at 500 ºC for 4 hours. Wear behavior and the hardness of the base metal as well as FSPed samples before and after annealing was measured. Microstructural observation was performed using optical (OM) and scanning electron microscope (SEM), and phase formation was identified with X-Ray diffraction (XRD). Microstructural examination revealed that applying the FSP, resulted in fine and equiaxed grains with more uniform distribution of reinforcing particles. It was also observed that chemical reaction occurred at the interface between the aluminum matrix and the metallic powders, to form aluminides of Al3Zr and Al3Ti. The post annealing heat treatment activated these solid state reactions and more aluminides were formed. It was also found that, the maximum hardness and wear resistance were obtained by the FSPed and annealed hybrid composite sample.

In this article, different defects in the carbon fiber reinforced polymer matrix laminated composite under tensile loading have been detected by the vibration analysis. For this objective, the tensile test on open-hole composite standard specimens was performed based on the ASTM-D5766 standard. The tensile loading was considered as 2 mm/min, based on the mentioned standard. Acceleration sensors was installed on standard specimens and vibration signals were acquired during tensile loading. In order to detect different defects, in addition to composite standard samples, pure resin and pure fiber specimens were also tested under tensile loading. Signals for pure resin and pure fiber samples were analyzed by the Fourier transform method and signals for open-hole composite standard specimens were analyzed by the wavelet transform approach. Obtained results from the signal analysis showed that the vibration analysis could be a proper method to detect three types of defects in the carbon fiber reinforced polymer matrix laminated composite, including the fiber breakage, matrix cracking and other failures. These other failures were debonding, the delamination and the pull-out. Then also, the maximum percentage of failure mechanisms in the open-hole composite standard samples was due to debonding of fibers from the matrix, the delamination and the pull-out failure. Such these results had an agreement with images from the scanning electron microscopy, which obtained from the fracture surface of standard specimens, after tensile testing.

With the development of the applications of magnesium components in many industries, relatively low corrosion and wear resistance of this alloy leads to the development of different protective layers. In this paper, the effect of SiC reinforcement on the cold spraying behavior of Al-SiC powder on a magnesium alloy substrate is addressed. The pure Al powder is blended with different amount of SiC powder including 25, 50 and 75 wt.%. The feedstock is sprayed on sand blasted AZ31B substrate. The process is carried out with 30bar pressure and 300°C temperature of process gas (Nitrogen). A 20mm standoff distance is used for spraying. The effect of different values of SiC on the deposition behavior of the Al-SiC powders are investigated. The coatings cross-section is evaluated by scanning electron microscopy, image analysis software and microhardness test. The results showed that the high velocity reinforcement particles leads to the SiC particle breaking during the process. This phenomenon increases the porosity of the coating. Furthermore, the higher value of reinforcement in initial powder leads to the homogenous distribution of them and the higher coating hardness. The hardness of the Al-75wt% SiC coating is about 90 HV, which is increased by 80% compared to pure Al coating microhardness.

Effectively joining metals and composites in an efficient manner is challenging due to their dissimilar physical compositions and mechanical properties. Failure of bonded joints is generally strongly influenced by the non-uniform distribution of stresses and strains that usually with the maximum value, commonly located near the ends of the overlaps. In this study, carbon is used as a reinforcing element in the adhesive layer and to improve the distribution of stress, properties are graded by fibers along the overlap. Also, using a new method, the effect of the reverse step on joint strength has been investigated. In addition, finite element modeling is used to express the distribution of shear and peel stresses in the adhesive layer and also to analyze the reasons for increasing joint strength in stepped specimens. Use of carbon at the joint surface, grading of the joint area and mechanical interference through reverse steps, have positive effects on strength. By grading the overlap by carbon and glass, the distribution of shear and peel stress have become more uniform and load and displacement of failure compared to the base specimen, which has a shear strength of 1.92 kN, increased by 34%. Creating the reverse step changes the failure mode. The presence of one step 40%, and the placement of carbon at the joint interface of that, has increased 112% of strength. But the greatest increase in strength and displacement failure is achieved using two reverse steps and carbon in the joint surface, by a significant amount of 172%.

In this paper, the effect of graphene oxide (GO) nano-plates on the ballistic properties and energy absorption of Al6061 aluminum matrix composites produced by stir casting and hot rolling was investigated. The Al6061-Go nano-composites were fabricated by mixing GO nano-plates with weight percentages of 0.0, 0.2, 0.5 and 0.8, in the molten aluminum. Then, hot rolling was carried out at 530 °C on the cast samples. Mechanical behavior of nano-composites was investigated by performing quasi-static tensile tests. The perforation tests on the Al6061-GO plates, with the dimension of 60604.2 mm, was carried out using flat head projectiles with the aspect ratio of L/d >3, at the speeds of 100-300 m/s. The initial and residual velocity of projectiles was measured through 24 experiments, and the ballistic limit velocity was calculated for the fabricated nano-composites. The toughness, the fracture mode and energy absorption of the samples, were evaluated through the tensile and perforation tests, respectively. The results showed that by adding GO nano-plates, the ballistic limit velocity of the composite specimens improves by 24 % with respect to the base alloy. Also, the energy absorption of composite specimens in quasi-static and impact loading was respectively ameliorated by 116 % and 107 %. These results indicated that GO nano-plates are very effective on the energy absorption of 6061 aluminum alloy.

As the nanoscale materials and nano-composites are increasingly used in everyday life and industrial applications, extensive research has begun into this field. For this reason, in the course of previous research, carbon nanotubes and nano-graphene materials were added separately with weight percentages of 0.1, 0.3 and 0.5 in the composite phase consisting of epoxy resin and basalt fiber, and nano-composites laminates with 6 layers of basalt fiber were made through hand layup. In order to determine the amount of energy absorbed during impact, composite and nanocomposite samples were subjected to Charpy impact test, and the specimen deformations were studied under electron microscopy. An increase in the energy absorbed by samples containing nanoscale materials with all weight percentages was observed in comparison with conventional composite specimens. The highest increase in absorbed energy in nanocomposite samples with regard to the composite specimens was observed in samples containing 0.1% graphene particles by weight. The highest increase in absorbed energy in carbon nanotubes composites was detected in samples consisting of 0.3% carbon nanotubes in the matrix.

In this study, thermoplastic elastomer (TPE) nanocomposites based on polyamide-6 (PA6) and acrylonitrile butadiene rubber (NBR) reinforced by Graphene nanoparticle (GNP) were prepared via a Haake internal mixer. The effects of GNP content (0.5, 1 and 2 wt %) on the thermal, mechanical, and microstructure properties of three composition ratios of PA6/NBR (90/10, 70/30 and 50/50) nanocomposites were investigated. X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), scanning electron microscopy (SEM) and mechanical (tensile and impact) test were performed to determine the morphology and mechanical and thermal properties of this nanocomposite. The results showed that the mechanical characteristics of the PA6/NBR/GNP nanocomposites such as the tensile and modulus strength increased with increasing of GNP content in PA6/NBR blends, while these properties decreased when NBR content increased. Investigating the effect of GNP and NBR content on the crystallization behavior of PA6/NBR/GNP nanocomposites show that the crystallization temperature of PA6 increased with the presence of GNP whereas the increase in NBR phase content leads to reduction of crystallization temperature. The storage modulus of PA6 shifts to higher value with the presence of GNP. The improvement of the storage modulus, with the introduction of nanoparticles was the result of the extraordinary stiffness of GNPs and the restricted mobility of the polymer chains.

In this study, the effects of Cloisite 20A modified nanoclay and graphene oxide on the compression behavior of polycarbonate nanocomposite were examined by experiment. Samples were prepared based on injection and the masterbatch method was used for a better dispersion of nano particles in the matrix phase. The masterbatch of nanoclay was prepared through the direct method using an extruder, and the masterbatch of graphene oxide was prepared using the solvent method. The clay reinforced nanocomposite were prepared for three weight percentages of 0.5%, 1%, 3%, and samples of graphene oxide nanocomposites were produced for 0.3%, 0.6%, 0.9%. The compression test was performed at three strain rates of ε ̇=〖10〗^(-3),〖10〗^(-2),〖10〗^(-1) s^(-1) at ambient temperature using a universal testing machine, Santam. The results showed that, by increasing the strain rate, the yield stress is increased. Moreover, the best weight percentage of clay and graphene oxide was 1% and 0.6%, respectively, which made improvement of 7.6% and 6.2% in the compression yield stress, respectively. Additionally, a model was proposed for predicting the compressive stress-strain curve at various strain rates based on a modified G’sell-Jonas model. The proposed model could reasonably predict the stress-strain curves at the applied strain rates. Finally, based on the combination of Eyring model and the micromechanical model of Turcsanyi, a model was proposed for describing the yield stress of the nanocomposite based on volume percentage of filler and strain rate.

Dental composites are widely used for dental restorations due to features such as maintaining the beauty of the teeth, non-invasive and conservative nature, and improving the physical and mechanical properties. Dental composites are susceptible to damages such as micro-cracking caused by thermal and mechanical stresses, which can weaken the properties of these materials. In dental composites, the detection of micro-cracks is very difficult and in some cases impossible. In addition, it is not possible to repair these damages in situ by using conventional materials and methods. Therefore, the self-healing ability in dental composites is necessary. In recent years, the spontaneous repair of damages such as micro-cracking in dental composite materials has been developed without any type of human intervention and the replacement of new components. The most common method for the preparation of self-healing dental composites is microencapsulation of healing agent in polymeric shell and dispersion of the prepared microcapsules in the acrylate matrix of dental composite. The self-healing properties of dental composites can be investigated by determining the fracture toughness of composites before and after healing performance using single edge V-notch beam test. In the present study, the studies on self-healing smart dental composites will be reviewed.

One of the main challenges in nanoindentation tests is to work-out a method in order to obtain the material properties through the test results. Using a hybrid method which combines the experimental results of nanoindentation tests with FEM analysis is considered as one of the main solutions for this problem. In order to calculate the mechanical properties, an explicit method was developed on the basis of modified dimensional analysis method. The main advantage of this method is to provide unique answers without any need for iteration so that it would minimize the calculations significantly. In this paper, the mechanical properties of Titanium in plastic phase (yield stress and strain hardening Module) are calculated by utilizing this method. For the first time, the dimensional analysis was used for the bilinear constitutive equation (with two dimensionless parameters), and in the finite element analysis, the general form of the Johnson-Cook equation was utilized. The most important property of plastic state, namely, the yield stress, was extracted in proper agreement with reference values. In the process of solving, a new method for error analysis based on calculating the resultant errors and determining the extremum error in the entire range of parameters was successfully developed and applied. Finally, in order to calibrate the solution, it was also proposed to set up the critical conditions of the problem, such as the indenter tip radius. It was concluded that the use of a radius more than 200 nm leads to a more consistent response to the experiment.

Bipolar plates are one of the most important components in a PEM fuel cell. In this study, a bipolar plate made of stamping method is developed to increase electrical conductivity and mechanical behavior and manufacturing productivity of the fuel cell and to decrease electrical resistance according to DOE. For fabrication these plates, phenolic resins were used as matrix and expanded graphite to increase electrical conductivity and graphite to filler and carbon fiber to increase flexural strength and optimize electrical conductivity. The electrical conductivity increased up to 40 percent respect to the DOE. The flexural strength and impact strength of the measured specimens were improved respect to the DOE about 11 and 170 percent, respectively. The experimental results are in accordance with DOE. According to SEM images and test curves, electric conductivity increases with expanded graphite filler. Finally, the results showed that expanded graphite weight gain did not affect the mechanical behavior of the composite and increased the electrical conductivity.

In this study, Al-Al2O3 composite coating produced by cold spray method on Al-7075-T6 sheet. The pure Al powder is blended with different amount of Al2O3 powder including 25, 50 and 75 wt. %. The feedstock is sprayed on sand blasted substrate using nitrogen gas at a constant temperature of 300 °C, pressure of 30 bar and the stand-off distance of 20 mm. The effect of different values of Al2O3 on the deposition behavior of the Al-Al2O3 powders are investigated. Microstructural characteristics of the coatings are evaluated by scanning electron microscopy, image analysis software, microhardness and X-ray diffraction tests. The results showed that the high velocity of particles leads to the Al2O3 particle breaking during the process. This phenomenon increases the porosity of the coatings Furthermore, the higher value of reinforcement in the initial powder leads to the homogenous distribution of them and the higher coating hardness. The hardness of the Al-75Al2O3 coating is 104 HV, which is increased by 85% compared to pure Al coating. X-ray diffraction test indicated the fine-grained structure, no-oxidation and no phase transformation in the pure and composite coatings.

Hydroxyapatite has been studied intensively as an alternative to bone due to its biocompatibility and the chemical composition of the bone mineral matrix. Despite the good biological properties of hydroxyapatite, this material has poor mechanical properties. Flourhydroxyapatite due to its higher thermal stability than hydroxyapatite, has better mechanical properties and its combination with with alginate as an composite scaffold, while improving its biological properties, can be used as a substitute for hydroxyapatite. In this study, flourohydroxyapatite was prepared using a co-precipitation method, and then Alginate- Flourohydroxyapatite composites with 40, 50 and 60 wt% flourohydroxyapatite were synthesized by freeze-drying technique. In order to characterize the scaffolds, MTT, ALP, FTIR, XRD, XRF, TG/DSC and compressive tests were used. Surface morphology, as well as the connection and growth of bone cells on the scaffold surface, were studied using SEM. Data analysis were performed using one-way ANOVA. The results showed that Alginate-60wt% flourhydroxyapatite composite scaffold has sutble and optimal conditions for bio-mechanical and biologiical properties. in comparison with two other scaffolds tha prepared in this study.