نشریه علوم و فناوری کامپوزیت
سال هشتم شماره 2 (پیاپی 28، تابستان 1400)

Today, polymer-based smart windows have been considered for their thermal capabilities to reduce energy consumption in the buildings. The important issue about these smart products is their optimal design and construction which is the main focus of this study. The proposed window operates the way that the percentage of the light passing through the window depends on the degree of conformity of the refractive index of the nanofluid inside the window and the polymeric plates. Nanocomposite film has also been used to provide self-cleaning and photocatalytic behavior on the external surfaces. The materials used include polymethyl methacrylate (plates), methyl salicylate (fluid), and zinc oxide nanoparticles, which have been used to fabricate the nanocomposite, and nanofluid. After accomplishing the design and fabrication steps, characterization tests have been performed to determine mechanical (tensile strength, toughness, flexural strength), physical (contact angle), structural (size and shape of nanoparticles), optical (light transmission rate), and thermal (temperature ranges, heat transfer coefficient) properties. In addition, the performance of the window has been analyzed and compared with the other smart windows in terms of energy consumption and light transmission, in a quantitative analysis by two dimensionless parameters of light transmission ratio and temperature difference. According to the results, the range of variation in the transparency has been more than the maximum for other smart windows by 2 times while its energy consumption and temperature adjustment performance index has been higher than the other smart windows by 2.1 times.

In recent years, polymer-based nanocomposites have been widely used in various industries such as shipping, aircraft, automotive, and medical industries due to their good mechanical, chemical, and thermal properties. The aim of this study was to investigate the effect of halloysite nanotube nanoparticles (HNTs) and the nitrile butadiene rubber (NBR) content on the mechanical properties and microstructure of polyvinyl chloride / acrylonitrile-butadiene rubber (PVC/NBR) thermoplastic elastomer nanocomposites. Response surface methodology (RSM) and central composite design (CCD) were used to study the tensile strength and elongation at break. The morphology of PVC/NBR/HNT nanocomposites was investigated by scanning electron microscopy (SEM). The results showed that the maximum tensile strength was obtained at the HNT amount of 4.7 wt. %, while at high HNT levels the tensile strength will be decreased. Increase in NBR content from 20 wt. % to 40 wt. % causes an appreciable decrease in tensile strength. The elongation at break increased with increasing the NBR content, while the elongation at break decreased when the HNT content increased. The results of SEM show that the fractured surface of the samples gets rougher, the tensile strength increases.

In this research, the behavior of the initial strength of a composite lattice cylinder structure under axial compressive force in the first loading and its residual strength in the second loading stages have been studied. For this purpose, in the experimental method, first, the composite cylindrical structure, with a hexagonal lattice pattern, is made using a silicone mold and filament winding process. In the first experimental loading test, the structure is subjected to axial compressive force and its initial strength at the beginning of collapse (first damage) is obtained. Then, in order to study the residual strength, the damaged structure is subjected to the second loading stage after complete unloading and recovers its initial length. Validation of force-displacement results obtained from ABAQUS finite element software has been done in comparison with the results of experimental loading tests. Next, the numerical analysis of the effect of various rhombic and triangular lattice patterns on the initial strength and residual strength of the structure is performed. The results show that the highest ratio of bearing force to weight on the collapse threshold of the structure in first loading stage is related to the triangular, hexagonal and rhombic, lattice patterns and hexagonal, triangular and rhombic lattice patterns, respectively in the second loading stage. After the second loading stage, hexagonal, triangular and rhombic lattice patterns retained 80.5%, 69.11% and 54.01% of their original strength, respectively. Also, hexagonal, triangular and rhombic lattice patterns have the highest specific absorbed energy up to the collapse threshold, respectively.

In this study, the effects of temperature and stacking sequences of fibers on the flexural properties of the hybrid composites including epoxy resin, basalt fibers, and thin-ply unidirectional (UD) carbon fibers were investigated. The hybrid composites were prepared by hand lay-up method with 2 layers of carbon thin-ply and 6 layers of basalt fibers. The samples were fabricated with three different stacking sequences of fibers in which the position of thin-ply UD carbon fibers changed from the center to the outermost layers. Also, the temperature effects on the flexural properties of samples were investigated by applying different temperatures of 25, 60, and 95 ºC. All samples were fractured gradually and showed pseudo-ductility phenomenon due to thin-ply UD carbon fibers. Results showed that by placing the thin-ply UD carbon fibers at the outermost layers, the flexural strength and modulus of samples increased significantly. For example, at the temperature of 25 ºC, the flexural modulus of the samples was about 42% higher than that of the sample with thin-ply UD carbon fibers at the center of samples. However, the strain values of samples increased by nearing the thin-ply UD carbon fibers to the center layers. Also, results indicated that increasing the temperature caused the reduction of flexural strength and modulus of samples while the strain values increased.

In this study, the effect of fluid dynamic pressure on the linear vibrations of annular sector plate made of Functionally Graded Material (FGM) is investigated. Analysis of the plate is based on First-order Shear Deformation Plate Theory (FSDT) with consideration of rotational inertial effects and transverse shear stresses. The governing equations of motion of the plate are derived by considering the kinetic and potential energies and using the Hamilton’s principle. Also, the pressure applied from the fluid to the plate is determined by solving the velocity potential function of the fluid and the velocity equality at the contact surface of the fluid and the sector in terms of vertical displacement of the sector. The shape of the studied plate modes is based on satisfying the boundary conditions of the plate. By placing hypothetical modes, harmonic responses and using the Galerkin method, the governing equation have become the characteristic equation and by using the semi-analytical method that used for all boundary conditions, the natural frequencies are obtained. Furthermore, the numerical results are presented for a sample plate and the effect of different parameters such as sector angle, boundary conditions, fluid density, and fluid height is investigated. Finally, the obtained results are validated without considering the fluid with previous researches, and in case of contact with the fluid with finite element model (ANSYS software).

In recent scientific studies, the use of graphene has been considered due to its positive effect on the properties of composites, including mechanical, electrical and thermal properties. In this research, the microstructural and mechanical properties of pure aluminum nanocomposite cast reinforced with 0.5 wt% graphene with mechanical-electromagnetic stirrer and then hot extrusion and finally annealing, in two methods of using ball milling and without using ball milling process, was investigated. By applying both mechanical and electromagnetic stirring techniques, combining both shear and body forces can cause more turbulence in the molten metal that lead to as well as distribute reinforcing particles, decreasing the dendritic structures and refining the grains during solidification. The microstructural studies showed that in the ball mill method, the distribution of graphene nanoparticles and reduce grain size in the matrix phase is significantly better than the non-ball mill method. Also, in the method of ball mill, hardness, tensile strength and compressive strength increased by 19.7, 142.8 and 11.7%, respectively, and in the method without mill, 9, 85.2 and 13.5%, respectively, compared to pure aluminum. The elongation decreased by 6.8% in the ball mill method and 35.4% in the non-ball mill method.

The aim of this research is to attain the maximum carried-load under compressive axial loading for a composite lattice cylindrical structure with a specified geometry by an experimental–statistical method. For this purpose, after studying the researches in the field of fabrication factors of structures manufactured by filament winding process and also available facilities, the influence of four fabrication factors including fiber (roving) tension, winding speed, cure cycle and fiber type on the product quality and strength of the composite lattice cylinders is investigated. For this purpose design of experiment (DOE) with Taguchi method is applied to investigate the effect of fabrication factors on the the response variables in three levels without considering their interactions. According to Taguchi method nine structures are manufactured and tested and the results of the test are analyzed using analysis of variance to determine the influence of the fabrication factors on the response variables. Two response variables including specific maximum carried-load and compressive efficiency have been considered. Fiber type with 88.33 % and fiber tension with 9.67 % have greater influence, respectively, on the specific maximum carried-load while the effect of winding speed with 0.7 % and cure cycle with 0.29 % are negligible. Fiber type with 54.20 %, fiber tension with 23.54 % and winding speed with 14.86 % have greater influence, respectively, on the compressive efficiency while the effect of cure cycle with 1.85 % is negligilble. Manufacturing parameters are optimized according to the compressive efficiency response variable. In order to verify the resu

Auxetic structures as a part of lattice structures are designed with a negative Poisson’s ratio. The use of these structures is increasing due to their customized behavior in the aerospace and automotive industries. Several theoretical relations have been proposed to predict Poisson’s ratio of 2D auxetic structures. Most simple relations could not predict the Poisson’s ratio with a reasonable accuracy due to the absence of structure thickness. In this work, a numerical model based on finite element method is first validated by experimental results. In order to verify the numerical model accuracy, the constructed model is validated by experiment. Samples are printed, and the Poisson’s ratio is measured using the DIC method during the compression test. A correction factor based on the geometrical parameters of the structure, especially the structure thickness, is then introduced. This dimensionless correction factor not only consists of the minimum number of parameters but also significantly improves the theatrical model accuracy. The results showed that the theoretical relation error is cumulated by increasing the structural angle and thickness. The present correction factor is successfully reduced the error of theoretical relation from 800% to less than 2%.

In this paper physical and biodegradable properties of green composite made of cotton fabric and biodegradable resins (starch, poly vinyl alcohol (PVA) & carboxy methyl cellulose (CMC)) prepared by a solution casting method have been studied. The obtained results show that the best tensile strength (equivalent to 27.8 MPa ± 2.1 MPa) as well as the highest amount of Young modulus (8.3 GPa ± 0.8 GPa), is observed in the composites made of cotton fabric content (60 vol.%), 5 wt% starch, 7 wt% PVA & 1.5 wt% CMC by weight), which is comparable to conventional composites. This property is more than just cotton fabric and the film made from biodegradable resin. Morphological examination by scanning electron microscopy shows that the composite is reinforced by cotton fibers. This is due to the strong interaction between the cotton fabric and biodegradable resin. By increasing the percentage of CMC, the resistance of composites to moisture penetration is improved. The biodegradability test shows that the addition of CMC reduces the biodegradability of the composites and the addition of starch and polyvinyl alcohol increases it. These composites can be a good candidate for high performance biodegradable polymer composites.

Nano-reinforcers are identified as one of the ways of strengthening composites as an optimal and light alternative for common materials like metals. Adding nano-particles is done in different loadings so as to strengthen the resistance and stability. The aim of the present study was to scrutinize the simultaneous effect of nano- particles of silica and clay in the amount of resistance changes onto the impacts of sandwich panels in the low velocity impact test. The face sheets of the panels were made by glass fibers and resin epoxy with nanoparticles of silica and clay. The type of making process was manual layering. The ultra-sonic device was applied to perfectly distribute nano-particles through the face sheet matrix of the sandwich panels. The low velocity impact tests were done by the drop weight equipment. The low velocity impact test was done in two levels of energy including 15J and 30J. The damaged parts of the panels were inspected by SEM. The experimental results indicated that the amount of resistance to the impact of sandwich panels were changed and improved after using nano-particles. Thus, the amount of resistance to the impact holding cases of 3% of nano-silica and 1% of nano- clay was 13.65% higher than the case without nano and the case of 1% of nano- silica and 3% of nano- clay was actually 6.6% more than the case without nano.

The use of resin based cement is a common method for strengthening and retaliation the damaged bones material. However due to lack of sufficient adhesion in the interface of two materials (i.e. bone and injected cement) a crack can be initiated in the interface and consequently it can be fractured due to application of external loads to the repaired bone part. In order to investigate the load carrying capacity and reliability of bi-material joint of bone's soft tissue-hydroxyl apatite cement, a number of bi-material bone-cement specimens in the shape of circular disc containing a center crack in the interface of disc and subjected to diametral compression were tested. The bi-material specimens were load under different inclination angles of crack related to the loading direction. This results in application of different mixed mode I+II (i.e. tensile-shear deformation) in the interface of center crack. The results showed that the fracture load and fracture energy becomes more by increasing the crack inclination angle (i.e. increasing the contribution of shear mode deformation relative to mode I component). In addition the overall strength of bi-material bone-cement system was higher than the neat one material bone material. The fracture of all tested bi-material samples was extended along the interface line of Brazilian disc specimen with no kinking into any of two bone or cement materials.

In this article, the effect of adding nanoparticles into the matrix on improving the buckling strength of polymeric nanocomposite plates was investigated through finite element analysis. Two types of nanoparticles, including Carbon nanotubes (CNTs) and Nanoclays with different volume fractions (VF), were added randomly into the Epoxy matrix and mechanical properties of the reinforced matrix were estimated using simulation of a representative volume element (RVE). Moreover, a python script was generated to distribute CNT nanoparticles in aligned orientations and calculate the equivalent Young's modulus in horizontal and vertical directions. Afterwards, the critical buckling load of nanocomposite plates made of unidirectional glass fibers and nanoparticle reinforced Epoxy matrix were studied, using Eigenvalue analysis. Results were validated by previous studies and a very good agreement was obtained. In general, adding nanoparticles into the matrix led to increasing the critical buckling load with an increase of nano-additive’s VFs. When nanoparticles were dispersed aligned with fiber directions, which is the same as loading direction, a higher increase of critical buckling load was observed. For the case of reinforcing pure polymeric plates without fibers, when nanoparticles were aligned in the longitudinal direction, axial critical buckling load rose to 55.3%, whereas for the random distribution, it was increased by 14.2%. Finally, a parametric study was conducted to evaluate the effect of nanoparticle orientations, the aspect ratio of plates, transverse loading, type, and volume fraction of nano-additives on the critical buckling load of polymeric plates.

The use of multilayer pipes has increased recently thanks to their superior mechanical and chemical properties as a replacement of homogeneous single-layer pipes. Therefore, applicable inspections and non-destructive tests for multilayer pipes should be investigated. In this study, the governing equations of torsional wave propagation in the multilayer pipe were initially developed, and the relations between the displacement fields and dynamic stresses in the multilayer pipe were calculated. Then, the dispersion curves and group velocity for the multilayer pipe are plotted according to the boundary conditions. The torsional wave propagation in the multilayer pipe was also simulated using the finite element method via ABAQUS software. By comparing the analytical results and the numerical simulations, a complete agreement was observed between the results. Finally, the influence of effective parameters on torsional wave propagation in two- and three-layer pipes was investigated. The obtained results showed how the thickness, lay-up, and mechanical properties of the layers could affect the velocity of torsional wave propagation in the multilayer pipes.

In this research, the impact behavior of trapezoidal corrugated core sandwich panel reinforced with SMA wires, has been investigated experimentally and numerically. Composite specimens were made to perform tensile, compression and shear tests, and the requisite properties were acquired from the tests. Then, sandwich structures with aluminum corrugated core and 4-layer glass/epoxy composites face-sheets were made using the hand-layup technique. In order to reinforce the composite face-sheets, SMA wires were used in two models: 3 SMA wires without pre strain, 3 SMA wires with 3% pre-strain and 3 SMA wires with 6% pre-strain. The test was performed using a gas gun. To validate and compare the results, the numerical models of the specimens were prepared in LS-Dyna, considering the experimental testing conditions. The results, including ballistic limited velocity and the absorbed energy of the structure were compared and validated by the experimental solutions. The aim of this study was to investigate the effect of adding shape memory alloy wire to reinforce the face-sheets and the effect of pre strain on the ballistic behavior of the sandwich structure. The results shows that presence of the SMA wires and applying pre-strain, leads to increasing energy absorption. Comparing to the wireless sample, the absorbed energy increased about 10%, 22% and 30% in the 3-wires sample without pre-strain, 3-wires sample with 3% pre-strain and 3-wires sample with 6% pre-strain, respectively.