Journal of Science and Technology of Composites
Year:2019 | Volume:5 | Issue:4 |Papers Count:16

Composite tubes may be subjected to quasi-static loads during placement or operation. By determining the impact properties of composite tubes and using them in the design process, the accuracy of the behavior of these structures in a quasi-static loading condition is guaranteed. In the present study, the effect of changing parameters such as pipe diameter, fiber density, fiber alignment angle and the addition of foam on the behavior of glass/epoxy composite tubes under axial loading has been investigated. The force-displacement diagram was extracted for all experiments and compared with other experiments. Also, the specific energy absorption in each experiment was calculated for all samples. The results of this study showed that the change of parameters mentioned on the energy absorption of composite tubes is effective. As the sample's internal diameter and the density of the fibers used to make the sample increases, the specific absorbed energy also increases. Also, the results showed that with increasing foam density up to 1400 Kg/m3, the sample resistance was increased against the loading and the specific energy absorption was increased. From the present study, it was also clear that for samples with fiber density of 400 g/m2 and angle of alignment [± 45], the clustering mode was folding with a special pattern, similar to the destruction of metal samples reported by other researchers.

In this study, microstructure and mechanical properties of AA7068 nanocomposite reinforced with 1, 2, 3 and 5 wt. % SiC nanoparticles (SiCnp) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with 2000 W powers was used for mixing alloy and nanoparticles. Also scanning electron microscopy was used for microstructure studies. The microstructure of nanocomposite was investigated by scanning electron microscope. The microstructural studies of the nanocomposite revealed that SiCnp addition reduces the grain size, but adding higher SiCnp content (5 wt. %) does not change the grain size considerably. Further investigations on hardness revealed that the addition of SiCnp increases hardness. At higher SiCnp contents (5 wt. %), the presence of SiCnp agglomerate on grain boundaries was found that causes decrease the hardness. The optimum amount of nanoparticles is 3 wt. % SiCnp that nanocomposite exhibits hardness of 155 BHN. According to the results of hardness for the initial samples and nanocomposites reinforced with 3 wt. % SiC, 24% increase in hardness can be seen.

Due to unique properties, lattice composite shells are used extensively in aviation, marine and automotive industry. The aim of this research is experimental and numerical free vibration analysis of composite sandwich cylindrical shells with lozenge cores. For the fabrication of this shells, silicone mold, filament winding, and hand lay-up method were used. Stiffened shells and simple shells are fabricated, separately. Then, composite sandwich cylindrical shells with lozenge cores were created by attaching the two parts together. The modal test is done on the shells and natural frequencies have been extracted. The comparison of experimental results and, numerical results obtained from Abaqus showed that there is a good agreement between them. By using Taguchi method, a parametric study was performed on the vibrational behavior of sandwich shells with lozenge cores via six parameters that such as stiffeners’ pair number, stiffener thickness, unit cell number, skin thickness, layers sequence and boundary condition. The results show that the natural frequency has a most sensitive to the boundary condition, skin thickness and least sensitive to stiffener thickness, layers sequence. To evaluate the efficiency of a sandwich shell, the natural frequency of sandwich shell are compared with simple shell in the different boundary condition. The results show that the natural frequency of sandwich shell with lozenge core is 176% and 34% higher than an equivalent simple shell at free and clamp boundary condition, respectively.

This paper studies the shear and peel strength of composite AA1050 aluminum and SS 316 steel manufactured by accumulative roll bonding (ARB) process. The ARB samples were tested for shear and peel strength under a single axial tensile test. The layer strength was measured in each sample and the results of the experiments were compared. The results showed that the shear strength of layers was higher than the peel strength; also the microstructure of the sheet after performing 5 cycles of the ARB process was observed. To test the strength of the samples during different passes of the process, tensile tests were carried out; the results indicated a general increase in strength. Further studies on the scanning electron microscope (SEM) images of the fracture sections of the samples showed that by increasing the number of passes, the thickness of the steel layers was less than that in the pass 3 of these layers to tear. In the following, hardness changes along the sheet thickness were studied in successive passes. The results indicated that the pass 2 had an impressive increase in hardness.

In this paper the electromechanical behavior of fuzzy fiber reinforcement hybrid composites containing carbon nanotubes (CNTs) is investigated. A unit cell micromechanical model and electromechanical coupled constitutive equations are used to obtain the elastic and electrical coefficients of the hybrid composites. This hybrid composite is made up of piezoelectric fiber and CNT as reinforcement and polymer matrix. The piezoelectric fibers are coated with radially aligned CNTs. An interphase region is considered due to the interaction between CNT and matrix. The effect of volume fraction and size of CNT on the overall hybrid composite properties is investigated. These effects are remarkable in the transverse direction due to the aligned CNTs in the fiber radial direction. Considering PZT-7A as reinforcement piezoelectric fiber, study of its mechanical strength compared to PZT-5A was implemented in order to make a better composite. By comparing the proposed model with another micromechanical model, the validation of the proposed model is studied. Generally, a good agreement is observed between the results of these two models. The results also reveal that for the improved transverse electromechanical properties, using a CNT with a lower diameter is suggested.

In this paper, high velocity impact behavior of honeycomb structures was modeled by implementing high strain rate dependent properties of honeycomb and its ballistic limit velocities in collision with hemispherical as well as flat ended projectiles were calculated. The obtained results were validated with those available in open literature and numerical ballistic limit velocities were found to be in good agreement with experimental ballistic limit velocities. In addition, ballistic limit velocities in models without strain rate dependent properties were calculated and compared with those in previous models to evaluate the influence of strain rate dependent properties. Comparing the results of these two kinds of models showed that using strain rate dependent properties increases absorbed energy as plastic dissipated and frictional dissipated energies which improve accuracy of numerical modeling significantly. On the other hand, fracture mechanisms and damaged zones were investigated in numerical models and were compared with experimental output. Damaged zones in front of honeycombs in numerical models were similar to experiments but honeycomb manufacturing process and random collision of projectile with honeycomb, made some differences in damaged zone at the back of the honeycombs.

There are various types of composites among which these with layered structure are susceptible to delamination under the applied loads. Phenolic resin/glass fiber composites, one of the most commonly used composites, are prone to delamination. In this research, the improvement of the delamination resistance of phenolic composites via the addition of polyvinyl butyral (PVB), a thermoplastic additive at various contents (i. e. 1, 3, 5, 10 and 20 phr) has been studied. For this purpose a phenolic/glass fiber prepreg modified with thermoplastic additive was prepared and brought to a partially cured (B-stage) by using a specified temperature-time condition. The flow ability of the prepared prepregs was measured. Samples for the flexural test were then prepared by compression molding of the prepregs having the flow abilities of 10%. Three-point bending test results showed that the addition of PVB relatively improves the strength and delamination resistance of the composites, the extent of which depends on the additive content. The addition of PVB at 3 phr increased the fracture toughness up to 58. 2%, however beyond which it was reduced; hence 3phr was regarded as the optimum value. Inspection of the fracture surface morphology by SEM revealed the inhibition of crack propagation even at 1 phr of PVB.

This study investigates the free vibration of a thick FG circular plate in contact with an inviscid and incompressible fluid. Analysis of the plate is based on First-order Shear Deformation Plate Theory (FSDT) with consideration of rotational inertial effects and transverse shear stresses. Dynamic transverse displacements of the plate are approximated by set of admissible Chebyshev functions which is required to satisfy the geometric boundary conditions. Potential theory together Bernouli’ s equation are utilized to obtain the fluid pressure on the free surface of the plate. The governing equation of the oscillatory behavior of the fluid is obtained by solving Laplace equation and satisfying its boundary conditions. The natural frequencies and mode shapes of the plate are determined using Rayleith-Ritz method based on minimizing the Rayleith quotient. The effects of the geometrical parameters such as plate thickness to its radius ratio, boundary conditions, fluid density, volume fraction index, and height of the fluid on natural frequencies and mode shapes are investigated. Comparison of analytically outcome of this study is made with results of the experimental modal test for homogeneous Aluminum plate.

Vinyl ester resins are widely used in structural composites and industry because of their excellent mechanical properties and good chemical resistance. One of the main goals of adding nanofillers to polymer matrix is to enhance the Young’ s modulus and strength of the original base polymers. Due to the rigid structure of carbon nanotube as well as their aspect ratios, they can effectively increase the elastic modulus and stiffness of the polymer matrix. The main practical target of the present study is to obtain the best distribution of the multi-walled carbon nanotubes (MWCNTs) with carboxylic group in order to simultaneously improve the elastic modulus, tensile strength and toughness of the resulted nanocomposite. In this regard, nanocomposites with six different weight fractions (wt%) of MWCNTs are made and the specimens are subjected to the tensile test. The results exhibit that addition of MWCNTs with low concentration leads to improvement in the mechanical properties of the vinyl ester polymer such that the optimum mechanical properties are obtained with 0. 25wt% of MWCNTs. In this case, the fracture toughness, tensile strength and Young’ s modulus are respectively enhanced by amount of 52%, 23%, and 14%. In order to validate the experimental results and investigation the role of MWCNTs on tensile behavior of vinyl ester resin, the scanning electron microscope (SEM) is used and the most important failure mechanisms are discussed and studied in details. Also, in order to provide a theoretical model for predicting the elastic modulus of the nanocomposite, the experimental results are compared with existing theoretical models and a new correction factor based on the Hirsch’ s theory and experimental results is introduced for future industrial applications.

In the present work static buckling behavior of laminated cylindrical composite shells were investigated experimentally. The laminated composite shells were fabricated from carbon-epoxy composite by filament winding process. The stacking sequences were +55˚ /-55˚ /SMA/+55˚ /-55˚ and +75˚ /-75˚ /SMA/+75˚ /-75˚ . The superelastic SMA wires placed between plies 2 and 3 of the four layers laminate. Shape memory alloy wires were used in the middle of the composite in two cases, without pre-strain and with 5% pre-strain. All of buckling test were performed using 2. 5 ton universal test machine with crosshead speed of about 0. 1 mm/min. The buckling tests were arranged with two kinds of boundary conditions, simply supported-simply supported and clamped-clamped boundary conditions. Several tests were done to achieve the mechanical properties of composite shells, like standard tensile test of the resin samples, mechanical tensile test of the nol ring, tensile test of the unidirectional composite samples and the tensile test of the superelastic shape memory alloy wire. The experimental buckling analyses of the cylindrical composite shells with embedded superelastic SMA wires show that the critical buckling load increased by using the SMA wires. Also, in the laminated composite with stacking sequences +75˚ /-75˚ /SMA/+75˚ /-75˚ , the buckling load of shells was increased. In addition the buckling capability of composite shells in the simply supported-simply supported boundary condition is greater than the clamped-clamped boundary condition.

In this research, influence of foam filling technique in double layer trapezoid-shape corrugated core by using lightweight rigid polyurethane foam is investigation. Five types of Aluminum corrugated cores both bare and foam-filled were subjected to unidirectional quasi-static compression. In the following, using numerical simulation by Abaqus software to evaluation the impact parameters, including Specific Energy Absorption (SEA) as discussed testing purposes. The energy absorbing system can be used in the aerospace industry, shipbuilding, automotive, railway industry and elevators to absorb impact energy. The FEM results are compared with Experimental results which reveal a good conformity. FEM and experimental results showed that foam filling technique can significantly increase specific absorbed energy. Results show that the increase in core sheet thickness up to two times increases the specific energy absorption by 509. 47 %. The results of axial crushing tests showed that the SEA of foam-filled sandwich panel increased by 91. 42%, comparing to the hollow panel. Also, double-layered core in the panel caused to increase the specific energy absorption by 81. 42%. Finally, appropriate geometric parameters and the best examples of criteria considered with respect to the objectives, are introduced.

Nowadays, there is an increasing demand for magnesium and its alloys as the lightest commercial metal with a high strength to density ratio. Nevertheles, afew undesirable properties, such as low hardness and poor wear resistance, have limited the applications of this exclusive metal. Fabrication of magnesium matrix composite could improve hardness and wear resistance in addition to strength increasing. Since converting all of a metal piece to composite could make it more brittle and increase the costs, fabrication of surface composite could be a solution. In this paper, a magnesium sheet with a surface composite has been fabricated by applying warm rolling process. Indeed, a layer of magnesium matrix composite (which has been fabricated by stir-casting) has been conjoined to a magnesium substrate layer using a zinc interlayer. This method could increase the production speed and decrease the costs. In addition to the connection of two layers together, the zinc interlayer would preserve the surfaces of the layers from oxidation without using any controlled atmosphere. The results show a proper connection between the surface composite and the substrate. According to the microhardness results, the hardness of surface composite increased about 23% and 52% in the cross-section and the surface, respectively. Moreover, wear resistance of surface composite improved about 43% in comparison to magnesium substrate. Also, wear rate decreased in the surface composite.

Metal matrix composites are bunch of materials that have wide range of uses such as construction, abrasion, and heat. This type of composite exhibits better dimension than the base metal such as temperature applications, strength, rigidity, thermal conductivity, wear resistance, creep resistance and stability. In this study, the methods of producing aluminum composite reinforced with ceramic particles, especially the processes of sever plastic deformation, have been investigated. The main focus of this research is to study the microstructure, mechanical properties and mechanisms governing this type of composite produced by two ARB and cross CARB methods. The results of the research showed that in the initial passes of the processed composites there is no proper distribution of reinforcing particles but by increasing the number of passes, the particle distribution is improved and the reinforcing particles are distributed in longitudinal and transverse directions. Tensile strength and microhardness have the same trend which they gradually increased with increasing strain rates and improvement of particle distribution but elongation at first decreased in the initial passes due to the inappropriate distribution of the particles, porosity and cluster particles, and then improved with the elimination of these imperfections and distribution. However, the mechanical and microstructural properties of the CARB method are more favorable. Also, the governing mechanisms for microstructure modification in produced composites by rolling processes are the formation of the Orowan loop, role of reinforcing particles, difference in the coefficient of thermal expansion of the matrix and reinforcement, and so on.

Textile composites, in which a textile preform is used as the reinforcement phase, can easily take the form of complex parts and possess a more efficient and reliable structure, hence, they are a suitable substitute for conventional laminates. Among the textile composites, braided composites are of great importance and they are used more extensively, one of the important factors in mechanical properties of final composite part is the braid angle. In this paper, at first, a brief explanation of the new analytical relationships is presented. Also, a new strategy for changing and controlling the braid angle on each face of the flat mandrel by changing the shape of the guide ring from circle to an ellipse and also controlling the eccentricity is discussed which was previously developed by the authors. Then a comprehensive program is presented which predicts the mechanical properties of the final composite considering the braid angles. To validate the results, they are compared with the results of previous studies. After investigations, it was determined that the results of the developed program and micromechanical relationships show very good consistency in predicting the properties of the final composite. Therefore, it is possible to control the mechanical properties on any of the mandrel's faces by changing the mentioned parameters.

The present research work was aimed at developing conductive polymer-based composites in order to have a higher Conductivity than the standard level of the Energy Institute of America. In this case, the composites can be applied to make electrodes. For this purpose, carbon clack particles, carbon nanotube and expanded graphite with different weight percentages (5%, 10%, 15%, 25%, and 35%) were added to the epoxy resin and the electrical conductivity of the samples was measured according to the four-point standard method. The average electrical conductivity threshold for carbon clack particles, carbon nanotube and expanded graphite was determined at 25, 10, and 15, respectively. Furthermore, the effect of different construction parameters such as the use of vacuum pumps and heating on the electrical conductivity of the composite samples was also investigated. The experiments revealed that the use of the vacuum pump increased the electrical conductivity by 10. 8%, 11. 4% and 9. 6% in carbon black, carbon nanotube, and expanded graphite samples, respectively. In order to increase the mechanical strength of the conductive polymer samples, ten layers of unidirectional carbon fabric were used. The results obtained showed that the use of carbon fibers enhanced the electrical conductivity by 23. 2%, 27. 3%, and 24. 7% for carbon black, expanded graphite, and carbon nanotube samples, respectively. Ultimately, using the scanned electron microscopy images, the quality of the nanoparticle distribution in the samples was investigated.

In this research, the effect of size and type of silica nanoparticle structure on the morphology and tensile behavior of flexible polyurethane foams were investigated. For this purpose, silica nanoparticles were prepared with two structures rigid and hollow with average particle size of 40 and 150 nm respectively, and reinforcement phases were dispersed in the matrix of flexible polyurethane foam with weight percentages of 0. 1, 0. 2 and 0. 3. Then, comparison and investigation of nanocomposite and pure samples were studied by scanning electron microscopy (SEM) and the effect of structure on the tensile behavior examined. The results of the SEM shown that among all of the samples, polyurethane/rigid silica nanocomposites have more than the size and number of cells. Also, the results of the tensile test shown that by increasing weight percentage of the reinforcement phase in the matrix, the tensile strength were increased and elongation at break were decreased. The addition, there was direct relationship with tensile properties and size and number of cells. So that, the nanocomposite reinforced with rigid and hollow silica nanoparticles at 0. 3% wt, increased tensile strength by 78% and 34%, and decrease the elongation at break by 44% and 30%, respectively, relative to the pure sample.