Journal of Science and Technology of Composites
Year:2019 | Volume:6 | Issue:1 |Papers Count:16

In the current study tensile properties of a self-healing metal matrix composite with a matrix made of Sn-13%Bi alloy and Ni-Ti SMA wires as reinforcement have been studied experimentaly utilizing taguchi method in order to determine the effect of wires volume fraction, pre-strain and healing temperature on results. Matrix alloy was molten in furnace at 300℃ and was casted in a preheated metallic mold. SMA wires was installed inside the mold in different quantities (1, 2, 3 wires) and different pre-strains (0, 2, 4 percent). By considering 3 healing temperature and using L-9 taguchi array, specimens in 9 main state was fabricated and tensile tested until failure. After the first test and fracture, specimens was placed in a furnace at healing temperature for 24 hours and then another tensile test was conducted in order to calculate the amount of recovered mechanical properties and introduce the efficiency level of each parameter on healing effectiveness. Results show that the presence of 2 wires with 4 percent of pre-strain and consecutively 190℃ and 180℃ healing temperatures create the best circumstances to achive highest amont of self healing efficiency for ultimate tensile strength and toughness.

Most of composite cylindrical shells always are used under dynamic loads not static loads in working cycle of them and Application of dynamic loads cause to large deformation and strength reduction. One way to reduce this negative characteristic is to make the fiber metal laminated shells that named FML in abbreviation. Also dynamic loads cause to vibration in structure. In the present study, firstly the fabrication of stiffened-FML cylindrical shell is explained. Then the vibration behavior and natural frequencies of three samples of FML-stiffened cylindrical shells are derived under clamp-free boundary condition. Moreover the vibration behaviors of these shells are investigated using abaqus finite element software and the FEM results are compared with experimental results in order to shows in agreement with each other. Also the effects of various parameters are studied in this article. For this purpose the frequency response of stiffened and unstiffened FML shells are compared with together and the vibration behavior of FML-shell are compared with glass/epoxy composite shell. One of the most innovations of this study is the experimental results that can be used as a benchmark for further study.

Stress concentration on the geometric discontinuities is one of the factors of structure failure. Nowadays, plates with holes are inseparable parts of designs and pieces, therefore studying the stress concentration caused by these holes is necessary to prevent structure failure. So the designer for presenting a design must be aware of the stress concentration in the hole and according to it design the basis. In this research, by using the regression method and on the basis of the mechanical properties of the materials and the radius of curvature in the corner of the hole, we try to present an explicit relation for estimating stress concentration in the orthotropic plates with quasi-square hole. This relation, in addition to easing the use and bypassing the hard and complex process of analytical solution, provides designer with the opportunity to calculate stress of perforated viscoelastic plates by using the effective module method or Boltzmann's superposition principle. At first, with analytical solution based on the Lekhnitskii method the stress values are calculated in many composite plates with quasi-square hole. Then, by using multiple linear regression and on the grounds of mechanical properties, is given an explicit relation for the stress concentration coefficient. The results show that the multiple regression model is able to predict the circumferential stress with a maximum error of 2%.

This paper investigates free vibration of a smart sandwich composite polymeric micro-panel blend of polyvinylidene fluoride reinforced with boron nitride nanotubes under an electric field resting on an elastic substrate using first order shear deformation theory. The distribution of nanotubes in the polymeric matrix is assumed uniformly. The Winkler springs and Pasternak shear layer are used for modeling the elastomeric substrate and the higher-order modified strain gradient theory is implemented to investigate the effects of size. First, using the microstructural modeling technique, the constitutive equations of the nanocomposite are extracted for a representative volume element, and then the stress-strain relations are obtained in terms of mechanical and electrical terms. Also, the equations of motion are derived using the Hamilton principle, and finally using the method of variational calculus and extracting the mass and stiffness matrices, the natural frequency of the micro-panel is obtained. The results of this paper show that by increasing the aspect ratio and reducing the volume fraction of nanotubes, the panel's hardness decreases and the natural frequency decreases. Further, various parameters such as the stiffness of elastic medium, the effect of electric field, different modes, aspect ratio and other factors are investigated. A comparison is also made between the classical, modified coupled stress, and higher-order modified strain gradient theories.

Using a stiffener is one of the ways to increase the buckling load capacity of the plate. However, to reduce the weight, the optimum design of the stiffener is necessary. In this study, buckling and post buckling behavior of composite plate with circular cut-out at its center with three types of stiffeners is investigated to achieve a plate with highest resistant to axial loading as buckling load. The Planer stiffener is made in the form of a thin, square layer and is attached around the opening. Two other stiffeners are named as Longitudinal and Ring types. These two stiffeners are thin layers which are attached perpendicular to the compression loading direction and at hoop direction around the openness, respectively. Plate and stiffeners are made as an orthogonal and symmetric layered composite. To model the above items in the Ansys software, tensile and shear tests on composite specimens were performed in accordance with international standards to achieve the required mechanical properties. Buckling behavior of plate with stiffener is analyzed by finite element method and the results are consistent with experimental results. The results of this research show that among the offered stiffeners, the plate with a longitudinal stiffener has maximum buckling load in comparison to the weight and minimum ratio of the buckling load to the weight is related to the ring stiffener.

In this paper by implementing energy based theory, growth of induced delamination due to matrix cracking have been studied in symmetric composite laminates subjected to constant in-plane stresses and constant thermal stresses. Two unconstrained and generalized plane strain states have been analyzed here. Matrix cracking as a primary assumption has been supposed in both states and the impact of matrix cracking and delamination on the stiffness degradation is calculated. Afterwards some thermoelastic constants, which are only depended on, ply material properties of composite lamina are. Then by relating stiffness matrix elements using these constants, a simple equation due for Gibbs free energy acquired. By differentiating the Gibbs free energy equation for delamination length other simple equation was obtained to compute energy release rate. To verify the obtained results, ANSYS finite element software is used. The obtained results reveal that there is good agreement between the extended and FE approaches.

Nowadays, functionally graded materials have different applications in various industries, such as Aerospace industry, turbomachinery, coating industry, etc., due to their unique ability in providing multiple and sometimes opposite properties in a material volume. The purpose of this paper is to fabricate functionally graded material sheet of aluminum based composite with SiC reinforcing particles, using powder metallurgy and hot rolling methods. In this regard, the amount of reinforcement in the direction of thickness has been changed from the value of 0 to 4 weight percent. The samples were prepared in four steps including ball-milling, degassing, cold pressing and sintering, and then were hot-rolled up to three passes. The distribution of the reinforcing particles in the matrix phase was evaluated using optical microscope. Furthermore, the mechanical properties of the FGM samples including their hardness, tensile strength and flexural strength were measured and reported. Finally, the fracture surfaces in the tensile and flexural tests were observed using scanning electron microscope (SEM). According to the images obtained from the microstructure of the samples, the reinforcing particles have an acceptable distribution in the matrix phase. Also, the results indicate that the hardness and strength are enhanced by increasing reinforcing particles and the number of rolling passes. In addition, the main fracture mechanism in pure aluminum layer is the initiation and propagation of cracks between initial aluminum powder particles, while separation of two phases in the matrix-reinforcement interface and small SiC particle agglomerations are responsible for crack initiation in the composite layers.

In this study, the static and dynamic analysis of composite wing is investigated using analytical method. The wing is modeled as a cantilevered thin walled beam with a single-cell closed cross section and the circumferentially asymmetric stiffness (CAS) configuration. The non-classical effects such as transverse shear, warping restraint, rotary inertia, nonuniform torsional model and material anisotropy are considered in the beam model. The governing equations were derived by means of the extended Hamilton’ s principle and are solved based on the extended Galerkin’ s method. From the validation process, the obtained results are in good agreement with the numerical results and experimental data. In this paper, a linear spanwise variation of the fiber orientation along the thin-walled beam span resulting in a variable-stiffness structure is investigated for the first time. Therefore, two fiber path definitions will be used with linear fiber orientation variation and with constant curvature of the fiber path. Numerical results indicate that eigenfrequencies and bending-torsion couplings depend on fiber angle, resulting improvements of wings with curvilinear fiber over conventional, straight ones through the variation of fiber angle along the beam span and increase of the design space.

In the present research, using a micromechanical approach, a novel analytical method was developed to predict the stiffness and damage initiation load of single-lap composite joints. The elastic and strength properties of fiber and matrix were used to characterize the elastic and strength properties of unidirectional composites. Based on the layup and geometrical parameters of the single-lap joint and using a nonlinear spring-mass model, the stiffness of the joint was predicted. Then, by defining the stress concentration factor and using the maximum stress failure criteria, the damage initiation load of the single-lap composite joint was predicted with a good accuracy. This model was used to simulate the mechanical behavior of single-lap joints with layups [− 45/0/45/90]𝑠 and[90/− 452/45]𝑠 . Composite joints with these two layups were manufactured and tested. A comparison between the results of the model and experiments shows maximum errors of 2. 17% and 3. 91% for joints with these two layups, respectively.

The increasing need for manufacturing of eco-friendly products has led researchers to explore the possibility of using of natural fibers in the fabricating of composites. In the current study, plain-woven plant fibers of cotton and kenaf, and animal fiber of wool with were used as the reinforcement of epoxy-based laminated composites. Moreover, in order to evaluate the mechanical properties of the natural fibers reinforced laminated composites, plain-woven E-glass/epoxy composites were also manufactured. The mechanical properties of the samples subjected to tensile, shear and flexural loadings were determined. The results showed that the fraction of the specific tensile strength of the cotton/epoxy laminates to laminates reinforced by kenaf or wool fiber is equal to 1. 71 and 4. 47, respectively. Under shear loading, the specific strength of the samples was also 1. 24 and 2. 45 times greater by changing the kenaf and wool fibers to cotton fiber, respectively. In addition, the specific flexural strength of the cotton/epoxy composites was respectively obtained 1. 42 and 2. 34 times greater than that of the kenaf/epoxy and wool/epoxy composites. Moreover, the specific energy absorption related to the cotton/epoxy laminated composites under tensile loading is 2. 7 times greater than that of the glass fiber reinforced laminated composites. At the end, in order to measure the amount of water absorbed by different samples, moisture absorption test was also carried out at intervals of 3 and 10 days. It was revealed that the greatest percent of the water absorption (7. 47%) is related to the cotton reinforced specimen at interval of 10 days.

In this paper, the effect of adding graphene particles to resin and the use of basalt fibers in composite sandwich panels on the quasi-static permeation response and energy absorption has been studied. In this study graphene with a 90% degree of purity, 8 layers of basalt fiber with a mass unit area of 350 g / m2, a polyurethane foam core of 1 cm thickness with a mass volume of 80 Kilograms per cubic meters, resin and EPR1080 hardener have been used. The samples of a mass percentage of 0, 0. 3, 0. 7, 1. Graphene have been made. The quasi-static penetration test was performed on the samples by loading at a speed of 8 mm / min. The results of the quasi-static penetration test on the above samples show the improvement of performance in the composite sandwich panel containing graphene. The results show that the best performance is related to the 0. 7% graphene sample. The samples are tested under SEM testing. The images of this experiment show that in a sample with 0. 7% graphene, there is a better microscopic structure than other samples. The sample with 0. 7% graphene has the highest energy absorption before the failure of the composite sandwich panel and the least damage after full penetration.

The purpose of this study is determination of the optimal process parameters such as recycled PET (RP), compatibilizer (COM), and wood flour (W) in HDPE/rPET/wood composites to maximize specified strength (the ratio of tensile strength to density) by consideration of water absorption (WA), tensile modulus (M), and impact energy (IE) as the constraints. In this regards, the wood composites samples were prepared with various contents of rPET (0, 15, 25, and 35 phr), MAPE as a compatibilizer (4, 8, and 12 phr), and wood flour (30 and 40 % wt. ). The experimental tests were carried out to determine tensile strength (TS), tensile modulus, impact energy (IM), density (ρ ), and water absorption (WA). Response surface methodology (RSM) was used to create the mathematical models between input parameters (RP, COM, W) and responses (TS, ρ , WA, M, and IE). The analysis of variance (ANOVA) was done to determine the significance of the model and each input parameter. Genetic algorithm (GA) code was performed to determine optimum condition. Specific strength formed the main function for GA, and water absorption, tensile modulus, and impact energy constituted the constraints of the function.

The attempts to resolve shortcomings of the equivalent single-layer and layerwise theories has resulted in the development of the global-local plate theories. In the present paper, dynamic responses of rectangular sandwich plates with composite face sheets reinforced by SMA wires under low-velocity impact is investigated using a new higher-order hyperbolic global-local theory. In order to obtain accurate results, non-uniform and time-dependent distribution of the phases of the SMA and the transverse compliance of the soft core are considered. A refined contact law is proposed instead of using the traditional Hertz law and different contact laws are considered for the loading and unloading phases. Stiffness effects of all layers along with effect of the plate thickness on contact stiffness are considered. The obtained nonlinear finite element governing equations are solved by making use of an iterative algorithm at each time step. The present results are compared with the experimental results, and the current results and verified. Finally, effects of the SMA wires, presence of the auxetic core, stiffness of the core, thickness of the core, eccentricity of the impact and the in-plane biaxial preloads on impact responses of the sandwich plat are investigated. The results show that the tensile biaxial preloads increase the contact force and martensite volume fraction and decrease the lateral deflection and contact time due to the reduction of the lateral mobility of the plate and increasing the stiffness of the structure whereas the compressive biaxial preloads, due to the tendency to create larger deflections, lead to opposite results.

Metal matrix composites are relatively low-weight materials comprising of reinforcing elements in their structure which tend to improve the hardness, abrasion resistance as well as well as fatigue resistance of the material. One of the metal matrix composites with significant mechanical features are titanium metal matrix composites (Ti-MMCs) which can be considered as an alternative to nickel based superalloys in wide range of applications in numerous manufacturing sectors, including automotive, and aerospace. Despite significant features aforementioned, due to high manufacturing costs and presence of reinforcing elements in metal matrices, machining and machinability of Ti-MMCs is a complex subject. Knowing that limited studies are available on machining Ti-MMC under various lubrication modes and lubrication rates, adequate knowledge on the effects of cutting parameters and lubrication modes on machinability attributes of Ti-MMCs is a delicate subject. Therefore, the first aim of this work is to present the effects of cutting parameters, including lubrication modes and lubrication rate on machinability attributes, including surface quality. Furthermore, the Fast Fourier transform (FFT) will be used to evaluate the effects of cutting parameters on frequency domain of recorded cutting forces.

Nowadays, reinforced polymers using by means of glass fibers are extensively used in industry. One of the used loads that composite cylinders undergo during use are lateral compression loading. To investigate the buckling and post-buckling behavior of filament wound composite cylinder, some prototypes were prepared with winding angle equal to ± 75 degree. The samples were pressurized by means of two parallel rigid plates according to ASTM standard. The force-displacement diagrams resulting from normal loading on the rigid plates were plotted experimentally. In addition to experimental tests, numerical simulations were carried out by means of Abaqus commercial software. Since the composite cylinder experiences damage, the Hashin’ s three dimensional damage model was utilized to consider the damage effects occurring during loading. To apply Hashin’ s three dimensional damage model, a UMAT subroutine coding procedure was conducted using program Fortran 77. The mechanical properties and composite cylinder fracture strengths were obtained by measuring fiber and resin properties based on the relative standard and then separately by micro mechanical relations concerning the layers. The cylinder undergoes buckling because of the existence of pressure between the parallel rigid plates. However since the cylinder undergoes a stability condition after buckling. This phenomena does not have significant effected on the overall behavior of the cylinders. Appropriate agreement is observed between the experimental results and the numerical simulations.

The method of wave function expansion is adopted to study the three dimensional scattering of a plane progressive harmonic acoustic wave incident upon an arbitrarily thick-walled helically filament-wound composite cylindrical shell submerged in and filled with compressible ideal fluids. An approximate laminate model in the context of the so-called state space formulation is employed for the construction of T-matrix solution to solve for the unknown modal scattering coefficients. Considering the nonaxisymmetric wave propagation phenomenon in anisotropic cylindrical components and following the resonance scattering theory (RST) which determines the resonance and background scattering fields, the stimulated resonance frequencies of the shell are isolated and classified due to their fundamental mode of excitation, overtone and style of propagation along the cylindrical axis (i. e., clockwise or anticlockwise propagation around the shell) and are identified as the helically circumnavigating waves. The solution is particularly used for the quantitative sensitivity analysis of excited resonance frequencies of an air-filled and water submerged Graphite/Epoxy cylindrical shell to the perturbation in the material’ s elastic constants.