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Fiber Metal Laminates are new composite structures in which several thin metal sheets and composite layers are connected together. These structures have properties such as high fatigue resistance, high impact resistance and high energy absorption, which have led to a growing use of them in various industries. In this study, damage in FMLs under tensile static loading, including matrix cracking, delamination induced by matrix cracking and plasticity in metal layers, was examined. Using the analytical model, stress distribution and energy release rate were extracted in FML containing matrix cracking and delamination. Numerical modeling of FML containing such damages was also performed. The stress distribution results obtained from the analytical and numerical models were compared, and good agreement between the results was observed. Furthermore, the FML samples were subjected to tensile test and the damages that occurred in them were displayed. By using the analytical model and calculating energy release rate, the matrix crack saturation and the initiation of delamination at the crack density of 0.38 (the distance between two cracks is 2.7 mm) were extracted. By observing the experimental samples, this crack density was observed in most of the length of the sample, but due to various reasons such as manufacturing defects, in some areas the distance between the cracks was larger than the mentioned value.

In the present research, classic micromechanical methods and their application as constitutive models in conjugation with incremental theory were developed. Using the modified Eshelby model, the Eigen strain concept in polymeric composite, and a modified form of self-consistent model the elastic properties of nanocomposites were predicted. Also, the stress-strain behavior of elastomer nanocomposites was calculated and validated by the experimentally determined ones. The results showed that the new model can predict the stress-strain behavior of elastomer nanocomposite at different particle volume fractions.

Polymeric composites having high specific strength and stiffness compared to the traditional material are weak in outof-plane mechanical properties. More than above, these kinds of structures in some industrial applications are undergoing cyclic temperatures. In this manuscript, the effect of 200 thermal cycles in the range of -30 to +65 degrees Celsius on the fracture toughness of the carbon/epoxy composites is evaluated. Carbon/epoxy composite laminates are fabricated using carbon fabrics and epoxy resin in the form of the double cantilever beam (DCB), and end notched flexure (ENF) specimens. Samples are exposed to the 200 thermal cycles, and fracture tests are carried out in modes I and II. Test results revealed that the initiation fracture toughness of the samples in mode I (DCB) and mode II (ENF) are reduced 5.7 and 15.5 percent, respectively, compared to those are tested at room temperatures. Also, crack surfaces are investigated using an optical microscope and scanning electron microscope (SEM) in the specimens exposed to the thermal cycles.

In this study, the residual strength of the carbon/epoxy composite plates exposed to the thermal cycles and subjected to low-velocity impact was evaluated using an experimental procedure. Composite plates with a layup of [45/02/-45/902]s and thickness of 2.9 mm under three impact energy levels of 10J, 15J, and 20J and exposed to 200 thermal cycles in the range of -30 to 65° C went under low-velocity impact and compression after impact tests. In performing impact tests, a drop weight test device was used to investigate the behavior of damaged composites, force-time, force-displacement, and energy-time curves at all test temperatures were analyzed. Finally, the effect of temperature and associated damages at different levels of impact was evaluated using radiographic analysis and optical microscopy. Applying 200 thermal cycles in the temperature range of -30 to 65 ° C caused small cracks in the matrix and reduced the energy absorption of the samples. The highest drop in compressive strength is related to the highest impact energy, 20 J, which has a 31.12% decrease in strength. The thermal cycle at different impact energy levels of 10J, 15J, and 20J has led to an increase in the stiffness and compressive strength of the composite specimens. Finally, material parameters of the semi-empirical Caprino model to estimate the residual compressive strength of the carbon/epoxy plates under low-velocity impact and thermal cycles are obtained.

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.

Nowadays, low-velocity impact resistance and damage tolerance have become very important in the design of composite structures, especially in the aerospace industry, and have led researchers to evaluate the low velocity impact response in the design of composites. In this research, a numerical model for low velocity impact (LVI) of carbon /epoxy composite laminate is proposed. This 3D damage model is based on continuum damage mechanics with subroutine development (UMAT) in Abaqus/Explicit. In this model, the interlaminar and intralaminar damage is considered and the nonlinear shear behavior is applied to consider the plasticity in the matrix. To evaluate the results obtained from the numerical model, impact testing was performed at three levels of impact energy (10 J, 15 J and 20 J). In addition, in order to verify the failure mechanisms and the amount of damage caused by the impact, delamination area was measured using radiology technique. By comparing the response of the impact behavior, a good correlation was obtained between the experimental test results and the simulation, which shows that the failure model used is well able to predict the behavior of the composite in this process.

The sandwich panel is a combination of a soft core and two stiff, high-strength facesheets. In many cases, the connection between the facesheet and the core is considered as a critical point that can damages the integrity of the sandwich structure. In this study, the debonding toughness between the facesheet and the core in sandwich beams with grooved cores made of Kevlar 49/polyester facesheets and polyurethane foam core has been measured experimentally. The values ​​of the strain energy release rate obtained at the onset of crack growth for the tested specimens are in the range of 340 (J/Square meters) and increase with the crack growth up to 500 (J/Square meters). One of the innovations of the present study is to investigate the effect of grooving the core of the sandwich panel on the resistance of the structure to the growth of interfacial cracks. The results show that by placing the groove inside the core of the sandwich panel, the interfacial crack stops during growth by hitting each groove and requires higher force to restart its growth. This phenomenon increases the resistance of this type of structure against the growth of cracks in the face/core area. In this research, a model based on cohesive zone theory was used to simulate crack growth in the tested specimens. Comparison of load-displacement curves obtained from the analysis shows that the proposed model has a good ability to predict the behavior of the structure under similar loading conditions.

In recent decades, the use of composite materials in engineering structures has increased dramatically.. Therefore, it is necessary to understand the structure and mechanisms of damage to these materials. Among the most common damages in composite materials, delamination is one of the catastrophic failure modes. Cohesive zone model is one of the appropriate tools for analyzing the phenomenon of delamination in the laminated composites. The cohesive zone model analyzes the delamination by tracking the damage from its onset to its evolution. In the cohesive zone model, the area behind the crack tip, where the cohesive forces are active, is of great importance. This zone is directly affected by loading mode, fracture energy and cohesive strength, active elastic modulus, and structural geometry. Many models have been proposed to estimate the length of the cohesive zone. In this study, the length of the cohesive zone in first and second pure mode was obtained by using finite element analysis in Abaqus software. The results of the simulation were compared with the analytical models for estimating the length of the cohesive zone. It was observed a more accurate estimate of the cohesive zone length in models that consider the material type and effect of structural geometry.

purpose of this study was to investigate the effect of bending load on the electrical conductivity of carbon-epoxy composites containing various nanoparticles. The developed samples, while having sufficient flexural strength, must have the electrical conductivity proposed by the U.S Energy Institute to be used in the manufacturing of electrodes. For this purpose, carbon black nanoparticles, carbon nanotubes and expanded graphite with unidirectional carbon fabrics and epoxy resin were used to make the samples. Carbon black particles, carbon nanotube and expanded graphite with optimum weight percentages (25, 10 and 15%) were added to carbon/epoxy composite and the electrical conductivity threshold of the samples was measured according to the four-point strength method. The average electrical conductivity permeability threshold for composites containing carbon black, expanded graphite and carbon nanotubes was 23.2, 27.3 and 24.7%, respectively. The samples were then subjected to bending load and for the 0.5, 1, 1.5, 2 and 2.5 mm transverse displacement, the electrical conductivity value was measured during loading and unloading. The results showed that the value of electrical conductivity loss in carbon/epoxy samples containing carbon nanotubes caused by bending was at lowest and in the carbon/ epoxy containing carbon black samples displayed the highest value. Then, the flexural strength of the specimens was measured using a three-point bending test method. The pattern of nanoparticle distribution in the samples was studied on images acquired by scanning electron microscope images. The result of this research could be used in manufacturing of composite electrodes which are subjected to flexural loading (electrostatic desalting crude oil tanks) in services.

In this paper A progressive damage model based on multi-scale modeling has been developed to predict the initiation and propagation of damage in plain weave fabrics. For this purpose, microscopic damage in yarns and resin is calculated by an RVE (Representative Volume Element) FE simulation. By applying suitable boundary conditions of RVE, macro-scale average stresses were derived to extract the components of the equivalent stiffness matrix. Finally, by developing UMAT and USDFLD subroutines in the ABAQUS commercial software, the strength of the woven composite rings is predicted numerically. In order to confirm the numerical predictions, composite rings using the woven glass tapes of 5 cm width and epoxy resin are fabricated according to ASTM D2290 and tested. A good correlation between experimental and numerical results could confirm the accuracy of the finite element simulation.

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.

Friction Stir Welding is a solid-state process, which means that the objects are joined without reaching melting point. Which has demonstrated very high suitability for the joining of dissimilar aluminium alloys. The aim of this investigation was to study residual stress and micro hardness distribution in different zones of dissimilar friction stir welding of AA6061-T6 and AA7075-T6 and compare it with the tungsten inert gas (TIG) welding of AA6061-T6 by using increment hole drilling technique. Also The evolution of the residual stresses in the thickness direction was investigated, it was found that the maximum residual stresses are below the yield strength of the material in the shoulder region and showed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses. Vickers micro hardness measurements were performed in the transverse cross section of the samples, the results showed that Hardness peak values were observed in SZ region adjacent to the advancing side whereas low hardness regions were measured across the weld corresponding to the HAZ of both alloys and at the SZ adjacent to the retreating side.

In the current paper, a micromechanical based model is presented to estimate the stress transfer in interphase of three-phase reinforced composites. The symmetric model consists of fiber, matrix and a layer in between them. In this study, composite constituents were considered as linear elastic materials. Also, the matrix was treated as isotropic material while the fiber and the interphase were considered as transversely isotropic materials. The stress distribution solutions for an intact model and partially debonded model are obtained. A pair of uncoupled partial differentiation equations were obtained in terms of unknown displacement components. The separation of variable with Eigenfunction expansion methods were used to derive the exact solution of the PDE’s. Analytical solutions for the free boundary conditions on the external surface of the matrix are obtained to simulate the pullout test. In both cases, numerical findings revealed a good correlation with the analytical results. By comparing the shear, radial and axial stress components become clear that three- phase composite adopts smaller amounts than of two- phase composites. Also, it was shown that the stress field in the partially debonded model has small quantities in comparison to the intact model.

In this paper, flexural behavior of composite sandwich beams under four point bending loading has been studied experimentally and numerically. The skins and the core of the sandwich composite beam have been made of woven glass/epoxy composites and polyvinylchloride foam with 70 kg/m3 density, respectively. The experiments were performed on the beams with different lengths and two different types of layup sequence for the skins as 0/90 and ±45. Failure was initiated in the beams due to indentation of the foam and extended to the face sheet failure under the loading roller. Numerical simulation of the sandwich beam has been performed using ABAQUS commercial software to verify experimental results. During the numerical simulations, the nonlinear material models were employed for shear stress-strain behavior modeling of the foam and the face sheets. In addition, due to the large deformation during bending test geometrical nonlinearity assumption was used in FE analysis. Failure initiation was predicted in the face sheets using modified Hashin criteria. Nonlinear stress analysis and failure predictions in the face sheets and the foam were conducted using USDFLD subroutine in ABAQUS software. Also crushable foam model was employed to simulate the plastic behavior of the foam core. The load-displacement curves and failure mechanisms predicted by the numerical simulations illustrated good correlation with the experimental data.

Since characterization of in-plane shear properties of composite materials is necessary for designing composite structures, there are many methods for shear testing of composite materials. V-notched rail (VNR) shear test method is the latest method published as ASTM D7078 in 2005. Strain and stress states of VNR specimens were investigated numerically by adopting a commercial finite element software. The effect of measurement errors on the results was also analyzed. Although, the experimental programs were implemented based on standard considerations, the possibility of some errors was unavoidable. The sources of errors originated from misalignment of the specimen with respect to the loading axis, application of end loading instead of face loading and fiber misalignment. According to the obtained results, slipping of the specimen within the fixture grip plates had the most important effect on the results in comparison to two other error sources. In addition, fiber misalignment was another important source of erroneous results which needed to be considered during testing. Misalignment of the specimen with respect to loading axis showed the least effect on the shear properties of the specimens compared to others. Some other errors also affected the stress state of the specimen. However, our investigations showed that their effect on the shear properties was negligible. Finally, glass/epoxy specimens were evaluated experimentally by V-notched rail shear test method. Shear modulus of the V-notched specimens was almost equal with the modulus of three rail specimens. However, the shear strength measured by the V-notched rail shear test method was approximately 36% higher than that measured by the three rail test method.

Shape Memory Alloys (SMAs) are a type of Shape Memory Materials (SMMs) which can recover large deformation and return to their primary shape by rising temperature. In this study, numerical simulation of thermo mechanical behavior of composites reinforced with shape memory alloys under static uniaxial loading was conducted. By inserting SMA wires inside the host composite the macro mechanical behavior of hybrid composite changed to a bilinear curve which is due to the phase transformation of SMA wires and nonlinear behavior of host composite. Simulated results are compared with available data in the literature. Validated model is used to evaluate the effect of various parameters as, wires pre-strain, temperature, interface conditions between SMA wires and Epoxy matrix on hybrid composite behavior. Also a theoretical method was developed to calculate the compressive and tensile strain induced in host composites and wires, after releasing of SMA wires. According to the results obtained, considering weak interface between SMAs wires and matrix improved simulation results rather than perfect bonding assumption. Pre-strained SMA wires would cause initial compressive stress in the host composite and its value will increased by increasing service temperature, however, it will increased interface separation of SMA and host materials, too. Therefore, in design of Shape memory alloys hybrid composites, optimum amount of applied pre-strain on SMA wires and working temperature should be selected.

When a cylindrical shell subject to a compressive load, because of various imperfections happened during processes as manufacturing, handling, assembling and machining, buckling occurs in loads lower than corresponding static failure load. Still many of cylindrical shell structures are designed against buckling based on experimental data introduced by NASA SP-8007 as conservative lower bound curves. In the manuscript, non-linear methods of Modified Linear Buckling Modeshape Imperfections (M-LBMI) and Simple Perturbation Load Imperfections (SPLI) for composite cylindrical shell with and without cutout are investigated. In order to evaluate the numerical results composite cylinder with stacking sequence of [90/�23/90] are manufactured by using filament winding method and buckling tests are performed under axial loading. Non-linear numerical results in cylinder with and without cutout are close together and have good agreement with experimental data. . It was concluded that buckling load predicted by SPLI and modified LBMI method on cylinder with cutout is close to result of case without apply geometric imperfections. In summary, it was concluded that cutout on the cylinder body act as an imperfection to trigger buckling of the structures so there is no need to apply geometrical imperfections.

The analysis of notched composite parts in a structure due to the existence of high stress concentration and undetermined behavior is an exigent issue. In this research, the progressive damage analysis has been applied to predict the failure of notched woven glass- epoxy composite laminates under tensile loading. Stress analysis and investigation of the effect of the hole size on it have been performed by the analytical and numerical methods. Developing an UMAT in the ABAQUS finite element package has made the utilization of the 3D progressive damage analysis feasible. Max. Stress, Yamada- Sun and Tsai- Wu failure criterions have been implemented to predict the damage initiation due to the absence of significant failure criteria for woven composites. Instantaneous and recursive property degradation methods have been used to simulate the damage propagation. The tensile characteristic distance has been computed without any experiments. The comparison of stress and failure analysis with experimental results shows good agreement. Finally, using tensile characteristic length obtained by progressive damage method, the possibility of safety factor determination in the composite joints in order to optimum design has been provided.

In this paper an analytical approach for determining load distribution in single-column multi-bolt composite joints by considering elastic nonlinear behavior of the composite materials is presented. Load distribution was calculated by writing the governing equations of the motion. This closed form solution is an integration of spring-based models with nonlinear behavior of composite plate materials. Developed method is capable to calculate taken load by each bolt and its displacement by simultaneous solving of governing equilibrium equations of the system. This manuscript specifically focused on the influence of composite material nonlinearity on the load distribution of single bolted composite joints. For this purpose, load changes versus displacement are plotted by taking into account both the linear and nonlinear material behavior. The achieved results via suggested solution revealed that displacements were increased upto 2.5-5 percent in comparison with the results of linear method available in the literature. In addition, due to the manufacturing tolerances, bolt–hole clearances can vary within allowable limits and fits. Therefore the effect of bolt hole-clearance on the composite joints with linear and nonlinear material properties was also investigated.

Buckling and vibration characteristics of thin symmetrically laminated elliptical composite plates under initial in-plane edge loads and resting on Winkler-type elastic foundation are presented based on the classical laminated plate theory. The governing equations are obtained from the variational approach and solved by the Ritz method. Extensive numerical data are provided for the first three natural frequencies as a function of in-plane load for various classical edge conditions (free، clamped and simply supported). Moreover، the effects of fiber orientation on the natural frequencies and buckling loads of laminated angle-ply plates with stacking sequence of [(β /-β / β /-β)]s، are studied for chosen foundation parameter. Also، selected deformation mode shapes are illustrated. The accuracy of calculations is checked by performing good convergence studies، and the correctness of results is established by comparison with the existing results in the literature as well as FEM data.

Because of inhomogeneity and anisotropy of composite materials, defining a unique fatigue criterion to be suitable for different loading conditions is much more difficult in comparison with traditional materials. For this reason many tests on evaluating the damages such as crack density, stiffness reduction and residual strength are used by various researchers to monitor the fatigue process. In this research the residual strain energy density is defined as a suitable fatigue measure and used in a micromechanical static failure model to predict the fatigue life of unidirectional composites in different fiber load angles. In contrast to stress based fatigue models the new developed model employed both stiffness and strength reduction to predict the fatigue life with more accuracy. To measure the residual strain energy density stiffness and strength failure of models given by Shokrieh et al. are modified and used in this research. Available experimental data on unidirectional carbon/epoxy composites with the stress ratios of R=0 and 0.1 on stress states of 50, 60, 70 and 80 percent of static strength are used to evaluate the proposed model. The results predicted by the model underestimates the fatigue life in comparison with the experimental data.