نشریه علوم و فناوری کامپوزیت
سال دوم شماره 1 (پیاپی 3، بهار 1394)

Shape memory alloys (SMAs) due to their extraordinary physical and mechanical properties، recently are used to enhance the mechanical properties of composites. In the present paper micromechanics model based on Eshelby’s equivalent inclusion and Halpin-Tsai model was used in order to predict the elastic properties of randomly oriented shape memory alloy short wires reinforced epoxy. The presented incremental micromechanics model considers the gradual changes in the elastic modulus of the SMA wires due to martensite phase transformation. Experimental tensile tests were applied to the shape memory alloy short wires/epoxy composites to investigate the accuracy of the model. The micromechanics results were in good agreement with the experimental results and also the previously reported results in the literature. The effect of shape memory alloy wires volume fraction as well as the aspect ratio of the wires was investigated on the elastic modulus of SMA/epoxy composites. Moreover the effect of orientation of SMA wires on the modulus of composites was studied. Micromechanics results showed that in SMA volume fractions lower than 5%، the minimum acceptable aspect ratio of wires is about 25، However for SMA volume fraction above 15%، aspects ratios above 40 are required in order to enhance the elastic modulus of the composites efficiently.

Polyaniline was synthesized chemically in acidic medium in the presence of ammonium peroxydisulphate (APS) as oxidizing agent. PANI-ZnO nanocomposites prepared in the presence of various amount of nano ZnO (from 1 to 5 wt. %) by solution casting method، free standing film of polyaniline and its nano-composites was obtain by vaporization of solvent content. The composition، morphology and structure of the polymer and the nanocomposites were characterized by Fourier transform infrared spectroscopy FT-IR spectra، scanning electron microscopy (SEM) image and XRD pattern also thermal stability was studied by TGA analysis، electrical conductivity was measured by four point probe technique and mechanical properties were studied by tensile strength. The characteristic FTIR peaks of PANI were found to shift to lower number in nanocomposites due to formation of H-bonding. XRD results revealed that the crystallinity of PANI was more pronounced after addition of nano ZnO، while the intensity of the peaks increased by addition of ZnO nanoparticles. Also، TGA results showed that the decomposition of the nanocomposite was less than that of pure polyaniline which confirms the successful fabrication of products. Young’s modulus and strength at break point was increased in case of Nanocomposite، Addition electrical conductivity of the PANI–ZnO nanocomposite film was found to be smaller than that of the PANI film.

Composite materials behavior is complicated more than metallic material because of different mechanisms of damage، damage growth rate and effect of them in each other. In this paper، a continuum damage mechanic based model is proposed to predict the fatigue life of symmetric cross ply laminated composites under fatigue loading. According to fiber and matrix elastic properties، Elastic material constants of lamina are defined base on micromechanical approach. Two damage variable of matrix and fiber direction are considered to explain stiffness degradation on the scale of the plies، which thus makes it possible to use in any stacking sequences of cross ply laminated composites. Also، it is capable to predicted fatigue life and residual stiffness of laminates under different states of stress and stress ratio. The available tension-tension fatigue tests on 0◦ and 90◦ unidirectional laminates are used to identify material parameters of damage evolution equations in matrix and fiber direction. Finally، the stiffness degradation and final failure cycle of laminates during the fatigue loading on unidirectional plies and cross-ply layups are compared with available experiments. The obtained results are show a good agreement with the experiments.

Pultrusion is the continues process for production of composite constant cross section profiles that reinforced by continues unidirectional fibers or fabrics. Usually this process is used for production of thermoplastic composites. Recently pultruded thermoplastic composites are considered. Pultruded Thermoplastic composites are considered because high resistance to impact، high tensile strength، Recyclability and high strength of bending. Objective of this paper is the investigation of production parameters and determine of these Parameter values to die design and production of tubular pultruded composite and achieving to valid product with Acceptable surface roughness، uniform geometry and good impregnation between thermoplastic resin and glass fiber. For this purpose، first wire prepreg has been produced from Glass fiber continuous roving and high density polyethylene (HDPE) granules in deferent production parameters. Volume fraction of voids and glass contents measured in each prepreg and impregnation was investigated from microscopic photos qualitatively. Finally، choosing the best prepreg، tubular profile produced using pultrusion die that designed specifically to help production of tubular profile from Prepared prepreg. Also، the three point bending mechanical test was performed from the samples produced.

In this research the effect of temperature and volume fraction of reinforcement on wear behavior of the Al/x vol% SiCp (x=0، 1، 3، 5) nanocomposite was investigated. Results revealed that addition of reinforcement particles increases transition to severe wear temperature of the samples، so that the temperature of transition to severe wear for the un-reinforced aluminum، Al-1%SiC، and Al-3%SiC and Al-5%SiC samples is 125°C، 150°C، and 175°C، respectively. Also، the composite samples showed lower wear rate and friction coefficient compared to the un-enforced aluminum، and with increase of volume fraction of SiC particles، wear resistance of the samples was improved. FESEM images from the surface of the samples worn at different temperatures revealed that wear mechanism in the mild wear area of all samples is the abrasive mode، but with increase of temperature and transition to severe wear area، wear mechanism of all samples except Al-5%SiC is the adhesive mode. The Al-5%SiC sample still shows the abrasive mode، which indicates the positive effect of the reinforcement phase.

In this paper، vibration control of a cracked، functoinally graded، uncertain beam allocated in a thermal environment has been investigated. For this purpose، piezoelectric patches are used as sensors to measure the displacement of the beam and also as actuators to apply control forces. In this way، firstly، partial differential equation governing the dynamics of the system is derived by considering the Euler-Bernoulli assumption using Lagrange method. Approximate solution of eigenvalue equation is achieved using Rayleigh–Ritz method. After that، time dependent ordinary differential equations is obtained using Galerkin projection scheme and then represented in the state-space form. Based on this model، a robust observer-based output feedback controller is designed for this continuous-time model. In this regard، controller and observer gains are designed by a Lyapunov-based method. This procedure is done by solving a set on linear matrix inequalities. Simulation studies show the effectiveness of the proposed method.

In the present paper the geometrically nonlinear analysis of single and doubly curved shells is investigated using finite element method. The finite element formulation includes the nonlinear strain terms in order to take the large deformation effects in to account. The material behavior is assumed to be orthotropic linear elastic. The problem is formulated based on the shallow doubly curved shell theory using first order shear deformation theory of shells. A precise high performance 4-noded bilinear doubly curved element is presented. All FEM calculations carried out in the elemental natural coordinate system. The developed special element have the curvature effects along two main in-plane directions inside its formulation. The full equilibrium path of the geometrically nonlinear problem of shells has been extracted using the arc-length algorithm. Using arc-length algorithm، the method can follow the panel equilibrium path beyond the possible limit points and also is able to anticipate the snap-through phenomena. A MATLAB program code is developed. Some case studies are considered and the results are compared to available ones in the literature. The results show that in spite of its relatively low degrees of freedom، the developed formulation is capable to predict the equilibrium path of thin to moderately thick curved panels precisely.

In this study، formation of composite coating containing silicon carbide amplifiers on ASTM A106-Gr B steel surface using the gas tungsten arc welding process is investigated. Therefore silicon carbide particles with different volume percentages on the steel surface were placed and by changing the current density، melting and mixing process was done with the base metal. The study coating microstructure by optical microscopy and scanning electron microscopy (SEM) was conducted alongside the spot analysis. The result showed that the dendritic structure of the resulting coating contains silicon carbide is capable of reinforcing that could be improved hardness and wear behavior of the coatings. Hard coatings by a micro-hardness measurement and with slab vickers and wear behavior of the coatings was evaluated by testing the wear-trip basis. Microhardness test results showed increased hardness was created (about 650 to 1150 Vickers) compared to uncoated samples (about 200 Vickers) is. Reviews wear behavior of coatings represent significant improvements in wear behavior of is added silicon carbide reinforcement. The main wear mechanism of uncoated samples delamination wear and surface oxidation and the samples were coated with a mixture of delamination wear، surface oxidation and adhesive wear were detected.