Journal of Science and Technology of Composites
Year:2017 | Volume:4 | Issue:2 |Papers Count:12

Vibrational methods is one of the common nondestructive damage detection methods for detecting the damage parameters. The most important problem of these methods is their low sensitivity to detect the damage in the presence of noise. In this article, a hybrid damage detection method has been studied to increase the robustness of vibrational method to noise. First, the primary damage location has been detected by the wavelet transform. Next, all the damage parameters including location, depth and intensity of damage have been identified by the model updating process based on the Genetic Algorithm. The signal based on the strain energy ratio in intact and damaged states has been examined to primarily and approximately detect the location of damage thought applying wavelet transform. Also the selected error function in the updating process is based on the strain energy difference between these two states. Using the proposed method leads to raise level of robustness in the presence of noise, also the solution performs faster than the prior methods with the less computational cost. In this work, the solution robustness against noise in traditional model updating method and the proposed hybrid method based on the wavelet transform and updating process has been compared together. The case study has been the laminated composite plate with the delamination damage.

In the present study, Mg–20 vol% SiC nanocomposite powders were produced by mechanical milling. The effect of milling time on the microstructural characteristics of nanocomposite powders during mechanical milling was investigated. The structural evolution during milling was monitored using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray mapping and X-ray diffraction methods.  Crystallite size and lattice strain of nanocomposite powders were estimated from the broadening of XRD peaks by Williamson-Hall equation. The results indicated that no intermetallic phases have been synthesized during ball milling; also X-ray map’s results exhibited a uniform distribution of reinforcement particles in magnesium matrix without any agglomeration. With all this taken into account, it can be demonstrated that mechanical milling can be used for producing Mg nanocomposite with 20 percent SiC particles. In spite of all that, the observation of Fe impurity in EDS results can be a weak point of mechanical alloying rout for fabricating Mg- 20% SiC nanocomposite.

In this study, the nonlinear responses of graphene-based nanocomposite to harmonic resonances have been discussed. This paper presents results of a study aimed at representing dynamic interactions in nanocomposite with simultaneous consideration of geometrical nonlinearity and energy damping effect by viscoelastic medium and internal damping. Based on nonlocal elasticity theory and invoking the nonlinear von Karman strain- displacement relations, the nonlinear governing equation is extracted using the Hamilton principle. To reduce the equation of motion to a nonlinear ordinary differential equation, the Galerkin’s procedure is implemented; then using the multiple scale method, the obtained equation is solved analytically to assess the closed form nonlinear amplitude-frequency relations relevant to graphene with simply supported boundary conditions under harmonic excitation. The detailed parametric study is conducted, focusing on the series effects of nonlocal parameter, aspect ratio and both damping coefficients (internal and external), and frequency of excitation load. The outcomes show a hardening nonlinearity effect for the primary resonance as well as illustrate some phenomena different from the linear vibration.

The aim of this paper is to study the free vibration of composite rectangular piezoelectric nanoplate subjected to an electro-mechanical loading includes a biaxial force and an external voltage based on exponential shear deformation theory and trigonometric shear deformation theory in conjunction with the nonlocal elasticity theory under the simply supported boundary condition. The nonlocal theory states that stress at a point is a function of strains at all points in the continuum. The nonlocal elasticity theory becomes significant for small length scale in micro and nanostructures. In exponential shear deformation theory andtrigonometric shear deformation theory, exponential and trigonometric functions are used in terms of thickness coordinate to include the effect of transverse shear deformation and rotary inertia.  Nonlocal elasticity theory is employed to investigate effect of small scale on natural frequency of composite rectangular piezoelectric nanoplate. It is assumed that the composite rectangular piezoelectric nanoplate made of PZT 4 composite piezoelectric material includes crystal compounds of Pb, Zr and Ti to achieve metal-ceramic and piezoelectric properties. The governingdifferential equations of the vibration of the composite rectangular piezoelectric nanoplate are derived by using the Hamilton’s principle, which are then solved by using the Navier method to obtain the natural frequencies of the composite rectangular piezoelectric nanoplate. The detailed parametric study is conducted to discuss the influences of the nonlocal parameter, biaxial force external electric voltage and geometrical ratios on the first six nondimensional frequencies of the composite rectangular piezoelectric nanoplate.

One of the designers concerns is structural failure as a result of stress concentration in the geometrical discontinuities. Understanding the effective parameters on stress concentration and proper selection of these parameters enables the designer to achieve a reliable design. In the analysis of perforated orthotropic plate, the effective parameters on stress distribution around cutouts include fiber angle, load angle, curvature radius of the corner of the cutout, rotation angle of the cutout and at last material of the plate. This paper tries to examine effective parameters on stress analysis of infinite orthotropic plate with central pentagonal cutout with imperialist competitive algorithm (ICA) introduced the optimum parameters to achieve the least amount of stress around the cutout. Like other evolutionary algorithms, ICA is becoming an important tool for optimization and other complex problem solving. The results reported in this review provide evidence of performance achievement of the ICA in terms of both computing time and quality of solution. In this paper, an analytical method has been used to Lekhnitskii theory for circular and elliptical cutouts. Finite element numerical solution is employed to examine the results of present analytical solution. Overlap of the results of the two methods confirms the validity of the presented solution. Results show that by selecting the aforementioned parameters properly, less amounts of stress could be achieved around the cutout leading to an increase in load-bearing capacity of the structure.

In this study, equal channel angular pressing (ECAP) process was used to consolidate an Al-Cu-Ti metallic glass reinforced aluminum matrix composite. The role of strengthening mechanisms in the strength of developed composite was investigated. The composite with 13 wt% of amorphous reinforcements was produced and the mechanical properties were compared with pure Al specimen which consolidated in the same conditions. Precise study of microstructural features as well as phase transformations is necessary for evaluating the role of strengthening mechanisms on mechanical properties of consolidated specimens. Hence, microstructural evolutions were examined using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) method. Also, dislocations density was calculated through equations based on the characteristics of crystalline peaks in XRD patterns. Clemex software was also used to quantify the constituents of microstructures. The densities of the consolidated samples were measured by Archimedes method. Uniaxial compression test was utilized to determine the mechanical properties. Microstructural studies and assessment of microstructural features such as grain size and stored dislocations density revealed that strain hardening mechanism play the major role in the strengthening of consolidated specimens. On the other hand, presence of microstructural defects led to some discrepancies between measured and anticipated strength.

In this study the vibration behavior of a laminated composite cantilever plate with an attached strip mass was studied. In order to extract flutter speed, the Rayleigh-Ritz method was used by choosing selected shape functions. In this method, strain energy of the plate is calculated and the effect of attached mass is considered as kinetic energy for the system. After reaching an eigenvalue problem then natural frequencies, the force vibration of the plate is analyzed by piston method and flutter speed for each case study is obtained. The effect of the attached mass length is shown. Moreover results have shown that flutter speed was reduced continuously by increasing the mass density. Also by considering a specific laminate with different orientation of layers flutter speed is obtained. At the end attached mass offset from clamped edge is analyzed. In this paper effect of attachment mass, mass length and mass position on plate flutter frequency is analyzed. The results obtained through this study reveal that strip mass density, attached mass length, orientation of composite layers and attached mass position can change the system critical dynamic pressure significantly.

This study investigates the effect of mixed adhesive having different modulus on single lap joint and also under peel test. The study compares these joints with that of corresponding joint containing single adhesive under two loading rate of 5 and 100 mm/min and three temperature range of room, 100oC and 200oC. Five types of adhesives were used in this assessment namely: silicon, epoxy, mixed epoxy-silicon, epoxy toughened with liquid rubber (CTBN), mixed epoxy toughened with liquid rubber (CTBN)–epoxy. Result indicated better shear strength performance by mixed epoxy-silicon adhesive joint in the single lap shear at both loading speed followed by epoxy and liquid rubber modified epoxy joints. Similar assessment under the three temperature range also revealed better retention of shear strength for the mixed epoxy-silicon adhesive joint in particular at 200°C. This result revealed about 65 percent reduction in strength for epoxy adhesive as against 31 percent reduction for the mixed epoxy-silicon adhesive. Peel tests showed unstable peeling behavior in all joints except joint with rubber modified epoxy toughened adhesive joint. Further assessment of peel test results showed both mixed adhesives i.e. mixed epoxy-silicon, epoxy toughened with liquid rubber (CTBN), mixed epoxy toughened with liquid rubber (CTBN) -epoxy had higher peel strength compared to the other adhesive joint tested.

This study aims to obtain mechanical properties of multi-phase composite materials with high volume fraction of inclusion. For this purpose, a new method is presented for the homogenization of multi-phase composites. A new homogenization method was developed based on a combination of the Mori-Tanaka model and the differential model. The new homogenization method was named MT-DS model which consists of four stages. In the first stage, average strain created in the inclusion is calculated. Then, based on the modified differential scheme, the stiffness tensor for the homogenized material is calculated. In the third stage, based on the Mori-Tanaka model as well as Eshelby equations, the strain concentration tensor is calculated. Finally, in the fourth stage, using the MT-DS model, the strain concentration and stiffness tensors for the homogenized material are calculated. For homogenization, according to shape of the inclusion as well as its volume fraction, the strain concentration tensor is calculated and the homogenized material is used in order to calculate the stiffness tensor. Using this method, in each stage, instead of properties of the raw matrix material, properties of the homogenized matrix material are included in the calculations. The effect of other inclusions on the adjacent inclusions is also considered. This procedure is continuously repeated until the equivalent stiffness tensor is obtained. To validate the new proposed model, obtained results were evaluated in a comparison with the results of the experiments.

Nowadays the formability of multi-layered tubes through different kinds of forming processes has been of interest to researchers due to its vast applications in aerospace, oil and petrochemical industries. This study compares cold forming and hot forming of bi-layered composite tubes via hydroforming and gas blow forming the tubes in geometrical model of a closed die bulge. The effect of these forming processes operational conditions on the bilayered copper (inside)– aluminum (outside) tubes forming, wrinkling, bursting, buckling and the thickness distribution controlling on the die profile region in various situations were investigated. Hydroforming process was executed at ambient temperature with the maximum pressure of 300 bar. The process of blow gas forming at 550oC temperature and 40 bar pressure was implemented. The expansion ratio of the bi-layered tube during the gas blow forming process exceeded 1.35 % in comparison that of hydroforming process. In addition, the die experienced burst before the fitting during the gas blow forming process. The undamaged closed die bulge was formed through 280 bar hydroforming process with the conditions of 6 mm linear loading and 1.65 mm maximum thinning.

Composites made of dissimilar metals are designed and used in components subjected to various condition such as serious mechanical force, heat and erosion. Fabrication of Al- brass hollow cylinder, as a composite bimetallic part, is an example. In this work, Al-brass bimetallic hollow cylinders were produced using vertical centrifugal casting device and effective variables were studied. To achieve this, Al melt at 1.5 and 2.5 melt-to-solid volume ratio was cast into 100-400oC preheated cylindrical brass bush rotating at 800 and 1600 revolutions per minute (rpm) respectively and the interface characteristics were investigated. The results of scanning electron microscope (SEM) showed that the achieved interface consisted of four discrete layers from the brass side, including Al2Cu5Zn4, Al3Cu3Zn, Al2Cu precipitates scattering in aluminum matrix and finally a-Al/Al2Cu anomalous eutectic structure near the aluminum side. Micro hardness measurements showed that the hardness of various presented phases decreases from the brass side to the aluminum side.

In this article, elastoplastic properties of polymeric nanocomposites embedded with carbon nanotubes (CNTs) are explored with emphasis on the meso-scale phenomena. To this end, a combination of finite element method and micromechanics is implemented. Accordingly, at first, considering the non-bonded nature of nanotube/polymer interactions, a multiscale finite element method is employed to replace the matrix, CNT, and polymer atoms neighboring it with a perfectly bonded equivalent nanofiller. Subsequently, nanocomposite stress-strain curves are extracted based on the mean field homogenization approach. Using this model, the effects of CNTs orientation and their agglomeration on the mechanical behavior of nanocomposite samples are thoroughly studied. Moreover, it is found that to have an efficient reinforcing effect, the CNT length should be greater than 10 nm. On the other hand, it can be concluded that there is an optimum value of this parameter (i.e. 300 nm) above which, there is no any extra stiffening effect. Furthermore, regarding the CNTs agglomeration, it is revealed that although, theoretical investigations show that increasing CNT volume fraction(VF) leads to an increase in the stiffness, occurring this phenomenon can have a deteriorative role in terms of influencing the mechanical behavior of these nanocomposites at higher VFs.