Mechanics of Advanced Composite Structures
Volume:8 Issue: 2, Summer-Autumn 2021

In the present paper, the exact modeling and frequency analysis of the mass sensor nanobeam are investigated based on a higher-order elasticity theory with taking into account the longitudinal discontinuity. The energy equations of the beam are expressed considering discontinuity, and finally, the vibration equations and boundary conditions of the non-uniform nanobeam are derived using Hamilton’s principle. By the implementation of an analytical solution, the number of shape functions equal to longitudinal discontinuities is assumed. Then, by expressing the compatibility and boundary conditions, the frequency equation of the discontinuous nanobeam is obtained and solved. Effects of different parameters such as sensed mass and size effects on the frequency behavior of the nanobeam are investigated at various vibrational modes. The results show that accurate modeling of discontinuous nanobeam is important. Also, Changing the position of the sensed mass to the free end of the nanotube increases the sensing feature of the beam, and the size effect reduces it.  The size effect reduces the frequency and increases the amplitude of the mode shape, especially at higher vibrational modes. The results also show that the sensing feature of the mass sensor nanobeam is more prominent at higher modes of vibration, and therefore the use of mass sensor nanobeam at higher vibrational modes is recommended.

In this paper, the aim is to propose a new model to obtain the mechanical properties of sand/glass polymeric concrete including modulus of elasticity and the ultimate tensile stress. The neural network soft computation, support vector machine (SVM), and active learning method (ALM) that is a fuzzy regression model are all used to construct a simple and reliable model based on experimental datasets. The experimental data are obtained via the tensile and bending tests of sand/glass reinforced polymer with different weight percentages of sand and chopped glass fibers. The extracted results are then used for training and testing of the neural network models. Two different types of neural networks including feed-forward neural network (FFNN) and radial basis neural network (RBNN) are employed for connecting the properties of the sand/glass reinforced polymer to the properties of the resin and weight percentages of sand and glass fibers. Besides the neural network models, the SVM and ALM models are applied to the problem. The models are compared with each other with respect to the statistical indices for both train and test datasets. Finally, to obtain the properties of the sand/glass reinforced polymer, the most accurate model is presented as an FFNN model.

In this paper, a solution procedure is presented for free vibration of combined cylindrical-conical composite shells including the shear deformation effect of the shell. The solution presented in this study is obtained directly from the governing equations for five displacement components according to Hamilton’s principle. This solution is in the form of a power series in terms of a particularly convenient coordinate system. In this study, the effects of geometry and material parameters on the natural frequencies are investigated. Also, to illustrate the validity of the present solution procedure, analytical results are verified with many studies and compared with those of the present numerical ABAQUS analysis. The outcomes showed a good agreement between the obtained results. The novelty of the present study is incorporating the transverse shear deformation in calculating the natural frequencies of the joined cylindrical-conical shells. In previous literature, this topic has not been studied in such a wide scope.

In this research, the preparation conducting polymer poly(O-Toluidine) emeraldine salt (ES) doped with HCL (POT/HCL) by oxidizing polymerization external doping by DBSA the effect of the solvent on the electrical characterization of Poly (O-toluidine) was studied.POT (EB) powder was completely dissolving in all solvents such as chloroform, formic acid, Toluene, and meta-cresol. The morphology and composition of POT were measured by SEM and EDX. Two-probe techniques were used to calculate electrical conductivity; an interdigitated finger electrode was used to measure electrical conductivity.  The effect of temperatures on electrical conductivity was also studied to provide heating in the range of (303-373 K) and used to the found activation energy of (POT) in a different solvent.

In this work, two-step sintering (TSS) of Al/8wt%TiC with microwave heating has been performed successfully. The composites were fabricated by uniaxial pressing of mixed Al and TiC powders and subsequent sintering in an argon atmosphere at different sintering schedules. The observational studies show a well-dispersed TiC reinforcement in the Al matrix. According to the results, relative density and strength increased from about 95.5% and 90 MPa to 97% and 100 MPa for sintered composites at 640 °C for 2 h and 600 °C for 10 h with single step sintering by a conventional method, respectively. Also, applying the TSS method enhanced the values from 97% and 101 MPa for conventional TSS (T1=640, T2=600 °C) to 98% and 211 MPa for microwave-assisted TSS technique. It can be related to the more effective activation of the surface mechanism during fast microwave heating than the tube furnace dilatory heating. Consequently, decreasing the sintering temperature (T2) can proceed with densifying mechanisms.

The present paper describes the study of nonlinear bending characteristics of smart Functionally Graded (FG) plates combined with piezoelectric composites. Material properties for the base FG plate are considered to vary along the thickness direction following the power-law principle. In this analysis, commercially available active fiber composite (AFC) material is utilized as the piezoelectric composite. A finite element (FE) model is made for the FG plate combined with AFC material. Simulation models for the smart FG plates are also developed using ANSYS software taking into account the effect of temperature on the material properties. Nonlinear deformations for the smart FG plate for various values of power index and different boundary conditions are presented for thermo-mechanical loading conditions considering the properties to be temperature as well as position dependent. Efforts are made to examine the performance of AFC patches towards control of nonlinear deflections. Various configurations for the smart FG plates are considered and the best location for placing the AFC patches is identified based on the efficiency of AFC material for controlling nonlinear deformations of the FG plates.

This paper presents the thermal post-buckling analysis of functionally graded annular sector plates subjected to uniform temperature rise for the first time. The plate is consisting of a composed ceramic-metal material which the volume fraction of the component materials is assumed to change continuously through the thickness via a simple power law distribution.3D elasticity theory and non-linear Green strain tensor are used to derive the governing equations which are extended based on the principle of virtual work and solved via the graded finite element method. The non-linear equilibrium equations are solved by applying the Newton–Raphson procedure. The influences of material gradient exponent, various sector angles, thickness ratio, aspect ratio on the thermal post-buckling response of FGM annular sector plates subjected to uniform temperature rise are presented. Results indicate that the thermal post-buckling response of FGM annular sector plates can be considered as a bifurcation point following a stable post-buckling path.

In this study, a finite difference method is presented for longitudinal stress wave propagation analysis in functionally graded 2D plane strain media. The plane material consists of two ceramics (SiC and Al2O3) and two metals (Al 1100 and Ti-6A1-4V (TC4)) with power‐law variation for mechanical properties in terms of volume fractions of the constituents. Firstly, the governing equations of wave propagation in the functionally graded plane strain media were derived in Cartesian coordinate. It’s assumed that elastic module, density, and Poisson’s ratio are variable in all of the media. Secondly, the finite difference method was used to discretize the equations. Time step size was obtained using the von Neumann stability approach. The materials distribution effects are studied in different states and history of stress, strain, and displacement. To validate the numerical simulation, stress is compared with theoretical equations in special states. Results show that the wave propagation behavior is considerably influenced by material composition variation.

In this study, copper matrix composites reinforced by 2.5, 5.5, and 8 wt% steel nanoparticles less than 130 nm in diameter were prepared by the casting method. The steel nanoparticles were made of steel machining chips. Disc mill and ball mill instruments were used to produce nanoparticles from machining chips. Copper was melted using an induction furnace, and the steel nanoparticles were injected into the copper melt by gas gun. The nanoparticle content effect on microstructure, mechanical properties, fracture toughness, and electrical conductivity of the composites are investigated in this paper. Increasing the reinforcement content to 2.5 wt% in the produced composite increases the yield strength, tensile strength, and ductility by 20%, 49%, and 13%, respectively, and then the strengthening effects deteriorate. By increasing the nanoparticle content, elongation and ductility almost continuously increase. Maximum elongation and Charpy impact energy of 90 J and 37% are achieved in this research for the composite grade reinforced by 8 wt% of steel nanoparticles that these values are almost 8.2 and 1.2 times greater than impact energy and elongation of the pure copper sample. Furthermore, the addition of steel nanoparticles shows a little adverse effect on the electrical conductivity but dramatically improves the composite toughness.

Metal matrix composites are widely used in engineering applications because of their better mechanical properties. This review focuses on fabrication methods and fracture behaviors of aluminum metal matrix composites (AMMCs). This paper also discusses its applications. Based on the review study, it is observed that the properties of AMMC vary depending on the reinforcement used, fabrication techniques, and reinforcement disbursement in the matrix material. It is also found that the place where the composite materials are used and the difficulties behind the manufacturing processes decide the selection of reinforcements and the types of fabrication method. It is noticed that the reinforcement of AMMCs is in the form of continuous fibers, short fibers, whiskers, and particulates. The objective of this review study is to summarize the details about the techniques used for fabricating aluminum metal matrix composites, the effects of processing parameters on the mechanical behaviors of composites, the different types of test specimens, and the fixtures used to apply load for fractures experimentations of AMMC with the applications of AMMCs in various fields.

The analysis of the propagation behaviour of seismic waves in porous medium requires a mathematical backup. That is pictured here. The present study investigates the propagation behavior of Love-type waves in a poro-elastic medium. A staggered grid finite-difference (SFD) scheme in time-space domain formulation for Biot’s equation of poro-elasticity is presented and applied to the problem. Complete theoretical seismograms for the horizontal and vertical components of displacement are obtained. The dispersion curves are evaluated considering the material parameters of different models. The stability analysis of the above numerical scheme is deliberated. From different graphs, it is noticed that there is a difference in phase velocity for various models. By observing the behaviour of the curve, we can understand the nature of the composite structure.  Our outcomes also endorse that finite-difference modeling is an important numerical tool to acquire knowledge about the transmission of seismic waves in a porous medium. The agreement is excellent.

The present work deals with the experimental and finite element free vibration studies on areca leaf sheath reinforced polymer composites. In this study fundamental frequencies are obtained for five boundary conditions numerically (such as CFFF, CFCF, SSSS, CSCS and CCCC) and only for 2 boundary conditions (CFFF and CFCF) experimentally. The natural frequencies were determined using the CQUAD8 finite element of MSC/NASTRAN and a comparison made between the experimental values and the finite element solution. The effects of age of areca palm, number of layers, type of surface modification, and boundary conditions on the natural frequencies of composites were studied. The experimental values of the first, second, and third natural frequencies agree with those of the finite element solution in the case of areca leaf sheath reinforced composites under CFFF and CFCF boundary conditions. The natural frequency values increased with an increase in the number of layers, age of areca palm, and alkali percentage from 5 to 15%. Among the different boundary conditions considered, composites with the CCCC boundary condition have exhibited higher values of natural frequencies than other boundary conditions under finite element solutions.

In this work, mechanical vibration analysis of rotating bi-directional functionally graded Euler-Bernoulli nanobeams is investigated, which has not already been studied deeply based on the latest authors’ knowledge. Material properties vary along the thickness and axis directions based on power-law distribution. The nonlocal elasticity theory of Eringen (NET) is utilized for modeling small-scale effects. Different boundary conditions are considered as clamped-clamped (C-C), clamped-simply (C-S), and clamped-free (C-F). Governing equations and associated boundary conditions are derived based on minimum total potential energy, and the generalized differential quadrature (GDQ) method is employed for the solution process. Convergence and verification studies are accomplished to affirm this work, and in the continuation, the effects of various parameters, namely hub ratio, rotation speed, and power indexes along x and z directions on the dimensionless natural frequencies, are investigated. It is revealed that the decrement made by the different values of  in the natural frequency, parameter is more effective than the reduction caused by the , especially for the higher rotation speed.

This paper presents applied electric voltage performance in hydrothermal magneto flexo electric nanobeams embedded in the Winkler-Pasternak foundation based on nonlocal elasticity theory. Higher-order refined beam theory via Hamilton's principle is utilized to arrive at the governing equations of nonlocal nanobeams and solved by implementing an analytical solution. A parametric study is presented to analyze the effect of the applied electric voltage on dimensionless deflection via nonlocal parameters, slenderness, moisture constant, critical temperature, and foundation constants. It is found that physical variants and beam geometrical parameters significantly affect the dimensionless deflection of nanoscale beams. The accuracy and efficiency of the presented model are verified by comparing the results with that of published researches. A good agreement has arrived. The numerical examples are presented to explain how each variant can affect the structure's stability endurance. This type of model and its physical output show the great potential of hygro-magneto-thermo-flexo electric combination in the design of intelligent composite structures and use in structural health scanners. Recent advances in the application of nanotechnology have resulted in the manufacture of nanoelectromechanical devices. The attractiveness of them is due to their excellent and distinctive mechanical and electrical properties.

In this work, the three-dimensional mesh-free (3D-Mfree) method is used for free vibration analysis of functionally graded (FG) cylindrical panels reinforced by carbon nanotubes. The material properties of panels are considered to be changed linearly in the thickness direction, and the effective material properties of the panels are estimated by the rule of mixture. Five models of carbon nanotubes distribution, including a uniform distributed model and four FG distributed models, are considered. The weak form governing equations of motion are derived using Hamilton’s principle, and the moving least squares (MLS) approximation is used to construct the 3D-Mfree shape functions in cylindrical coordinates. Various boundary conditions are considered, and effects of boundary conditions, carbon nanotube distribution, the volume fraction of carbon nanotubes, and the panel geometry on the natural frequencies are studied. The results are compared with other results available in the literature, and a close agreement is observed.

This paper presents an experimentally validated finite element analysis of the low-velocity impact on viscoelastic laminates with consideration of large deflection and higher-order shear deformation effects in the time domain. The generalized Maxwell model (Wiechert) is incorporated into the FEM procedure to simulate the viscoelastic feature of the structure. In a geometrically nonlinear analysis, a displacement field considering higher-order shear deformation and large deflection of the laminate is assumed, and the finite element formulation is extracted. To evaluate the contact force, the modified Hertzian contact law is implemented into the finite element program. Numerical results including contact force output histories and deflections are then derived and compared with the experimental data. The obtained results show that the viscoelasticity effect and large deflection have a significant effect on the results, so they must be considered to gain a precise description of the low-velocity impact response. This model achieved good conformance with experimental results.

This paper develops the new logarithmic higher-order shear deformation theory (LHSDT) incorporating isogeometric method for free and forced vibration analyses of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) plates. In this theory, a logarithmic function is employed to approximate the distribution of shear strains along the plate thickness which satisfies the condition of zero tractions on the top and bottom surfaces of the plate. The plate is assumed to be fabricated from a mixture of carbon nanotubes (CNTs) and a polymeric matrix. The CNTs are either uniformly distributed or functionally graded (FG) along the thickness direction of the plate. The modified rule of mixture scheme is applied to estimate the effective mechanical properties of FG-CNTRC plates. The governing equations are derived from Hamilton’s principle. Furthermore, the Newmark approach is utilized to predict the temporal response of FG-CNTRC plates under different transverse dynamical loadings. The applicability and efficiency of the present formulation in predicting vibrational characteristics of FG-CNTRC plates are investigated through an extensive set of numerical examples considering different configurations of the plate. It is revealed that the computed results are in excellent agreement with other solution methods extracted by the 3D model and other plate theories. Eventually, a detailed parametric study is conducted to explore the influence of related parameters on the natural frequencies and temporal response of FG-CNTRC plates.

In this study, the buckling analysis of multilayer composite closed cylindrical shells, as well as composite grid cylindrical shells, was investigated using a high-order theory modified from Reddy’s third-order shear theory under simply supported conditions. The advantage of the present theory compared to other high-order theories is the calculation of the effect of the term of the shell section trapezoidal coefficient on relations related to displacement and strain fields, which improves the accuracy of the results. In grid shells, the discontinuous distribution of stiffness and mass of the shell between the reinforcing ribs and the distance between them is expressed by a suitable distribution function. In the case of integrated and grid cylindrical shells, the validation of the results was performed in comparison with other studies, as well as with the results of the numerical solution obtained using Abaqus software. It is shown that for the first buckling mode, the critical load first increases and then reaches a constant value and for the second buckling mode, the critical load first decreases and then reaches a constant value. Also, in the case of grid shells, by increasing the ratio of the cavity dimension to the dimensions of the whole shell, whether in single-cavity or multi-cavity mode, the present theory and finite element solution find more difference, indicating the higher accuracy of the present theory for integrated shells.