Mechanics of Advanced Composite Structures
Volume:8 Issue: 1, Winter-Spring 2021

This paper investigates the influence of reinforcement sheet on the bending strength of corrugated composite panel by numerical and experimental analysis based on three-point bending tests in both longitudinal and transverse directions. In the numerical analysis, Hashin failure criterion was used to detect the failure, and an instantaneous material properties degradation model via a VUSDFLD subroutine developed in the commercial software ABAQUS was employed to simulate the behavior of the panel after damage initiation. At first, the adequate position of the reinforcement sheet, which improved bending strength of the panel, is discovered among some proposed positions by numerical analysis. Then, the desired panel with optimum reinforcement sheet as an improved panel and a panel without the reinforcement sheet as a base panel were investigated by numerical and experimental analyses and the results were compared with each other. The results showed that for the longitudinal direction, adding a reinforcement sheet has an unfavorable effect on the bending strength to weight ratio of the panel, but for the transverse direction, it increases the bending strength to weight ratio significantly. Furthermore, the experimental results demonstrate that using Balsa wood as a core in the corrugated panels also leads to increasing the bending strength to weight ratio. All in all, it can be found from finite element analysis that the VUSDFLD subroutine is adequate for quick damage analysis with acceptable accuracy.

In this study, an analytical solution is presented based on the voltage feedback control method for the two-dimensional electro-elastic static response of functionally graded piezoelectric material (FGPM) cylinders. Using first-order shear deformation theory as well as first-order electric potential theory and applying the energy method, a differential equations system is extracted, which is solved as a classical eigenvalue problem. The results show the significant impact of heterogeneity on the electromechanical behavior of the cylinders. Furthermore, control gain affects the electric potential and electromechanical behavior of the head where the voltage is applied. The present research also introduces an analytical solution with no limitation to specific conditions in cylinder heads and without any need for convergence check. Moreover, the results show that any changes in cylinder head conditions affect the behavior of FGPM cylinders. The results were compared with those from the finite element method (FEM), leading us to a reasonable agreement.

In this paper, a magnetostrictive material (MSM)-based energy harvesting device is proposed. The device is made up of a steel beam laminated with Metglas 2605sc as the magnetostrictive material; the device undergoes mechanical strain due to the external base excitation. The mechanical strain yields in a magnetic field around the beam. A pickup coil is surrounded around the beam which converts the magnetic field into electrical current. The equation of motion is derived based on the nonlinear Euler-Bernoulli beam theory to account for large deflections. Kirchhoff and Faraday's laws are also benefited to couple the mechanical, magnetic and electrical fields. The equation is discretized based on the Galerkin method and numerically integrated over time. Energy conservation is examined and the response in the frequency domain is obtained. In the case of initial displacement, in the absence of mechanical damping, vibration amplitude attenuates as the electrical current induces in the pickup coil; this was attributed to the attenuation of the total mechanical energy of the beam as it was harvested from the pickup coil. The temporal response was fitted to that of a single degree of freedom mass-spring-damped and the equivalent damping ratio was determined. The attenuation rate was studied with different values of resistance and the number of turns in the pickup coil and the relation between these two factors was obtained to maximize the output electrical power.

The bending behavior of foam-filled double (FFD) tubes was studied in this study. The goal was to create an optimal structure that could absorb the most energy while weighing the least. On aluminum FFD tubes composed of inner and outer tubes (1100 aluminum alloy) and a composite foam core (with A356 cast alloy base and 0.6 g/cm3 density), three-point bending tests were conducted. Additionally, a finite element model of tube bending was developed and its outputs were validated using experimental data. Following that, the response surface methodology (RSM) was used to (numerically) investigate the influence of inner and outer tube diameters, inner and outer tube thickness, and foam density on bending energy and weight of FFD tubes. The impact of the investigated factors was investigated using analysis of variance (ANOVA). Finally, RSM was used to compute the best values of the parameters that result in the maximum energy absorption in bending and the lightest weight of the FFD tube. The optimization process resulted in a 141.4% increase in absorbed bending energy and a 4.63% reduction in the FFD composite tube's weight (in comparison to the initial design of the FFD tube).

Low weight and high strength requirements are prime target design objectives in strength demanding applications. Skillful design of low density, low weight and eco-friendly natural fiber composites could provide an alternative material route to the actualization of lighter structures. The present study proposed ANN-FEM computational framework for the macro-mechanical analysis of multi-oriented Plantain Empty Fruit Bunch Fiber Laminate (PEFBFL) and Plantain Pseudo Stem Fiber Laminate (PPSFL). Control factors were numerically varied using Finite Element Method (FEM) and the resultant FEM models which encapsulated material properties of the laminate was streamlined into Artificial Neural Network (ANN) training scheme. A standard feed-forward backpropagation network was adopted and the ANN model consists of stacking sequence, laminate aspect ratio and fiber orientation as input variables while the selected network outputs variables include average stress and displacement. The laminate constitutive equation was developed which enabled the establishment of laminate load deformation affiliation and equivalent elastic constants. The damage onset for individual lamina was detected by the maximum principal stress theory and the overall laminate strength of 40.12 N/mm^2 was obtained for PEFBFL and 32.16N/mm^2 for PPSFL. On the whole, there was steady reduction in laminates elastic modulus which points to compromised stiffness in material principal axis arising from gradual failure of the plies, this trend continued until the last ply failure occurred in ply 3 and 4 at 90 degrees in tensile mode of transverse direction. Stresses and displacements observed using CLT agree very closely with predictions of ANN.

Metal matrix composites (MMCs) are now gaining their usage in aerospace, automotive industries because of their excellent engineering properties like low wear rate and high strength to weight ratio. MMCs are hardly machined due to the presence of hard particles in the base phase, such as silicon carbide particles. In this paper, the effect of several factors (spindle speed, depth of cut, feed rate and weight percent of silicon carbide) have been investigated on the parameters of surface roughness and cutting force in the turning operation of AL7032 composite reinforced with SiC. Using the Minitab software and Taguchi method, the design of experiments was carried out in nine experiments in two types of dry machining and machining using mineral oil. Also, analysis of variance and signal-to-noise ratio (S/N) were used to compare the machining conditions and the effect of each input parameter on surface roughness and cutting force. Analysis of variance shows that the weight percentages of silicon carbide and depth of cut have the greatest effect on the surface roughness. On the other hand, the main factors affecting cutting force are the depth of cut and feed rate. It was also found that the use of mineral oil during machining has a significant effect on reducing surface roughness and cutting force.

In this paper, we built a mathematical model to study the influence of the initial stress on the propagation of waves in a hollow infinite multilayered composite cylinder. The elastic cylinder assumed to be made of inner and outer thermo piezoelectric layer bonded together with Linear Elastic Material with Voids (LEMV) layer. The model described by the equations of elasticity, the effect of the initial stress and the framework of linearized, three-dimensional theory of thermo elasticity. The displacement components obtained by founding the analytical solutions of the motion’s equations. The frequency equations that include the interaction between the composite hollow cylinders are obtained by the perfect-slip boundary conditions using the Bessel function solutions. The numerical calculations carried out for the material PZT-5A and the computed non-dimensional frequency against various parameters are plotted as the dispersion curve by comparing LEMV with Carbon Fiber Reinforced Polymer (CFRP). From the graph, it is clear that those are analyzed in the presence of hydrostatic stress   is compression and tension.

In this study, a weighted sum, consisting two non-dimensionalized quantities critical buckling force and natural frequency, is employed to maximize the objective function for a laminated composite circular cylindrical shell. The function is considered to find the optimum solutions as the goal. Orientation angels of fibers are mentioned in a well-known configuration as candidate design, and critical buckling force and natural frequency values are derived with the first order shear deformation theory. The composite shell is considered with 8 layers, also the boundary conditions are assumed to be fully simply support and to satisfy boundary conditions displacement and slope components are defined in form of double Fourier series. After combination of differential operators and Fourier series, eventually the matrix L is found and Galerkin method gains function values. For this purpose, a program based on MATLAB is employed for the process. Validations of numerical results show that the used method is moderately satisfactory and acceptable in predicting the critical buckling force and the natural frequency of the shell in comparison with other works. As the conclusion, the effect of different weighting ratios, shell length-to-radius ratios, and shell thickness-to-radius ratios on the optimal designs are investigated and the results are compared.

In this study, different methods of pultrusion including the out-of-mold and in-mold ultraviolet (UV)-cured and thermal pultrusion methods were investigated by comparing the mechanical and physical properties of the manufactured glass fiber-reinforced composite rods. The experimental results showed that the specimens fabricated by the UV-based methods were cured more uniformly and six times faster compared to the specimens made by thermal pultrusion. However, the specimens fabricated using the out-of-mold methods had higher diameter expansion and void content due to the lack of mold pressure during the curing process. Moreover, the mechanical responses of the specimens manufactured by different pultrusion methods were compared by conducting quasi-static tensile and low-velocity Charpy impact tests. The quasi-static tensile and Charpy impact strengths of the in-mold UV-cured specimens were 15.2% and 34.8% higher than those of the out-of-mold UV-cured specimens and 6.7% and 7.4% higher than those of the thermal-cured specimens, respectively. Furthermore, the fracture surfaces of the specimens were analyzed using SEM photography.

In this study, the characterization of Thevetia Peruviana shell powder and Thevetia ash powder incinerated at various temperatures (400, 500, 600, 700, 800 and 900ᵒC) is presented. The Thevetia shells were sourced, sun dried for three days and thereafter grounded into powder. The process of making the ash involves heating the powder to the desired temperature followed by conditioning it at the same temperature for 3 hours and then cooling to a room temperature in the furnace. Elemental compositions of both Thevetia shell powder (TSP) and Thevetia ash powers (TAP) were determined using SEM-EDS analysis. The crystallinity, as well as the phases present, was evaluated with the aid of X-ray diffraction (XRD) and the results revealed that TSP is completely amorphous while TAP showed some level of crystallinity depending on the ashing temperature. Through Fourier Transform Infrared (FTIR), functional groups peculiar to TSP and TAP were elucidated which characterize both the shell powder and the ash samples. Thermal stability of the TSP and TAP was studied using differential scanning calorimetry in the temperature range (25-350ᵒC) and the absence of volatile matters and moisture were observed in the ash samples. Scanning electron microscopy study of the samples showed that TSP image is smooth without porous structure while TAP images are fine, rough and porous, thus making the ash suitable filler materials in polymer matrix composites. Finally, Thevetia powder ashed at 600ᵒC has proven to be the best candidate filler material in the polymer matrix due to its high silica to alumina ratio as well as its characteristic morphology.

In the present work, the mechanical properties of the Halloysite nanotube (HNT) and Nano-Alumina particle additions in glass-epoxy nanocomposites are investigated experimentally. The composite specimens for tensile, flexural, interlaminar shear strength (ILSS) and impact tests are prepared by vacuum bag moulding process and tested in accordance with the ASTM standards. HNT/Nano-Alumina particle contents are varied from 0 to 4 wt. %, while the weight fraction of glass fiber is kept constant at 60%. The strength values of the respective tests are obtained and compared graphically to study the effect of nanoparticle type and content on the mechanical properties. From the experimentation and subsequent result analysis, considerable improvements in the mechanical properties are observed with the addition of nanoparticles as compared to neat composites. The 3 wt.% addition of HNT in the nanocomposites resulted in increase in tensile strength, elastic modulus, flexural strength, flexural modulus, ILSS and impact energy values by 12.7%, 6.96%, 5.46%, 4.49%, 7.44% and 119.3% respectively in comparison with the same weight percentage of Nano-Alumina. HNT modified composites reveal an improvement in mechanical properties, hence qualifying it as a most promising cost-effective reinforcing filler for glass-epoxy composites. Further, the SEM micrographs of fractured surfaces are analyzed to study the failure mechanisms and fracture morphologies of higher loaded composites (4 wt.%) and understand the reason for decline in mechanical properties.

In this paper, a different method, incremental load technique in conjunction with dynamic relaxation (DR) method, is employed to analyze the buckling behavior of composite plates reinforced with functionally graded (FG) distributions of single-walled carbon nanotubes (SWCNTs) along the thickness direction. The properties of carbon-nanotubes reinforced composite (CNTRC) plate were determined through modified rule of mixture. The nonlinear governing relations are obtained incrementally in the form of partial differential equations (PDEs) based on first-order shear deformation theory (FSDT) and Von Karman nonlinear strain. In the proposed method, for finding the critical buckling load, the mechanical loads are applied to the CNTRC plate incrementally so that in each load step the incremental form of PDEs are solved by the DR method combined with the finite difference (FD) discretization technique. Finally, the critical buckling load is determined from the load-displacement curve. In order to verify the accuracy of the present method, the results are compared with those available in the literatures. Finally, a detailed parametric study is carried out and results demonstrate that the change of carbon nanotube volume fraction, plate width-to-thickness ratio, plate aspect ratio, boundary condition and loading condition have pronounced effects on the buckling strength of CNTRC plates. It is seen that for all types of loading, boundary conditions and both cases of with and without presence of elastic foundation the FG-X and FG-O have the highest and lowest values of buckling loads.

Top-hat hollow-section beams are widely used in passenger vehicle’s body-in-white structure because of their proper shape for the montage process and also crashworthiness advantages. Hollow section beams with top-hat cross-section are mostly employed in structures like B-pillar, rocker sill, and roof rail which are engaged in side impact collisions. In the present investigation, simplified top-hat beams are developed based on a conventional B-pillar with the aim of improving energy absorption characteristics. Reinforcements are conducted by employing fiber glass-epoxy composite material. Three types of reinforced beams are presented which are either improved by composite-laminating, or by installation of an extra composite-made internal reinforcement. Experimental tests are performed in quasi-static three-point bending condition and based on results, a FE simulation is developed using LS-Dyna explicit code. Specimens are compared based on peak load, total energy absorption (TEA) and specific energy absorption (SEA) amounts. Also, to illustrate the extent of improvements, a not-reinforced top-hat beam is experimentally subjected under three-point bending test. Results depict a significant difference between the performance of beams reinforced by different methods. Comparison between specimens, considering their respective load-displacement diagram and crashworthiness characteristics, show that applying composite laminates to the inside surface of a hat-shaped beam would produce a beam with satisfying flexural behavior.

In the current study, the modified shear deformation theories are used for analyzing the electro-mechanical vibration of inhomogeneous piezoelectric nanoplates in conjunction with the nonlocal elasticity theory. These theories not only satisfy transverse shear traction-free conditions on the top and bottom surfaces of the plate but also consider exponential and trigonometric distributions for the transverse shear deformations. Heterogeneity of the structure is supposed to be in the thickness direction of the nanoplate and it is assumed that the simply supported functionally graded piezoelectric nanoplate is subjected to a biaxial force and an external electric voltage. The governing equations of the vibrating functionally graded piezoelectric nanoplate are obtained by using Hamilton’s principle, which are then solved by using Navier’s method to achieve the vibrational behavior of the structure. The detailed discussion is presented to explain the influences of the various parameters on the natural frequencies of functionally graded piezoelectric nanoplates. It is concluded that increasing gradient index parameter, nonlocal parameter, thickness ratio and compressive forces lead to a decrease in natural frequencies while rising tensile forces and aspect ratio increase the natural frequencies.

Nowadays, polymers in cement-based mortars are frequently used to improve mechanical properties and increase the adhesion between the repair mortar and concrete substrate. In the present study, the mechanical properties of the polymer-modified mortars in the various ages were evaluated using the semi-destructive and in-situ “friction-transfer” and “pull-off” tests. For this purpose, the repair mortar was prepared with various styrene butadiene rubber (SBR) latex-cement ratios (10, 15, and 20%) and tested at 7, 42, and 90 days of age. The correlation between the results from semi-destructive tests and the compressive and flexural strengths of mortars were determined. The calibration diagrams were presented to determine the mechanical properties of the mortars. Also, the effect of the polymer was investigated on the shrinkage and bond strength between mortars and concrete substrate. Finally, the stress and cracks obtained from the “friction-transfer” and “pull-off” tests were presented using the finite element analysis software (ABAQUS). There was excellent congruence between the results from the above tests and the finite element analysis. There was a high correlation between the results of the “friction-transfer” and “pull-off” tests. Therefore, the simple and inexpensive “friction-transfer” device can be used instead of the expensive “pull-off” device. Besides, the significant correlation between the mechanical properties of the polymer-modified mortars and the above tests shows the suitability of the semi-destructive methods in investigating the mechanical properties of the mortars.

In this research article, thermal and hygrothermal stress analysis of composite layered and sandwich plate having one dimension infinitely long and simply supported on the edges is presented using a new fifth-order theory.  The proposed theory considers, the effect of thickness stretching. The present theory uses a polynomial shape function to account for transverse shear deformation using the expansion of thickness up to the fifth-order while to consider the effect of thickness stretching the derivative of shape function is used in the transverse displacement. In this theory, the shear strain variation is assumed to be parabolic across the thickness.  The present displacement field satisfies zero shear stress condition both at the top and bottom surfaces and avoids the use of a shear correction factor.  The governing equations are derived using the virtual work principle.  For solution of problem, Navier’s solution technique is used.  The results generated using the present theory are compared with the existing elasticity solution wherever it is available.  However, many results for the cylindrical flexural analysis of laminated and sandwich plates subjected to environmental loading are presented for the first time in this paper.

This study presents a robust hybrid meta-heuristic optimization algorithm by merging Modified Colliding Bodies Optimization and Genetic Algorithm that is called GMCBO. One of the inabilities of Colliding Bodies Optimization (CBO) is collapsing into the trap of local minima and not finding global optima. In this paper, to rectify this weak point, at first, some modifications are accomplished on the CBO process and then by using the concept of the genetic algorithm able to enhance the convergence rate, establishing a balance between the feature exploration and exploitation processes, the increasing power of finding global optimal design and escaping of local optimal. For evaluating the performance of the proposed method, the optimal design of laminated composite materials has been considered. Compare the results of structural analysis with GMCBO and other optimization methods shows a high convergence rate and its ability to find the global optimal solution of the proposed algorithm for structural optimization problems.

In the present study, fracture response of centrally cracked symmetric angle ply laminated composite plates subjected to biaxially applied tensile, shear and tensile and shear combined stresses by implementing well established extended finite element method (XFEM) are studied. Typical numerical results are presented in terms of mixed mode stress intensity factors (MSIFs) to examine the effects of, different biaxial load factors, crack angles, crack lengths, the eccentricity of the crack in X and or Y directions and fiber angle under the action of different types of biaxial stresses. The effect of loadings on the crack growth and crack propagation direction and their effects on the MSIFs using global tracking crack growth algorithm is also presented. The results of the present investigation will be useful for accurate prediction of fracture response of cracked composite structures, crack growth and crack propagation behavior which ultimately effects on the structural safety and integrity of the composite structures.