Mechanics of Advanced Composite Structures
Volume:9 Issue: 1, Winter-Spring 2022

This article presents the study of wave mechanics in a multiferroic structure having imperfection in the structure’s interface. This article reflects the study of shear horizontal (SH) wave propagation in a layered cylindrical structure consisting of thin layers of different materials (reinforced material and piezomagnetic material) with an imperfect interface. The interface considered between both materials is mechanically imperfect. Dispersion relations are achieved analytically. Distinct graphs are drawn (numerically) to exhibit the influence of parameters like rotation, initial stress, and mechanically imperfect parameters on phase velocity. Numerical results are drawn analytically and explained for each affecting distinct parameters for materials and interface. Parametric results on the phase velocities yield a significant conclusion of which some are: (a) Performance of Piezo with reinforcement material have an influential impact on wave velocity. (b) The mechanical imperfection affects the significantly on wave velocity (c) The Reinforcement/PM stiffening can monotonically up the velocity of phase velocity.

The purpose of this paper is to introduce a simple and novel method for discussing the lateral-torsional stability of thin-walled symmetric balanced laminated beams with varying I-section. Based on the classic lamination theory and Vlasov‘s model, the total potential energy for the flexural displacements and the twist angle is established. The variational formulation is then constructed only in terms of the angle of twist using an auxiliary function. The buckling loads are finally determined by applying the Ritz method. To demonstrate the accuracy of the proposed formulation, the analytical solutions for a sample case of tapered I-beam are compared with results obtained from ANSYS's shell element. Moreover, this new procedure is very efficient in reducing the computational effort. Eventually, based on a selected load, the influences of some parameters such as the tapering ratios, transverse load position, and fiber orientation on lateral stability resistance of composite tapered I-beams under simply supported end conditions are discussed in detail. The results show that the lateral buckling resistance of composite beam with tapered I-section decreases significantly as the fiber angle in both flanges is rotated off-axis. Also, the maximum lateral buckling load for simply supported web and flanges tapered beam under uniformly distributed load is obtained by placing fibersin the web and  in both flanges.

Helmet liners are employed to prevent or reduce head injuries caused by impact loads. Liners minimize the collision damage by impact shock attenuation and absorbing the collision energy. In order to improve crashworthiness characteristics of helmet liner, in the present study, an innovative structure designed by a combination of Polyurethane (PU) foam and auxetic lattice structure is suggested to replace the conventional EPS foams usually employed in the liner section. The baseline liner section is divided into two main layers. In one layer, PU foam is used instead of EPS and in the second layer, an arrowhead pattern auxetic structure is used to improve energy absorbing capacity. By employing three kinds of PU foam with different densities and four 3D printable materials for the lattice structure, 6 combinations of the modified liner are presented. An explicit finite element method is employed to model the innovative helmet structure under impact loading and results are compared with the conventional case based on the trend of acceleration, energy absorption, weight, and Head Injury Criteria (HIC) factor.

Recently, automotive companies are interested in the usage of composite materials, because of their mechanical properties such as high strength-to-weight ratio, high stiffness, and flexibility in layout configurations. In the present work, fatigue failure was determined based on Lessard and Shokrieh progressive model in composite sub-frame subjected to fatigue loading in its service life, and a genetic algorithm was used to find the optimum stacking sequence to achieve maximum fatigue life. According to the results, [±454/012]s laminate was determined as the optimum orientation. Since the simulation results have shown usage of 90◦ layers as consecutive plies end up a progression of matrix damage and increase of stress while using ±45◦ layers as outer layers lead to increase the stiffness, toughness, and impact resistance of laminate and postpone the failure in laminate. It can be seen that the elements failed in matrix and delamination modes around 40% and 50% of total life, respectively. Moreover, before catastrophic failure, 7%, 8.55%, and 13% degradation happened in longitudinal, transverse, and shear stiffness respectively. Like wisely, 20%, 23%, and 46% degradation occurred in longitudinal, transverse, and shear strength discretely.

In this article, temperature and moisture distributions in a finite-length hollow cylinder made of functionally graded material (FGM) under transient coupled hygrothermal condition was presented. The coupled equations of heat conduction and moisture diffusion were solved employing the Fourier series expansion method along the longitudinal direction, the differential quadrature method (DQM) along the radial direction, and the Newmark method for the time domain. Finally, the history of temperature and moisture potentials was obtained. The effect of coupled and uncoupled hygrothermal loading, grading index, and hygrothermal boundary conditions was illustrated in numerical examples. Results show that the difference between the coupled model and uncoupled model is more obvious in the moisture rather than the temperature. Also, the negative grading index increases the temperature and moisture. While the effect of the positive grading index is vice versa. Moreover, to have a more accurate analysis of the transient hygrothermal process, it is important to employ the coupled model.

This study investigated the effects of different arrangements of three-dimensional fibers on polymer matrix composite thermal conductivity under heat flux boundary conditions. The thermal lattice Boltzmann based on the D3Q7 (three dimensions and seven temperature vectors) method is utilized to illustrate the thermal conductivity in 7 cases of PMC with a different arrangement of 3D fibers. Nondimensional temperature fields, isothermals, nondimensional thermal conductivity coefficient, nondimensional mean, and local temperature in 7 cases of PMCs have been investigated. The non-dimensional thermal conductivity coefficient in each PMC has been analyzed to predict optimal levels of factors affecting this simulation to maximize and minimize the heat transfer rate. The results signified that nondimensional temperature field in a PMC with the arrangement of a fiber, triplet, and triangular perpendicular to heat flux had a greater rate than a PMC with the arrangement of fibers along the way heat flux. Also, the Maximum and minimum of nondimensional thermal conductivity coefficient were in PMC with the arrangement of triplet fibers perpendicular to heat flux,  and triangular fibers along the way heat flux, respectively.

The buckling and nonlinear free vibration problems of functionally graded porous (FGP) micro-beam resting on an elastic foundation are presented through the nonlocal strain gradient theory (NSGT) and the Euler-Bernoulli beam theory (EBT) with the von-Kármán’s geometrical nonlinearity. The micro-beam is made up of metal and ceramic in which the material properties are assumed to be varied continuously in the thickness direction through a simple exponential law. Two porosity distribution models, including even and uneven distributions, are considered. The governing equation of motion is derived by employing Hamilton’s principle. The analytical expressions of the critical buckling force and nonlinear frequency of the FGP micro-beam with simply supported (S-S) boundary conditions (BCs) are obtained by utilizing the Galerkin technique and the equivalent linearization method (ELM). The reliability of the obtained results has been checked. Effects of the power-law index, the porosity distribution factor, the length-thickness ratio, the material length scale parameter (MLSP), the nonlocal parameter (NP), and the coefficients of the elastic foundation on the buckling and nonlinear free vibration responses of the FGP micro-beam are investigated and discussed in this work.

In this paper, the free vibration analysis of laminated composite and sandwich, cylindrical and spherical shells is presented using a new higher-order shear and normal deformation theory. The novelty of the present theory is that it includes the effects of both transverse shear and normal deformations along with higher order expansions of displacement field. A fifth-order polynomial type shape function is used in the in-plane displacements to represent the effect of transverse shear deformation for the first time whereas transverse displacement is a function of x, y, and z coordinates to account for the effect of transverse normal deformation. The equations of motion are derived using Hamilton’s principle. Navier’s solution technique is employed to obtain the non-dimensional fundamental frequencies. To validate the accuracy of the present theory, the present results are compared with other higher-order theories available in the literature. It is observed that the values of fundamental frequencies obtained using the present theory are in close agreement with those available in the literature.

Due to the excellent mechanical properties, availability, and low cost, natural fiber is considered as potential reinforcement to make composite for many applications. In this study, the mechanical properties of jute-bamboo natural fiber based polymer composites are investigated both experimentally and numerically. Another attempt has been made to fabricate sports and safety equipment such as skateboards and helmets and investigated its mechanical performances. The materials were chosen epoxy resin as the matrix and woven jute and bamboo fiber as reinforcement. Hand layup techniques were used to fabricate the composites. The composites thus made were tested for their mechanical properties like the tensile test, flexural test, and impact test. Experimental results indicated that by incorporating the optimum amount of jute and bamboo fibers, the overall strength of the composite can be increased. Tensile strength; flexural strength and impact strength of composite sample JB31 are found to be higher 49.89 MPa, 45.43 MPa, and 132 J/m2 respectively. Based on the test results and cost analysis, these composites can be used as the replacement of traditional material for making skateboards and safety helmets. A numerical procedure based on 3D modeling was carried out to evaluate the overall behavior of these composites. Modeling is carried out in Solid works and imported to ANSYS software. The analysis results were found to be closer to the experimental results.

In this research, thermal variation and internal pressure effects on stresses and strains of the creep behavior of composite laminates are investigated. Schapery's viscoelastic approach as a nonlinear model is used by Prandtl‐Reuss theory and Mendelson's approximation to explain the stress/strains creep treatment. History of the radial, circumferential, and axial creep stresses and strains of a laminated composite cylindrical shell made of the E-glass/Vinylester laminated composites are studied and examined. Different laminated sequences of lay-ups, linear variation of thermal loading, various composite materials accomplished with internal pressure loading are investigated. For this purpose, two laminated lay-ups as [ / / / ] and [ / / / ] are selected, and Schapery integral nonlinear viscoelastic model of creep stress and strain approach for the constitutive equation is used. It was believed that the circumferential creep strain and absolute values of axial and radial creep strains are increasing with time and Also, creep stresses/strains in the multilayer composite cross-ply [ / / / ] is more than the [ / / / ] laminated composite cylindrical shells.

In this paper, a generalized solution for 1-D steady-state thermo-mechanical analysis of the FG rotating hollow spherical body is presented. Deformation and stresses are calculated for a spherical body subjected to rotation, gravitation force, and uniform heat generation. Temperature distribution with uniform heat generation to the spherical body is assumed to vary along the radius. General thermal and mechanical boundary conditions at the inner surface and outer surfaces of the hollow spherical body are applied. Material properties are assumed as a power function of the radius with grading indices ranging from -2 to 3. Governing differential equation for the FG spherical body is developed and solved analytically. The obtained results are verified with benchmark results and are found to be in very good agreement. The result shows that deformation and stresses in the FG body are less compared to the homogeneous material body and the same is reported to decrease with increasing value of the grading parameter.

The development of polystyrene composites, by solvent casting method, with iron filling waste as fillers is considered to improve the mechanical, crystallographic, and microstructural properties for definite uses. Tensile tests were conducted based on the ASTM D638-10 standard. X-ray Diffraction (XRD) analysis and microstructural analysis were also conducted. The Young’s modulus increased (from 335.2 N/mm2 to 1131.3 N/mm2) with increasing filler concentration (0 – 15 wt%) and vice versa occurred for elongation at break (from 4.9 mm to 1.6 mm). XRD revealed that there is a good structural interaction between the iron filings particles and the polystyrene based resin (PBR) matrix. The composites combine the amorphous and crystalline natures of polystyrene and the iron filings respectively. There was also no chemical reaction observed, but the development of synergistic structural reinforcement in the polystyrene matrix. Microstructural analysis revealed that a good dispersion and distribution of iron filings particles in the polystyrene matrix. The composite with 15% filler had the best interfacial adhesion and the proper mix of the particles-matrix system.

In recent years, the use of various polymer composites in the aerospace, marine, and automotive industries have expanded due to their low weight and high mechanical strength. Due to hard phases and layered-type material structure, problems like poor surface quality, high cutting forces, and severe tool wear occur in the drilling of carbon fiber reinforced composites. A method that can reduce the mentioned effects in CFRP drilling is using ultrasonic waves in the drilling. In this paper, the idea of using a non-rotating vibratory tool ultrasonic method for drilling CFRP has been introduced and the effect of exerting ultrasonic waves on non-rotating drilling tool has been studied. The composite specimens were prepared by the layering method under load. The design of experiments using the Taguchi method was carried out, the optimal drilling parameters were determined, and the effects of ultrasonic on the surface roughness, surface quality (delamination, cracks, un-cut fibers), and cutting forces were investigated. The results indicated that ultrasonic waves in CFRP drilling could significantly reduce surface roughness (up to 49% surface roughness improvement) and the average axial force could decrease up to 57% compared with the condition that no ultrasonic waves have applied. Delamination of the drilled surface also decreased with the use of ultrasonic waves. This indicates that the idea of non-rotating ultrasonic tool can have similar effects as a rotating ultrasonic tool in drilling CFRPs.

In the present paper, for the first time, the contact problem of a rigid cylindrical indenter and a laminated composite beam is solved using an assumed contact stress approach. Results are presented for contact force - contact length relation and contact stresses. Then, the results of the analysis are generalized to determine the low velocity impact response. The close agreement observed between the present results and those which existed in the literature, confirms the validity and the accuracy of the present analysis. Performing a parametric study, the effects of some important parameters on the indentation and the low velocity impact responses of the composite beam are investigated and discussed. The results reveal that the lay-up [90/90 90/90] gives the maximum contact length and the minimum contact pressure, but, conversely, the lay-up [0/0/0/0] produces the minimum contact length and the maximum contact pressure. The results of the present research can be of great importance in the design and application of layered composite beams.

Air pollution is an increasing prevalence of environmental diseases. Previously, hazardous air pollutants (HAPs) on the ozone layer, which primarily constitute volatile organic compounds (VOCs), have become a major public concern. As a result, the Environmental Protection Agency (EPA) has introduced a strict regulation on the limit of VOCs content for various daily products such as paints and solvents to reduce the risk. Hence, the study aims to develop an eco-friendly coating with low VOCs content per the imposed regulation by deploying the leaves extract of Moringa Oleifera (MOE) for marine vessel protection. The formulated coating was characterized by using optical, electrochemical, and morphological analysis to study the effectiveness of its barrier property against the aggressive solution of seawater. Additionally, measurement of its VOCs content was conducted following the ASTM D2369-03. The results obtained suggested that the incorporation of 1 wt.% of MOE of C2 increased the resistivity of coating in reducing the penetration of ionic electrolytes up to 91.2% while exhibiting the traits of low VOCs content category at a value of 198 g/L.

In this paper, for the first time, the free vibrations of the conical shell with the locally attached mass are investigated. The equilibrium equations of the conical shell are written based on classical shell theory using the energy method and Hamilton’s principle. Boundary conditions are considered to be fully simply supported. According to the boundary conditions, the displacement components are written as double Fourier series expansions. Relationships of the strain-displacement and curvature-displacement are considered based on first Love’s approximation theory. The governing equations of the conical shell are solved using the Galerkin method and the natural frequencies are obtained. Also, for the first time, the effect of the attached mass using the cone differential operator and Heaviside function on equilibrium equations has been considered and its effect on the free vibration of the conical shell has been investigated. The results have been verified with the literature and ABAQUS finite element software. Finally, the effect of different parameters of attached mass including width, height, subtended angle, position, density, and elastic modulus on the free vibrations of the composite conical shell are investigated.

Some available One-Way reinforced concrete slabs show weak structural performance due to reduced flexural capacity and environmental deterioration. Some of these buildings and bridges have been severely damaged due to natural disasters such as earthquakes, fatigue of materials, and so on. Therefore, repairing and strengthening these structures using modern materials (such as high-performance composites) which have quite similar behavioral characteristics to concrete, can be vital and economical. In addition, it has other characteristics, including strain hardening behavior under tension and affordable cost. In this study, the behavior of slabs reinforced with precast Laminates of High-Performance Fiber-Reinforced Concrete Composite (HPFRCC) made of synthetic fibers was investigated with the help of full-scale test models and near-surface mount method (NSM). For this purpose, 12 specimens of the one-way slab were constructed. In the construction of these specimens, it has been used the same mixed design with characteristic strength f'c=21 MPa in accordance with the ACI318 regulation. Their dimensions are 1200×500 ×100 mm. A reinforced slab with four bars (No.8) in the tensile area was considered as the normal reference slab. The rest of the slab was weakened by reducing 50% of the tensile bars. Among weak slabs, a slab was defined as a reference slab and the other 10 slabs were reinforced with HPFRCC Laminates in the tension area. Composite Laminates were attached to the slab by epoxy grout and using the NSM method. All slabs were evaluated by a pure one-point bending test after preparation. Forces and displacements were recorded during the test process and the situation of cracks was examined. The results of this study indicated that the flexural strength of reinforced slabs compared to unreinforced weak slabs had a growth of 2 to 3 times and their displacements were limited.

Today, the use of composites has received widespread attention due to their special properties that cannot be found in alloys. Kevlar-Epoxy composite is one of the most widely used materials. In this paper, we analyze the heat transfer in rectangular fin and present an exact, Differential Transform Method and FEM solution for steady-state conduction heat transfer in rectangular composite laminates. The differential Transformation Method (DTM), is applied for predicting the temperature distribution in a rectangular composite fin. Laminate with fiber orientations of 0° is considered for the analysis. By validating the results in one composite layer, the temperature changes and heat flux in several composite layers were finally simulated in ABAQUS software and the effect of the number of composite layers and time on these parameters have been investigated. The selected composite fin’s material is Kevlar-epoxy. The results show that the exact solution and DTM predict the same trend compared to the FEM result and are very accurate and there is a good match between FEM results with DTM method and the exact solution. The thermo-geometric fin parameter (µ), the number of composite layers, and time have a significant effect on temperature distribution and heat flux. By increasing of thermo-geometric fin parameter (µ), heat flux and dimensionless variable for temperature distribution increase. When the number of layers increases, the dimensionless variable for temperature distribution and heat flux decrease along the fin. With increasing time, the temperature distribution and heat flux become more uniform and the ratio of heat flux changes decreases along the fin.