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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.17, #2)

Composite Materials: Characterization, Fabrication and Application-Research Challenges and Directions by Ahmad Varvani-Farahani (pp. 63-67).

Buckling Analysis of Laminated Composite Plates Using Higher Order Semi—Analytical Finite Strip Method by Hamid R. Ovesy; Sayyed Amir M. Ghannadpour; Mohammad H. Sherafat (pp. 69-80).

Rectangular plates made of laminated composite material because of the advantageously high strength and stiffness to weight ratio are used frequently as structural component in various branches of engineering, chief of which are aerospace and marine engineering. Design concepts of these plates that lead to the increase in the buckling load can directly lower the structural cost and/or weight. The finite strip method is one of a number of procedures which can be used to solve the buckling problem of plate structures. In the present work the main concern is with the buckling behavior of plates with simply supported ends subjected to uni-axial pure compression loads. The solution is sought by implementing the higher order semi-analytical finite strip method which incorporates additional degrees of freedom for each nodal line by using Reddy’s higher order plate theory. Therefore the current method is more universal in dealing with different plate thicknesses. In addition, in this semi-analytical finite strip method, all the displacements are postulated by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. The solution is based on the concept of principle of minimum potential energy and an eigen-value analysis is subsequently carried out. From the presented results it can be concluded that the higher order semi-analytical finite strip method is very reliable for the preliminary design of composite plates especially in the case of buckling analysis of relatively thick plates.

Keywords: Buckling analysis; Higher order plate theory (HOPT); Semi analytical; Finite strip method (FSM); Laminated composite plates

Levy Solution for Buckling Analysis of Functionally Graded Rectangular Plates by Meisam Mohammadi; Ali Reza Saidi; Emad Jomehzadeh (pp. 81-93).

In this article, an analytical method for buckling analysis of thin functionally graded (FG) rectangular plates is presented. It is assumed that the material properties of the plate vary through the thickness of the plate as a power function. Based on the classical plate theory (Kirchhoff theory), the governing equations are obtained for functionally graded rectangular plates using the principle of minimum total potential energy. The resulting equations are decoupled and solved for rectangular plate with different loading conditions. It is assumed that the plate is simply supported along two opposite edges and has arbitrary boundary conditions along the other edges. The critical buckling loads are presented for a rectangular plate with different boundary conditions, various powers of FGM and some aspect ratios.

Keywords: Buckling analysis; Functionally graded; Levy solution; Rectangular plate

Buckling and Delamination Growth Analysis of Composite Laminates Containing Embedded Delaminations by H. Hosseini-Toudeshky; S. Hosseini; B. Mohammadi (pp. 95-109).

The objective of this work is to study the post buckling behavior of composite laminates, containing embedded delamination, under uniaxial compression loading. For this purpose, delamination initiation and propagation is modeled using the softening behavior of interface elements. The full layer-wise plate theory is also employed for approximating the displacement field of laminates and the interface elements are considered as a numerical layer between any two adjacent layers which delamination is expected to propagate. A finite element program was developed and the geometric non-linearity in the von karman sense is incorporated to the strain/displacement relations, to obtain the buckling behavior. It will be shown that, the buckling load, delamination growth process and buckling mode of the composite plates depends on the size of delamination and stacking sequence of the laminates.

Keywords: Layerwise; Interface element; Delamination buckling; Composite; FEM

Unequal Faces Effect on Fracture of Composite Sandwich Beam with Flexible Core by Mojtaba Sadighi; Mahdi Saadati (pp. 111-120).

Sandwich panel higher order theory (SPHOT) which estimates core compression and face stresses is used to predict damage modes of a sandwich beam with unequal faces. It is shown that sandwich panel classical theory (SPCT) which is based on investigating of behavior of the structure with considering core shear stress in simply supported boundary conditions and neglecting shear modulus of core can not predict the failure load in the case of unequal faces when core yielding is happened. Comparing the results obtained by SPHOT, SPCT and available experimental ones shows that the higher order theory is a suitable approach to predict failure loads in this case for different damage modes.

Keywords: Sandwich beam; Composite skins; Higher order theory; Critical load; Fracture; Unequal faces

Stress Corrosion Cracking of Basalt/Epoxy Composites under Bending Loading by Mahmood M. Shokrieh; Mahdi Memar (pp. 121-135).

The purpose of this research is to study the stress corrosion behavior of basalt/epoxy composites under bending loading and submerged in 5% sulfuric acid corrosive medium. There are limited numbers of research in durability of fiber reinforced polymer composites. Moreover, studies on basalt fibers and its composites are very limited. In this research, mechanical property degradation of basalt/epoxy composites under bending loading and submerged in acidic corrosive medium is investigated. Three states of stress, equal to 30%, 50% and 70% of the ultimate strength of composites, are applied on samples. High stress states are applied to the samples to accelerate the testing procedure. Mechanical properties degradation consists of bending strength, bending modulus of elasticity and fracture energy of samples are examined. Also, a normalized strength degradation model for stress corrosion condition is presented. Finally, microscopic images of broken cross sections of samples are examined.

Keywords: Basalt/epoxy; Stress corrosion cracking (SCC); Static fatigue; Mechanical properties

A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0/θ) Laminate Systems by Alireza Shirazi; A. Varvani-Farahani (pp. 137-150).

The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0˚ and θ° plies and (0/θ) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional composite laminates as the number of cycles progresses. The proposed model enabled damage assessment of FRP (0/θ) composite laminates by integrating the fatigue damage values of 0˚ and θ° plies. A weighting factor η was introduced to partition the efficiency of load carrying plies of 0° and θ° in the (0/θ) composite lamina. The fatigue damage curves of unidirectional FRP composite samples with off-axis angles of 0˚, 30˚, 45˚, and 90˚ and composite laminate systems of (0˚/30˚), (0˚/45˚) and (0˚/90˚) predicted based on the proposed damage model were found in good agreement with experimental data reported at various cyclic stress levels and stress ratios in the literature.

Keywords: Fatigue damage; FRP (0/θ) composite system; Matrix cracking; Fiber-matrix interface; Weighting factor

Effects of Mixing the Steel and Carbon Fibers on the Friction and Wear Properties of a PMC Friction Material by Sedigheh Bagheri Kazem Abadi; Alireza Khavandi; Yosouf Kharazi (pp. 151-158).

Friction, fade and wear characteristics of a PMC friction material containing phenolic resin, short carbon fiber, graphite, quartz, barite and steel fiber were investigated through using a small-scale friction testing machine. Four different friction materials with different relative amounts of the carbon fiber and steel fiber were manufactured and tested. Comparing with our previous work which contained only steel fiber as reinforcement, friction characteristics such as fade and recovery and wear resistance were improved significantly by adding a small amount of carbon fiber. For the mixing of carbon and steel fiber, the best frictional and wear behavior was observed with sample containing 4 weight percentage carbon fiber. Worn surface of this specimen was observed by optical microscopy. Results showed that carbon fibers played a significant role in the formation of friction film, which was closely related to the friction performance. The brake pad with Steel fibers in our previous work, showed low friction coefficient and high wear rate. In addition, a friction film was formed on the surface with a relatively poor quality. In contrast, the samples with mixing the steel and carbon fiber generated a stable friction film on the pad surface, which provided excellent friction stability with less wear.

Keywords: Brake pad; Composites; Steel fibers; Carbon fibers; Friction coefficient; Wear rate

Optimum Structural and Manufacturing Design of a Braided Hollow Composite Part by Hossein Ghiasi; Larry Lessard; Damiano Pasini; Maxime Thouin (pp. 159-173).

Simultaneous material consolidation and shaping, as performed in manufacturing of composite materials, causes a strong interconnection between structural and manufacturing parameters which makes the design process complicated. In this paper, the design of a carbon fiber bicycle stem is examined through the application of a multi-objective optimization method to illustrate the interconnection between structural and manufacturing objectives. To demonstrate the proposed method, a test case dealing with the design of composite part with complex geometry, small size and hollow structure is described. Bladder-assisted Resin Transfer Molding is chosen as the manufacturing method. A finite element model of the stem is created to evaluate the objectives of the structural design, while a simplified 2D model is used to simulate the flow inside the preform during the injection process. Both models are formulated to take into account the variation of fiber orientation, thickness and fiber volume fraction as a function of braid diameters, injection pressure and bladder pressure. Finally, a multiobjective optimization method, called Normalized Normal Constraint Method, is used to find a set of solutions that simultaneously optimizes weight, filling time and strength. The solution to the problem is a set of optimum designs which represent the Pareto frontier of the problem. Pareto frontier helps to gain insight into the trade-off among objectives, whose presence and importance is confirmed by the numerical results presented in this paper.

Keywords: Optimum design; Composite material; Resin Transfer Molding; Multiobjective optimization; Bicycle stem

Design of Semi-composite Pressure Vessel using Fuzzy and FEM by Mohammad H. Sabour; Mohammad F. Foghani (pp. 175-182).

The present study attempts to present a new method to design a semi-composite pressure vessel (known as hoop-wrapped composite cylinder) using fuzzy decision making and finite element method. A metal-composite vessel was designed based on ISO criteria and then the weight of the vessel was optimized for various fibers of carbon, glass and Kevlar in the cylindrical vessel. Failure criteria of von-Mises and Hoffman were respectively employed for the steel liner and the composite reinforcement to characterize the yielding/ buckling of the cylindrical pressure vessel. The fuzzy decision maker was used to estimate the thickness of the steel liner and the number of composite layers. The ratio of stresses on the composite fibers and the working pressure as well as the ratio of stresses on the composite fibers and the burst (failure) pressure were assessed. ANSYS nonlinear finite element solver was used to analyze the residual stress in the steel liner induced due to an auto-frettage process. Result of analysis verified that carbon fibers are the most suitable reinforcement to increase strength of cylinder while the weight stayed appreciably low.

Keywords: Fuzzy decision maker; Vessel; Composite

Water Absorption and Thickness Swelling Behavior of Polypropylene Reinforced with Hybrid Recycled Newspaper and Glass Fiber by Alireza Shakeri; Ali Ghasemian (pp. 183-193).

This study aims to investigate the moisture absorption of recycled newspaper fiber and recycled newspaper-glass fiber hybrid reinforced polypropylene composites to study their suitability in outdoor applications. In this work composite materials were made from E-glass fiber (G), recycled newspaper (NP) and polypropylene (PP), by using internal mixing and hot-pressing molding. Long-term water absorption (WA) and thickness swelling (TS) kinetics of the composites was investigated with water immersion. It was found that the WA and TS increase with NP content in composite and water immersion time before an equilibrium condition was reached. Composites made from the NP show comparable results as those made of the hybrid fiber. The results suggest that the water absorption and thickness swelling composite decrease with increasing glass fiber contents in hybrid fiber composite. It is interesting to find that the WA and TS can be reduced significantly with incorporation of a coupling agent (maleated polypropylene) in the composite formulation. Further studies were conducted to model the water diffusion and thickness swelling of the composites. Diffusion coefficients and swelling rate parameters in the models were obtained by fitting the model predictions with the experimental data.

Keywords: Composite; Recycled newspaper; Water absorption kinetics; Thickness swelling

Experimental Study of RC Rectangular Liquid Containing Structures Retrofitted with GFRP Composites by R. Sadjadi; A. Ziari; M. R. Kianoush (pp. 195-207).

The continual functioning of Liquid Containing Structures “LCS” is necessary for the well being of a society. These structures are designed based on serviceability criteria such as cracking that leads to leakage. Cracks form in liquid containing structures (LCS) for different reasons such as restrained thermal and shrinkage deformations, applied external loads such as earthquake loads, etc. These cracks can create exposure condition to initiate the corrosion process in reinforcement. The effectiveness of glass fiber reinforced polymer (GFRP) composites in recovering the structural strength of damaged members is widely recognized by engineers. However, the effectiveness on the use of GFRP composites as a protecting layer to prevent the passage of liquid through the cracks has not yet been reported in the literature. This concept inspires the main purpose of the investigation in this experimental study. Cracked reinforced concrete specimens subjected to different conditions of loading such as direct tension and cyclic flexure are repaired externally using GFRP sheets. The specimens are then subjected to hydrostatic pressure using a water pressure chamber at the crack location. This study shows that the application of GFRP composites for crack remediation in liquid containing structures could be very effective under monotonic loading. However, the effectiveness under cyclic flexure especially under higher load levels is questionable.

Keywords: Liquid containing; Reinforced concrete; Repair; Tank; GFRP; Cracking

Flexural Upgrading of Steel-Concrete Composite Girders Using Externally Bonded CFRP Reinforcement by Mohammad Z. Kabir; M. Eshaghian (pp. 209-224).

This study focuses on the flexural performance of composite steel-concrete beam girders retrofitted with CFRP. The current work is a numerical study of the load carrying capacity of a section which is strengthened by externally bonding of CFRP to the tension flange. At the primarily stage of the work, the model is verified by published experimental data. The three dimensional interactive failure Tsai-Wu criteria was implemented to retrofitted composite girder in order to identify the failure mode. Then a detailed parametric study is carried out to investigate the effects of geometry parameters and material characteristics on flexural performance of a composite section.

Keywords: Fiber reinforced materials; Epoxy adhesive; Flexural; Steel; Concrete; Retrofitting; Structures

Prediction of Vibrational Behavior of Composite Cylindrical Shells under Various Boundary Conditions by Milad Hemmatnezhad; Reza Ansari; Mansour Darvizeh (pp. 225-241).

In this paper, a unified analytical approach is applied to investigate the vibrational behavior of composite cylindrical shells. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. The Influence of some commonly used boundary conditions and the effect of variations in shell geometrical parameters on the shell frequencies are studied. The results obtained for a number of particular cases show good agreement with those available in the open literature. The simplicity and the capability of the present method are also discussed.

Keywords: Composite cylindrical shells; Exact; Arbitrary boundary conditions; Sanders’ theory

Transient Dynamic Response of Clamped-Free Hybrid Composite Circular Cylindrical Shells by Keramat Malekzadeh; S. Mohammad Reza Khalili; Ali Davar; Puneet Mahajan (pp. 243-257).

Dynamic response of multilayer circular cylindrical shells composed of hybrid composite materials subjected to lateral impulse load is studied in this paper. The boundary conditions (B.C.s) are considered to be clamped-free. Both isotropic (metal) and orthotropic (composite) layers are used simultaneously in the hybrid lamination. There is no limitation for fibre orientation. First order shear deformation theory (FSDT) and Love’s first approximation theory are utilized in the shell’s equilibrium equations. Equilibrium equations for free and forced vibration problems of the shell are solved using Galerkin method. Finally, time response of displacement components of Fibre-Metal Laminate (FML) cylindrical shells is derived using mode superposition method. The effect of lay up, material properties, fibre orientation and volume fraction of metal layers on the dynamic response of the shell are investigated. New interesting results are obtained and discussed providing a helpful insight for aircraft structure’s designers.

Keywords: Fibre-metal laminate; Hybrid composite; Cylindrical shell; Dynamic response; Free vibration

A Quasi-Exact Dynamic Finite Element for Free Vibration Analysis of Sandwich Beams by Seyed M. Hashemi; Ernest J. Adique (pp. 259-269).

A Dynamic Finite Element (DFE) model for the vibration analysis of three-layered sandwich beams is presented. The governing differential equations of motion of the sandwich beam for the general case, when the properties of each layer are dissimilar, are exploited. Displacement fields are imposed such that the face layers follow the Rayleigh beam assumptions, while the core is governed by Timoshenko beam theory. The DFE model is then used to examine the free-vibration characteristics of an asymmetric soft-core sandwich beam with steel face layers and a rubber core. The natural frequency results for the first four modes, in this case, show the exact match between the DFE and ‘exact’ Dynamic Stiffness Matrix (DSM) formulations, using only a one-element mesh, justifying the use of Quasi-Exact (QE-DFE) title. Convergence-wise, the QE-DFE formulation also outperforms the conventional FEM, which makes it useful in benchmarking other studies or the examination of high frequency response where FEM requires the use of large number of elements in order to achieve better accuracy. The application of the DFE to a lead-core sandwich beam is also discussed.

Keywords: Soft-core sandwich beam; Free vibration; FEM; Dynamic stiffness matrix (DSM); Dynamic finite element (DFE)

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.17, #2)

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.17, #2)