Optimal Fiber Orientation Research Articles

Tailoring of composite cantilever beam for maximum stiffness and minimum weight

As the natural resources goes on decreasing now a days and to meet the needs of natural resources conservation, energy economy most of the manufacturers and their sub contractors are attempting to reduce the weight of the members in recent years. In this approach they are searching for low cost, high strength to weight ratio materials. Substituting composite structures for conventional metallic structures has many advantages because of higher specific stiffness and strength of composite materials. Composite materials have the major advantage of high strength to weight ratio with continuously decreasing travel of cost in addition to other advantages like excellent corrosive resistance, superior torsional buckling and fatigue strength and high specific strain energy storage capacity. The present work aims at the suitability of composite materials usage, by the identification of optimal fiber orientation stacking sequence and tailoring for laminate thickness/width for maximum stiffness and minimum weight design of laminated composite beam. The structural response is evaluated from conventional metallic structure with optimization techniques for maximizing stiffness and minimum weight. These metallic optimum values are extended initially to composite beam to maintain strength with the developed of optimization algorithm. Later with topology optimization and by tailoring cross-sections algorithm of the beam is evaluated with optimal fiber orientations and stacking sequence to maintain strength as in additional advantage of less weight for composites. Tailoring is done based on gradual decrement in cross-section over the length in both thickness and width direction. Numerical results are presented for cantilever beam with different geometries showing the maximizing stiffness and with minimum weight. The results indicate that the devised strategy is well suited for finding optimal fiber orientations and laminate thickness/width in the tailoring design of slender laminated composite structure.

Maximization of fundamental frequency of axially compressed laminated curved panels with cutouts

Free vibration analyses of laminated curved panels with central circular cutouts and subjected to axial compressive forces are carried out by employing the Abaqus finite element program. The fundamental frequencies of these composite laminated curved panels with a given material system are then maximized with respect to fiber orientations by using the golden section method. Through parametric studies, the significant influences of the panel aspect ratio, the panel curvature, the cutout size and the compressive force on the maximum fundamental frequencies, the optimal fiber orientations and the associated fundamental vibration modes of these panels are demonstrated and discussed.

The effect of aspect ratios and edge conditions on the optimal damping design of thin soft core sandwich plates and beams

An optimal design is presented to maximize the fundamental damping loss factor of sandwich rectangle plates and beams with general boundary conditions. With an extensive development of the classical laminate theory and energy method, the loss factor of sandwich laminate with a thin viscoelastic core is deduced. For sandwich-laminated plates and beams, the effect of fiber orientation of the orthotropic layer on the loss factor has been studied. The aspect ratio is very important in structural design for plates and beams. In this work, the effects of aspect ratios of sandwich laminates on optimal fundamental loss factors are investigated. The maximum fundamental loss factor and optimal fiber orientation have been obtained and analyzed for different sandwich laminates with the aspect ratio as a variable.

Analysis and optimal design for the damping property of laminated viscoelastic plates under general edge conditions

The present paper is concerned with analysis and optimal design for the damping loss factor of laminated plates under general edge conditions. In the analysis based on the classical lamination theory, the loss factor is deduced from the energy formulation for symmetrically laminated thin plates comprised of fiber reinforced layers and viscoelastic layers. The effects of location and thickness of viscoelastic layers are studied on the loss factor of the plates, and those of the fiber orientation angles are also clarified. In the optimal lay-up design problem, a layerwise optimization (LO) method is applied to the plates comprised of two different orthotropic materials, and the optimal fiber orientation angles are determined to obtain the maximum loss factor in the fundamental mode. These numerical simulation results uncovered that the present approach is quite useful in analyzing and designing the loss factor of the plates.

COMPOSITE PRESSURE VESSELS

Cylindrical pressure vessels are widely used for commercial, under water vehicles and in aerospace applications. At present the outer shells of the pressure vessels are made up of conventional metals like steels and aluminum alloys. The payload performance/ speed/ operating range depends upon the weight. The lower the weight the better the performance, one way of reducing the weight is by reducing the weight of the shell structure. The use of composite materials improves the performance of the vessel and offers a significant amount of material savings. Moreover, the stacking sequence is very crucial to the strength of the composite material. This Project involves various objective functions such as stiffness, buckling load and Weight at each level of optimization. Usually composite pressure vessels are designed for minimum mass under strength constraints. A graphical analysis is presented to find optimum fiber orientation for given layer thicknesses. In the present work, an analytical model is developed for the Prediction of the minimum buckling load with / without stiffener composite shell of continuous angle ply laminas (±45°,±55°,±65°,±75°,±85°) for investigation. Comparisons are made for two different approaches i.e. the finite element model and the theoretical model. A 3-D finite element analysis is built using ANSYS-12.0 version software into consideration, for static and buckling analysis on the pressure vessel.

Plasticity modeling of FRP-confined circular reinforced concrete columns subjected to eccentric axial loading

This paper presents a numerical study on FRP-wrap strengthened reinforced concrete columns subjected to eccentric axial loads using ABAQUS®. For modeling of concrete dilation under non-uniform confinement pressure, a smooth cap plasticity model was combined with concrete damaged plasticity model. This model includes different concrete compaction–dilation behaviors which is pressure-dependent. Proposed model has been calibrated and verified for concrete in number of unconfined and full-wrapped columns under combination of axial force and bending moment. Presented numerical predictions are shown to be in close agreement with existing experimental results. The effect of laminate stacking sequences and column slenderness on strength and ductility of members was examined thoroughly. The results of this study recommend taking fiber angles between zero (circumferential) and 30° can improve ultimate strength and ductility of confined short concrete columns. However, for slender concrete columns the optimum fiber orientation can be set between 15° and 30°.

Thermal Buckling Optimization of Temperature-Dependent Laminated Composite Skew Plates

AbstractAs a first endeavor, the differential quadrature method in conjunction with the genetic algorithms (GAs) is applied to obtain the optimum (maximum) buckling temperature of laminated composite skew plates. The material properties are assumed to be temperature dependent and the governing equations are based on the first-order shear deformation plate theory. After discretizing the governing equations and the related boundary conditions, a direct iterative method in conjunction with GAs is used to determine the optimum fiber orientation for the maximum buckling temperature. The applicability, rapid rate of convergence, and high accuracy of the method are established by solving various examples and by comparing the results with those in the existing literature. Then, the effects of the temperature dependence of the material properties, boundary conditions, length-to-thickness ratio, number of layers, and skew angle on the maximum buckling temperature of the laminated skew plates are presented.

806 板厚最適配置による局所異方性を有する複合材積層板の固有振動数最大化

The present study proposes an optimization method of laminated CFRP plates with variable thickness. The objective function is the fundamental frequency calculated by the originally developed finite element code with a 4-node rectangular (ACM) element, and design variable are placements of elements with reinforcement layer. A simple genetic algorithm method is employed with elitist tactics as an optimizer. The obtained plates with optimum placement of reinforcements and optimum fiber orientation angle result in the highest fundamental frequency among representative models. Then, based on the optimization results, the test specimens are fabricated by using hand lay-up and vacuum curing technique with pattern paper which keeps thicknesses difference clearly. Measured frequencies and modes shapes agree well with the calculated results and the fabricated optimum plate also indicates the higher fundamental frequency than other representative ones. Furthermore, the optimum variable thickness plate yields higher frequency compared with the homogenous thickness plate due to its small mass. This observation demonstrates an advantage of the variables thickness plate in terms of vibration characteristics.

Adaptive reorientation of cardiac myofibers: The long-term effect of initial and boundary conditions

On the basis of results from modeling and experimental studies it has been hypothesized that myocytes adapt their orientation to achieve a preferred mechanical load. In a previous computational model study in which fiber reorientation was considered as a local response to local fiber cross-fiber shear strain, we have shown that predicted left ventricular (LV) myofiber orientations agreed well with experimental data. In this study, we investigated in the latter model the effect of initial and boundary conditions on predicted fiber orientations on the long term. After adaptation, predicted fiber orientation and deformation became more realistic, irrespective of initial and boundary conditions. As adaptation proceeded, the effect of initial conditions was found to disappear, suggesting that one single optimal fiber orientation field exists for the heart. In contrast, the effect of the boundary conditions persisted, indicating that modeling of in particular the interaction between myocardium and valvular annulus is relevant for predicting LV myofiber reorientation.

Layer optimization for maximum fundamental frequency of rigid point‐supported laminated composite plates

AbstractIn this study, the layer optimization was carried out for maximizing the lowest (first) fundamental frequency of symmetrically laminated square and rectangular laminated composite plates resting on rigid point supports distributed in eight different arrangements. Genetic Algorithm (GA) was used for searching the optimal stacking sequences of laminated composite plates, which is maximizing the first natural frequency defined as an objective function (fitness function). The first natural frequencies of the composite plates with various stacking sequences was calculated using the finite element method (FEM). However, the calculation of the first natural frequency for each new lay‐up sequence and point‐support arrangement needs a longer time than the evaluation period of GA. In order to reduce the searching time of the optimal lay‐up sequence, the artificial neural network models were proposed and trained with small training and testing data composed of the natural frequencies of the composite plates calculated for random lay‐up sequences, layer number, eight‐point support arrangements, and four‐plate length/width ratios using the FEM. The GA combined with these trained neural networks predicted successfully the optimal layer sequences without yielding a local optimum on the contrary the Ritz‐based layerwise optimization method (Narita and Hodgkinson, Compos. Struct., 69, 127 (2005)). The maximized fundamental frequencies were always better than those obtained for typical cross‐ply, angle‐ply, and quasi‐isotropic lay‐ups. Theeffects of the rigid‐point support locations, the optimum fiber orientation angles and the layer number on the maximum lowest natural frequency are also discussed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Tailoring the morphology and crystallinity of poly(L-lactide acid) electrospun membranes

Biodegradable poly(L-lactic acid) (PLLA) microfibers were prepared by electrospinning by varying the applied potential, solution flow rate and collector conditions. PLLA fibers with smoothly oriented and random morphologies were obtained and characterized by scanning electron microscopy. The optimum fiber orientation was obtained at 1000 rpm using a 20.3 cm diameter collecting drum, while for higher and lower drum rotation speeds, the rapid random motion of the jets resulted in a random fiber distribution. The deformation of the jet with rapid solidification during electrospinning often results in a metastable phase. PLLA electrospun fibers are amorphous but contain numerous crystal nuclei that rapidly grow when the sample is heated to 70–140 °C. In this way, the degree of crystallinity of the fibers can be tailored between 0 and 50% by annealing. Infrared transmission spectra revealed that the processing conditions do not affect the PLLA samples at the molecular level and that the crystallinity of the samples is related to the presence of α-crystals.

Tailoring the morphology and crystallinity of poly(L-lactide acid) electrospun membranes

Biodegradable poly(L-lactic acid) (PLLA) microfibers were prepared by electrospinning by varying the applied potential, solution flow rate and collector conditions. PLLA fibers with smoothly oriented and random morphologies were obtained and characterized by scanning electron microscopy. The optimum fiber orientation was obtained at 1000 rpm using a 20.3 cm diameter collecting drum, while for higher and lower drum rotation speeds, the rapid random motion of the jets resulted in a random fiber distribution. The deformation of the jet with rapid solidification during electrospinning often results in a metastable phase. PLLA electrospun fibers are amorphous but contain numerous crystal nuclei that rapidly grow when the sample is heated to 70-140 °C. In this way, the degree of crystallinity of the fibers can be tailored between 0 and 50% by annealing. Infrared transmission spectra revealed that the processing conditions do not affect the PLLA samples at the molecular level and that the crystallinity of the samples is related to the presence of α-crystals.

Maximum stiffness and minimum weight optimization of laminated composite beams using continuous fiber angles

This paper deals with identification of optimal fiber orientations and laminate thicknesses in maximum stiffness and minimum weight design of laminated composite beams. The structural response is evaluated using beam finite elements which correctly account for the influence of the fiber orientation and cross section geometry. The resulting finite element matrices are significantly smaller than those obtained using equivalent finite element models. This modeling approach is therefore an attractive alternative in computationally intensive applications at the conceptual design stage where the focus is on the global structural response. An optimization strategy is presented which aims at enabling the use of fiber angles as continuous design variables albeit the problems may have many local minima. A sequence of closely related problems with an increasing number of design variables is treated. The design found for a problem in the sequence is projected to generate the starting point for the next problem in the sequence. Numerical results are presented for cantilever beams with different geometries and load cases. The results indicate that the devised strategy is well suited for finding optimal fiber orientations and laminate thicknesses in the design of slender laminated composite structures.

Theoretical and Experimental Predictions of First-Ply Failure of a Laminated Composite Elevated Floor Plate

Experimental and theoretical approaches are studied via the first-ply failure strength on anti-symmetrically laminated composite elevated floor plates with various length-to-depth ratios, aspect ratios, and optimal fibre orientations subjected to central point loads. Optimal angle-ply orientations of anti-symmetric [ϑ/—ϑ…] —S laminated composite plates designed for maximum stiffness were investigated. A vacuum-assisted resin transfer moulding (VARTM) technique was used to manufacture an elevated floor plate by the stacking of JPMEces of glass-fibre fabrics in a vacuum pressure mould. In VARTM, resin is injected under pressure into a rigid mould filled with fibre preform and subsequent curing. The failure modes of the composite plates were studied, and the experimental results were used to verify the theoretical predictions. The first-ply failure loads of the composite plates are determined using the acoustic emission AMS3 system. The results have been proved to be efficient and effective in the theoretical and experimental analyses of first-ply failure loads of the composite plates.

Optimal laminate sequence of thin-walled composite beams of generic section using evolution strategies

A problem formulation and solution methodology for design optimization of laminated thin-walled composite beams of generic section is presented. Objective functions and constraint equations are given in the form of beam stiffness. For two different problems one for open section and the other for closed section, the objective function considered is bending stiffness about x-axis. Depending upon the case, one can consider bending, torsional and axial stiffnesses. The different search and optimization algorithm, known as Strategies (ES) has been applied to find the optimal fibre orientation of composite laminates. A multi-level optimization approach is also implemented by narrowing down the size of search space for individual design variables in each successive level of optimization process. The numerical results presented demonstrate the computational advantage of the proposed method Evolution strategies which become pronounced to solve optimization of thin-walled composite beams of generic section.

Maximization of Fundamental Frequencies of Axially Compressed Laminated Plates Against Fiber Orientation

Summary The applications of fiber-composite laminate materials to aerospace industrial such as spacecraft, high-speed aircraft, missile and satellite have increased rapidly in recent years. The most major components of the aerospace structures are frequently made of curved panels and subjected to various kinds of compressive forces. Therefore, knowledge of the dynamic characteristics of composite laminated curved panels in compression, such as their fundamental natural frequency, is essential. The fundamental natural frequency of composite laminated curved panels highly depends on the ply orientation, end conditions, geometries (i.e., aspect ratio and curvature) and compressive force. Therefore, proper selection of appropriate lamination to maximize the fundamental frequency of composite laminated curved panels in compression becomes a crucial problem. Research on the subject of structural optimization has been reported by many investigators and has been widely employed to study the dynamic behavior of composite structures. Among various optimization schemes, the golden section method is a simple technique and can be easily programmed for solution on the computer. In this investigation, maximization of the fundamental natural frequency of composite laminated curved panels in compression with respect to fiber orientations is performed by using the golden section method. The fundamental frequencies of the composite laminated curved panels are calculated by using the Abaqus finite element program. In the paper, the constitutive equations for fiber-composite lamina, vibration analysis and golden section method are briefly reviewed. The influence of the end conditions, the panel aspect ratio, the panel curvature and the compressive force on the maximum fundamental natural frequency, the associated optimal fiber orientations and the vibration mode of the laminated curved panels is presented and important conclusions obtained from the study are given.

Discrete Optimization for Vibration Design of Composite Plates by Using Lamination Parameters

A design method is proposed to optimize the stacking sequence of laminated composite plates for desired vibration characteristics. The objective functions are the natural frequencies of the laminated plates, and three types of optimization problems are studied where the fundamental frequency and the difference of two adjacent frequencies are maximized, and the difference between the target and actual frequencies is minimized. The design variables are a set of discrete values of fiber orientation angles with prescribed increment in the layers of the plates. The four lamination parameters are used to describe the bending property of a symmetrically laminated plate, and are optimized by a gradient method in the first stage. A new technique is introduced in the second stage to convert from the optimum four lamination parameters into the stacking sequence that is composed of the optimum fiber orientation angles of all the layers. Plates are divided into sub-domains composed of the small number of layers and designed sequentially from outer domains. For each domain, the optimum angles are determined by minimizing the errors between the optimum lamination parameters obtained in the first step and the parameters for all possible discrete stacking sequence designs. It is shown in numerical examples that this design method can provide with accurate optimum solutions for the stacking sequence of vibrating composite plates with various boundary conditions.

Strength Optimization of Laminated Composite Plates

A procedure to select the optimum fiber orientations and determine the maximum load-bearing capacity of the simply supported symmetrically laminated plates combined the bidirectional tension loads and bending moments is described. The fiber orientation is considered a design variable. The optimization problem consists of two stages. The objective of the first stage is to maximize the strength of the laminated plates by determining the fiber orientations optimally while the objective of the second stage is to maximize each of the bidirectional tension loads and bending moments subject to the Tsai—Wu failure criterion for the optimum fiber orientations obtained from the first stage. The modified feasible direction method (MFD) is used as an optimization procedure. Therefore, a FORTRAN program is used for the finite element analysis and optimization routine. Also, the optimum fiber orientations are obtained using the golden section (GS) method to compare the results. Finally, the effect of the different plate aspect ratio, width-to thickness ratio, the uncertainties in the material properties and the uncertainties in the fiber orientations on the optimum results is investigated and the results are compared.

Vibration Analysis of Rotating Laminated Cylindrical Shells

Free vibration analyses of rotating laminated cylindrical shells are carried out by the ABAQUS© finite element program. The fundamental frequencies of rotating laminated cylindrical shells with a given material system are then maximized with respect to fiber orientations by using the golden section method. The significant influences of rotating speed, end conditions, shell thickness, shell length, and shell radius on the maximum fundamental frequencies and the associated optimal fiber orientations are demonstrated.

Optimal design of laminated composite plates to maximise fundamental frequency using MFD method

This paper deals with optimal fibre orientations of symmetrically laminated fibre reinforced composite structures for maximising the fundamental frequency of small-amplitude. A set of fiber orientation angles in the layers are considered as design variable. The Modified Feasible Direction method is used in order to obtain the optimal designs. The effects of number of layers, boundary conditions, laminate thicknesses, aspect ratios and in-plane loads on the optimal designs are studied.