Optimal Laminate Research Articles

A two-step optimization scheme for maximum stiffness design of laminated plates based on lamination parameters

The purpose of this paper is to propose an effective solution scheme of simultaneous optimization design of layup configuration and fiber distribution for maximum stiffness design of laminated plates. Firstly, a numerical analysis of the lamination parameters feasible region for a laminated plate consisting of various given number of ply groups (each ply group may have different thickness and all the fibers in one ply group are orientated in an identical direction) is carried out, and it is found that the feasible region based on only a few ply groups is very close to the overall one determined by infinite plies. Therefore, it is suggested that the feasible region of lamination parameters of a laminated plate could be approximately determined by the layup configuration of least ply groups. Secondly, a two-step simultaneous optimization scheme of layup configuration and fiber distribution for maximum stiffness design of laminated plates is proposed. Accordingly, by using ply thickness, fiber orientation angle and fiber volume fraction in a laminated plate of least ply groups as design variables, the optimal lamination parameters for maximum stiffness is obtained. Then, taking the optimal lamination parameters as the design objective, a detailed layup design optimization is implemented by considering some limitations on manufacturing, such as preset ply thickness, and specific fiber orientation angle and a limited maximum number of consecutive plies in the same fiber orientation. Numerical examples are also presented to validate the proposed two-step optimization scheme.

Multi-material topology optimization of laminated composite beam cross sections

This paper presents a novel framework for simultaneous optimization of topology and laminate properties in structural design of laminated composite beam cross sections. The structural response of the beam is evaluated using a beam finite element model comprising a cross section analysis tool which is suitable for the analysis of anisotropic and inhomogeneous sections of arbitrary geometry. The optimization framework is based on a multi-material topology optimization model in which the design variables represent the amount of the given materials in the cross section. Existing material interpolation, penalization, and filtering schemes have been extended to accommodate any number of anisotropic materials. The methodology is applied to the optimal design of several laminated composite beams with different cross sections. Solutions are presented for a minimum compliance (maximum stiffness) problem with constraints on the weight, and the shear and mass center positions. The practical applicability of the method is illustrated by performing optimal design of an idealized wind turbine blade subjected to static loading of aerodynamic nature. The numerical results suggest that the proposed framework is suitable for simultaneous optimization of cross section topology and identification of optimal laminate properties in structural design of laminated composite beams.

Structural and Electrical Properties of Flip Chip Laminated Metal–Molecule–Silicon Structures Varying Molecular Backbone and Atomic Tether

Formation of electrical contacts to organic molecules by using a scalable technique that preserves molecular integrity is a key development toward reliable fabrication of nanoscale molecular architectures. Here we report the structural and electrical properties of metal–monolayer–silicon junctions fabricated by using Flip Chip Lamination (FCL), a novel, low cost, and nondestructive approach. The effect of junction formation is studied with both aliphatic and aromatic molecular backbones. The ω-functionalized monolayers are first formed on ultrasmooth gold via a thiol linkage and then laminated to H–Si via a thiol or alkene linkage. The application of pressure and temperature enables formation of the nanoscale molecular junctions chemically tethered to two electrodes. The molecular structure and interfacial chemistry within the electrical structure are investigated by using polarized backside-reflection absorption infrared spectroscopy (pb-RAIRS) and current–voltage (I–V) measurements. The confined organic monolayers maintain an overall structure similar to the original self-assembled monolayers (SAMs) on gold with small changes in the configuration of the molecular backbone attributed to lamination and bonding of the molecular terminal group to silicon and exhibiting electrical dielectric integrity. The optimal lamination conditions for each monolayer are dependent on the surface free energy, monolayer conformation, ambient conditions, and reaction of the molecular functionality with the silicon substrate. We demonstrate the structural and electrical integrity at the monolayer level of a variety of organic molecules bonded to both silicon and metal electrodes by probing the effect of molecular backbone (aliphatic vs aromatic) and molecule–electrode interface. FCL enables formation of an extended variety of molecular junctions to identify the critical factors in charge transport across metal–molecule–silicon nanoelectronic architectures.

환경하중하의 풍력발전 시스템 구조물의 수치 해석적 기법 연구

*Department of Precision Mechanical Engineering, Pusan National University, Busan, Korea**Pusan Educational Center for Computer Aided Machine Design, Pusan National University, Busan, KoreaKEY WORDS: Windpower system structure 풍력시스템 구조물, Composite shell 복합재 셸, Ply orientation 적층방향, Lamination pattern 적층순서, FEM 유한 요소법ABSTRACT: The purpose of this study was to develop a buckling analysis te chnique for a windpower system structure under environmental loadings (hydrostatic pressure) using FEM. We analyzed an isotr opic material and composite material and made a comparison usin g buckling pressure formulas. First, finite element analyses for an isotro pic material (SC410) were performed to obtain the variation of buckling pressure for the number of elements and boundary conditions in a pressure-sh ell model, and the numerical results were compared with those o f existing empirical formulas. Then, additional finite element analyses ba sed on the results of the isotropic material (SC410) were perfo rmed to determine the optimum lamination angle and pattern for a composite material (URN300). The results of the FE analyses for the composite mater ial were also compared with those of existing empirical formulas. The ply ori entations (lamination angles) used in the FE analyses were 0 °, 15°, 30°, 45°, 60°, 75°, and . The lamination patterns in the FE analyses were and . T he lamination pattern was assumed to be the equivalent model of . The results of the FE analyses for the isotropic material (SC410) indicated that the optimal values for the number of elements and the bou ndary conditions were 6000 and both simply supported, respectively. The results of the FE analyses for the composite material (URN300) showed t hat the optimal ply orientation was 60°~75°교신저자 홍철현: 부산광역시 금정구 장전동 산 30, 051-510-1665, chhong@pusan.ac.kr

Development of a ferromagnetic fibre metal laminate

This study introduces the concept of a multifunctional fibre metal laminate (FML), specifically, one which utilises ferromagnetic foil in combination with carbon fibre reinforced epoxy to produce a FML which is magnetically functional and structurally efficient. The aim is to develop such a material/structure for use in future high output, low mass, electrical machines and embedded actuation. The work presented here compares surface treatment schemes of the metal foil and the use of two different resin films for optimum laminate manufacture. Laminates with different thicknesses of Fe–Co steel foil and either two or four plies of carbon fibre reinforced epoxy were manufactured and their mechanical properties evaluated.

Design optimization of laminated composites using a new variant of simulated annealing

The aim of this study is to minimize the thickness (or weight) of laminated composite plates subject to both in-plane and out-of-plane loading. A new variant of the simulated annealing algorithm is proposed to optimize the lay-up design. Fiber orientation angle and number of plies in each lamina are used as design variables. Considering static failure as the critical failure mode, the maximum stress and Tsai–Wu criteria are used together to predict failure. Numerical results show that the optimization methodology proposed in this study can find the globally optimum laminate designs even with a high number of design variables.

Optimum Nonlinear Response of Composite Panels Subjected to Aerodynamic and Thermal Loadings

A nonlinear finite element model is provided for the thermal post buckling and linear flutter behavior of composite panels. Panel subjects to combined aerodynamic and thermal loads. The governing equations are derived using the classical plate theory and the principle of virtual work. The effect of large deflection is included in the formulation through the von Karman nonlinear strain-displacement relations. To account for the temperature dependence on material properties, the thermal strain is stated as an integral quantity of the thermal expansion coefficient with respect to temperature. The aerodynamic pressure is modeled using the quasi-steady first order piston theory. The Newton–Raphson iteration method is employed to obtain the nonlinear aero-thermal post-buckling deflections, and a frequency-domain solution is presented to predict the critical dynamic pressure at different elevated temperatures. Finally, numerical results are provided to depict the optimum lamination scheme in order to maximize the aero-thermal stability of such panels. The optimum solution is obtained by Genetic Algorithms.

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.

A simulated annealing method for design of laminates with required stiffness properties

Abstract Designing a laminate based on its stiffness properties requires finding the optimum lamination stacking sequence to yield the required stiffness properties. The design variables to be considered are the number of layers and orientation angle of fibers in each layer group, which are treated as discrete-variables. The optimum lamination is then obtained by minimizing a cost function composed of the relative difference between the calculated effective stiffness properties and weight of trial laminate and the desired properties. This error minimization problem was solved using a modified simulated annealing heuristic method. The new simulated annealing implementation comprises a cooling procedure in which the temperature decrease relied adaptively on the objective function evolution. It is shown that the proposed method can give rise to an improvement in convergence speed. To achieve a further improvement in the performance of the method, simulated annealing parallelization implemented using the proposed cooling process. The main features of this algorithm are described and its encouraging results are presented.

Low-velocity impact damage on dispersed stacking sequence laminates. Part I: Experiments

The stacking sequence design of composite laminates is often limited to combinations of 0°, 90°, and ±45° fibre angle plies. Furthermore, in order to comply to certain stiffness requirements, clustering of plies becomes unavoidable. Although such laminates might have the desired stiffness properties, they may show poor impact and/or compression-after-impact behaviour. A method to redesign the traditional stacking sequences such that the alternative laminates have improved damage resistance whilst keeping similar in-plane and bending stiffness properties as their original traditional stacking sequences is proposed. This method makes use of optimisation tools based on genetic algorithms. In the alternative laminates, the difference between fibre angles of two consecutive plies is maximised and allowed to vary in the 0–90° fibre angle range at intervals of 5°. Manufacturing of such laminates is practical nowadays as the industry is changing its production techniques into accurate automated fibre-placement and tape-laying technologies. A two-step approach is proposed for the design of laminates. In the first step, the optimal laminate is designed in the traditional fashion to cope with the expected quasi-static loads on the structure. The second step consists of redesigning this laminate to better withstand impact loads by dispersing its stacking sequence while keeping similar stiffness properties as in the first step. A traditional laminate and two dispersed stacking sequence alternative layups were tested under low-velocity impact and compression-after-impact loads in order to compare their impact resistance and damage tolerance characteristics. The evaluation of these laminates will also be carried out by the innovative numerical tools proposed in the follow-up of the present paper.

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.

A theory for elastic properties of single crystals with microstructure and its application to diffusion induced segregation

AbstractIn this article a general theory for elastically stressed single crystals in the presence of microstructure is presented and an explicit formula for the resulting non‐linear stored mechanical energy is obtained. The optimal microstructure under applied stress is characterised and the optimal laminates are identified in 2D. The analysis is based on a sharp lower estimate of the energy that relies on relaxation. The new theory is then used to extend existing models for diffusion induced segregation (DIS) in the case of (Zn,Fe)S single crystals. Numerical simulations based on finite elements are carried out and the results are compared with former computations of the homogeneous case. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Extended storage of ‘Red Globe’ grapes in modified SO 2 generating pads

Grapes intended for storage of a few weeks or longer are stored at 0 °C in boxes with a dual release SO 2 generating pad (quick release plus a slow release phase). This method can prevent decay caused by Botrytis cinerea for a number of weeks, but the level of SO 2 surrounding the grapes falls to below 1 μL L −1 after 60–80 d [Lichter, A., Zutahy, Y., Kaplunov, T., Lurie, S., 2008]. Evaluation of table grape storage in boxes with sulfur dioxide releasing pads with either an internal plastic liner or external wrap. HortTechnology]. Therefore, other methods are needed for grapes, such as ‘Red Globe’ that can withstand storage for 4 months or longer without losing eating quality. The SO 2 generating pad was enclosed in a plastic laminate with macro-perforation. This additional barrier to water vapor penetration into the pad and SO 2 diffusion out of the pad decreased the initial SO 2 peak released by the pad and extended the lifetime of the pad threefold. The effect of different diameter of macro-perforation was examined from 3 to 9 mm, and the effect of varying the number of holes in the laminate. Grapes were stored for 3 and 6 months and their quality assessed after 3 d of shelf-life. The optimum laminate was found to be 32 perforations of 6 mm diameter. This pad was tested under commercial storage conditions and the quality of the grapes after storage from 92 to 116 d was assessed compared to storage with regular dual release SO 2 pads. Decay as well as SO 2 damage was greater in the grapes with dual release pads than the macro-perforated laminated pads. This modification of the SO 2 generating pad shows promise as a means of maintaining quality of grapes in extended storage.

Automation of optimal laminate design

Composite laminates are in widespread use in the aerospace industry. As well as satisfying strength and stiffness criteria, the final laminate design has to be manufacturable in terms of compatibility between adjacent panels, thus introducing conflicting constraints on the allowed laminate stacking sequences. An attempt to automate the laminate design process is described in this paper. The method uses a mixture of a genetic algorithm and heuristics to satisfy the various design and manufacturing constraints. Multiple zones are allowed, where each zone defines a panel together with a set of applied loads. Guide laminates and a blending methodology allow each zone to share common plies. This creates ply continuity across the structure, and avoids the scenario seen in other laminate optimisation tools where each optimised zone contains unrelated laminates that are not practical from a manufacturing perspective.

Soft magnetic properties and high frequency permeability in [CoAlO/oxide] multilayer films

A CoAlO thin film was found to have good soft magnetic properties and gigahertz frequency response when it had a thickness of tens of nanometres. Increasing the thickness by more than 100 nm rapidly increased the coercivity and seriously degraded the high frequency response. A multilayering technique (laminating the magnetic layer with oxide spacers) was exploited to improve the magnetic properties in thick films. AlOx and SiOx were used as the oxide spacing layers in this experiment. For the 105 nm CoAlO films, the easy and hard axis coercivities were reduced by more than 8 times by introducing 2 nm AlOx or 5 nm SiOx spacers. With our optimum lamination [CoAlO (52.5 nm)/AlOx (2 nm)]7, good soft magnetic properties (easy and hard axis coercivities: 21 and 14 Oe and effective anisotropy field: 54 Oe) and high frequency response (real permeability: >200 up to ∼2 GHz) were successfully obtained in a multilayer film at a thickness of 380 nm. The changes in the microstructures and film stress with the introduction of the oxide spacers are discussed in this paper.

Weight Optimization of Composite Flat and Curved Wings Satisfying Both Flutter and Divergence Constrains

Aeroelastic tailoring studies using effective computational method with genetic algorithm have been conducted to find an optimized lamination set which give minimum structural weight. The efficient and robust computational system for the flutter optimization has been developed using the coupled computational method based on the micro genetic algorithm. It is shown that the wing structural weight with both divergence and flutter constrains can be significantly reduced using composite materials with proper optimum lamination compared to the case of isotropic wing model.

SIFAT MEKANIS LAMINASI LENGKUNGAN BAMBU BETUNG (Dendrocalamus asper (Schulters f.) Backer ex Heyne) dan TALI (Gigantochloa apus (J.A. & J.H. Schultes) Kurz).

AbstractPreface study shows a possibility of bamboo to be bent and also proves that species affects to the results of mechanical properties. Bamboo was bent with the radius of curvature of 28 CM, as an example, used PVAc (industrial specification), and _formed manually in cold pressed at pressure setting at room temperature for 24 hours. In order to examine the best composition of optimal laminate effect, influence of node existing, and effect of shape; 24 samples of 2 cm x 2 cm x 30 cm were made and three replicates were prepared. In order to compare species influence were selected Dendrocalamus asper (Schultes f) Backer ex Heyne and Gigantochloa apus (J.A. & Schultes) Kurz that have different anatomical structure.Results indicate that node presence not significantly affects mechanical properties of Betting bamboo but significantly for Tali bamboo. To get the optimum mechanical properties, thickness of laminate is about 4 mm to 5 min. Decreasing of mechanical properties of laminated bended bamboo is not caused by node presence but by shape influence. The modulus of elasticity (MOE) value of Belling bamboo is decreasing almost 50% from the mechanical properties. Meanwhile, the MOE value of laminated straight bamboo of Tali decreases until 5 times from its mechanical properties, and the MOE value of laminated ['ended bamboo of decreases until 25% from laminated straight bamboo. Conversely, the modulus of rupture (MOR) of both of laminated bamboo is not significantly.

Multiphase laminates of extremal effective conductivity in two dimensions

This paper deals with two-dimensional composites made of several isotropic linearly conducting phases in prescribed volume fractions. The primary focus is on the three-phase case; the generalization to a larger number of phases is straightforward. A class of high- but finite-rank laminates is introduced. The laminates saturate the known inequality bounds—due to the work of Hashin and Shtrikman, Lurie and Cherkaev, Tartar, and Murat and Tartar—on the effective conductivity tensor of any composite. These bounds depend only on the constituent material properties and volume fractions and not on the placement of these materials in the composite. The bounds are known not to be optimal for all admissible choices of the conductivities and volume fractions. However, they are now known to be realizable in a much larger range of these parameters than was previously known. The range of effective properties of our multiphase laminates strictly includes those corresponding to the composites found earlier by Milton and Kohn, Lurie and Cherkaev, and Gibiansky and Sigmund. The new optimal laminates are found in a systematic fashion by satisfying sufficient conditions on the fields in each layer. This leads to a simple algorithm for generating optimal laminates. In addition a new supplementary bound for multiphase structures is also proven which must be satisfied by composites with smooth interfaces.

Lamination Optimization of Composite Curved Wing for Maximum Flutter Stability Using Micro Genetic Algorithm

Flutter characteristics of composite curved wing are investigated in this study. The efficient and robust computational system for the flutter optimization has been developed using the coupled computational method based on the micro genetic algorithms. The present results show that the micro genetic algorithm is very efficient in order to find optimized lay-ups for a composite curved wing model. It is found that the flutter stability of curved wing model can be significantly increased using composite materials with proper optimum lamination design when compared to the case of isotropic wing model under the same weight condition.

Optimization with non-homogeneous failure criteria like Tsai–Wu for composite laminates

In designing composite laminates, minimization of a suitable failure criterion is sometimes selected as the objective function. However, for non-homogeneous criteria, e.g., the Tsai–Wu criterion, this objective function will not maximize the failure load, when it is carried at a load which is different from the failure load. We suggest that the use of a safety factor for the objective function is more appropriate for maximizing for the faiure load. In fact we show losses of more than 40% in the load carrying capacity even when the load carrying capacity of the optimal laminate is 75% of the applied load.