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Today, the Structural Health Monitorin (SHM) methodology is the main way to deal with the detection and identification of damages in a range of engineering sectors, mainly in the military and civil aerospace industry. The need to monitor damages and failures in increasingly complex structures has led to the development of various detection techniques. Identification of damages through intelligent signal processing and optimization algorithms are particularly emphasized. The methods discussed here are mainly elaborated by the evaluation of modal data due to the great potential of their application. Moreover, the optimization of damage identification is approached through methods of optimal positioning of sensors for the acquisition of the data that must be evaluated so that conclusions can be made. This article discusses the use of computational and intelligent techniques for structural monitoring in the form of a review with emphasis on composite materials. Despite the excellent mechanical performance already known about composite materials, they have a weak point. While damages, in a metallic material are easily visible (in some cases), composite materials often have the superficial appearance as if in perfect condition, when, inside, there are serious damages. This paper can be seen as a guideline or a starting point for developing and improving SHM systems. The contents of this paper aim to help engineers and researchers find a starting point in developing a better solution to their specific structural monitoring problems, either by inverse methods, pattern recognition, and intelligent signal processing. [ABSTRACT FROM AUTHOR]

Public concerns about the environment, climate change, energy consumption and greenhouse gas emissions have placed increasing demands for the use of sustainable materials in the built environment. Natural fibres such as flax, jute and hemp have recently been considered for fibre-resin composites, with a major motivation for their implementation being their notable sustainability attributes. However, many studies have noted the relatively modest mechanical properties of natural fibre composites. Despite this, a recent paper by the author demonstrated that the compression strength of flat plates and plain channel sections may be suitable for light structural applications. This paper presents the geometric optimisation of channel sections via the inclusion of complex web, flange-edge and flange-interior stiffeners. It is demonstrated that the inclusion of geometric stiffeners restricts the development of local buckling, creating less slender channel sections with greater compression strength. Compression strengths are compared with steel and timber wall stud strengths and shown to be suitable for residential building applications. The combined plain channel and stiffened channel experimental data covers a broad range of section slenderness values, and design models are developed to predict their compression strength. [ABSTRACT FROM AUTHOR]

The goal of this paper is to present a review of multi-objective optimization (MOO) techniques used in the damage assessment of composite laminates, with regard to damage identification, damage detection, damage quantification, and damage prediction models or approaches. Prior recognition of damage is crucial to ensure the performance and integrity of a structure of high structural responsibility. It is only then catastrophic structural failure or massive property loss and even in human casualties, in extreme situations, can be avoided or at least reduced. As such damage assessment is required, especially using advanced optimization and multi-objective optimization techniques, to prevent the failure of structural laminated composites. According to researchers, AI-based optimization algorithms are preferable to programmed inspections, conventional methods (like ultrasonic and magnetic damage or acoustic damage assessment methods), model or non-model (feature-based methods), and both in the sense that they are quick, universal, and less expensive methods for damage assessment. Unfortunately, there have only been a few or a small number of research investigations, particularly for damage prediction. [ABSTRACT FROM AUTHOR]

Modern composite structures offer multiple avenues of optimising performance. One avenue is to optimise a single stacking sequence over the structure leading to constant stiffness designs. Another avenue is to allow the stacking sequence to vary over the structure leading to variable stiffness laminates. This may be achieved either by dropping plies or by steering the fibres. When using ply drops to optimise the thickness distribution two different set of decisions are involved: the selection of ply drop boundaries, and the selection of the ply drop order. In this paper, the fibre angle distribution, the ply drop boundaries, and the ply drop order are simultaneously optimised. The optimisation of fibre angle distribution lends itself easily to gradient based methods. The ply drop boundary optimisation is formulated using topology optimisation techniques and is thus solvable using gradient based methods as well. The ply drop order optimisation requires discrete variables and is hence approached using an evolutionary algorithm based on stacking sequence tables. In this paper an efficient multi-step algorithm is developed to combine the optimisation of all aspects of variable stiffness laminates. The results indicate that significantly improved designs may be obtained by including the ply drop order in the optimisation. [ABSTRACT FROM AUTHOR]

A new and practical cohesive zone model (CZM) considering the coupling between damage mechanics and plasticity is proposed to facilitate structural-scale finite-element (FE) simulations for concrete members strengthened with fiber-reinforced polymer (FRP). The model dwells on an adaptive sub-stepping technique to overcome common convergence difficulties during mixed-mode debonding between FRP and concrete. Additionally, it automatically adjusts the computational time increment based on the convergence performance of Newton-Raphson iterations, ensuring efficiency by applying time stepping selectively to critical integration points with diverging problems. Moreover, the model introduces a transformation between effective stress and nominal stress to enhance numerical stability when dealing with complex interfacial behaviors like stiffness degradation, plastic deformation, dilation effects, and mixed-mode failure. Thus, the paper's novelty lies in the development of a stable and versatile 3D interface model achieved through advanced numerical optimization techniques. The resulting FE models have accurately reproduced various failure modes, such as FRP-concrete debonding and local buckling of FRP plates, demonstrating a high level of reliability and computational efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Over recent decades, industry has used more and more frequently composite laminates. If many Non-Destructive Testing (NDT) methods have already been developed to test such structures, detecting defects in polymer matrix laminates remains difficult. After a short overview of the main existing NDT methods, this paper focuses on two techniques which appear to be very promising: thermosonics and infra-red (IR) thermography. For thermosonics tests, an ultrasonic horn mechanically loads the sample, while an IR camera records the defect heating. For thermography tests, the heating is due to an optical wave. If minor improvements on the test device are presented for thermosonics tests, IR thermography tests are achieved with a CO2 laser as excitation source, which is a very innovative approach. This paper provides many experimental results obtained from an aeronautical carbon–epoxy plate with a central delamination. It is shown that both methods are very suitable for detecting such a defect, even if each method has its own advantages. Finally, some improvements to further optimize the thermography tests are proposed in conclusion. [Copyright &y& Elsevier]

Abstract Damping performance of the free-layer damping structure mainly depends on the damping material layout and its material physical properties. This paper proposes a concurrent topology optimization method for the design of the multi-scale free-layer damping structures with damping composite materials. In order to maximize the structural damping performance, the density-based topology optimization method is adopted to find the optimal layout on both macro and micro scales. For this coupled system, the macrostructure is composed of periodic damping composite materials, a stiff damping material which is designed for maintaining the structural stiffness and a soft damping material which is used for improving structural damping. The homogenized effective complex elastic matrix is obtained by considering the two damping materials layout in the microstructure. Mathematical model is established and sensitivity analysis is deduced. Several numerical examples are presented to demonstrate the effectiveness of the proposed multi-scale optimization method. In-depth discussions are given for the effects of the volume fraction of soft damping material in the micro scale on the design results. The results show that there is an optimal volume ratio of the stiff and soft damping material to make the structure reach optimal vibration performance due to the effective competition of soft and stiff characteristics of different damping materials. The optimal microstructure has relatively great loss moduli and high material loss factor, and it also presents a negative Poisson's ratio. The structural vibration performance of the optimal multi-scale layer damping structure with damping composite materials is significantly improved. [ABSTRACT FROM AUTHOR]

Abstract Sandwich panels with truss cores (SPTCs) are a class of novel structures with superior load bearing performance. In recent years, many efforts have been made in designing the SPTCs. However, the majority of related researches are conducted under the prespecified structural topologies of the truss cores according to subjective judgment and experience. In this paper, a novel approach under moving morphable components (MMC) based topology optimization framework is proposed for the design of SPTCs. To describe the SPTCs in an explicit and geometrical way, a multi-component topology description function (MCTDF) is developed in both 2D and 3D cases. By optimizing the configurations and layouts of the multi-components, the topological design of SPTCs with better structural performance can be generated. In this regard, the original topology optimization problem is transformed into a parameter optimization problem with only a small number of design variables. To determine the number of beams in truss core, a deletion strategy is proposed to remove the redundant multi-components. The minimum compliance problem subject to structural volume fraction constraint is investigated, and the relevant sensitivity analysis is shown. Both 2D and 3D numerical examples are presented to test the validity and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract In this paper a new approach to the Reliability-based Robust Design Optimization (RBRDO) of angle-ply composite laminate structures is presented. The problem is defined as a bi-objective Robust Design Optimization (RDO) problem, with deterministic and probabilistic constraints. Design optimization is considered as the minimization problem of the weight (optimality) and the determinant of the variance-covariance matrix of the response functionals of the system (robustness). Reliability assessment is executed by the Reliability Index Approach (RIA), as an inner cycle. The key concept of this methodology is the exclusive use of evolutionary algorithms with elitist strategy, allowing for global convergence in the two optimization cycles. The RIA problem was reformulated and a set of new evolutionary operators were developed. A numerical example is presented and the results compared with other RBRDO and RDO formulations. Results show that deterministic and probabilistic structural integrity measures are quite sensitive to uncertainty, for multi-component composite structures. [ABSTRACT FROM AUTHOR]

Abstract In practical engineering, the uncertainties commonly exist in the design process of composite structures due to the dispersion of composite materials. This paper proposes an uncertain optimization method based on interval model updating technique and non-probabilistic reliability (NPR) theory. A novel interval model updating method is firstly established by modifying the deterministic constraint condition parameters, which retains the quantification results of the material parameters and has a convinced updating model. In the design section, a new two-step optimization process for composite structures, which combines NPR method and progressive failure theory, is presented based on the updated simulation model. The traditional composite structural design method (safety factor based method) is also introduced to be compared. The NPR based optimization can optimize the nominal value and deviation of the structural response simultaneously, and will achieve a more significant weight reduction effect. A complete process including the uncertainty quantification, interval model updating, NPR based optimization and experimental verification for a composite stiffened plate under the compressive and shear load conditions were performed to verify the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

Abstract Material interface-related uncertainties induced by inter-diffusion or reactions between two different materials may deteriorate the actual performance of a structural design achieved by topology optimization. Thus a rational methodology is needed to address this issue in the design of hybrid-material engineering products implemented by some novel fabrication techniques such as additive manufacturing. This paper presents a robust shape and topology optimization method accounting for uncertain graded interface properties of multi-material structures. A level set function is used to track the evolving material interfaces during the optimization process, and the material interface uncertainties is modeled by introducing an intermediate zone with graded properties represented by a random field. On the basis of discretizing the input random field by means of the Expansion Optimal Linear Estimation (EOLE) method, the uncertain propagation analysis is implemented with the Polynomial Chaos expansion (PCE) to predict the stochastic response. Then the robust shape and topology optimization problem is stated as a multi-criteria optimization problem, in which the expected value and the standard deviation of the performance function of interest are to be minimized under a given material volume constraint. The shape derivative of the stochastic response is derived in the context of Eulerian description, and then used to advance the evolution of the level set function through the Hamilton-Jacobi equation. In the numerical examples, the proposed robust design method is exemplified by the mean compliance minimization problems. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a theoretical evaluation on modal damping of hybrid fiber reinforced polymer (FRP) cable with smart damper design in long-span cable-stayed bridge. The principles and design consideration of smart dampers were first clarified. Based on the energy principle, the theoretical equations of modal damping were derived for in-plane and out-of-plane vibrations, respectively. The parameters that influence the damping effect were further analyzed. Finally, an example of hybrid basalt and carbon FRP cable with smart dampers was selected to evaluate damping ratio in terms of the equations derived in the paper. The results show that (1) the smart dampers with discontinuous distribution benefit not only static and dynamic behavior of a cable but also optimization of damping; (2) the gap width, bonding, length and modulus of each smart damper can be optimized to obtain maximum of potential damping; (3) an example of smart damper designed hybrid FRP cable demonstrates its effectiveness for mitigating large magnitude of in-plane vibration, while more dominant damping effect is observed for suppressing out-of-plane vibration. [Copyright &y& Elsevier]

Abstract This paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically increasing loads. Such procedures are designed with the objective of reducing the computational cost required in these types of analysis. Starting from virtual tests of the microscale, the solution of the macroscale structure via Classical First-Order Multiscale Method will be replaced by an interpolation of a discrete number of homogenized surfaces previously calculated. These surfaces describe the stress evolution of the microscale at fixed levels of an equivalent damage parameter ( d eq ). The information required for these surfaces to conduct the analysis is stored in a Data Base using a json format. Of the two methods developed, the first one uses the pre-computed homogenized surface just to obtain the material non-linear threshold, and generates a Representative Volume Element (RVE) once the material point goes into the nonlinear range; the second method is completely off-line and is capable of describing the material linear and non-linear behavior just by using the discrete homogenized surfaces stored in the Data Base. After describing the two procedures developed, this manuscript provides two examples to validate the capabilities of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents a topology optimization method for the sequential design of material layout and fiber orientation in functionally graded fiber-reinforced composite structures. Specifically, the proposed method can find the optimal structural layout of matrix and fiber materials together with optimal discrete fiber orientations. In this method, an orientation design variable in the Cartesian coordinate system is employed with a conventional density design variable. The orientation design variable controls not only the fiber orientation, but also fiber volume fraction. The fiber volume fraction control can be used to relax the orientation design problem and simultaneously design a functionally graded structural layout of fiber material. To avoid intermediate fiber orientations and achieve discrete fiber orientation design, a penalization scheme is applied to the orientation design variable. For solving the optimization problem which involves multiple design variables such as the density variable, fiber orientation variable, and target discrete orientation set, a three-step sequential optimization procedure is proposed. In this procedure, the result for each step provides the isotropic design, continuous fiber orientation design, and functionally graded discrete orientation design, respectively. To validate the effectiveness of the proposed approach, numerical examples for structural compliance minimization and compliant mechanism design are provided. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers maximisation of the natural frequency of composite panels. The use of composite materials allows greater freedom in tailoring the response of the panels. The tailoring potential of composite panels is further expanded by introducing the concept of variable stiffness laminates. Variable stiffness implies that fibre paths are not necessarily straight but can be continuously curved. In this fashion, the stiffness properties at every point of the panel can be varied independently leading to optimal tailoring of the composite panel to design requirements. In this paper, the variation of the stiffness properties is parameterised using lamination parameters, and the fundamental frequency is predicted based on classical lamination theory. A new structural approximation scheme is introduced which is referred to as the generalised reciprocal approximation. The optimality conditions for the problem are formulated based on this generalised reciprocal approximation. Results indicate that significant increase can be achieved of the optimal fundamental natural frequency of variable stiffness panels as compared with panels of constant stiffness. [Copyright &y& Elsevier]

Abstract: The problem of finding laminates having null thermal and hygral expansion or curvature coefficients is addressed in the paper, as well as the case of laminates having an isotropic response to thermal or moisture variations. The main feature of this research is the fact that the problem is treated and solved in the most general case: no simplifying hypotheses are made about the type of the stacking sequence, and the design procedure can also take into account elastic properties of the laminate, such as orthotropy, uncoupling and so on. The authors state the problem as a nonlinear programming problem, where a unique objective function includes all the requirements to be satisfied by the solutions. The nonlinear optimisation problem is stated and solved in the framework of the polar-genetic approach: the formulation is a function of the laminate polar parameters, while a genetic algorithm is used as numerical solving technique. A large number of numerical results are shown in the paper. [Copyright &y& Elsevier]

Abstract: This paper explores the metaheuristic approach called scatter search for lay-up sequence optimisation of laminate composite panels. Scatter search is an evolutionary method that has recently been found to be promising for solving combinatorial optimisation problems. The scatter search framework is flexible and allows the development of alternative implementations with varying degree of sophistication. The main objective of this paper is to demonstrate the effectiveness of the proposed scatter search algorithm for the combinatorial problem like stacking sequence optimisation of laminate composite panels. Preliminary investigations have been carried out to compare the optimal stacking sequences obtained using scatter search algorithm for buckling load maximisation with the best known published results. Studies indicate that the optimal buckling load factors obtained using the proposed scatter search algorithm found to be either superior or comparable to the best known published results. Later, two case studies have been considered in this paper. Thermal buckling optimisation of laminated composite plates subjected to temperature rise is considered as the first case study. The results obtained are compared with an exact enumerative study conducted on the problem to demonstrate the effectiveness and performance of the proposed scatter search algorithm. The second case study is optimisation of hybrid laminate composite panels for weight and cost with frequency and buckling constraints. The two objectives are considered individually and also collectively to solve as multi-objective optimisation problem. Finally the computational efficiency of the proposed scatter search algorithm has been investigated by comparing the results with various implementations of genetic algorithm customised for laminate composites. It was shown in this paper through numerical experiments that the scatter search is capable of finding practical solutions for optimal lay-up sequence optimisation of composite laminates and results are comparable and sometimes even superior to genetic algorithms. [Copyright &y& Elsevier]

In the present paper, we propose a method for the optimization of composite structures with continuous spatial variation of fiber angle. The key idea is to construct a continuous global function interpolating scattered design points to represent the fiber angle arrangement throughout the design domain. To be more specific, the Shepard interpolation method is employed to construct the interpolation function. The angles at scattered design points are taken as the design variables to be optimized. The Shepard interpolation inherently guarantees spatial continuity of fiber angle. In addition, the design freedom of the proposed method can be readily enlarged by increasing the number of design points or the number of design variables to accommodate complex or rapid local variation of fiber angle. Several examples with in-plane load are investigated. In the simple representative numerical examples, the proposed method shows good performance. [ABSTRACT FROM AUTHOR]

One of the fundamental criteria in the design of air structures is to achieve required strength at the highest possible reduction of structure weight w . However, it is necessary to keep the second design parameter i.e. stiffness of the air structural element on the proper level in order to satisfy durability and reliability of aircrafts. This paper presents the application of an integrated system based on artificial neural networks and calculations by the finite element method (FEM) for the optimization of geometry of a thin-walled element of an air structure. The main criterion of optimization was to reduce the structure’s weight w at the lowest possible deformation (high stress level) of the tested object. The objective of the analyses – using artificial neural networks (ANN) – was to investigate the effect of 4 individual variables defining geometry of the model (including: system of ribs and their inclination, system of holes in ribs and side walls) on its deformation and final value of the reduced weight w . Numerical analysis showed that the most important variable is the diameter of holes in the side walls of the model. [ABSTRACT FROM AUTHOR]

Structural damage identification has been researched for a long time and continues to be an active research topic. This paper proposes the use of the natural frequencies of a novel composite structures made of glass fibre reinforced polymer (GFRP). The proposed methodology consists of an improved Artificial Neural Network (ANN) using optimization algorithms to detect the exact crack length. In the first step, the characterization of fabricated material is provided to determine Young's modulus using an experimental static bending test, tensile test and modal analysis test. Next, numerical validation is performed using commercial software ABAQUS to extract more data for different crack locations in the structure. The comparison between experimental and numerical results shows a good agreement. ANN has been improved using recent optimization techniques such as Jaya, enhanced Jaya (E-Jaya), Whale Optimization Algorithm (WOA) and Arithmetic Optimization Algorithm (AOA) to calibrate the influential parameters during training. After considering several scenarios, the results show that the accuracy of E-Jaya is better than other optimization techniques. This study on crack identification using improved ANN can be used to investigate the safety and soundness of composite structures. [ABSTRACT FROM AUTHOR]

The paper describes the novel optimization techniques for lightweight design of composite beams. The optimization model is to find width and depth of composite beams to minimize the mass of beams under the stiffness, strength and delamination failure constraints. The exact formulae for displacements, stresses and their sensitivities with respect to width and depth are derived using Timoshenko continuous beam theory. The analytical stiffness, strength and delamination failure functions, and their gradients are obtained using the exact expressions of displacements and stresses, and their sensitivities. The mass and its gradient are also expressed analytically. The standard gradient-based nonlinear programming algorithms are employed to solve lightweight design problems of composite beams. The lightweight designs of composite beams are performed using the proposed optimization techniques. Three standard gradient-based optimization methods (SQP, interior-point and active-set) using exact derivatives converge to the same lightweight design. However, gradient-based algorithms using finite difference sensitivities may not lead to optimal lightweight designs. It is necessary to develop exact sensitivity analysis method instead of the difference methods for gradient-based algorithms. [ABSTRACT FROM AUTHOR]

This paper presents the application of the harmony search algorithm (HSA) and some of its variants in the optimization of the stacking sequence of laminated composites. The optimization objective is to maximize the bucking load of a symmetric and balanced laminated plate. Performance and sensitivity to the parameters harmony memory size (HMS), harmony memory consideration rate (HMCR) and pitch adjusting rate (PAR) are determined based on the algorithm apparent reliability. A modified version of the pitch adjustment is proposed and its positive impact on the reliability is demonstrated. The best performance of the basic HSA is obtained using low PAR with high HMS and HMCR. The variants of HSA consider a linear variation of the pitch adjusting rate during the optimization. Increasing PAR reduce the HSA sensitivity to this parameter and lead to fast rise of reliability in the beginning of the optimization and high reliability at the end of the search. Decreasing PAR resulted in excellent reliability for long searches, but the chance to find a global optimum is drastically reduced for short optimizations. The last example demonstrate that HSA is more efficient than other metaheuristic methods, although it is less reliable than a special version of genetic algorithm. [ABSTRACT FROM AUTHOR]

The problem of design and failure analysis of composite tank covers is discussed in the paper. Covering systems consist of segmental parts of tanks, independently on tank structure. Composite covers have several advantages connected with structure, transport and assembly. Additionally, the construction divided into several sections enables repair and inspection improving. However, on the one hand, failure of the tank covers, which are occurred sometimes, and on the other hand new applications, make it necessary to develop design, analysis and optimization of these structures. In this study, the main advantages of the GRP covers are shown against other covers and roofs systems. The construction of the representative rectangular composite tank cover, segments and joints are described. Failure analysis of the covering segment under combined loading is presented. The exemplary cover was built in the sewage treatment plant in Poland. The cover is built of repetitive two-wave segments with flanges overlapping one another. The segments are made of mixed glass-fiber reinforced plastic laminates. The cover is subjected to the following static loads: dead load, technological vacuum, snow and ice and local load (workers with tools). Static analysis of the exemplary cover was conducted using the finite element code MSC.Marc. The considerations include shell geometry of the cover, structural GRP laminates with specified ply sequences, segment connections of rivet nut–bolt and anchor–nut types, friction at the interface between flanges and between flanges and tank walls. Safety coefficients have been analyzed for the different elements of the exemplary composite cover. [ABSTRACT FROM AUTHOR]

The improvement of blast resistance of supporting elements by application of protective cover is the main goal of this paper. Developed sandwich panel is very effective in blast protection, however, such solutions are sensitive to the design parameters including thickness of components, stiffness and strength of materials and panel lay-up. Therefore, a numerical optimization based on computational mechanics was implemented to reduce deformations of protected supporting structure caused by blast loading. Optimization was based on the simplified FE model which consisted of laminate parts, metallic foam, steel external cover and I-beam pillar. The model was automatically generated depending on the optimization variables using a developed pre-processor script. The delamination process was also taken into consideration. Dynamic response of structural components subjected to the blast wave in different cases was analysed. Obtained results clearly showed that application of the optimized blast panel reduces the plastic deformation of the structure and significantly increases the blast resistance. Moreover, the obtained parameters were verified using fully 3D FE model of protective panel with pillar with FSI interface. [ABSTRACT FROM AUTHOR]

3D woven composites have the potential to revolutionise structural composites, provided the knock-down in in-plane properties can be minimised through weave optimisation. Since binder tow interactions produce waviness in warp and weft tows, 3D weaving process needs optimisation. This paper presents a predictive modelling tool based on Representative Volume Elements (RVEs) of 3D weaves capturing the binder size as a function of the weaving process. Implemented in Abaqus, this predictive tool is able to predict elastic constants and strength with a reasonable accuracy compared to experimental data. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to generate and optimize parallel fiber trajectories on general non planar surfaces based on level-sets and the Fast Marching Method. Starting with a (possibly curved) reference fiber direction defined on a (possibly curved) meshed surface, the new method allows defining a level-set representation of the fiber network for each ply, and so defining the fiber trajectories. This new approach is then used to solve optimization problems, in which the stiffness of the structure is maximized (minimum compliance problem). The design variables are the parameters defining the position and the shape of the reference curve. The shape of the design space is discussed, regarding local and global optimal solutions. The possibility to include in the optimization problem a limitation on the curvature of the trajectories is also addressed. [ABSTRACT FROM AUTHOR]

The anisotropic hexagonal honeycomb is one of the common honeycombs. To increase its in-plane stiffness greatly, in this paper the anisotropic multifunctional hierarchical honeycomb (AMHH) is proposed. It is constructed by replacing the solid cell walls of the original anisotropic hexagonal honeycomb (OAHH) with the equal mass isotropic substructures, triangular or Kagome honeycombs. Two kinds of AMHH structures are proposed. One corresponds to the OAHH with 120° angles between the jointed cell walls, the other one corresponds to the OAHH with angles between the jointed cell walls different from 120°. Through Euler beam theory, the in-plane stiffness of these two kinds of AMHH is analyzed. Results show that the triangular honeycomb substructures could greatly increase the in-plane stiffness of the AMHH by 1.5 times or even more than 100 times, depending on the thickness-to-length ratio of the oblique cell wall of the OAHH. And the validation of the range for the thickness-to-length ratio of the oblique cell wall, which is related to the density of the OAHH, could reach to 0.1. The present theory could be used for designing new tailorable anisotropic hierarchical honeycomb materials for multifunctional applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a non-parametric material-orientation optimization method for frequency response, a dynamic design problem of a laminated shell structure composed of orthotropic carbon-fiber-reinforced plastic (CFRP) materials. The squared vibration displacements in the arbitrarily prescribed evaluation area are minimized at a given frequency or in a given frequency band. This optimal design problem to determine the optimal material-orientation distribution is formulated as a distributed-parameter system optimization problem based on the variational method, and the sensitivity function with respect to the variation of the material-orientation is theoretically derived. The optimal material-orientation distribution is determined by the H1 gradient method with Poisson's equation. With this method, the objective function is minimized while controlling the smoothness and the curvature distribution of the material-orientation. Numerical results show the effectiveness of the proposed method for obtaining the optimal material-orientation distribution of each layer that minimizes the squared vibration displacements at the given frequency or in the given frequency band. Also, the prototypes for the initial and the optimized material-orientation distribution are fabricated by the tailored fiber placement technique (TFP), and the static stiffness and the frequency response are experimentally evaluated. The results are compared with the calculated ones and discussed. [ABSTRACT FROM AUTHOR]

Core shearing and core/face debonding are two common failure states of sandwich beams which are mainly the result of excessive shear stresses in the core. Generally, the core made of homogeneous Fiber Reinforced Polymer (FRP) shows better shear resistance in comparison with that made of pure polymer. Usually, this enhancement is however somewhat limited. This paper proposes a methodology to decrease interfacial stresses by presenting the optimal distribution of reinforcing ingredients in the polymeric matrix. For this purpose, a Non-Uniform Rational B-spline (NURBS) based reinforcement distribution optimizer is developed. This technique aims at the local stress minimization within any arbitrary zone of the design domain. In our methodology, optimization and model analysis (calculation of the objective function and the design constraints) have common data sets. The quadratic NURBS basis functions smoothly define the reinforcement distribution function as a NURBS surface. The core and face sheets are modeled as multi-patches and compatibility in the displacement field is enforced by the penalty method. An adjoint sensitivity method is devised to minimize the objective function within areas of interest defined over arbitrary regions in the design domain. It is also used for efficient updating of design variables through optimization iterations. The method is verified by several examples. [ABSTRACT FROM AUTHOR]

This paper introduces a two-scale topology optimization approach by integrating optimized structures with the design of their materials. The optimization aims to find a multifunctional structure composed of homogeneous porous material. Driven by the multi-objective functions, macrostructural stiffness and material thermal conductivity, stiff but lightweight structures composed of thermal insulation materials can be achieved through optimizing the topologies of the macrostructures and their material microstructure simultaneously. For such a two-scale optimization problem, the effective properties of materials derived from the homogenization method are applied to the analysis of macrostructure. Meanwhile, the displacement field of the macrostructure under given boundary conditions is used for the sensitivity analysis of the material microstructure. Then, the bi-directional evolutionary structural optimization (BESO) method is employed to iteratively update the macrostructures and material microstructures by ranking elemental sensitivity numbers at the both scales. Finally, some 2D and 3D numerical examples are presented to demonstrate the effectiveness of the proposed optimization algorithm. A variety of optimal macrostructures and their optimal material microstructures are obtained. [ABSTRACT FROM AUTHOR]

This paper proposes a novel anchor toward large-sized fiber-reinforced polymer (FRP) cable with multi tendons and optimizes the key factors that affect anchor efficiency using finite element method (FEM). The limitations of conventional anchors for FRP tendons/cables were first analyzed. A new type of conical anchor with novel continuous-fiber-reinforced load transfer component (LTC) was proposed to overcome shortcomings of conventional anchors. The four key factors affecting anchor efficiency including modulus variation, conical degree, anchor length and the thickness of LTC were analyzed respectively. The results show that the proposed anchor not only owns an essential advantage in bonding by integrating LTC and FRP cable but also realizes the variable modulus of LTC by changing the winding angle of fiber roving. The optimization of key factors reveals that the avoidance of shear and compressive stress concentration can be realized by LTC modulus variation, while the conical degree of LTC significantly affects compressive stress distribution and cable axial displacements. The anchor length controls both compressive stress distribution and peak shear stresses, whereas the LTC thickness at the loading end only affects the peak compressive stresses and axial displacement. The optimization of above four factors determines the design of the proposal anchor. [ABSTRACT FROM AUTHOR]

This work deals with the problem of the optimum design of a sandwich panel. The design process is based on a general two-level optimisation strategy involving different scales: the meso-scale for both the unit cell of the core and the constitutive layer of the laminated skins and the macro-scale for the whole panel. Concerning the meso-scale of the honeycomb core, an appropriate model of the unit cell able to properly provide its effective elastic properties (to be used at the macro-scale) must be conceived. To this purpose, in this first paper, we present the numerical homogenisation technique as well as the related finite element model of the unit cell which makes use of solid elements instead of the usual shell ones. A numerical study to determine the effective properties of the honeycomb along with a comparison with existing models and a sensitive analysis in terms of the geometric parameters of the unit cell have been conducted. Numerical results show that shell-based models are no longer adapted to evaluate the core properties, mostly in the context of an optimisation procedure where the parameters of the unit cell can get values that go beyond the limits imposed by a 2D model. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a methodology for simultaneous topology and material optimization in optimal design of laminated composite beams with eigenfrequency constraints. The structural response is analyzed using beam finite elements. The beam sectional properties are evaluated using a finite element based cross section analysis tool which is able to account for effects stemming from material anisotropy and inhomogeneity in sections of arbitrary geometry. The optimization is performed within a multi-material topology optimization framework where the continuous design variables represent the volume fractions of different candidate materials at each point in the cross section. An approach based on the Kreisselmeier–Steinhauser function is proposed to deal with the non-differentiability issues typically encountered when dealing with eigenfrequency constraints. The framework is applied to the optimal design of a laminated composite cantilever beam with constant cross section. Solutions are presented for problems dealing with the maximization of the minimum eigenfrequency and maximization of the gap between consecutive eigenfrequencies with constraints on the weight and shear center position. The results suggest that the devised methodology is suitable for simultaneous optimization of the cross section topology and material properties in design of beams with eigenfrequency constraints. [Copyright &y& Elsevier]

Abstract: An optimization scheme using the Cell-based Smoothed Finite Element Method (CS-FEM) combined with a Genetic Algorithm (GA) framework is proposed in this paper to design shape adaptive laminated composite marine propellers. The proposed scheme utilize the bend-twist coupling characteristics of the composites to achieve the required performance. An iterative procedure to evaluate the unloaded shape of the propeller blade is proposed, confirming the manufacturing requirements at the initial stage. The optimization algorithm and codes developed in this work were implemented under a variety of parameter settings and compared against the requirement to achieve an ideally passive pitch varying propeller. Recommendations for the required thickness of the propeller blade to achieve optimum bend-twist coupling performance without resulting large rake deformations are also presented. [Copyright &y& Elsevier]

Abstract: The potential for enhanced postbuckling performance of flat plates using variable angle tow (VAT), in comparison with conventional laminated composites, has been shown previously. This paper presents an optimisation strategy for the design of postbuckling behaviour of VAT composite laminates under axial compression. The postbuckling performance of composite laminated plates for a given compression loading is assessed by studying both the maximum transverse displacement and the end-shortening strain. For the postbuckling analysis of VAT composite plates, an efficient tool based on the variational principle and the Rayleigh–Ritz method is developed. In the optimisation study, a mathematical definition based on Lagrangian polynomials, which requires few design parameters, is used to define a general fiber angle distribution of the VAT plate. A genetic algorithm is subsequently used to determine the optimal VAT configuration for maximum postbuckling performance. The optimisation of square VAT laminates under compression loading for different in-plane boundary conditions is studied and compared with straight fiber designs. [Copyright &y& Elsevier]

Abstract: This paper presents a study of the impact resistance of honeycomb structure with the purpose to mitigate impact forces. The objective is to aid in the choice of optimal parameters to minimize the thickness of the honeycomb structure while providing adequate protection to prevent injury due to head impact. Studies are presented using explicit dynamic finite element analysis representing the case of an unprotected drop of a rigid impactor onto a simulated floor consisting of vinyl composition tile and concrete. Analysis of honeycomb material to reduce resulting accelerations is also presented where parameters such as honeycomb material modulus, wall thickness, cell geometry and structure depth are compared to the unprotected case. A simplified optimization analysis technique using a genetic algorithm is presented to demonstrate the use of this method to select a minimum honeycomb depth to achieve a desired acceleration level at a given level of input energy. It is important to select a minimum material depth in that smaller dimensions lead toward more aesthetic design that increase the likelihood that the device is used. [Copyright &y& Elsevier]

Abstract: Hybrid Composite Structures (HCSs) are consisting of alternating layers of Fiber-Reinforced Polymer and metal sheets. Mechanical properties and responses for off-design conditions of HCSs can be improved using an innovative methodology coupling Multi-Objective Genetic Algorithm and robust design method. The concept of robust design approach ensures that a structure will be tolerant to unexpected loading and operating conditions. In this paper, two applications are considered; the first is to maximise the stiffness of the HCS while minimising its total weight through a Multi-Objective Design Optimisation. The second application considers a Robust Multi-Objective Design Optimisation (RMDO) to minimise total weight of HCS and to minimise both, the normalised mean displacement and the standard deviations of displacement, considering critical load cases. For the optimisation process, a distributed/parallel Multi-Objective Genetic Algorithm in robust multi-objective optimisation platform is used and it is coupled to a Finite Element Analysis based composite structure analysis tool to find the optimal combination of laminates sequences for HCSs. Numerical results show the advantages in mechanical properties of HCS over the metal structures, and also the use of RMDO methodology to obtain higher characteristics of HCS in terms of mechanical properties and its stability at the variability of load cases. [Copyright &y& Elsevier]

Abstract: A multi-parameter optimization approach for a lightweight FRP composite triangular truss under nonlinear structural response constraints is presented in this paper. The composite truss exhibited bilinear behavior under three-point bending which was observed by both experimental and numerical investigation. Sensitivity analysis was conducted to evaluate the effects of geometric parameters on the flexural performance of the composite truss. A response surface, developed from a finite element analysis, was employed to replicate the outputs of nonlinear structural responses with respect to four key geometric parameters. Gradient-based and Genetic Algorithm optimization processes were selected and implemented from the MATLAB Optimization Toolbox. Final adjustments to the optimal design, obtained using MATLAB, were made according to the results of sensitivity analysis. The results show that significant improvement in terms of weight saving were achieved by adopting the proposed optimization design procedure. [Copyright &y& Elsevier]

Abstract: Sandwich structures are shown to have better blast resistance when compared to the solid metallic plate for the same weight. Hybrid Sandwich Panel (HSP) further increases the blast resistance with addition of hyper-elastic material in between the face sheet and core. In this paper, the studied HSPs are composed of five layers, where the front and back face sheets are made of Rolled Homogeneous Armor (RHA) steel, and two interlayers of polyurethane (PU) and aluminum alloy foam (Alporas™) core. Finite element analysis (FEA) software (Abaqus®) is used to simulate deflection and energy absorption of a circular clamped HSP under a spherical blast loading from a fixed distance. Twenty-eight FE models with different design configuration are sampled using modified Grid Sampling method. Based on the FE simulated samples, a surrogate model is developed using Kriging for the fast computation of the HSP performance in the design optimization. The HSP is optimized to achieve two conflicting objectives, light weight and high energy absorption, with an overall panel thickness limit of 100mm. [Copyright &y& Elsevier]

Abstract: This paper presents an optimization procedure to design laminated composites with improved damage resistance and tolerance. The ant colony optimization algorithm is used to minimize the predicted induced damage during a low velocity drop weight impact event on a dispersed panel. The orientation angle for each layer can be selected as a discrete variable in the domain of −85° to 90°, at 5° intervals. Two case studies are analyzed. In the first one the predicted damage area is minimized whereas, in the second one, the absorbed elastic strain energy is maximized. The results show that this problem is a multi-optimum problem. By using this methodology on dispersed laminates, the predicted impact damage area can be reduced by more than 20% while the objective function of the second case can be improved by 8% compared to the traditionally designed configurations. These results evidence the possibility to improve the damage tolerance using dispersed laminates. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this paper a global optimisation technique for the design of damping properties of hybrid elastomer/composite laminates is presented. The goal of the procedure is to maximise the first N modal loss factors of the laminate subject to constraints on the in-plane and out-of-plane stiffness along with a constraint on the weight of the plate. The problem is considered in the most general case: no simplifying hypotheses are made on the behaviour of the hybrid laminate, thus allowing us to consider as design variables the number of layers (both of the elastic and viscoelastic layers), their thickness and orientations as well as the position of the viscoelastic plies within the stacking sequence. The proposed approach relies on one hand, upon the dynamic response of the structure in terms of natural undamped frequencies and modal loss factors which are evaluated using the well-known Iterative Modal Strain Energy (IMSE) method, and on the other hand on the use of genetic algorithms as optimisation tool to perform the solution’s search. As an example, the method is applied to a rectangular plate and the results demonstrate the effectiveness of the proposed strategy. [Copyright &y& Elsevier]

Abstract: This paper discusses three different rim design cases of a hybrid composite flywheel rotor using strength ratio optimization. The rotor is composed of four hybrid composite rims. These rims are made from carbon–glass/epoxy with varying volume fractions of hoop wound reinforcements. Optimization is performed to reduce the maximum strength ratio during two rotor states: stationary and the maximum allowable rotational speed. The input specifications for optimization are: maximum useable energy (35kWh), rotational speed (15,000rpm), height, and inner radius. In the first case, the rims are wound simultaneously by continuous winding. However, in the second case, the rims are wound separately, and interferences are incorporated for their assembly by press fit. In the third case, a hybrid version of the first two cases is used, whereby two pairs of rims are wound at the same time, and in a secondary operation, the first pair is press fitted to the second pair. Each case has different fabrication costs and different strength ratios. The third case rotor has been successfully manufactured by filament winding with in situ curing, followed by press fit assembly of machined rims. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: This investigation pursues two goals. One of them is developing a three-dimensional finite element with an embedded interface for analyzing the laminated composite structure. The composite element efficiency is numerically proven. Delaminatoin is an important failure mechanism in certain types of composite structures. Detecting this type of damage is currently a problem of interest to the structural health monitoring community. The second goal of the paper is presenting a novel and well-organized procedure for the identification of delaminatoin in laminated composite beams. The damage identification scheme is formulated by an inverse problem, where analysis data from related finite element modeling, are used to quantify the magnitude and local of delaminatoin. The inverse problem is then transformed to an optimization statement, and the optimum delaminatoin parameters are found by minimizing the objective function. In this study, a genetic algorithm is used for the optimization process. Several numerical examples are analyzed for the accuracy test, and a few of them are presented here. [Copyright &y& Elsevier]

Abstract: A variable stiffness design can increase the structural performance of a composite plate and provides flexibility for trade-offs between structural properties. In this paper, we examine the simultaneous optimization of stiffness and buckling load of a composite laminate plate with curvilinear fiber paths. The problem, which falls in the area of multi-objective optimization, is formulated and solved through a surrogate-based optimization algorithm capable of finding the set of optimum Pareto solutions. We integrate surrogate modeling into an evolutionary algorithm to reduce the high computational cost required to solve the optimization process. The results show that a curvilinear fiber path can increase both buckling load and stiffness simultaneously over the quasi-isotropic laminate. Furthermore, the optimum direction for varying the fiber angle is dependent on the loading direction and boundary conditions. The results for a plate under uniform compression with free transverse edges shows that varying the fiber orientation perpendicular to the loading direction can increase the buckling load by 116% with respect to that of a quasi-isotropic laminate. [Copyright &y& Elsevier]

Abstract: This paper deals with the structural response of fully-clamped quadrangular GLARE panels subjected to an intense air-blast load using the commercial finite element software, LS-DYNA. A cohesive tie-break algorithm is implemented to model interfacial debonding between adjacent plies. The blast loads was simulated using a ConWep blast algorithm and a multi-material ALE formulation with fluid–structure interaction to determine the performance of each method. Numerical model validation have been performed considering case studies of GLARE panels subjected to spherical explosive charges of C-4, for which experimental data on the back face-displacement and post-damage observations were available. Excellent agreement of mid-point deflections and evidence of severe yield line deformation were presented and discussed against the performed blast tests. [Copyright &y& Elsevier]

Abstract: This paper deals with optimizing the representative volume element (RVE) of 2.5D interlock composites for enhanced damage resistance and elastic stiffness. The elastic moduli of the composite are determined as a volume average of the moduli of the matrix and fiber, while the overall resistance to failure is obtained through incremental use of the 3D Tsai-Wu failure criterion. The variables considered for the optimization problem are the volume fractions of the fibers, their proportions in each direction and the weaving step of the vertical reinforcement. The optimization is carried out using a sequential quadratic programming approach (SQP) and the results are validated against experimental data obtained for 2.5D interlocks with carbon reinforcements. [Copyright &y& Elsevier]

Abstract: This paper presents a multiobjective optimization methodology for composite stiffened panels. The purpose is to improve the performances of an existing design of stiffened composite panels in terms of both its first buckling load and ultimate collapse or failure loads. The design variables are the stacking sequences of the skin and of the stiffeners of the panel. The optimization is performed using a multiobjective evolutionary algorithm specifically developed for the design of laminated parts. The algorithm takes into account the industrial design guidelines for stacking sequence design. An original method is proposed for the initialization of the optimization that significantly accelerates the search for the Pareto front. In order to reduce the calculation time, Radial Basis Functions under Tension are used to approximate the objective functions. Special attention is paid to generalization errors around the optimum. The multiobjective optimization results in a wide set of trade-offs, offering important improvements for both considered objectives, among which the designer can make a choice. [ABSTRACT FROM AUTHOR]