Design Of Composite Laminates Research Articles

Stacking sequence optimization of composite laminates for maximum buckling load using permutation search algorithm

Due to the involvement of large number of design variables, it is still one of the key concerns to build an efficient optimization algorithm for the stacking sequence design of composite laminates with various constraints. In this work, the flexural stiffness parameters are expressed in terms of the ply orientations, which helps to formulate the maximum of buckling load factor as a problem of identifying the optimum ply orientation at stacking positions. Afterwards, we suggest a permutation search (PS) algorithm to reduce the evaluations in stacking sequence optimization of composite laminates. In the first stage, permutation operations are sequentially performed for each permutation position, and in the second stage a repair strategy is adopted for overcoming the violation of constraints while maximizing the value of the objective function. A comparison has been performed between the PS and three genetic algorithm (GAs) methods. It has been demonstrated that the number of process analyses for stacking sequence optimization are greatly reduced by the PS algorithm. The novel PS algorithm combined with the modified repair strategy outperforms the studied GA methods for constrained stacking sequence optimization of composite laminate both in computational performance and finding the optimal objective value with high reliability.

Effect of interlaminar toughness on the low‐velocity impact damage in composite laminates

Based on the continuum damage mechanics (CDM) and the cohesive zone model (CZM), a numerical analysis method for the evaluation of damage in composite laminates under low‐velocity impact is proposed. The intraply damage including matrix crack and fiber fracture is represented by the CDM which takes into account the progressive failure behavior in the ply, using the damage variable to describe the intraply damage state. The delamination is characterized by a special contact law including the CZM which takes into account the normal crack and the tangential slip. The effect of the interlaminar toughness on the impact damage is investigated, which is as yet seldom discussed in detail. The results reveal that as the interlaminar fracture toughness enhances, the delamination area and the dissipated energy caused by delamination decrease. The contribution of normal crack and tangential slip to delamination is evaluated numerically, and the later one is the dominant delamination type during the impact process. Meanwhile, the numerical prediction has a good agreement with the experimental results. The study is helpful for the optimal design and application of composite laminates, especially for the design of interlaminar toughness according to certain requirements. POLYM. COMPOS. 37:1085–1092, 2016. © 2014 Society of Plastics Engineers

3D FEA modelling of laminated composites in bending and their failure mechanisms

This paper developed three-dimensional (3D) Finite Element Analysis (FEA) to investigate the effect of fibre lay-up on the initiation of failure of laminated composites in bending. Tsai-Hill failure criterion was applied to identify the critical areas of failure in composite laminates. In accordance with the 3D FEA, unidirectional ([0]16), cross-ply ([0/90]4s) and angle-ply ([±45]4s) laminates made up of pre-preg Carbon Fibre Reinforced Plastics (CFRP) composites were manufactured and tested under three-point bending. The basic principles of Classical Laminate Theory (CLT) were extended to three-dimension, and the analytical solution was critically compared with the FEA results. The 3D FEA results revealed significant transverse normal stresses in the cross-ply laminate and in-plane shear stress in the angle-ply laminate near free edge regions which are overlooked by conventional laminate model. The microscopic images showed that these free edge effects were the main reason for stiffness reduction observed in the bending tests. The study illustrated the significant effects of fibre lay-up on the flexural failure mechanisms in composite laminates which lead to some suggestions to improve the design of composite laminates.

Stacking Design of Composite Laminate in Wheelchair Structure under Seat Loading

For designing the wheelchair structure under the seat loading, the stresses and failure indexes in each ply of the composite laminate are obtained by the finite element analysis. Using the Tsai-Wu criterion and delamination criterion, the stacking sequence [04/904/454/-45]s is the final optimal design for the wheelchair frame. On the contrary, the uni-directional laminates, i.e. [9013] s, [4513] s and [-4513] s, are bad designs.

Study on Mechanical Behaviors of Variable-Stiffness Composite Laminates

In this paper, we study the mechanical behaviors of variable-stiffness composite laminates by setting curvilinear fiber paths. We assume that the fiber orientation angles vary linearly with the reference axis. Based on the different fiber paths, we vary the fiber placement formats and the curvilinear fiber orientation angles of the composite laminates, and then make the simulation for the buckling loads of the three kinds of laminates: the straight fiber placement, the curvilinear fiber placement and the mixed fiber placement. By comparing and analyzing, we give the best fiber placement format and the curvilinear fiber orientation angle. The study provides references to the design of variable-stiffness composite laminates.

Novel fabrication techniques for low-mass composite structures in silicon particle detectors

The structural design of silicon-based particle detectors is governed by competing demands of reducing mass while maximizing stability and accuracy. These demands can only be met by fiber reinforced composite laminates (CFRP). As detecting sensors and electronics become lower mass, the motivation to reduce structure as a proportion of overall mass pushes modern detector structures to the lower limits of composite ply thickness, while demanding maximum stiffness. However, classical approaches to composite laminate design require symmetric laminates and flat structures, in order to minimize warping during fabrication. This constraint of symmetry in laminate design, and a “flat plate” approach to fabrication, results in more massive structures. This study presents an approach to fabricating stable and accurate, geometrically complex composite structures by bonding warped, asymmetric, but ultra-thin component laminates together in an accurate tool, achieving final overall precision normally associated with planar structures. This technique has been used to fabricate a prototype “I-beam” that supports two layers of detecting elements, while being up to 20times stiffer and up to 30% lower mass than comparable, independent planar structures (typically known as “staves”).

Optimization of Laminated Composites by Using Genetic Algorithm and the Polar Description of Plane Anisotropy

The object of the present work is the development and application of a quite general approach to optimal design of composite laminates where elastic symmetries can also be explicitly expressed as criteria of the optimization process. Our formulation is in the form of a highly nonlinear and nonconvex single- or multi-objective optimization problem subject to equality and inequality constraints. We show here applications to the design of maximum stiffness, maximum buckling load, maximum eigenfrequencies, maximum strength for laminated plates, as well as combinations of the aforementioned criteria; all types of elastic symmetries can be taken into account. We show here a number of numerical solutions found using the genetic algorithm BIANCA.

Optimization of fiber-reinforced laminates for a maximum fatigue life by using the particle swarm optimization. Part I

In practice, the problems connected with the fatigue of composites are intricate because of their complex structure and the fatigue loading. Fatigue tests under different fiber orientation angles are time-consuming and also very expensive. Therefore, it is important to establish a technique to consider the fatigue damage at any fiber orientation angle without having to perform excessive amounts of testing. The general purpose is to elaborate a methodology for finding a globally optimum design of composite laminates subjected to in-plane loads. In this part of the study, the Fawaz–Ellyin model of fatigue life prediction is presented and further validated. The results obtained show that the model can be applied to optimization problems of composites.

Optimization of Stiffness Characteristics for the Design of Bistable Composite Laminates

Asymmetric composite laminates can have a bistable response to mechanical loading. The large deflections that can be achieved by snap-through from one stable state to another, along with a need for small and removable energy input,make themof interest for awide range of engineering applications. After 30 years of research efforts the shapes and response to applied strains of laminates of general layup have been well characterized. More recently, with the development of smart actuators, the design and application of bistable laminates has been considered. This paper presents an optimization technique for the design of bistable laminates enabled by an analytical solution for an asymmetric laminate design. The optimization formulationmaximizes the bending stiffness in the direction of known loading condition while the bending stiffness in the direction of snap-through is minimized. A minimum deflection requirement is applied as a constraint. The design problem has multiple local optima, with the global optimum not intuitively obvious from the problem definition, differing from the typical high-deflection cross-ply solution.

Design of composite laminates for optimum frequency response

In this study, natural frequency response of symmetrically laminated composite plates was optimized. An analytical model accounting for bending–twisting effects was used to determine the laminate natural frequency. Two different problems, fundamental frequency maximization and frequency separation maximization, were considered. Fiber orientation angles were chosen as design variables. Because of the existence of numerous local optimums, a global search algorithm, a variant of simulated annealing, was utilized to find the optimal designs. Results were obtained for different plate aspect ratios. Effects of the number of design variables and the range of values they may take on the optimal frequency were investigated. Problems in which fiber angles showed uncertainty were considered. Optimal frequency response of laminates subjected to static loads was also investigated.

Fold-Resistant Characteristics of the Laminate Composites for Flexible Structure

There is considerable interest in the use of flexible laminate composite materials to improve the deployable structures for space applications. Critical to acceptance of these materials is the ability to achieve high packaging strains without damage. However, there does exist more or less damage during the process of folding and unfolding for the laminate composites. Better understanding of folding damage, therefore, is needed for the design of laminate composites and folding pattern. In this work we present a study on the fold-resistant characteristics of two different laminate composites, which were fabricated by covering the aramid fiber/epoxy and carbon fiber/epoxy prepregs respectively with polyimide film on both sides. The results of tensile tests on 3-layer structure laminate composites show that the fold-resistant properties of aramid fiber/epoxy composites could be improved with increasing of the resin content and decreasing of the fiber bundle diameter. For carbon fiber/epoxy composites, the effects of resin content and fiber bundle diameter on reduction rate of fracture strength were more complex. There existed a best range of resin content and fiber bundle diameter. The microscopic observations show that folding resulted in piling up of resin and damage of reinforcing fiber, which would decrease the mechanical properties.

Reliability-based design of blast-resistant composite laminates incorporating carbon nanotubes

Research efforts have reported on the ability of carbon nanotubes (CNTs) to enhance the stiffness and strength of carbon fiber composites. Systematic design of blast-resistant composites requires considering CNTs–carbon composites characteristics and the uncertainty of blast events. This article suggests a systematic reliability-based design approach where system reliability is used to compute the probability of failure of a composite laminate. A case study for the design of a five-layer composite laminate incorporating CNTs and subjected to uncertain blast event is demonstrated. 0.5–1% CNTs contents by weight seem capable of significantly reducing the composite probability of failure during blast.

Optimum design of laminated composite under axial compressive load

In the present study optimal design of composite laminates, with and without rectangular cut-out, is carried out for maximizing the buckling load. Optimization study is carried out for obtaining the maximum buckling load with design variables as ply thickness, cut-out size and orientation of cut-out with respect to laminate. Buckling load is evaluated using a ‘simple higher order shear deformation theory’ based on four unknown displacements u, v, w b and w s . A C1 continuous shear flexible finite element based on HSDT model is developed using Hermite cubic polynomial. It is observed that for thick anti-symmetric laminates, the non-dimensional buckling load decreases with increase in aspect ratio and increase in fibre orientation angle. There is a decrease in the non-dimensional buckling load of symmetric laminate in the presence of cut-out.

A mean-field micromechanical approach to design of multiphase composite laminates

A mean-field micromechanical model has been applied to design and analysis of nonlinear behavior of multiphase composite laminates. The analysis accounts for visco-elastic–plastic deformations of the composites. Using the developed model, a numerical study has been made, which includes the tensile behavior of angle-ply carbon fiber/polycarbonate composite laminates, thermal expansion behavior of angle-ply grass fiber/polypropylene composite laminates, and thermo-mechanical behavior of angle-ply grass fiber/SiCw/polycarbonate hybrid composite laminates with a high thermal dimensional stability. The simulation has well represented experimental data and provided a new insight into design of multiphase composite laminates.

A general strategy for the optimal design of composite laminates by the polar-genetic method

The object of the present work is the development and application of a totally general approach to optimal design of composite laminates where all the required properties for the laminate are explicitly expressed as criteria of the optimisation process. Our formulation is in the form of a highly non-linear and non-convex single- or multi-objective optimisation problem subject to equality and inequality constraints. We show here applications to the design of maximum stiffness, maximum buckling load, maximum eigenfrequencies, maximum strength as well as combinations of the afore mentioned criteria; all types of elastic symmetries can also be taken into account. In order to keep the same greatest generality in solving our optimisation problem, we developed an evolved version of the genetic algorithm BIANCA for the design of composite laminates. We show here a number of numerical solutions found using BIANCA.

Optimal design of composite laminates with and without cutout undergoing free vibration

In this article, the optimal designs of freely vibrating composite laminates with and without cutout undergoing are investigated. A simple higher order shear deformation theory (HSDT) with four unknown displacements (u 0, v 0, wb, ws ) is employed to obtain the vibration response. A C 1 continuity shear flexible element based on HSDT using the Hermite cubic polynomial is used for the rectangular element. The optimisation exercise is performed using genetic algorithms to maximise the fundamental frequency of vibration. The aspect ratio of the laminate, fibre orientation, thickness of plies, modulus are treated as design variables. On the basis of the investigation, it is observed that the non-dimensional frequency of the laminate with cutout can be higher or lower than those of the laminate without cutout depending on the size of the cutout. The presence of cutout significantly affects the frequency.

Optimum stacking sequence design of composite materials Part II: Variable stiffness design

A composite laminate may be designed as a permutation of several straight-fiber layers or as a matrix embracing fibers positioned in curvilinear paths. The former called a constant stiffness design and the latter known as variable stiffness design. The optimization algorithms used in constant stiffness design were studied in Part I of this review article. This paper completes the previous article by focusing on variable stiffness design of composite laminates. Different parameterization and optimization algorithms are briefly explained and compared and the advantages and shortcomings of each algorithm are discussed.

Design of plates with curved fibre format

Abstract Benefits of directional properties of fibre reinforced composites could be fully utilized by proper placement of the fibres in their optimal spatial orientations. This paper investigates an application of the Rayleigh–Ritz method for design of variable stiffness composite laminates. Local fibre orientation angles are treated as continuous design variables, and their spatial distribution is determined based on an optimality criterion formulation for minimum compliance design. Numerical examples for simply supported rectangular plates are used to demonstrate the improvement in bending stiffness comparing with the results for fixed (constant) fibre orientations in the whole plate domain or for fixed (0°, 45° or 90°) fibre orientations in the unknown in advance sub-domains of the plate.

BIANCA: a genetic algorithm to solve hard combinatorial optimisation problems in engineering

The genetic algorithm BIANCA, developed for design and optimisation of composite laminates, is a multi-population genetic algorithm, capable to deal with unconstrained and constrained hard combinatorial optimisation problems in engineering. The effectiveness and robustness of BIANCA rely on the great generality and richness in the representation of the information, i.e. the structure of populations and individuals in BIANCA, and on the way the information is extensively exploited during genetic operations. Moreover, we developed proper and original strategies to treat constrained optimisation problems through the generalisation of penalisation methods. BIANCA can also treat constrained multi-objective problems based on the construction of the Pareto frontier. Therefore, BIANCA allows us to approach very general design problems for composite laminates, but also to make a step forward to the treatment of more general problems of optimisation of materials and structures. In this paper, we describe specifically the case of optimal design of composite laminates, concerning both the theoretical formulation and the numeric resolution.

Conservative Design Optimization of Laminated Composite Structures Using Genetic Algorithms and Multiple Failure Criteria

This article analyzes the effect of devising a new failure envelope by the combination of the most commonly used failure criteria for the composite laminates, on the design of composite structures. The failure criteria considered for the study are maximum stress and Tsai—Wu criteria. In addition to these popular phenomenological-based failure criteria, a micromechanics-based failure criterion called failure mechanism-based failure criterion is also considered. The failure envelopes obtained by these failure criteria are superimposed over one another and a new failure envelope is constructed based on the lowest absolute values of the strengths predicted by these failure criteria. Thus, the new failure envelope so obtained is named as most conservative failure envelope. A minimum weight design of composite laminates is performed using genetic algorithms. In addition to this, the effect of stacking sequence on the minimum weight of the laminate is also studied. Results are compared for the different failure envelopes and the conservative design is evaluated, with respect to the designs obtained by using only one failure criteria. The design approach is recommended for structures where composites are the key load-carrying members such as helicopter rotor blades.