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The double–double (DD) laminate families that contain two continuous angles, which were proposed by Tsai (“Double–Double: New Family of Composite Laminates,” AIAA Journal, Vol. 59, No. 11, 2021, pp. 4293–4305), opened up a whole new era for composite layups, which are easy to manufacture and design. In the present study, the design space referred to as feasible regions is derived explicitly based on novel formulations for the lamination parameters of DD laminates. This enables the boundaries of the design space to be obtained analytically, providing mathematical support for DD families. The obtained result shows that their design space is larger than that of conventional quadaxial laminates in terms of industrial practices. A homogenization criterion is implemented into the design space, based on which a tailored DD laminate is proposed, expanding design possibilities and enabling homogenization to be achieved using only 16 plies/4 repeats. The work proposed offers significant benefits through practical solutions to making design, manufacturing, and testing simpler and more competitive.

In order to reduce the negative impact on the environment of the current composite materials, renewable sources have been used as raw materials. One of the most promising approaches is the ...

For the past six years, we have been benefiting from the discovery by Tsai and Melo (2014) that the trace of the plane stress stiffness matrix ( tr ( Q ) ) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr ( Q ) turns out to be a measure of the summation of the moduli of the material. It is, therefore, a material property. Additionally, since tr ( Q ) is an invariant of the stiffness tensor Q , independently of the coordinate system, the number of layers, layup sequence and loading condition (in-plane or flexural) in a laminate, if the material system remains the same, tr ( Q ) = tr ( A ∗ ) = tr ( D ∗ ) is still the same. Therefore, tr ( Q ) is the total stiffness that one can work with making it one of the most powerful and fundamental concepts discovered in the theory of composites recently. By reducing the number of variables, this concept shall simplify the design, analysis and optimization of composite laminates, thus enabling lighter, stronger and better parts. The reduced number of variables shall result in reducing the number and type of tests required for characterization of composite laminates, thus reducing bureaucratic certification burden. These effects shall enable a new era in the progress of composites in the future. For the above-mentioned reasons, it is proposed here to call this fundamental property, tr ( Q ) , as Tsai’s Modulus.

The present article deals with micromechanical composite modeling. Both analytical and computational micromechanics approaches are described as well as micromechanical modeling of damage. Based on micromechanics of failure theory, a user subroutine including a progressive damage algorithm is programmed for finite element analysis. Three theory-experiment correlations of tubes under a three-point bending test have been carried out using the bi-phase material model developed along with this project. These studies include three-ply schedules., All the presented work was carried out within the project MATISSE funded by European Commission’s 7th Framework Programme.

Sandwich structures are highly demanded where a high flexural stiffness per weight ratio is needed. The main limiting factor of these materials is the core/skin interface, which tends to delaminate. Tufting is one of the most promising technologies to reinforce this interface along the z-direction. In this article, the energy absorption of tufted sandwich structures under impact loads is evaluated. Six different types of tufted specimens were tested, including both carbon and glass fiber faces with three different tufting densities. The impact behavior of a sandwich panel is proved to be effectively improved by the tufting process.

A general theory of elasticity-based finite element formulation applied to the free edge effect is described in this paper. The F.E. error estimation is also addressed. Optimum mesh criteria based on the even distribution of global and specific error are shown. This technique has been applied to a [±25°/90°] s T300/934 laminate. Four different numerical models have been compared in terms of through-thickness tensile and shear interlaminar stresses, with varying degrees of complexity and yielding various degrees of error. As a result of this study, a reliable numerical model with a low level of error has been obtained. Finally, a theory–experiment correlation study has been carried out over a (+45°, −45°, 0°) s laminate loaded in tension. Both, strain-to-failure and failure mode were successfully correlated.

The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thicknesses is experimentally studied by means of a four-point-bending test. Firstly, the relationships between the used formulae and the results obtained are analyzed on the curved beams with different thicknesses and tested in compliance with ASTM D6415 standard. Secondly, both the interlaminar tensile stresses and the post-failure behaviour are determined. Finally, the critical area, where delamination begins, is reinforced through-the-thickness by means of tufting technology with different densities. The influence on the maximum interlaminar tensile stress as well as delamination evolution of the carbon/epoxy laminated curved beams are analyzed. These results play an important role in the prediction of interlaminar tensile strength and post failure behaviour of laminated curved beams.

Nowadays, a major issue in transportation is weight reduction. This paper deals with weight reduction of about 3.5% over the total weight of a railway vehicle by substituting an aluminium roof with a composite material design. The design was done by static calculations, and this paper deals with the RSSB Standard GMRT 2100 requiring a roof sufficiently strong to resist the penetration into the vehicle of a concrete cube weighing 100 kg dropped from a height of 3.0 m above the roof at 300 km/h. Calculations are carried out by the finite analysis method. Both aluminium and composite roofs are compared.

Infrastructure and rail sectors share two singularities in terms of materials: highly structural performance and strict fire requirements. Moreover, there is a common growing interest in both sectors: the use of organic matrix composite materials due to their high performance, lightweight and in-service behavior. Traditionally, fire fillers have been added to the matrix, decreasing its mechanical performance in a critical way. A study about composite materials formed by three different matrices and four different carbon fibers will be presented in this paper. A number of laminates have been manufactured by using these composite materials in order to analyze both the resin processing and the compatibility of the different matrices and fibers. This study is a need due to the fact that these matrices are fire-related and therefore further problems may arise in comparison with standard matrices.

A key parameter in taking advantage of the exceptional mechanical and physical properties of carbon nanotubes (CNT) is getting a homogeneous dispersion of the nanofiller in the matrix. Micromechanical models are used to predict the properties of composites, but in most cases the calculated results are not comparable with those from experimentation. In the case of epoxy matrices, poorly dispersed CNT are obtained, as has been observed by scanning electron microscopy. The influence of the dispersion in nanocomposite stiffness is estimated developing a new micromechanical model. Several micromechanical models and experimental results are compared with this new model, showing that the latter has better agreement with mechanical tests. In addition, this mathematical formulation could be used with other reinforcements that are poorly dispersed, not only with CNT.

Composite materials are increasing their use in structures used for road transportation vehicles. From car bodies to trucks, these materials are being more popular. This use is obliging designers to take care of topics different to the traditional ones already studied for aerospace applications. Design must be simplified and, what is even more important, commercial codes should be used to continue with the extension of the use of composite materials in non aerospace industry. One of the most important problems arising when dealing with finite element design of composite materials including delamination is the requirement of using huge computer resources to solve the three dimensional stress field in the vicinity of free edges, holes, changes of number of layers and similar discontinuities. To solve this problem, there are some well known techniques as global-local approaches that can be used for designing with good results. From an engineering point of view, the problem is that they are not usually implemented in commercial finite element codes so that engineers can not use them for everyday calculations.

A new analytical mesomechanical approach valid for three-axial as well as 3D braided composite materials is described in this paper. This approach is based on a unit cell scheme and takes into account the geometry and the mechanical properties of both phases, the fiber and the matrix. A finite element analysis has been carried out in order to obtain comparable results between this numerical technique and the new analytical approach proposed in this paper. Two different configurations of 3D braided carbon fiber/epoxy matrix composites have been studied, according to the geometry of the braided preforms: [0°/±20°] and [0°/±30°]. A failure criterion taking into account yarn and matrix degradation has been applied to predict theoretically failure in both configurations. In order to assess the accuracy of the results from both analytical and finite element approaches, an experimental program was performed. A uniaxial tensile stress testing was carried out in both longitudinal and transverse directions of three axial braided specimens. Results obtained in the tests as well as the analytical and finite element approaches will be discussed.

Single-walled carbon nanotubes (SWNT) presents outstanding mechanical properties and therefore are considered very promising reinforcing materials associated to polymeric matrices for high performance applications. In order to obtain such composite materials, it is necessary to purify the SWNTs, and obtain a homogeneous dispersion in the matrix. This paper describes a purification/dispersion process. Two different curing cycles are applied, and their mechanical properties are obtained. The Young's modulus and the tensile strength are studied in both cases.

Angle joints, also named T-joints, used for structural connection of fiberglass bulkheads and decks together or to the ship's shell, have been accomplished by means of boundary angles featuring great thickness and a minimum fillet radius, so that the joints could resist shock loads produced by underwater explosions. IZAR (former Bazan) and the University of Zaragoza have carried out the development of calculations, tools, as well as design and qualification of a new set of T-joints, featuring a large fillet radius and low thickness boundary angle. These joints are lighter, easier to produce, more resistant and tougher than the former ones. This paper describes the process of qualification and assessment of the joint's behavior, based on destructive full-scale tests, which were supported by FE modeling and calculations. This research could allow the designer to design and predict the behavior of any desired new joint. For full consistency of the modeling and calculations, the joint failure mechanism and the point of initiation of failure have been obtained by means of additional acoustic emission tests.

This paper deals with a basic methodology for the application of the finite element (FE) simulation and linear elastic fracture mechanics (LEFM) to predict the onset of delamination growth. The first step of the proposed methodology is the experimental characterisation of material interlaminar fracture in pure mode I (DCB test), pure mode II (ENF test) and mixed mode I+II (MMB test). In the second step, the results of the interlaminar fracture tests are translated from load/displacement data to strain energy release rates by means of test FE simulations; thus, the critical strain energy release rate (Gc), or fracture toughness are obtained as a function of mode ratio. The third step of the methodology consists of applying FE simulations to determine the strain energy release rate (G) and mode ratio for the delamination and then comparing the result to the values of the Gccurve. The main innovative aspect of the paper is that FE simulation is used as a part of the material characterisation process; in fact, data reduction of interlaminar fracture tests is carried out by means of FE simulations. In addition, regarding the practical details of FE application to the proposed methodology, some innovative aspects are introduced, such as the analysis is carried out as a non-linear geometric problem (taken into account large displacements) and considering inside each simulation different elastic properties for the material depending on whether it is under tension or compression. These aspects and the rest of the proposed methodology are validated by the experimental results presented in the paper.

The present article is concerned with the application of the finite element method to the analysis of the onset of delamination growth in composites by means of the virtual crack closure technique (VCCT). The article reviews first the application of linear elastic fracture mechanics (LEFM) to the analysis of delamination, as well as the reasons why the VCC technique is the standard method of combining LEFM and the finite element method to predict onset of delamination growth. The article also reviews the different solutions proposed in the literature to deal with the oscillatory singularity associated with a crack between two dissimilar materials (as is the case for a delamination) and the practical details of the VCCT application in a general 3D analysis. Finally, the results of a numerical study of the mixed mode bending (MMB) interlaminar fracture test are shown. The study applies the concepts reviewed along the rest of this article and presents some practical recommendations for the analysis of a delamination front using finite elements. This review article includes 77 references.

The phenomenon of fatigue is critical for designing structures including elements made of composite materials. The accurate prediction of the life and fatigue resistance of laminated composites is one of the subjects of inquiry in materials science. The ability of predicting the life of laminates is important for designing, operation, and safety analysis of a composite structure under specific conditions. To predict reliably the life of structures, it is necessary to know the mechanisms of cyclic deformation and damage. It is also necessary to develop a qualitative theory of fatigue failure that should be based on the concepts of solids mechanics. Developing such a theory requires to evaluate the microscopic parameters and the macroscopic variables of the material at the level of a laminate and the structure and to determine exactly the load modes acting on the system.

There are two mainstreams in the building industry in the area of carbon fibers: rehabilitation and use as building material. The using of carbon fiber as a building material is taking place slower than as rehab system due to the very low cost of traditional building materials, the limitations of composite structure manufacturing processes and the conservative building regulations concerning materials in all the industrialized countries. However, these three issues are being solved in a very efficient way, as we will see along the coming paragraphs of this paper. This paper is split in two parts, first the carbon fiber as a material system, its typologies, manufacturing processes and industrial presentations will be described. Second, rehab and building applications will be analyzed., En el área de fibra de carbono en la construcción hay actualmente dos líneas de trabajo: reparaciones e implantación en obra: La implantación en la obra civil está avanzando más despacio que la utilización en reparaciones debido al bajo coste de los materiales tradicionales, a la limitación de procesos de fabricación de estructuras de materiales compuestos y al conservadurismo de las normativas de edificación y obra civil en todos los países industrializados. Sin embargo, los tres asuntos mencionados están siendo abordados con eficiencia, como se explicará más adelante. En el presente artículo, se va a describir, el primer lugar, la fibra de carbono, sus tipos, procesos de fabricación y presentaciones industriales. En segundo lugar se tratarán las aplicaciones en la construcción, haciendo énfasis en las reparaciones y en la implantación en obra civil.

This paper presents an experimental study on the energy absorption capability of two different composite profiles; both are realised in glass-polyester pultrusion. One of the profiles is a unidirectional box section, whilst the other, an I section, consists of alternating layers of mat and fabric. For each one of the two profiles, six different trigger geometries are analysed. The results show that the I profile is a good candidate for being considered for energy absorption applications. It is also concluded that when studying a trigger geometry, slight modifications (as the bevel angle of a bevel trigger) can result in important variations of the results.

Composite materials applied to transportation are usually subjected to cyclic loads that extend for periods of time longer than the ones traditionally studied. Therefore, it seems necessary to define a prediction model which would extend its range beyond the traditional 10 6 cycles of the S – N curves. This paper develops a prediction model based on the residual strength degradation of composites when subjected to cyclic loads.