High-Velocity Impact Behaviour of Prestressed Composite Plates under Bird Strike Loading

An experimental and numerical analysis of the response of laminated composite plates under high-velocity impact loads of soft body gelatine projectiles (artificial birds) is presented. The plates are exposed to tensile and compressive preloads before impact in order to cover realistic loading conditions of representative aeronautic structures under foreign object impact. The modelling methodology for the composite material, delamination interfaces, impact projectile, and preload using the commercial finite element code Abaqus are presented in detail. Finally, the influence of prestress and of different delamination modelling approaches on the impact response is discussed and a comparison to experimental test data is given. Tensile and compressive preloading was found to have an influence on the damage pattern. Although this general behaviour could be predicted well by the simulations, further numerical challenges for improved bird strike simulation accuracy are highlighted

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools

Effects of fibre misalignment on the stability of double-curved composites

In the context of developing a novel technology for the automated production of continuously draped preforms, the effects of fibre misalignment on the stability of double-curved, unidirectional plies are investigated. The critical buckling stress as well as correlations with geometric parameters are analysed numerically using a parametric finite element model. For this purpose, a test program is conducted comprising various geometric configurations. The results provide a foundation for extending the investigation to laminates and indicate significant dependencies of the critical buckling stress on the curvature, length-to-thickness ratio and fibre angle

Melting behaviour and crystallisation kinetics of carbon-fibre-reinforced low-melting poly(aryl ether ketone)

The dependence of material properties and residual stress formation on the crystallinity of thermoplastic composites necessitates detailed analyses regarding the melting behaviour and the crystallisation kinetics of employed semi-crystalline matrices as well as accurate crystallisation models. This paper investigates a novel low-melting poly(aryl ether ketone) (LM-PAEK) reinforced with carbon fibres, in the form of TC1225 unidirectional tape, based on isothermal and non-isothermal differential scanning calorimetry (DSC). It is shown that the LM-PAEK matrix features a double melting behaviour and exhibits an absolute crystallinity of roughly . Kinetics parameters are derived from the DSC analyses and the applicability of selected crystallisation models for predicting the relative crystallinity is evaluated based on a comparison with the DSC data. Under isothermal conditions, the modified Hillier model and the parallel Velisaris–Seferis model yield good agreement. In contrast, a dual Nakamura model and a dual Kamal–Chu model yield merely moderate agreement under non-isothermal conditions

RESPONSE OF SANDWICHES UNDERGOING STATIC AND BLAST PULSE LOADING WITH TAILORING OPTIMIZATION AND STITCHING

A numerical study is presented where tailoring optimization and stitching are applied to improve the structural performances of sandwich plates undergoing static and blast pulse pressure loading. The purpose is to recover the critical interlaminar stresses at the interface with the core and contemporaneously keep maximal the flexural stiffness. Optimized distributions of the stiffness properties for the faces are obtained solving an extremal problem whose target is the minimization of the energy due to transverse shear and bending stresses under spatial variation of the stiffness properties, along with the maximization of the energy due to in-plane stresses. The contribution of stitching is computed through 3-D finite element analysis and it is incorporated as modified elastic moduli into the refined, hierarchic zig-zag model employed as structural model to carry out the analysis accurately accounting for the layerwise effects of the out-of-plane transverse shear and transverse normal stresses and deformations. Approximate solutions giving the ply fibre orientation at any point (compatible with the current manufacturing technologies) are considered in the numerical applications. The numerical results show that stitched sandwiches incorporating optimized low-cost glass-fibre plies can achieve the same bending stiffness as sandwiches with uniform stiffness carbon fibre faces, with a consistent reduction of critical out-of-plane stresses. The amplitude of vibrations under blast pulse loading can be consistently reduced with a proper choice of the curvilinear paths of fibres incorporated in the faces

Representative structural element approach for assessing the mechanical properties of automated fibre placement-induced defects

In this paper, a 3D finite element modelling approach is presented to assess the effects of manufacturing defects within composite structures. The mesoscale modelling approach derives the stress-strain response of a composite structure from a representative structural element. A set of tensile and bending loads is used to compute its ABD-Matrix. The boundary conditions of the model are described in detail as is the extraction of the strain and curvature response. The derived stiffness from the presented modelling approach is compared to the classical lamination theory and the models' shortcomings are discussed. Finally, the influence of a gap, an overlap and two different-sized fuzzballs on the macroscopic mechanical properties of a composite structure are evaluated using the presented multiscale modelling approach, thereby providing stiffness matrices influenced by the defects for the use in global models of composite parts

Automated fiber placement: The impact of manufacturing constraints on achieving structural property targets for CFRP-stiffeners

The use of automated fiber placement (AFP) to manufacture integrated CFRP stiffening structures leads to a conflict between structural requirements and process limitations in early design stages. In order to avoid costly design iterations, the presented analytical approach enables the computation of tool geometries that are at the limit of theoretical manufacturability. The model is able to determine the profile of manufacturable omega stiffeners with high accuracy. It is shown that the maximum manufacturable profile parameters depend non-linearly on the properties of the AFP system and the profile itself. This allows prioritization of the profile parameters for the efficient definition of omega stiffeners that should meet distinct structural property targets. The results show that current, non-optimized AFP systems already have the potential to manufacture omega stiffeners with sufficiently high stiffness values when taking into account current aerospace applications

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools

Choc mou basse énergie sur composite interlock 3X: approche expérimentale et numérique

Dans ce travail, on s’intéresse aux mécanismes d’endommagement qui appa- raîssent lors d’un choc mou entre un impacteur déformable en caoutchouc et une plaque composite tissée 3D (interlock 3X). Des impacts basses énergies sont réalisés à l’aide d’une tour de chute. L’impacteur en caoutchouc est de forme hémisphérique. La cible, obtenue par procédé RTM, est en fibre de carbone et résine RTM 6. Plusieurs impacteurs de différentes duretés et de différents diamètres d’une part, et des tissus avec différents degrés de renfort 3D d’autre part, sont disponibles pour cette étude pour permettre une analyse de variabilité ultérieure. Dans ce papier, les résultats obtenus avec un impacteur de diamètre 40 mm sont présentés. L’accent est mis à la fois sur les moyens expérimentaux employés pour l’analyse des endommagements (Analyse par stéréo-corrélation d’images, Thermographie IR, Micro- graphie) et sur les développements numériques menés en parallèle (FEM) avec le logiciel Abaqus. Contrairement aux composites stratifiés UD, la notion de délaminage n’est plus appropriée pour ce type de composite tissé 3D. Des décohésions et ruptures de torons ainsi que des fissurations matricielles sont majoritairement identifiées.AN

Virtual testing of advanced composites, cellular materials and biomaterials: A review

This paper documents the emergence of virtual testing frameworks for prediction of the constitutive responses of engineering materials. A detailed study is presented, of the philosophy underpinning virtual testing schemes: highlighting the structure, challenges and opportunities posed by a virtual testing strategy compared with traditional laboratory experiments. The virtual testing process has been discussed from atomistic to macrostructural length scales of analyses. Several implementations of virtual testing frameworks for diverse categories of materials are also presented, with particular emphasis on composites, cellular materials and biomaterials (collectively described as heterogeneous systems, in this context). The robustness of virtual frameworks for prediction of the constitutive behaviour of these materials is discussed. The paper also considers the current thinking on developing virtual laboratories in relation to availability of computational resources as well as the development of multi-scale material model algorithms. In conclusion, the paper highlights the challenges facing developments of future virtual testing frameworks. This review represents a comprehensive documentation of the state of knowledge on virtual testing from microscale to macroscale length scales for heterogeneous materials across constitutive responses from elastic to damage regimes