Influence of Process and Material Parameters on Impact Response in Composite Structure: Methodology Using Design of Experiments

Even if the mechanical performances of composite materials give new perspectives for the aircraft and space design, the variability of their behavior, linked to the presence of initial microscopic defects or led in service, constitute however a still important brake in their development. As regards particularly the response to fatigue loads or ageing, the behavior of these materials is affected by several sources of uncertainties, notably on the nature of the physical mechanisms of degradation, which are translated by a strong dispersion in life time. In aerospace industry, low energy impact phenomenon is not well known concerning composite materials and composite structures. Many manufacturers use important safety factors to design structures. The aim of this work is to define the most predominant parameters which permit a good response of damage using experiences plans. The differences of these parameters by using Resin Transfer Molding (RTM) or Liquid Resin Infusion (LRI) process than prepreg one is also studied in this work

Theory for planetary exospheres: III. Radiation pressure effect on the Circular Restricted Three Body Problem and its implication on planetary atmospheres

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the stellar radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this third paper, we investigate the effect of the stellar radiation pressure on the Circular Restricted Three Body Problem (CR3BP), called also the photogravitational CR3BP, and its implication on the escape and the stability of planetary exospheres, especially for Hot Jupiters. In particular, we describe the transformation of the equipotentials and the location of the Lagrange points, and we provide a modified equation for the Hill sphere radius that includes the influence of the radiation pressure. Finally, an application to the hot Jupiter HD 209458b reveals the existence of a blow-off escape regime induced by the stellar radiation pressure

Theory for planetary exospheres: I. Radiation pressure effect on dynamical trajectories

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this first paper, we present the complete exact solutions of particles trajectories, which are not conics, under the influence of the solar radiation pressure. This problem was recently partly solved by Lantoine and Russell (2011) and completely by Biscani and Izzo (2014). We give here the full set of solutions, including solutions not previously derived, as well as simpler formulations for previously known cases and comparisons with recent works. The solutions given may also be applied to the classical Stark problem (Stark,1914): we thus provide here for the first time the complete set of solutions for this well-known effect in term of Jacobi elliptic functions

The economic analysis of state aid: Some open questions

The last few years have seen both a significant shift in EU state aid policy towards a more sophisticated economic approach and a great enrichment of the economic literature on state aid. This paper examines the control of state aid in the EU in the light of the new literature. It begins with a discussion of the objectives of state aid control, taking account of the principle of subsidiarity. We discuss whether state aid control should concentrate on limiting the effects of aid on trade and competition (i.e. harm to rivals) or whether the purpose is broader and includes also considerations such as avoiding government failures and encouraging Member States to use state aid more sparingly and target it more efficiently. This leads to a brief analysis of how the appropriate welfare standard to be applied in state aid control would vary according to the weight given to different objectives. The paper then considers the objectives pursued by governments in granting aid with particular emphasis on the concept of market failure. The nature and magnitude of the market failure addressed by a state aid, together with the design of the aid, will strongly influence the extent of any anti-competitive effects. The last two parts (4 and 5) of the paper are devoted to specific problems of assessing anti-competitive effects using the types of information normally available to the aid-granting authorities and the European Commission. Part 4 discusses the problem of assessing the effects on competition of aid schemes and broad classes of aid, when the beneficiaries and even the affected markets are not known. Because Member States grant a vast number of individual aids every year, the Commission has to apply simple criteria to screen out those aids that are unlikely to have significant anti-competitive effects. We survey a range of indicators that can be used for this purpose and conclude that they all have drawbacks. Part 5 deals with the problems of assessing individual awards of aid which have failed the screening test, discussing how the main characteristics of firms (e.g. market share, vertical integration) and markets (such as product differentiation and market growth) may influence a state aid's impact on competition. Keywords: European Union, state aid, subsidies, competition policy.European Union, state aid, subsidies, competition policy, Buelens, Garnier, Meiklejohn, Johnson

Comparison of two non destructive tests in carbon/epoxy composites

An investigation of two nondestructive methods (ultrasounds and infrared thermography) is carried out. The defect detection by both methods is first examined. The determination of the position and dimensions are then studied. And finally, the feasibility and the time of the experimental protocol setting up is analysed. The aim is to compare two nondestructive methods: ultrasound and infrared thermography applied to composites samples. So, three different specimens are tested. It appears that the majority of the defects are detected very quickly with infrared thermography compared to ultrasounds method. However, certain defects are not visible by thermography IR

Impact damage evolution under fatigue loading by InfraRed Thermography on composite structures

This study deals with cumulative damage and its evolution in already impact damage composite structure. In order to follow the growing damage and to compare it with cumulative model, tests are monitored with an InfraRed thermography system. A carbon-epoxy composite is first low-energy impacted and then fatigued under tension-compression loading. This study also enables a very fast analysis of predicting the damage evolution coupling InfraRed Thermography as NDT method and InfraRed thermography as a following system

Etude du comportement dynamique des structures composites réalisées par LRI : application à l’impact et à la fatigue

Les industriels du secteur aéronautique sont, de plus en plus, à la recherche de procédés de fabrication à forte valeur ajoutée sans modifier les paramètres d’infusabilité de la résine lorsque l’on change de tissu. Nous avons donc mis en œuvre le procédé d’infusion de résine liquide sur des composites carbone/époxyde de forte épaisseur (e>4 mm) en modifiant les cycles de polymérisation, les matériaux utilisés et les séquences d’empilement. Tous les tissus sont en carbone et la résine utilisée est la résine commerciale RTM6. Les structures aéronautiques sont sollicitées, en service, de différentes façons. Elles peuvent être accidentellement impactées par des engins de maintenance, des outils, de la grêle ou toute autre forme d’impact. Le problème pour les industriels est de pouvoir détecter l’endommagement créé et de comprendre les mécanismes mis en jeu lors de l’impact mais aussi leur évolution pendant un cyclage en fatigue. Nos travaux se sont donc inscrits dans cet objectif et différentes méthodes ont été mises en œuvre : détection de défauts d’impact et suivi en temps réel par thermographie infrarouge, détection de l’indentation résiduelle par numérisation par projection de franges. Parallèlement, le phénomène d’impact a aussi été traité par une étude statistique par plan d’expérience et une modélisation avancée a été créée avec l’utilisation de surfaces cohésives. ABSTRACT: Aeronautical manufacturers are looking for the best manufacturing process giving high benefits. Moreover, it has to be implemented easily with change of woven fabrics. So, we realize thick carbon/epoxy composites (t>4 mm) by modifying cure cycles, woven fabrics and lay-up sequences. Concerning the constituent materials of the composites, woven fabrics are carbon made and the resin is the commercial product named RTM6. Aeronautical structures can be unfortunately stressed, in service, with different solicitations: holding, engine impact, falling objects impacts or other way. The main problem for industrials is to be able to detect the created damage, to understand the phenomena dealing with it and the damage evolution during fatigue cycles. By following this direction, different methods are developed: impact damage defects detection and evolution monitored with infrared thermography, impact residual depth measurement by fringes projection digitalization. At the same time, a statistical study made by design of experiments is completed. A numerical impact modeling is also developed by using cohesive surfaces

Finite Element Simulation of Low Velocity Impact Damage on an Aeronautical Carbon Composite Structure

Low velocity barely visible impact damage (BVID) in laminated carbon composite structures has a major importance for aeronautical industries. This contribution leads with the development of finite element models to simulate the initiation and the propagation of internal damage inside a carbon composite structure due by a low velocity impact. Composite plates made from liquid resin infusion process (LRI) have been subjected to low energy impacts (around 25 J) using a drop weight machine. In the experimental procedure, the internal damage is evaluated using an infrared thermographic camera while the indentation depth of the face is measured by optical measurement technique. In a first time we developed a robust model using homogenised shells based on degenerated tri-dimensional brick elements and in a second time we decided to modelize the whole stacking sequence of homogeneous layers and cohesive interlaminar interfaces in order to compare and validate the obtained results. Both layer and interface damage initiation and propagation models based on the Hashin and the Benzeggagh-Kenane criteria have been used for the numerical simulations. Comparison of numerical results and experiments has shown the accuracy of the proposed models