Optimisation of hybrid high-modulus/high-strength carbon fibre reinforced plastic composite drive shafts

International audienceThis study deals with the optimisation of hybrid composite drive shafts operating at subcritical or supercritical speeds, using a genetic algorithm. A formulation for the flexural vibrations of a composite drive shaft mounted on viscoelastic supports including shear effects is developed. In particular, an analytic stability criterion is developed to ensure the integrity of the system in the supercritical regime. Then it is shown that the torsional strength can be computed with the maximum stress criterion. A shell method is developed for computing drive shaft torsional buckling. The optimisation of a helicopter tail rotor driveline is then performed. In particular, original hybrid shafts consisting of high-modulus and high-strength carbon fibre reinforced epoxy plies were studied. The solutions obtained using the method presented here made it possible to greatly decrease the number of shafts and the weight of the driveline under subcritical conditions, and even more under supercritical conditions. This study yielded some general rules for designing an optimum composite shaft without any need for optimisation algorithms

Dynamics of a supercritical composite shaft mounted on viscoelastic supports

International audienceThe damping in a carbon fiber reinforced plastic (CFRP) laminate is greater than that which occurs in most metallic materials. In the supercritical regime, the damping can trigger unstable whirl oscillations, which can have catastrophic effects. The vibrations occurring in a supercritical composite drive shaft are investigated here in order to predict instabilities of this kind. A simply supported carbon/epoxy composite tube mounted on viscoelastic supports is studied, using an approximation of the Rayleigh-Timoshenko equation. The damping process is assumed to be hysteretic. The composite behavior is described in terms of modulus and loss factor, taking homogenized values. The critical speeds are obtained in several analytical forms in order to determine the effects of factors such as the rotatory inertia, the gyroscopic forces, the transverse shear and the supports stiffness. Assuming that the hysteretic damping can be expressed in terms of the equivalent viscous model, the threshold speed is obtained in the form of an analytical criterion. The influence of the various factors involved is quantified at the first critical speed of a subcritical composite shaft previously described in the literature. The influence of the coupling mechanisms on the unsymmetrical composite laminate and the end fittings is also investigated using a finite element model. None of these parameters were found to have a decisive influence in this case. Those having the greatest effects were the transverse shear and the supports stiffness. The effects of the composite stacking sequence, the shaft length and the supports stiffness on the threshold speed were then investigated. In particular, drive shafts consisting only of ±45° or ±30° plies can be said to be generally unstable in the supercritical regime due to their very high loss factors

Dynamic instability of supercritical driveshafts mounted on dissipative supports ― effect of viscous and hysteretic internal damping

International audienceThe case of a rotating shaft with internal damping mounted either on elastic dissipative bearings or on infinitely rigid bearings with viscoelastic suspensions is investigated in order to obtain the stability region. A Euler–Bernoulli shaft model is adopted, in which the transverse shear effects are neglected and the effects of translational and rotatory inertia, gyroscopic moments, and internal viscous or hysteretic damping are taken into account. The hysteretic damping is incorporated with an equivalent viscous damping coefficient. Free motion analysis yields critical speeds and threshold speeds for each damping model in analytical form. In the case of elastic dissipative bearings, the present results are compared with the results of previous studies on finite element models. In the case of infinitely rigid bearings with viscoelastic suspensions, it is established that viscoelastic supports increase the stability of long shafts, thus compensating for the loss of efficiency which occurs with classical bearings. The instability criteria also show that the effect of the coupling which occured between rigid modes introducing external damping and shaft modes are almost more important than damping factor. Lastly, comparisons between viscous and hysteretic damping conditions lead to the conclusion that an appropriate material damping model is essential to be able to assess these instabilities

Design of high rotation frequency composite tubes

International audienceThis work relates to the sizing of subcritical and supercritical laminated composite drive shafts. The hollows drive shafts are designed to transmit the torsional load and to minimize the dynamic effects due to rotation. To meet this need, these structures must combined strength, rigidity and lightness. New high modulus carbon fibres can be adapted to a progress in this field. This work presents sizing tools for optimisation of supercritical drive shafts mounted on viscoelastic suspensions. Two items are discussed: dynamic analysis (response to forces excitation; free motion; instability), strength (buckling of thin tubes; torsional strength). Supercritical drive shafts examples made of high modulus fibres or high-strength fibres are presented

Influence de l’endommagement matriciel sur la résistance en compression sens fibre pour des composites stratifiés

International audienceL'étude expérimentale proposée ici vise à caractériser le comportement d'un composite tissé verre/epoxy et d'étudier l'influence de l'endommagement matriciel sur ses propriétés à rupture en compression. Tout d'abord, des résultats sur l'influence de l'endommagement matriciel sont rappelés. Ensuite, le comportement en compression du matériau non endommagé est étudié en réalisant des essais de flexion quatre points et de compression normalisés (ASTM-D695). Dans un second temps, une campagne d'essais à haute température permet de montrer l'effet de la dégradation thermique de la matrice sur la résistance sens fibre. Enfin, l'effet de l'endommagement sur la rupture en compression est étudié. Abstract The present research focuses on the identification of the compressive behavior of a woven glass/epoxy composite and the influence of matrix damage on its compressive strength. First results concerning the influence of matrix damage on composite failure properties are reminded. In the following part the behavior of the glass/epoxy composite is identified via four-points flexion tests and standard compressive tests (ASTM-D695). Then, the results of high temperature flexion tests are presented to highlight the influence of matrix damage on compressive strength in fiber direction. Finally, effect of transverse damage on compressive strength is studied

Essai et simulation du comportement d'une structure sandwich entaillée jusqu'à rupture

International audienceUn nouvel essai sur une éprouvette sandwich entaillée de grande dimension et soumise à un chargement statique de flexion/torsion est proposé. L'éprouvette entaillée, constitué de plis tissés en verre/époxy et de mousse, ressemble à une pièce représentative d’une structure aéronautique présentant une fissure. L'objectif de l'essai est de générer l'initiation et la propagation stable d'une fissure au bord de l'entaille dans le cas d'un chargement complexe caractéristique d'une structure réelle. Cet essai est suivi par un système de corrélation d'image numérique 3D. Le résultat de l'essai est utilisé pour démontrer la validité d'un modèle basé sur la mécanique de l'endommagement et un critère non local. La très bonne corrélation entre la simulation et l'expérience au niveau des champs et de l'effort à rupture montre l’efficience de la méthode proposée

Influence de l'endommagement matriciel sur la rupture des stratifiés avec concentration de contraintes

International audienceThis work investigates the influence of matrix damage on the tensile and compressive strength of laminated composite fibers in experimental and numerical simulations. The proposed modeling is based on damage mechanics and the use of a non-local criterion (VCR). This method is first validated in the case of the traction of different laminates with various types of concentration. Then, a representative test of an aeronautical structure is developed. The method applied to the complete structure perfectly predicts the initiation of the crack. It requires relatively short calculation times quite suitable for an engineer approach. Finally, the case of compression is studied. The strong influence of the damage of the matrix on the compressive fracture in the fiber direction is shown and identified on homogeneous tubular specimens and specimens with stress concentration. It makes the prediction more complex. This last model has been implemented and allows a first comparison with the second experiments.Ce travail s'intéresse à l'influence de l'endommagement sur la résistance en traction et compression sens fibre des composites stratifiés en expérimental et en simulation. La modélisation proposée est basée sur la mécanique de l'endom-magement et l'utilisation d'un critère non local (VCR). Cette méthode est tout d'abord validée dans le cas de la traction de différents stratifiés avec différents types de concentration. Ensuite un essai de type structure aéronautique est développé. La méthode appliqué à la structure complète prédit ici parfaitement l'initiation de la fissure. Elle demande des temps de calculs relativement courts tout à fait adaptés à une approche ingénieur. Enfin le cas de la compression est étudié. La forte influence de l'endommagement de la matrice sur la rupture en compression sens fibre, est montrée et identifiée ici sur des essais homogènes sur tubes et des essais avec concentration. Elle rend la prédiction plus complexe. Ce dernier modèle a été implémenté et permet une première comparaison avec les secondes expériences

0328: Assessment of radiation exposure during cardiac device implantation: lessons learned from a multicenter registry

BackgroundFew data exist about radiation exposure during implantation of cardiac electrical device. No dose reference levels (DRLs) were reported.Purpose to define DRLs and to analyze factors related to an increased radiation dose delivered to patients and medical staff.Methods the Raypace study is a multicenter, prospective observational registry. Using a national database, patient demographic, procedural and radiation data were collected. Fluoroscopy time (FT) and dose-area product (DAP) were registered. Physician/staff exposure was measured using 2 real-time personal dosimeters, one worn under the lead apron and the other one worn outside the apron. Statistical analysis used log-transformation of DAP, FT and DAP/FT ratio.ResultsA total of 657 procedures from 9 institutions were reviewed. Pacemaker (PM) and cardioverter-defibrillator (ICD) implantation was performed in 481 and 176 patients, respectively. A cardiac resynchronization device was implanted in 153 patients. Fluoroscopy time was similar for PM and ICD implantations. Median fluoroscopy time was 836, 117 and 101 second and median DAP was 1410, 150 and 129 cGy.cm2 for biventricular, dual chamber and ventricular device implantation, respectively. LAO projection, in addition to AP projection, was used in 47% of the procedures. Five centers out of 9 used collimation. The median Hp (10) effective dose measured outside the lead apron was 4.6 µSv and 0.1 µSv under the lead apron.Regarding CRT implant procedures, four systems out of 6 were responsible for an increased exposure (p<0.001). DRLs were 2600, 338 and 332 cGy.cm2 for biventricular, dual chamber and ventricular device implantation, respectively.ConclusionsDAP reduction was improved with the use of latest generators but needed customized settings. Biventricular device implantation was responsible for the highest radiation exposure. However, radiation exposure during those procedures have decreased as compared to previously reported values

0107: Strategy of early detection and active management of supraventricular arrhythmia with remote monitoring: the randomized, multicenter SETAM trial

ObjectiveAtrial fibrillation (AF) is a common arrhythmia associated with increased risk of thromboembolic events or other complications. The French randomized, multicenter, SETAM trial assessed the impact of the home monitoring (HM) technology on detection and treatment of supra-ventricular arrhythmia (SVA).MethodsPatients (pts) implanted with a dual chamber pacemaker were enrolled in the study at hospital discharge if they had a sinusal rhythm at enrollment, no antiarrhythmic, anticoagulant or dual-antiplatelet therapy, and if they had a CHA2DS2-VASc score of 2 or more. The pts were randomly assigned to an active group (Act Gp), followed by Biotronik HM, or a control group (Cont Gp) without HM surveillance. The time from implantation to the first SVA-related intervention was compared between the 2 groups (primary endpoint).ResultsA total of 595 pts (mean age = 79±8 y.o, 63% male, mean CHA2DS2-VASc score = 3.7±1.2) were followed during 12.8±3.3Mo. The most prevalent co-morbidities were hypertension (82% pts), diabetes (29%) and vascular disease (24%). Implantation indications were atrio-ventricular blocks in 77% of pts, sinus node disease in 20% and others in 3%.The global SVA incidence was 25% (29% in the Act Gp vs 22% in the Cont Gp, p=ns).A therapy (drugs or ablation) was instituted for 49/291 pts (17%) in the Act Gp vs 43/304 pts (14%) in the Cont Gp (p=ns). The median time from implantation to the first therapy for SVA was 114 [44; 241] days in the Act Gp vs 224 [67; 366] days in the Cont Gp, representing a median gain of 110-days in SVA management (50% reduction, p=0.01). Over these 92 pts, 54 had AF (59%) and 38 had atrial flutter or tachyarrhythmia (41%). Anticoagulation was initiated in 80% of pts and antiarrhythmic drugs in 55%.ConclusionThe SETAM study demonstrated that HM allows earlier detection and treatment of SVA in pacemaker pts. The next step is to report how early detection of SVA with HM can possibly improve the patients clinical outcome

Comportement vibratoire des arbres de transmission composites surcritiques - Étude théorique, expérimentale et dimensionnement

ISBN : 2-746211408International audienceCe travail traite du dimensionnement d'arbres de transmission surcritiques composites. Ces systèmes doivent être conçus de manière à minimiser les effets dynamiques dus à la rotation. Nous présentons l’étude dynamique d’un arbre monté sur suspensions viscoélastiques. Nous proposons des solutions analytiques pour le mouvement forcé, le mouvement libre et l’instabilité. Cette étude fait apparaître un critère de stabilité qui met en évidence l’effet déstabilisant de l’amortissement tournant et le gain de stabilité donné par les supports viscoélastiques sous certaines conditions. Enfin, nous présentons une comparaison de deux fibres de carbone (haut module/ haute résistance) sur un exemple de transmission surcritique