Bird strike shielding materials: development of a high velocity impact test platform

Commercial aircraft structures are exposed to bird strike events causing serious damages. Certification is thus required by regulation organizations and tests are performed using gas guns and birds of mass 1,8kg (JAR 25.631) (or 3,6kg for tail parts), which are launched at approximately 175m/s. In the design phase, modelling and simulation are rather used to assess and optimize the response of materials and structures under bird strike. However, it is difficult to correlate simulations with tests because of the very limited availability of test platforms for characterization and qualification from the smallest coupons to shielded structural component. The purpose of our work is to set up a test platform in close partnership with Institut Clément Ader (ICA), equipped with advanced metrology and combined with a virtual testing approach for correlation of tests and simulations up to 1m scale shielding concepts. New bird strike shielding materials could then be further developed at a lower cost in reduced time frames. Nonetheless the platform and virtual testing approach could be derived to other high velocity impacts (hail, engine debris, tire debris)

Experimental study of bird strike response of sandwich structures: overall trends

Nowadays sandwich structures are used as bird shields to protect aircraft nose bulkhead. They are usually made of aluminum honeycomb and sheets. In order to optimize mass, cost and efficiency of such bird shields, aircraft manufacturers want to explore new materials and designs. In this context, this work aims at exhibiting influences of material and design parameters on the bird strike response of sandwich structures. Based on previous finite element calculations that enabled to determine the most influential parameters, a design of experiment has been defined to span a parameter space in 4 dimensions, namely the thickness of the front skin, the thickness of the core, the yield stress of the front skin and the crushing stress of the core. 13 configurations of sandwich structures are then tested according to this design of experiment. These samples are 800 mm x 800 mm square sandwiches simply supported on a rigid square frame. The impactor is a 1.6 kg gelatin bird substitute, thrown at a speed of 160 m/s. Based on high speed camera image correlation, an original approach is developed to measure and quantify the responses of the samples. For each configuration, the full displacement field of the rear face of the sandwich is calculated during the impact event. The final shapes for both rear and front faces of the shield are also reconstructed, enabling to compare the behaviors of the different structures regarding bending, indentation and core crushing… The exhibited trends in terms of influences of material and design parameters open prospects for pre-selection of candidate materials and designs for bird shield applications which could lead to mass and cost reduction while satisfying aircraft design constraints (no failure, low rear face displacement…)

3D digital image correlation applied to birdstrike tests

The development of new bird strike shielding materials for commercial aircrafts requires test campaigns. During these tests, measurement of the high speed deformation is needed to characterize and compare the mechanical response of the shielding samples and to correlate numerical simulations with experiments. In this work, 3D digital image correlation method is used with high speed (HSP) cameras to compute the displacement and strain fields on a large area (approximately 400mm wide) of the back side of impacted samples. Compromise on spatial resolution, frame rate of HSP camera and measurement error is discussed

Bearing damage identification in oxide/oxide ceramic matrix composite with a new test design

In this paper, the mechanisms of damage of an oxide/oxide ceramic matrix composite bearing are studied with a new experimental setup, the balanced quarter hole device (BQH). This test was designed to allow direct observation of the damage development on a material subjected to bearing failure. In a standard bearing experiment, real time monitoring is extremely difficult to set up, and post mortem observations of the bearing plane can be biased by the cutting operation. High speed cameras were used to take pictures of the bearing plane so that the damage development could be studied and a damage chronology established. The validity of the setup was verified by comparing the results obtained with those of a standard bearing test. Two different stacking sequences were studied, and the influence of the material microstructure and composite machining was investigated. It was shown that the first critical damage, matrix cracks, appeared before the load drop, and then led to delamination and kink bands, causing the final failure of the material

Stratégies de calcul intensif pour la simulation du post-flambement local des grandes structures composites raidies aéronautiques

Cette thèse s’inscrit dans le cadre de l’étude du post-flambement local des grandes struc- tures composites raidies. La simulation du post- flambement par la méthode des éléments- finis est aujourd’hui limitée par le coût du calcul en particulier pour les grandes structures. Seules des zones restreintes peuvent être étudiées, en négligeant les interactions global/local. L’objectif de cette thèse est de proposer une stratégie de calcul performante pour la simula- tion du post-flambement local des grandes structures raidies à partir des connaissances sur le comportement mécanique des structures en post-flambement et d’un découpage naturel le long des raidisseurs favorable au calcul parallèle.Dans la littérature, les méthodes de réduction de modèle adaptative ont démontré leur ca- pacité à réduire le nombre d’inconnues tout en maîtrisant l’erreur d’approximation de la solution des problèmes non-linéaires. Par ailleurs, les méthodes de décomposition de do- maine avec localisation non-linéaire sont particulièrement adaptées au calcul parallèle en mécanique des structures en présence de non-linéarités locales.Les travaux de thèse portent dans un premier temps sur une stratégie de réduction de modèle adaptative spécifique au cas du post-flambement. Dans le cas d’un flambement local d’une grande structure raidie une combinaison avec une méthode de décomposition de domaine primale est ensuite proposée. Toutes ces stratégies sont implémentées dans un code de re- cherche programmé pendant la thèse.This thesis is part of the study of local post-buckling of large stiffened composite struc- tures. The finite element simulation of structures subjected to post-bucking still faces com- putational limits, especially for large structures. Only restricted area may be studied for now, neglecting global/local interactions.The aim of the thesis is to propose an efficient computational strategy for local post-buckling analysis of large stiffened structures from knowledge on mechanical behavior of post-buckling structures and a natural partitionning along stiffeners conducive to parallel computation. In litterature, the adaptive model reduction solving techniques have demonstrated their abi- lity to drastically reduce the number of unknowns as well as to control the approximation error of solving non-linear problems. Furthermore, domain decomposition methods with a non-linear local step are suited to parallel computation in structural mechanics in the pre- sence of local non-linearities.Our work deals first with an adaptive model reduction strategy dedicated to post-buckling problems. In order to adress larger stiffened structures subjected to local post-buckling, like an aircraft fuselage, partitioning is then performed. The model reduction, as well as the adap- tive procedure are written in the framework of the primal domain decomposition method with a non-linear local step. These strategies are implemented in a research code developed for the purpose of the thesis

Bird strike shielding materials: development of a high velocity impact test platform

International audienceCommercial aircraft structures are exposed to bird strike events causing serious damages. Certification is thus required by regulation organizations and tests are performed using gas guns and birds of mass 1,8kg (JAR 25.631) (or 3,6kg for tail parts), which are launched at approximately 175m/s. In the design phase, modelling and simulation are rather used to assess and optimize the response of materials and structures under bird strike. However, it is difficult to correlate simulations with tests because of the very limited availability of test platforms for characterization and qualification from the smallest coupons to shielded structural component. The purpose of our work is to set up a test platform in close partnership with Institut Clément Ader (ICA), equipped with advanced metrology and combined with a virtual testing approach for correlation of tests and simulations up to 1m scale shielding concepts. New bird strike shielding materials could then be further developed at a lower cost in reduced time frames. Nonetheless the platform and virtual testing approach could be derived to other high velocity impacts (hail, engine debris, tire debris)

Methodology for identification of Impact behavior of materials: application to bird strike

This work proposes a methodology for identification of material parameters in the case of bird strike tests. A measure of displacement field of the backside of samples is performed by stereo-correlation of high speed cameras images. Hundreds of images are taken during the impact event, leading to reconstruction of corresponding deformed surfaces. The proposed identification methodology supposes that enough data is collected to identify both material parameters of an aluminum target plate and the ones of gelatin projectile. An error function is computed by comparison of the measured and simulated deformed surfaces. Due to the non-linear dependence of the error function on material parameters, a global optimization approach based on meta-modelling is considered. This methodology enables the direct identification of material parameters at the effective rates of loadings, without the need for lower scale coupon testing which do not always involve the right material and structural behaviors. Once the numerical model of gelatin projectile is identified, this approach could be derived to identification of more complex target material models like composite plates and sandwich structures

Identification of vibration damping in 3D-printed lattice structures

International audienceAs metallic 3D-printing opens the design space for lightweight structural applications, it also raiseschallenges in terms of low level vibration damping. Reducing the number of parts is avoiding someclassical damping phenomena due to friction mechanisms in mechanical assemblies. In addition,metallic materials do not exhibit intrinsic viscous properties that could significantly contribute to structuraldamping. In this work, the damping properties of lattice-based structures and possible design solutionsoffered by Powder Bed Fusion are investigated. In particular, auxetic behaviour [1], passive energytransfer [2], and viscoelastic shear layer [3] could be considered. The approach consists in identifyingpromising concepts from numerical simulations, and validate them experimentally. Underlying questionsof predictive capability of damping simulations and identification of damping properties from experimentsare addressed. In this work, focus is put on the passive energy transfer

Predicting early death in older adults with cancer

International audienceBACKGROUND: Predicting early death after a comprehensive geriatric assessment (CGA) is very difficult in clinical practice. The aim of this study was to develop a scoring system to estimate risk of death at 100 days in elderly cancer patients to assist the therapeutic decision. METHODS: This was a multicentric, prospective cohort study approved by an ethics committee. Elderly cancer patients aged older than 70 years were enrolled before the final therapeutic decision. A standardised CGA was made before the treatment decision at baseline. Within 100 days, event~(death), oncologic and geriatric data were collected. Multivariate logistic regression was used to select the risk factors for the overall population. Score points were assigned to each risk factor using the β coefficient. Internal validation was performed by a bootstrap method. Calibration was assessed with the Hosmer-Lemeshow goodness of fit test and accuracy with the mean c-statistic. FINDINGS: One thousand fifty patients (mean age: 82 years) joined the study from April 2012 to December 2014. The independent predictors were~metastatic cancers (odds ratio [OR] 2.5; 95% confidence interval [CI], [1.7-3.5] p\textless0 .001); gait speed\textless0.8~m/s (OR 2.1; 95% CI [1.3-3.3] p=0.001); Mini Nutritional Assessment (MNA)~\textless~17 (OR 8; 95% CI; [3.7-17.3] p\textless0.001), MNA <=23.5 and~>=~17 (OR 4.4; 95% CI, [2.1-9.1) p\textless0.001); performance status (PS)~\textgreater~2 (OR 1.7; 95% CI, [1.1-2.6)] p=0.015) and cancers other than breast cancer~(OR 4; 95% CI, [2.1-7.9] p\textless0.001). We attributed 4 points for MNA\textless17, 3 points for MNA between <=23.5 and~>=~17, 2 points for metastatic cancers, 1 point for gait speed \textless0.8~m/s, 1 point for PS~\textgreater~2 and 3 points for cancers other than breast cancer. The risk of death at 100 days was 4% for 0 to 6 points, 24% for 7 to 8 points, 39% for 9 to 10 points and 67% for 11 points. INTERPRETATION: To our knowledge, this is the first score which estimates early death in elderly cancer patients. The system could assist in the treatment decision for elderly cancer patients