Application of non destructive testing to the detection of aeronautical defects in composite structures

A study of two Non-destructive Testing methods (NDT) was carried out in specimens with different kinds of simulated defects. Ultrasonics test (US) and Infrared Thermography (IRT) were applied with the aim to evaluate the detectability and the accuracy of each method.These techniques have acquired great importance in the aeronautics industry because they allow to control the aerostructures without intervening in their physical and mechanical integrity. In the second part of the study, a comparison of both techniques was achieved in order toanalyse their limits and advantages. It appeared that detectability of defects was much better in a sample with flat-bottomed holes defects in the case of Ultrasonic Test. However it was found that Infrared Thermography is much more limited to the thickness of the specimen than the ultrasonic waves. On the other hand, defects were all revealed with IRT in a sandwich composite including Teflon inserts, which was not the case for US

Utilisation de la thermographie infrarouge et de l'émission acoustique pour l'identification de l'endommagement d'un composite stratifié carbone-époxy

Le manque de connaissances dans le comportement des matériaux composites à base carbone induit encore de nombreux surcoûts pour la fabrication des structures aéronautiques. Lorsqu’une structure stratifiée en matériaux composites est sollicitée, la dégradation de ses propriétés est effective avant sa rupture. Actuellement, un certain nombre de techniques de contrôle non destructif visent à caractériser les propriétés mécaniques d’un matériau de manière à estimer l’importance de cet endommagement. La caractérisation ultrasonore en immersion donne notamment accès aux constantes élastiques du matériau. La thermographie infrarouge et les émissions acoustiques permettent quant à elles de déterminer la charge élastique et de mettre en évidence le début de l’endommagement. Ce document présente un couplage de la thermographie infrarouge et de la mesure des émissions acoustiques de façon à contrôler la structure en temps réel lors du chargement. Cette méthodologie est mise en œuvre sur des composites carbone-époxy unidrectionnels sollicités en traction uniaxiale dans des situations dans et hors axes. La corrélation des différentes techniques permettent une compéhension fine de l’endommagement de ces structures composites

Identification of damage mechanisms in CFRP composites by coupling acoustic emission and infrared thermography

To study the mechanical behavior of CFRP composites, two methods of damage monitoring are coupled: the acoustic emission (AE) and the infrared thermography (IT). Several studies on the coupling of these two techniques have shown, for example, that it is possible to determine the fatigue strength of ceramic matrix composites under fatigue loading [1]. Other authors have shown the link between the temperature variation and the acoustic parameters evolution (like energy and the number of signals) during fatigue tests on epoxy glass composites [2] and on metallic materials [3]. The similarity of these studies concerns the kind of loading used: a cyclic loading. The aim of this study is to be able to improve the understanding and the characterization of damage mechanisms of unidirectional CFRP composites by coupling acoustic emission and infrared thermography. Besides, damage behavior of CFRP composites samples under static and cyclic loadings are compared

Identification de mécanismes d’endommagement de stratifiés carbone/époxy par couplage entre émission acoustique et thermographie infrarouge

Ce travail de recherche vise à améliorer la compréhension et la caractérisation des mécanismes d’endommagement pouvant affecter sous chargements quasi-statiques le comportement des composites carbone-époxy unidirectionnels en couplant deux méthodes de suivi de l’endommagement : l’émission acoustique (EA) et la thermographie infrarouge (TI)

Determination of the elastic properties in CFRP composites: comparison of different approaches based on tensile tests and ultrasonic characterization

The mechanical characterization of composite materials is nowadays a major interest due to their increasing use in the aeronautic industry. The design of most of these materials is based on their stiffness, which is mainly obtained by means of tensile tests with strain gauge measurement. For thin laminated composites, this classical method requires adequate samples with specific orientation and does not provide all the independent elastic constants. Regarding ultrasonic characterization, especially immersion technique, only one specimen is needed and the entire determination of the stiffness tensor is possible. This paper presents a study of different methods to determine the mechanical properties of transversely isotropic carbon fibre composite materials (gauge and correlation strain measurement during tensile tests, ultrasonic immersion technique). Results are compared to ISO standards and manufacturer data to evaluate the accuracy of these techniques

Damage detection in CFRP by coupling acoustic emission and infrared thermography

Acoustic emission (AE) and infrared thermography (IT) are simultaneously combined to identify damage evolution in carbon fibre reinforced composites. Samples are subjected to tensile static loads while acoustic emission sensors and an infrared camera record the acoustic signals and the temperature variations respectively. Unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals. Thermodynamic arguments are introduced to estimate global heat source fields from thermal measurements and anisotropic heat conduction behavior is taken into account by means of homogenization technique. A spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the AE and IT events amplitude are identified

Coupling infrared thermography and acoustic emission for damage study in CFRP composites

Improvement of the design and reliability of aeronautical composite structures requires an identification and characterization of their damage evolution. By providing surface thermal fields, infrared thermography has allowed considerable progress in the detection of degradation phenomena. On the other hand, acoustic emission is employed to record the transient waves resulting from released energy during a damage process. This study intends to combine simultaneously these nondestructive methods to investigate the damage behaviour of carbon-fibre composites under tensile load. Experimental results show some correlations between thermal and acoustic events induced by the load according to the damage development

Combining NDT tools for analysing the efficiency of repair techniques of wharves: the MAREO project

ISBN: 9780415669863Repair of structures in concrete is still a challenge, especially when access and environment offer a difficult context such as the case of wharves. Concerning the repair of concrete for marine structures, European standards give the requirements in predefined and standardised conditions. However, repair of wharves is performed in harsh conditions such as access, humidity and operator position. These conditions do not enable the direct application of standards. By accounting for these requirements, the repair technique consists in rebuilding the concrete cover and in some cases using protective coating for some beams. In this paper, we focus on the concrete repair techniques. The aim of MAREO project (French project of the National competitive cluster in Civil Engineering and Eco-Building) is to compare several repair techniques carried out in the most complex area for repair: the tidal zone. The project deals with initial performance, sustainability, cost of durability and concrete properties monitoring by Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The studied NDT techniques are: impact-echo, surface waves, multi-offset radar, and capacitive method. Both, beams placed in natural exposure and slabs specimens placed in accelerated conditions in laboratory are considered. For all the beams, the contaminated concrete was removed using high-velocity water jets (hydro-demolition). The selected techniques are wet shotcrete, dry shotcrete, formed concrete and manual repair. This paper focuses on the ability of NDT techniques to evaluate the changes of properties related to the chloride ingress in concrete both on site and in accelerated laboratory conditions. The interest of each technique and its sensitivity to several physical factors are highlighted. The need of NDT-combination is illustrated

Retention and loss of PIT tags and surgically implanted devices in the Eurasian beaver

Background Passive integrated transponder devices (PIT tags) are a valuable tool for individual identification of animals. Similarly, the surgical implantation of transmitters and bio-loggers can provide useful data on animal location, physiology and behavior. However, to avoid unnecessary recapture and related stress of study animals, PIT tags and bio-loggers should function reliably for long periods of time. Here, we evaluated the retention of PIT tags, and of very high frequency (VHF) transmitters and bio-loggers that were either implanted subcutaneously or into the peritoneal cavity of Eurasian beavers (Castor fiber). Results Over a 21-year period, we implanted PIT tags in 456 individuals and failed to detect a PIT tag at recapture in 30 cases, consisting of 26 individuals (6% of individuals). In all instances, we were still able to identify the individual due to the presence of unique ear tag numbers and tail scars. Moreover, we implanted 6 VHFs, 36 body temperature loggers and 21 heart rate loggers in 28 individuals, and experienced frequent loss of temperature loggers (at least 6 of 23 recaptured beavers) and heart rate loggers (10 of 18 recaptured beavers). No VHFs were lost in 2 recaptured beavers. Conclusions Possible causes for PIT tag loss (or non-detection) were incorrect implantation, migration of the tag within the body, a foreign body reaction leading to ejection, or malfunctioning of the tag. We speculate that logger loss was related to a foreign body reaction, and that loggers were either rejected through the incision wound or, in the case of temperature loggers, possibly adhered and encapsulated to intestines, and then engulfed by the gastro-intestinal tract and ejected. We discuss animal welfare implications and give recommendations for future studies implanting bio-loggers into wildlife