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 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)

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

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

C57BL/6 and Swiss Webster Mice Display Differences in Mobility, Gliosis, Microcavity Formation and Lesion Volume After Severe Spinal Cord Injury

Spinal cord injuries (SCI) are neuropathologies causing enormous physical and emotional anguish as well as irreversibly disabilities with great socio/economic burdens to our society. The availability of multiple mouse strains is important for studying the underlying pathophysiological response after SCI. Although strain differences have been shown to directly affect spontaneous functional recovery following incomplete SCI, its influence after complete lesion of the spinal cord is unclear. To study the influence of mouse strain on recovery after severe SCI, we first carried out behavioral analyses up to 6 weeks following complete transection of the spinal cord in mice with two different genetic backgrounds namely, C57BL/6 and Swiss Webster. Using immunohistochemistry, we then analyzed glial cell reactivity not only at different time-points after injury but also at different distances from the lesion epicenter. Behavioral assessments using CatWalk™ and open field analyses revealed increased mobility (measured using average speed) and differential forelimb gross sensory response in Swiss Webster compared to C57BL/6 mice after complete transection of the spinal cord. Comprehensive histological assessment revealed elevated microglia/macrophage reactivity and a moderate increase in astrogliosis in Swiss Webster that was associated with reduced microcavity formation and reduced lesion volume after spinal cord transection compared to C57BL/6 mice. Our results thus suggest that increased mobility correlates with enhanced gliosis and better tissue protection after complete transection of the spinal cord

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

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

Identification of the elastic properties of composite materials

The mechanical characterization of composite materials is a research axis of scientific and economic importance. In fact, it is essential to measure the elastic constants of a material with accuracy in order to realize structural analysis and to optimize the design. Among the developed methods, the static methods based on strain measurement present some disadvantages: destructive evaluation and difficulties of measuring the out-of-plane elastic modulus because of the thinness. These disadvantages could be avoided by the use of non-destructive dynamic methods such as modal analysis or ultrasonic waves evaluation. Among the non-destructive methods, ultrasounds are efficient. Besides, because of the accuracy of the results as well as the repeatability of the measures, scientists are generalizing this method. This paper presents a way to determine the mechanical properties of carbon fiber composite materials. This work underlines the results obtained of phase velocity at different incident angles with a dynamic characterization method which is developed as part of non-destructive evaluation by ultrasonic waves