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Dans le domaine aéronautique, la détection des défauts sur structures composites sefait lors des phases de maintenance. Celles-ci sont prévues de manière à détecter lesdéfauts avant que ceux-ci ne deviennent critiques pour la tenue des structures en service.L’optimisation des intervalles de maintenance représente donc un fort intérêt que ce soitau niveau financier ou opérationnel. Les dommages des structures composites sont aujourd’hui traités par la non-propagationdes défauts : lorsque ceux-ci apparaissent et qu’ils sont détectés, les pièces sont immédiatementréparées ou remplacées. Afin d’améliorer ces intervalles de maintenance, lecomportement des défauts soumis aux spectres de charges aéronautique nécessite d’êtrecaractérisé. Cela permettrait une transition vers une philosophie de tolérance aux dommages,en définissant des phases de propagation non-critique pour la tenue mécanique desstructures. Dans ce contexte, la propagation de délaminage est étudiée sous chargement de fatigue.En mode I de propagation, les effets de la fréquence de sollicitation et du rapport de chargesur la propagation de délaminage en fatigue sont déterminés. Ceux-ci amorcent l’étudede la propagation de délaminage sous spectre de charges à niveau variable. Les effets del’historique de chargement sont mis en évidence. En mode II de propagation, les effets de la fréquence de sollicitation sur la propagationde délaminage sont abordés pour quatre matériaux à l’aide d’un montage d’essaisvibratoires dédié. Une analyse thermique des essais est également conduite. De plus, leseffets du rapport de charge sont déterminés pour ce mode de propagation. / The detection of damage in composite aeronautical structures is carried out duringmaintenance phases. These operations are planned so that damage is detected beforereaching any critical size for the in-service structures. The optimization of maintenanceintervals is therefore of great interest both financially and operationally. Damage in composites structures is currently dealt through the no-growth approach :when damage appears and is detected, the affected parts are immediately repaired orreplaced. In order to improve the maintenance schedule, the behaviour of defects subjectedto aeronautical load spectra needs to be characterized. This would enable a transitiontowards a damage tolerance philosophy with a slow-growth approach by defining noncriticalpropagation phases for the mechanical strength of structures. In this context, delamination propagation under fatigue loading is studied. The effectsof loading frequency and load ratio on fatigue delamination propagation are determinedin mode I. Then a study of delamination propagation under complex load spectra isconducted for blocks at different loading amplitudes. Effects of the loading history arehighlighted. For the propagation in mode II, loading frequency effects on delamination propagationare investigated for four different composite materials using a dedicated vibration testingdevice. A thermal analysis is also conducted during high frequency tests. In addition, loadratio effects are determined for this propagation mode.

Impact resonance testing is a well-documented non-destructive testing method and its applications on asphalt concrete have also been implemented successfully. The test is carried out manually by inducing an impact in order to excite the test specimen and taking measurements of the vibrational response. In an effort to improve the manual procedure of impact resonance testing, an automated non-contact methodology is developed and its applicability with regards to low temperature behaviors of asphalt concrete is investigated. Results from this work show that repeatable fundamental resonance frequency measurements can be performed on a disc shaped specimen in an automated manner without the need to open the thermal chamber. The measurements obtained from the new method have been verified by taking similar resonance frequency measurements using an instrumented impact hammer. It has also been shown in this work that the proposed method is suitable to investigate the lone effects of cyclic thermal conditioning on asphalt concrete without any other possible biasing effects associated with contact in the conventional testing. A hysteretic behavior of stiffness modulus is obtained on three different asphalt concrete specimens subjected to repeated low temperature cyclic conditioning. Reduced modulus values at each temperature are obtained in all the tested specimens after a low temperature stepwise conditioning at temperatures from 0oC to -40 oC. This observed behavior shows that the dynamic modulus of the tested specimens is affected by low temperature conditioning. The norm of the complex modulus decreases and the phase angle or damping ratio increases after low temperature conditioning. Hence, valuable and practical low temperature characteristics of different asphalt concrete mixtures can possibly be obtained by using the proposed methodology.