Analyse par thermographie infrarouge de l'endommagement des structures composites sous sollicitations quasi statiques

La sensibilité des structures composites à la présence d'endommagements importants en zones singulières (trou, pointe d'entaille, ...) impose d'évaluer leur tolérance aux dommages. Dans ce contexte, ce travail s'attache à apporter des précisions quantitatives sur l'endommagement de ces structures à partir de la technique de thermographie infrarouge. Une première étude a été consacrée à la caractérisation des mécanismes de dégradation d'un stratifié tissé mince (verre/époxyde) sous sollicitations homogènes. En s'appuyant sur une approche calorimétrique locale, régie par le cadre de la Thermodynamique des Processus Irréversibles, les mesures thermiques sont utilisées pour localiser et quantifier les dissipations associées aux différents mécanismes de dégradation. Une démarche expérimentale est alors proposée pour évaluer le taux de restitution d'énergie dans plusieurs cas de fissuration. Dans un second temps, cette démarche est appliquée à l'étude de la fissuration de structures stratifiées constituées de plis unidirectionnels sous chargement de traction, puis de compression.The sensibility of the composite structures in the presence of important damages in singular zones (hole, notch tip, ...) involves to estimate their damage tolerance. In this context, this work attempts to bring quantitative precision on the damage of these structures by the mean of infrared thermography. A first study was dedicated to the characterization of the degradation mechanisms in a thin woven laminate (glass/epoxy) under homogeneous loading. Founded on a local calorimetric approach, governed by the frame of the Thermodynamics of Irreversible Processes, the thermal measures are used to locate and quantify the dissipative energy associated with the various mechanisms of degradation. An experimental approach is then proposed to estimate the energy release rate in several cases of cracking. Secondly, this approach is used to study the rupture of laminated structures made of unidirectional plies under tensile loading, then compressive loading

Damage of woven composite under translaminar cracking tests using infrared thermography

The aim of this work is to increase the study of the notch translaminar propagation of the woven structures, using the InfraRed Thermography (IRT). A test of notch propagation under quasi-static traction was developed and used to study the failure phenomena on two different draping sequences. For each study, a local estimation of dissipated energies, associated with different damages, is carried out using the measurement of the surface temperature field. The study of heat source fields combined with micrographic observations allowed to define the matrix micro-cracking as the predominant damage phenomenon in crack tip. The critical energy release rate, obtained using IRT, corresponds to critical energy release rate reported in the literature for translaminar rupture of laminates. Furthermore, when brittle cracking develops in a thermosetting matrix laminate, the majority of irreversible mechanical energy (>90%) is dissipated as heat. In the case of brittle cracking, the developed method proves to be an efficient alternative technique for the local measure of energy release rate, even in cases where the variations in stiffness due to cracking phenomena remain low

Measure of fracture toughness of compressive fiber failure in composite structures using infrared thermography

Fracture toughness is one of the most important properties of any material for a lot of design applications involving damage and crack growth. Unfortunately, its value can be difficult to evaluate with standard methods such as the ‘‘compliance’’ method. In this work, two special cases have been studied and infrared thermography has been used to overcome the limitations of conventional methods. Compressive fiber failure in unidirectional composite laminate has been chosen due to its difficulty to evaluate toughness. Infrared thermography has been employed to follow compressive failure mode developing during an indentation test and a compression after impact test, and to evaluate the fracture toughness of compressive fiber failure. The obtained results show a good correspondence with the value found in a previous work on FE analysis of impact damage and are consistent with the literature