## 1 Introduction  
Ceramic Matrix Composites (CMCs), and more particularly SiC/SiC composites are very attractive candidates for many high-temperature structural applications, because of their excellent creep resistance, high-temperature strength and light weight. Damage tolerance is achieved through the use of low shear strength fiber coatings that deflect cracks along the interfaces [1; 2; 3; 4; 5; 6; 7]. The multi-layered matrix was introduced in the new generations of SiC\({}_{\ell}\)/[Si-B-C] composites in order to improve the lifetime under medium and high temperatures thanks to the formation of sealant glasses [8; 9]. Future engine applications in civil acircrafts are foreseen for such composites. These applications require that the material can resist both severe conditions (temperatures up to 1200 \({}^{\circ}\)C under air) and very long static loadings at intermediate temperatures (400-700 \({}^{\circ}\)C during tens of thousands of hours). Various authors have studied the mechanical behavior of SiC\({}_{\ell}\)/SiC composites and the damage mechanisms occurring at high temperatures [1; 2; 3; 4; 5; 6; 7]. Now more information is needed at intermediate temperatures: the oxidation kinetics of the different constituents are complex, and the effect of matrix sealing on the lifetime of the composite has to be examined. Expected lifetimes in use conditions are several thousands of hours, which can hardly be reached by laboratory tests for practical reasons. Therefore, a real-time prediction of the remaining lifetime during tests is necessary. It requires the monitoring of damage evolution for which AE measurement is a suitable technique. In fact, the AEtechnique consists in the recording and analysis of elastic waves created during material damage. It provides real-time data on initiation and evolution of damage in terms of location and mode. Common analysis of AE is based on diagrams of cumulative hits or counts or histograms of amplitudes. Nevertheless, in the case of composite material, this approach is inadequate in order to identify the acoustic emission signature of several damage mechanisms. It was improved by grouping signals of similar shapes into clusters using classifier parameters [10]. Many works [11; 12; 13; 14; 15; 16] have shown that AE techniques and multivariable classification techniques are the basis of pattern recognition tools. [PERSON] [12], [PERSON] [13; 14], [PERSON] [15; 16] have identified different classes of AE signals which were attributed to damage modes in oxide/oxide, glass/polyester and SiCf/ [Si-B-C] composites. [PERSON] [16] analyzed the AE data using an unsupervised multi-variable clustering technique. This analysis showed that several types of signals may be distinguished, and that the obtained clusters were consistent with the expected damage modes in 3D SiC/SiC composites. In this way, a careful analysis of acoustic emission signals can lead to the discrimination of the different damage mechanisms occurring in a composite material. It is a possible solution for identification of damage during service with a view to component lifetime control. A second analysis is based on a global AE analysis, on the investigation of liberated energy, with a view to identify a critical point. Many researchers investigated the elastic energy release during the failure process of materials [17; 18; 19; 20; 21; 22; 23; 24]. They all observed that the energy release accelerated following a power law. These models are representative of an avalanche behavior very similar to that observed in seismicity. This study focuses on static fatigue experiments realized at intermediate temperature under air on a SiC\({}_{f}\)/[Si-B-C] composite with a self-healing matrix. A lifetime diagram is presented, and the evolution of several damage indicators is discussed. The objective of this approach is to propose a method based on acoustic energy in order to evaluate the remaining lifetime during long-term mechanical tests.