Fatigue damage accumulation in 3-dimensional SiC/SiC composites

The effect of fatigue loading on the mechanical performance of 3-D SiC/SiC composites was investigated. A non-destructive macromechanical approach was applied which permits for the evaluation of the material damage state by m onitoring its dynamic response as function of fatigue cycles. The correlati on of the results provided by this method to that of other non-destructive techniques such as Acoustic Emission (AE), leads to a detail micromechanica l- macromechanical monitoring of the material fatigue behaviour. The damage modes identification and their successive appearance, together with the ev aluation of the material performance at the different stages of fatigue loa ding, is among the inspection capabilities that provides the above mentione d combination of non-destructive techniques. The proposed methodology appli ed in the case of a 3-D SiC/SiC ceramic matrix composite material and the e ffect of fatigue loading on the material integrity was evaluated by measuri ng the degradation of the dynamic modulus of elasticity and the increase of the material damping. Conclusions, concerning design aspects using these m aterials, as well as fatigue life prediction were provided. Finally, the se nsitivity of the proposed methodology for the definition, the characterisat ion of the development and the separation of the different damage modes dur ing fatigue loading has been discussed. (C) 1998 Elsevier Science Limited. All rights reserved.