MODELING MECHANICAL RESPONSE OF SIC CAS-II CERAMIC COMPOSITE UNDER QUASI-STATIC LOADS USING A REAL-TIME ACOUSTOULTRASONIC NDE TECHNIQUE/

The onset of matrix cracks and their progression have been successfull y monitored by an acousto-ultrasonic (AU) NDE technique as shown by th e authors in previous work. The nonlinear behavior observed in a stres s-strain curve for a unidirectional ceramic composite has been predomi nantly attributed to the effect of matrix cracks. This effect of matri x cracks on the stress-strain curve has been previously modelled (AUSS R model) with the help of real-time AU data. The models presented in t his paper (modified AUSSR, AUSSR-WZ, AUSSR-WZ-WB models) attempt to de scribe the damage mechanisms occurring by assessing the combined effec t of matrix cracks and fiber breakage on the global strain response of the laminate to increasing loads. The strains at the outer surface pr edicted by the models described in this paper are compared to the expe rimentally observed strains from the extensometer attached to the oute r surface. Previous models from the literature are introduced outlinin g the history of development of successive models. It is shown here th at the modified acousto-ultrasonic stress-strain response (modified-AU SSR) model based on AU parameters is capable of predicting the strain response to increasing stress levels for unidirectional and cross-ply ceramic composite laminates. This work represents an integration of me asured experimental damage with analytical modelling to produce a bett er physical understanding of the damage development process in ceramic composites.