MicroCT (microtomography) quantification of microstructure related to macroscopic behaviour Part 2 - Damage in SiC-Al monofilament composites tested in monotonic tension and fatigue

The present paper reports results of monotonic tensile and of fatigue testing of an aligned monofilament composite SiC-Al. Macroscopic measures of damage (changes in unloading compliance and in unrecovered strain) correlate with noninvasive X-ray microCT (microtomography) quantification of microstructure (alteration of fibre separation, fibre misorientation relative to the load axis and amount of fibre fracture). Monotonic loading beyond yield (188 MPa) alters fibre arrangement and reduces fibre misorientation. Fracture of fibre carbon cores begins at 828 MPa and increases rapidly with rising stress concomitant with marked unloading modulus decreases and permanent strain increases. Fatigue at 621 MPa produces gradually increasing modulus and unrecovered strain with no evidence of fibre damage. At low cycles, the modulus, permanent strain and fraction of fractured C cores increase while fibre misorientation decreases; above 16 cycles, modulus decreases with gradual increases in the other quantities. Fracture in SiC could only be observed after the specimen broke.