Abstract
The effect of the porosity on the fracture behavior of 3D-woven SiC/SiC composites fabricated by multiple polymer impregnation pyrolysis (PIP) process was focused in this paper. The number of PIP cycles was varied as two, four and nine which yielded various porosities from 13 to 30%. The fracture behavior was examined by 4-point bending tests with the aid of acoustic emission (AE) monitoring. The microscopic observations of cross section after loading showed that the critical stress for the onset of crack formation on the tensile surface was increased with the decrease in porosity. However, the AE analysis indicated that the composite with the lowest porosity showed the earliest crack propagation in the rich PIP-SiC matrix region. The composite with intermediate porosity exhibited the most delayed onset of microdamage accumulation. Regardless of the porosity, the large pores located between fiber bundles did not arrest the crack growth from tensile side along thickness. The effect of the porosity on bending fracture process was explained by both the several crack propagation paths and the stress levels for the initiation of the cracks.
