Abstract
Electrical resistance has been used to detect in situ changes to SiC based material as damage occurs. Damage in the composite, typically in the form of matrix cracking, increases the resistance due to the local constrain of current flow. Efforts have been ongoing to quantify the effects of increasing potential drop with crack growth in a pre-preg SiC-based composite. Two variations of the pre-preg SiC-based composite were studied: one with a single layer of SiC monofilaments with carbon core (1 fiber/mm) inserted in the center of the composite and extending through the length of the composite and the other possessed three layers of monofilaments, one layer in the center of the composite and the other two layers near both surfaces of the composite. It was found that the high conductive Si phase varied considerably for the different variations of composites and dominated the current flow rather than C. Tension-tension fatigue tests were conducted at 815 °C in a static furnace for both composite systems, electrical resistance was monitored during the test along with acoustic emission. A ply level electric circuit was constructed, and ply resistivity at temperature was obtained based on the Si content in each ply. The function of the electric circuit was to interpret the change in resistance obtained during the fatigue testing of the MI material with the morphology of transverse crack growth. Microscopy and energy dispersive spectroscopy were conducted to better understand the crack morphology.
