Monitoring fatigue damage development in ceramic matrix composite tubular specimens by a thermoelastic technique

Tubular specimens made of borosilicate glass reinforced by chopped carbon fibers for high-temperature applications were designed and fabricated by an injection molding process. Specimens were cyclically loaded in tension-tension at maximum stresses of 60, 70, and 85% (R = 0.1) of the ultimate tensile strength at room temperature to one million cycles and then loaded to failure in quasistatic tension. A thermoelastic technique known as SPATE (stress pattern analysis by thermal emission) was used to characterize fatigue damage development in these tubular specimens. Qualitative SPATE results were shown to be related to surface crack initiation and growth in the specimens, circumferentially and radially. Damage initiation sites and subsequent growth of cracks as well as residual strengths were found to be primarily influenced by the local manufacturing related microstructure of individual specimens and secondarily influenced by fatigue damage.