The Effect of Hold Times on the Fatigue Behavior of an Oxide/Oxide Ceramic Matrix Composite

摘要

Ceramic matrix composites (CMCs) consisting of an oxide matrix, no fiber-matrix interphase, and an oxide fiber are attractive for high-temperature structural applications because of their inherent resistance to oxidation. Such a system has recently been evaluated using tension, tensile fatigue, and tensile creep rupture. The CMC system consists of an aluminosilicate matrix reinforced with Nextel 610 fibers. The Nextel 610 fibers were in the form of an 8HSW. Results from the mechanical behavior studies showed this CMC to perform extremely well in fatigue at both room temperature and 1000deg C. However, the system experienced significant creep strain under sustained loading because of creep deformation that occurs in the oxide fiber. To study the interaction between fatigue and creep, fatigue tests with hold times were conducted at a temperature of 1000deg C. For all tests, the maximum fatigue stress was 75 MPa and the load ratio was 0.01. Hold times of 1, 10, and 100 s were applied at maximum load to develop the creep deformation fully. Hold times to 10 seconds were also applied at both maximum and minimum load to study creep recovery. The effect of frequency was also characterized using frequencies of 1, 0.5, and 0.1 Hz. In all tests, the measured strain accumulation was found to be linear with time with no evidence of tertiary creep behavior. The CMC exhibited increased rates of strain accumulation with decrease in frequency and increase in hold times.