An oxide/oxide ceramic fiber‐matrix composite (CMC) has been extensively characterized for high‐temperature aerospace structural applications. This CMC is called GEN‐IV™, and it has a porous and cracked aluminosilicate matrix reinforced by 3M Nextel 610™ alumina fibers woven in a balanced eight harness weave (8HSW). This CMC has been specifically designed without an interphase between the fiber and matrix, and it relies on the porous matrix for flaw tolerance. Stress‐strain response is nearly linear to failure and without a well‐defined proportional limit in tension and compression. In‐plane shear and interlaminar strength increases with increasing temperature. The 1000°C fatigue limit in air at 105 cycles is 160 MPa, and the residual tensile strength of run‐out specimens is not affected by the fatigue loading. The creep‐rupture resistance above 1000°C is relatively poor, but it can be improved with a more‐creep‐resistant fiber.

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 1000°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 1000°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 of 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.