Evaluation Of Ceramic Matrix Composite Exhaust Nozzle Divergent Seals

Abstract

During the last six years substantial research efforts have been devoted towards evaluating ceramic matrix composite (CMC) materials for aerospace gas turbine engines. A majority of these technical activities have been directed towards the insertion of CMCs into the exhaust nozzles of aerospace military turbine engines that utilize an afterburner. The effort discussed here is studying an advanced self-sealing ceramic matrix composite called SEPCARBINOX A500. Carbon fibers are utilized as the reinforcement. The matrix is applied by Chemical Vapor Infiltration (CVI), and consists of a novel technology that utilizes sequential layers of Silicon Carbide (SiC) and specific sequences of Si, C, and B. The specific application involves the F100 gas turbine engine exhaust nozzle divergent seals. This CMC has been subjected to extensive material evaluations, subelement testing in simulated exhaust nozzle environment conditions, and over two years of ground testing. The lack of any degradation in the ground tested hardware run to 1.5X the design life prompted the start of a feld service evaluation (FSE). Starting in July, 2005, a total of 8 CMC divergent seals began flying at an operation base on two F-16 aircraft. In February, 2006, 20 additional CMC divergent seals began flying on F-15 aircraft at a second operational base. Discussion will address the unique CMC material and how it is performing in flight. A CMC seal has been removed from the FSE program and evaluated for retained tensile strength and microstructural stability. The seal showed no evidence of wear, the micrographs of the microstructure showed no signs of degradation, and no decrease in strength was measured.