Performance of Four Ceramic‐Matrix Composite Divergent Flap Inserts Following Ground Testing on an F110 Turbofan Engine

Four ceramic‐matrix composite flap inserts were evaluated following ground testing on a General Electric F110 turbofan engine. Three of the composites accumulated ∼117 h of engine time. The fourth composite, a Nextel TM 720 material with aluminosilicate matrix, accumulated ∼40 h. Large through‐thickness cracks developed along the longitudinal edges of a Nicalon™/Al 2 O 3 insert and the Nextel 720/aluminosilicate insert. The cracks developed because of high tensile stresses caused by the steep in‐plane thermal gradients induced across the flap width during afterburner lights. The Nextel 720/aluminosilicate insert also exhibited severe surface wear associated with the acoustic environment and contact with the adjacent divergent seals. Neither a Nicalon/silicon nitrocarbide insert nor a Nicalon/C insert exhibited significant signs of distress.