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 similar to 117 h of engine time. The fourth composite, a Nexte l(TM) 720 material with aluminosilicate matrix, accumulated similar to 40 h . Large through-thickness cracks developed along the longitudinal edges of a NicalonTM/Al2O3 insert and the Nextel 720/aluminosilicate insert. The cra cks 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 a ssociated with the acoustic environment and contact with the adjacent diver gent seals. Neither a Nicalon/silicon nitrocarbide insert nor a Nicalon/C i nsert exhibited significant signs of distress.