Sonic Fatigue Study of an Aircraft Flap like Structure

Acoustic fatigue failures in aircraft are caused by the dynamic response of structures to unsteady pressure loading from aerodynamic and engine acoustic sources. Structural life is difficult to assess accurately and maybe affected by steady, thermal, in-plane and out-of-plane panel loads. These failures result in increased maintenance and inspection burdens associated with the operation of the aircrafl. Much research was performed in the late 60’s to mid 70’s on dynamic response methods and the generation of endurance data, culminating in the ESDU data sheets and AFFDL design guide. This information is still used today. However, the airframe manufacturer is required to meet more stringent performance and mass targets, which have been achieved through developments in optimised and efficient design of structures, and the introduction of new materials. There is a corresponding need for development of acoustic fatigue design methods and data. A three year research project is currently in progress using advanced analytical procedures, finite element analysis and complementary experimental studies to develop dynamic response prediction procedures which will result in guides for the design of box-type structures, such as flaps, constructed from conventional aluminium alloys, CFRP and GLARE materials. This paper reports upon the experimental phase of the project and the results.