Procedures and Analyses Providing Accumulated Fatigue Life Computation Assessment for On-board Fatigue Life Counter (FALC)

The FALC system (see Proc. Int. Conf. on Aircraft Damage Assessment and Repair, 1991, Melbourne, Australia) produces real and timely flow of data relating to the fatigue accumulation of an aircraft structure. Signals are received from three-component rosette strain gauges located in areas around the structural critical points or structural significant items (SSI) of an airframe which, when processed and converted to readable data, represent the individual structural fatigue accumulated at a SSI during a determined flight. Constant and timely knowledge of the accumulated fatigue contributes to a more effective and efficient monitoring process with consequent advantages of a higher level of safety and lower cost in maintenance. There are two main methodological problems related to the computational assessment of individual structure fatigue accumulation: 1. Optimal location of FALC gauges in order to maximize number of SSI that can be serviced by restricted number of gauges. 2. FALC system tuning by parameter optimization of data treatment algorithm in order to minimize discrepancies between FALC results and 'standard' values of accumulated fatigue in as many SSI as possible. Solutions to these problems based on modern mathematical optimization methods have been developed by the authors. Results from FEM analyses for typical aircraft operation loading are used as strain inputs in the optimization procedure providing optimal FALC gauge locations.