Effects of truncation and elimination on composite fatigue life

摘要

An experimental investigation has been carried out regarding load-sequence effects on the fatigue life of composite structures. Different elimination levels were considered for various load spectra and for constant amplitude block loading. The spectra considered were an early design spectrum for the Gripen fighter aircraft, spectra associated with the aft fitting of the fin and to the upper fitting of the wing, and the compression dominated spectrum "Short Inverted Falstaff". Both experimental and calculated results show, that the elimination level can be set to approximately 50/100 of the maximum range occurring in the load sequence. This means that considerable time and cost reductions in structural verification testing can be achieved. This will also have impact on a life prediction methodology since only a characteristic number of loading states need to be considered. The resulting life for block testing, especially for a load ratio of R=-1, is highly influenced by elimination of high load ranges in the sequence. Spectrum fatigue test results accounting for ranges up to 90/100 of loading states were eliminated. Calculation results with the same technique, i.e. accounting for a characteristic number of cycles, show promising results.