Helicopter Dynamic Components Fatigue Safe Life Prediction

摘要

The safety-of-flight critical, non-redundant helicopter dynamic components are subjected to high cycles, low stresses and high stress ratio environment. Rotorcraft manufacturers have primarily relied on 6 pieces of full-scale test to determine the component retirement times. The test is time-consuming as well as cost prohibitive. In this paper the advantages and disadvantages of the nominal stress method, the stress-strain method and the field intensity method as a tool for the fatigue safety life prediction are discussed. Comparison of the methodologies is performed for both constant amplitude fatigue and spectrum fatigue. For constant amplitude fatigue, a comparison of the high cycle and low cycle fatigue prediction of the methodologies is performed by generating notched member S-N curves from smooth member data and comparing the results with those from handbook. For spectrum fatigue, a comparison is performed, using usage spectra for a helicopter main rotor. For the stress severity method and the field intensity method, the Goodman and Gerber mean stress correction are used. For the local stress-strain method, the Goodman and Smith-Watson-Topper stress ration correction are used. The Gerber and Smith-Watson-Topper correction appear to produce good agreement with the full-scale test result. It is liable to confirm fatigue crack initiation life interval using these methodologies in helicopter blade and parallel structures.