Deformation and Low-Cycle Fatigue Life of Steel due to the Multiple Repeated Loads under Rotating Bending

Abstract

Vehicles in general such as airplanes, automobiles and railroad cars, and structures in general, such as bridges, are subject to random repeated loads. To design machine elements included in those vehicles and structures, ordinary statistical summarization of stress spectra is performed and the“linear damage criterion”, (Σn/N)f=1, is applied to the resulting cumulative cycle ratio. The value of cumulative cycle ratio to fracture obtained from experiments does not always coincide with the value calculated from the linear damage criterion. As the authors consider that the cause of this fact comes from the variation of strain amplitude due to stress interaction, several series of low-cycle fatigue tests of steel are conducted under the condition of rotating bending with the multiple repeated loads and the relation between the deformation (deflection) measured during the tests and the resulting fatigue life is discussed.