Abstract
The fatigue strength of two kinds of gray cast iron under superimposed stress wave forms in tensile and compressive stress regions at room temperature, 300°C and 450°C were discussed.
Obtained main results through the investigations are following.
(1) In tensile stress region at room temperature the influence of the superimposed secondary stress over the fatigue strength for primary stress wave appears about at not less than 0.1 of stress ratio of secondary stress amplitude to primary stress amplitude.
(2) In compressive stress region at room temperature the influence of superimposed secondary stress over the fatigue strength for the primary stress wave is smaller than that in tensile stress region. For evaluation of mean stress in compressive stress region. Gelber's equation is most suitable.
(3) In tensile stress region at room temperature and elevated temperature the fatigue life under superimposed stress wave form is evaluated by using the modified Miner's rule and Yamada's evaluation equation of mean stress. In the case of elevated temperature the frequency modified S-N curves and the frequency modified evaluation equations of mean stress are used.
(4) In compressive stress region at elevated temperature the superimposed stress wave fatigue life can be estimated by the use of the next equation.
1/Nf=Aσα*1⋅exp(-m*σpe2)
where Nf: number of cycles to failure for primary stress wave
σ1: primary stress amplitude
σe2: equivalent secondary stress amplitude
A, ρ*, m*, p: material's constants
