繰返し変動ひずみ下でのピアノ線のねじり塑性疲労

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As a new method to predict the fatigue lives of metallic materials under the fatigue tests with multiple repeated loads or strains, the fatigue fracture criterion based on varying plastic strain amplitudes instead of the linear damage criterion Σ(n/N)=1 has already been verified experimentally by carrying out the low-cycle fatigue tests under tension-compression and rotating bending. However, for the plane bending and torsional fatigue tests it has not been verified so far experimentally whether the fatigue fracture criterion based on varying plastic strains is applicable or not. From such a view point, the authors have carried out the low-cycle torsional fatigue tests by using 0.84%C piano wires under multiple repeated strains, and investigated the applicability of the fatigue fracture criterion based on varying plastic strains experimentally. Furthermore, the applicability of the above fracture criterion has been also discussed on the basis of the experimentally determined correlation between the equivalent stress τ_<eq> and the equivalent plastic strain amplitude γ_<p.eq>. The main results obtained are summarized as follows: (1) The values obtained from the fatigue fracture criterion based on varying plastic strains were slightly closer to unity than those calculated from the linear damage criterion. Therefore, when used for predicting the fatigue lives under the strain control test, the fatigue fracture criterion based on varying plastic strains is better than the linear damage criterion. (2) From the test results the following exponential relationships were found to hold between the equivalent stress and the equivalent plastic strain amplitude. γ_<p.eq>=c・a^<τeq> up to fracture, γ_<p.eq>'=c'・a'^<τeq>' up to fracture initiation, where a, a' and c, c' are constants. (3) The strain ratio γ_<a2>/γ_<a1> or the number of cycle ratio n_2/n_0 had a little effect on the cumulative damage in this study.
社団法人日本材料学会の論文
1974-07-15

繰返し変動ひずみ下でのピアノ線のねじり塑性疲労

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