材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
ピアノ線のねじり塑性疲労寿命に及ぼす平均応力の影響
元津 彰夫藤谷 景三
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ジャーナル フリー

1979 年 28 巻 309 号 p. 485-490

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Although several ways have been proposed to predict low-cycle torsional fatigue life of metals under load controlled cycling conditions with mean stress, none of them is satisfactory for all materials and test methods.
In this study, in order to investigate the influence of mean stress on the fatigue life of piano wires in a constant load cycling test, the low-cycle torsional fatigue tests were carried out on 0.84% C piano wires under load controlled cycling conditions with various stress ratios.
The fatigue characteristic of each specimen was discussed and the fatigue fracture criteria, applicable to the load controlled fatigue test and given by the following equation, were proposed.
D=γpof+κ{1/C0N0Δγpadn+∫N0Δγcfdn}
κ=τ0maxN0maxN
where Δγp and Δγc are the ranges of plastic strain and permanent strain, respectively, dn is the infinitesimal increment of the number of strain cycles n, γp0 is the strain for the first cycle, a is a material constant, C0 is the average value of the constant C0 obtained from the equation 1/C0N0Δγpadn =1 when the mean stress is zero, N and τmax are the number of cycles to fracture and the maximum stress when the mean stress is applied, respectively, N0 and τ0max are those at zero mean stress, and γf is the fracture strain in the static test.
From the test results, it was confirmed that the above equation is well applicable to the fracture life in low-cycle torsional fatigue tests with mean stress under load controlled conditions.

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