軟鋼の変動応力振幅下における材料応答と疲労被害について

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In this study, seven types of load controlled fatigue tests were carried out under variable stress amplitude in order to clarify the stress-strain response and the fatigue strength of SS 41 and STPY41 plate specimens. The tests were conducted in constant stress amplitude loading, step stress amplitude loading, repeated high-to-low and low-to-high block loading, two types of block-random loading and random loading with exponential distribution. In each test, stress-strain loops were recorded with X-Y plotter from the start of cycling to visual crack initiation by using the strain gauges put them on the test piece. As a result, the following conclusions were obtained. (1 ) S_a-ε_<pa> (stress amplitude-plastic strain amplitude) curves are different with each variable loading patterns. (2) Cyclic softening for random loading is greater than that for constant stress amplitude in the conditions of Sa≧σ_y and S_a≦S_<aω>, while the relation is contrary to above in the conditions of S_<aω><S_a<σ_y,where S_<aω > is a fatigue limit and σ_y is a static yield stress of the material. (3) Sa-ε_<pa> curve for random loading with exponential distribution can be obtained approximately by the step stress amplitude loading. (4) Fatigue life estimations by Miner's rule and Modified Miner's rule make over estimation compared with experimental results for block, block-random and random loadings. (5) Fatigue life estimations by Manson-Cofiin's law do not coincide with the experimental results for block-random loading and random loading with exponential distribution included the large repeated number of stress amplitudes below fatigue limit. (6) Fatigue life estimations by Corten-Dolan's method fairly coincide with experimental results for various kind of variable stress amplitude loading.
社団法人日本船舶海洋工学会の論文

軟鋼の変動応力振幅下における材料応答と疲労被害について

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