The Effect of Holding Time on Elevated-Temperature Low-Cycle Fatigue

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  • 高温低サイクル疲労における負荷保持時間の影響
  • コウオン テイサイクル ヒロウ ニ オケル フカホモチジカン ノ エイキョウ

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Abstract

The low-cycle fatigue tests were conducted at elevated-temperatures on two alloys, Type SUS 32HP (equivalent to AISI 316) stainless steel and 1Cr-1/4 Mo steel, SCM3, and the effect of holding time at the absolutely maximum tensile or compressive strain was investigated.<br>A considerable reduction in their fatigue lives was observed when the test temperature was raised and the holding time was increased.<br>The linear fraction rule between creep and fatigue damage was compared with the experimental results, and it was found that there lie several serious problems in this rule, especially when applied to cyclic softening materials such as SCM3 steel.<br>The Endo's theory on corrosion-fatigue was modified to develop the following life-evaluating equation, which takes consideration for the relationships among the cycle-dependent effect by fatigue damage, the time-dependent effect by oxidation, and their combined effect.<br>(1+B·t0n1·Nfn1)·εpR·Nfα0=C0<br>where, t0, εpR, and Nf are the holding time during a half cycle, the plastic strain range, and the number of cycles to failure, respectively, and B, n1, n2, α0, and C0 are constants. This equation was shown to represent the experimental results well. The time-dependent effect may be interpreted to include other supplementary effects such as creep damage and deterioration of materials.

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