大形試験片による海水腐食曲げ疲労試験

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The authors have newly designed and manufactured a large rotating bending fatigue test machine (Cantilever type, Max. bending moment 7 t-m, Standard diameter of specimen 125 mmΦ) and tested specimens of 135 mmΦ under sea water corrosion.The specimens have been taken from steel bars forged from 1.4 ton ingots made by acid openhearth process (forged ratio=6) and annealed in the furnace. The chemical and mechanical properties of the specimensare as shown below : [table]10 mmΦ specimens of the same material having simillar shape have been also tested under sea water corrosion for comparison.The following facts have been revealed by the tests : (1) Fatigue strengths of 130 mmΦ and 10 mmΦ specimens at 10^8 stress reversal were 11.2kg/mm^2 and 3.5kg/mm^2 respectively.(2) Depth of cracks found on the corroded surface of specimens is calculated by the following formula : l=C×log_10(N/(Nc))where l : Depth of corrosion cracks (mm)C : Constant, determined by the method of corrosion (=0.86 in this experiment)Nc : Limit of stress reversal at which corrosion cracks will originate(=1.7×10^6 in this experiment)N : No. of stress reversals.(3) When N does not exceed 1.7×10^6,cracks will not originate.(4) A reversal stress limit (σ_C) at which surface cracks have originated on large corroded specimens may be pressumed about 5kg/mm^2.(5) There is also a reversal stress limit (σ_0) at which fine cracks on the non-corroded specimens begin to develope, σ_0 is assumed about 11 kg/mm^2 for the steel tested (6) Failure of corroded specimens may occur when reversal stress has increased as the result of reduction of effective area by surface cracks and exceeds σ_0.(8) Fatigue limit of large corroded specimens is designated by σ_0.(8) There may be no fatigue limit for small corroded specimens.
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大形試験片による海水腐食曲げ疲労試験

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