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<p>The fatigue characteristics under cumulative dynamic loads at increasing operating frequencies were beneficial for stating the structural response of the overall material, especially for offshore structures such as bridges. This study experimentally investigated the S–N curve sensitivity on the fatigue characteristics such as fatigue life, fatigue strength, and endurance limit, determined by performing high-cycle fatigue tests at an increase in operating frequency of 5, 10, and 15 Hz by a systematic decrease in stress range. Microstructural observations showed that E350 steel has 84.2% acicular ferrite, 3.4% pearlite, and 12.5% bainite, whereas S690QL steel has 73.7% tempered martensite and 27.2% bainite. S690QL steel exhibited good impact resistance with excellent toughness characteristics. Fractography revealed that the extent of microvoids on coarse particles of E350 steel, dispersoids in the matrix, and precipitates at the grain boundaries of S690QL steel influenced the ductility of the steels at higher frequencies. The overall results indicate that, irrespective of the ductility behaviour of the material, operating frequency had a notable influence on the dynamic characteristics.</p>

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Influence of operating frequency on fatigue and fracture characteristics of E350 and S690QL steel coupons with tangentially blended fillets: An experimental study

  • 期刊论文

  • 发表日期：

    2026年4月2日

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  • Nagaraju Doredla,
  • Kumar N Senthil

摘要

The fatigue characteristics under cumulative dynamic loads at increasing operating frequencies were beneficial for stating the structural response of the overall material, especially for offshore structures such as bridges. This study experimentally investigated the S–N curve sensitivity on the fatigue characteristics such as fatigue life, fatigue strength, and endurance limit, determined by performing high-cycle fatigue tests at an increase in operating frequency of 5, 10, and 15 Hz by a systematic decrease in stress range. Microstructural observations showed that E350 steel has 84.2% acicular ferrite, 3.4% pearlite, and 12.5% bainite, whereas S690QL steel has 73.7% tempered martensite and 27.2% bainite. S690QL steel exhibited good impact resistance with excellent toughness characteristics. Fractography revealed that the extent of microvoids on coarse particles of E350 steel, dispersoids in the matrix, and precipitates at the grain boundaries of S690QL steel influenced the ductility of the steels at higher frequencies. The overall results indicate that, irrespective of the ductility behaviour of the material, operating frequency had a notable influence on the dynamic characteristics.