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<p>This study investigates the catastrophic failure of a forged steel crankshaft from a 109-kW diesel engine after approximately 470,000 kilometers of operation. Comprehensive experimental analyses, including tensile testing, hardness measurements, chemical composition analysis, and surface roughness inspections, were conducted on specimens extracted from the fractured crankthrow. Fractographic examination revealed fatigue failure originating at the crankpin web filet, characterized by multiple crack initiation points with high-stress concentrations. Distinct features such as ratchet marks, beach marks, and river marks were identified, highlighting fatigue loading and bending force as significant contributors to failure. Further analysis revealed an uneven surface-hardened layer at the cracked web filet, with increased surface roughness and reduced surface hardness. These inconsistencies compromised the fatigue strength of the crankshaft, as evidenced by the formation of microvoid coalescence and crack propagation. Mechanical testing confirmed that the material properties met the JIS-S55C standard, except for localized deviations near the fractured regions. The findings emphasize the critical role of consistent surface hardening and quality control processes in preventing fatigue failure. Addressing surface roughness, hardness uniformity, and material properties during manufacturing can significantly enhance the durability and performance of forged steel crankshafts.</p>

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Failure and Root Cause Analysis of a Forged Steel Crankshaft

  • 期刊论文

  • 发表日期：

    2025年6月2日

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  • Pichai Janmanee,
  • Theerawat Kumnorkaew,
  • Weera Khuanlieng

摘要

This study investigates the catastrophic failure of a forged steel crankshaft from a 109-kW diesel engine after approximately 470,000 kilometers of operation. Comprehensive experimental analyses, including tensile testing, hardness measurements, chemical composition analysis, and surface roughness inspections, were conducted on specimens extracted from the fractured crankthrow. Fractographic examination revealed fatigue failure originating at the crankpin web filet, characterized by multiple crack initiation points with high-stress concentrations. Distinct features such as ratchet marks, beach marks, and river marks were identified, highlighting fatigue loading and bending force as significant contributors to failure. Further analysis revealed an uneven surface-hardened layer at the cracked web filet, with increased surface roughness and reduced surface hardness. These inconsistencies compromised the fatigue strength of the crankshaft, as evidenced by the formation of microvoid coalescence and crack propagation. Mechanical testing confirmed that the material properties met the JIS-S55C standard, except for localized deviations near the fractured regions. The findings emphasize the critical role of consistent surface hardening and quality control processes in preventing fatigue failure. Addressing surface roughness, hardness uniformity, and material properties during manufacturing can significantly enhance the durability and performance of forged steel crankshafts.