Crack analysis on the toothed mating surfaces of a diesel engine connecting rod

• The metallographic and fracture examination are investigated.
• Mechanical properties are tested to evaluate material strength.
• Contact stress near the crack is analyzed with FE model with bolt assembly.
• Material, tooth profile and bolt assembly force affect the crack generation.

This paper presents the failure analysis of a connecting rod used in a diesel generator set on an offshore platform. Cracks occurred on the toothed mating surface of the connecting rod after approximately 6000–10,000 h in service. To determine the failure mechanism, material characterization and numerical analyses are performed on the connecting rod. The macro and micro structures are analyzed by scanning electron microscope (SEM) and optical microscope. The chemical composition and metallographic structure investigation are conducted to study the characteristics of the material. Hardness and tensile tests are performed to verify the mechanical properties of the connecting rod. A nonlinear finite element (FE) analysis with the bolted assembly is performed to evaluate the local stress near the mating faces, and the results shows that the crack position is consistent with the high stress spots. As a result, lower yield strength of the material and high stress level or high stress concentration are concluded as the main reasons of failure of the connecting rod.