Analysis of fatigue crack growth in cylinder head bolts of gasoline engine based on experimental data

Engines cylinder head bolts failure from the thread location in cylinder block causes the problems during repairing time. Exact prediction of fatigue crack growth in bolts by experimental analysis and finite element method modeling can affect the Maintenance Planning and Scheduling Implementation. In this study, the fatigue analysis of cylinder head bolts of a four-cylinder gasoline engine imposed by premature failure is investigated. The bolts suffer a mechanical seizure on the threads about 2 x 10(8) cycles in service. For such aim, standard specimens are cut off from the bolts and examined to evaluate the mechanical properties and material chemical composition. Optical microscopes and scanning electron microscopy are employed to consider the microstructures, defects, fracture surface and failure cause. The morphology of the fracture surface shows the fatigue crack growth marks, including the beachmarks, the ratchet marks and the river cracks. The finite element analysis model is presented applying the elastic-plastic finite element analysis for the bolts under variable combustion pressure. The stress history is then used to calculate stress intensity factors and fatigue life of bolts. Numerical results show that crack existence to depth of 0.35 mm is the source of failure of premature fracture.