The fatigue life prediction of the brackets at the bolted joint interfaces subjected to vibration loads is not possible experimentally as we cannot instrument the strain gauges at the component interfaces. An example is a bolt on bracket connected to an IC engine block in which a crack can occur at the bolted joint interface when the bracket modes get into resonance. The finite element analysis (FEA) method can be used for fatigue life predictions at the component interface. The time domain analysis approach that includes the detailed dynamic behavior (frictional and contact interactions) of the bolted joint is not cost-effective as it takes huge memory and time. A new analysis methodology has been developed to predict the fatigue life using steady state dynamic frequency response analysis followed by ‘acceleration-mapped’ static analysis. First, the natural frequency modes of the component are calculated to determine the dominant modes (that cause lower fatigue life at the bolted joint interfaces) using modal analysis followed by a steady state dynamic frequency response analysis. Next, the modal accelerations at dominant modes are super-positioned to define a static loading using python scripting. The assembly (bolt preload) and non-linear effects of the bolted joint can be included in the ‘acceleration-mapped’ static analysis. This paper details this approach and compares the fatigue life results with other FEA approaches for a bolt on bracket connected to engine block.

Ameer is currently working at Mercury Marine (a division of Brunswick Corporation) as a Principal Engineer, leads vibration analysis projects for marine engine components using Finite Element Analysis (FEA) methods. He has more than 12 years’ experience in the field of vibration analysis. He is experienced in performing analytical modal and forced response analysis with base engine excitation to predict the component durability and analyze experimental test data like spectrum and waterfall plots, operating deflection shapes (ODS).