Novel Methodology for Assessment of Bolted Joints Under Vibration Fatigue

Bolts are one of the most standardized and preferred machine elements for connection and load transfer. On the other hand, since the mechanics of highly stressed bolted joints and the thread fatigue are complex issues, the design and validation of such joints is frequently carried out with major simplifications and assumptions, leading to either over-engineered solutions or to premature failures of the prototypes. Evaluating bolted joint for fatigue is itself complex phenomenon and with vibration loading it adds further challenges in terms modeling and simulation. Proven and most preferred method for vibration fatigue is modal superposition analysis. One major drawback of this method is its inability to include frictional contact. This leads to change in load path, causing incorrect fatigue life evaluation for these joints. In this paper, author presents two different methodologies to evaluate bolts under vibration fatigue capturing correct physics and load path. • Contact optimization of a bolted joint using contact pressure and load path study • Acceleration extraction using modal dynamic analysis and load super-position Outcome of these methods were validated with physical test and excellent co-relation was observed since it depicts accurate load path with appropriate frictional contacts and change in stiffness from dynamic response. These methods can be leveraged to any such structure prone to vibration loading where frictional contacts are involved. It overcomes conservative approach from inertia analysis procedure and consequently vibration fatigue analysis methodology provides more robust evaluation method resulting in more confidence and edge to play with different design proposals. Key Words: Vibration Fatigue, Bolted Joint, Modal/Load Superposition, Dynamic Analysis