Multi-Objectives Optimization of Fastener Location in a Bolted Joint

During component development of multiple fastener bolted joints, it was observed that one or two fasteners had a higher potential to slip when compared to other fasteners in the same joint. This condition indicated that uneven distribution of the service loads was occurring in the bolted joints. The need for an optimization tool was identified that would take into account various objectives and constraints based on real world design conditions. The objective of this paper is to present a method developed to determine optimized multiple fastener locations within a bolted joint for achieving evenly distributed loads across the fasteners during multiple load events. The method integrates finite element analysis (FEA) with optimization software using multi-objective optimization algorithms. Multiple constraints were also considered for the optimization analysis. In use, each bolted joint is subjected to multiple service load conditions (load cases). Each of these load cases requires evaluation to validate the fastened joint. Additionally, geometric limitations that define the available joint footprint had to be included in the analysis. The case study was conducted on 3-bolt and 4- bolt powertrain mount brackets. By using this multi-objective optimization tool, the fasteners' locations are determined based on equalizing the shear loads on each fastener for all the joint service load cases, and a robust joint design is achieved by identifying the minimum fastener size required to maintain joint integrity and fastener commonality.