Coupled topology optimization of structure and connections for bolted mechanical systems

This work introduces a new coupled topology optimization approach for a structural assembly. Considering several parts connected by bolts, the shape and topology of potentially each part, as well as the position and number of bolts are simultaneously optimized. The main ingredients of our optimization approach are the level-set method for structural optimization, a new notion of topological derivative of an idealized model of bolt in order to decide where it is advantageous to add a new bolt, coupled with a parametric gradient-based algorithm for its position optimization. Both idealized bolt and its topological derivative handle prestressed state complexity. Several 3d numerical test cases are performed to demonstrate the efficiency of the proposed strategy for mass minimization, considering Von Mises and fatigue constraints for the bolts and compliance constraint for the structure. In particular, a simplified but industrially representative example of an accessories bracket for car engines demonstrates significant benefits. Optimizing both the structure and its connections reduces the mass by 24% compared to classical “structure-only” optimization. • First work on bolted systems with level-sets and topological sensitivity analysis. • Idealized but realistic bolt model with pretension state and mechanical constraints. • Effectiveness of the coupled optimization on a representative industrial use case. • Lighter structure with equal mechanical efficacy than optimization with fixed bolts. • General methodology, reusable for a large class of problems and objective functions.