Multi-Domain Multi-Material Topology Optimization of a Roller Coaster Vehicle Bogie subject to Multi-Axial Fatigue Constraints

Structural and Multidisciplinary Systems Design Group (SMSD)
In Collaboration with Dynamic Structures

This research, conducted in collaboration with Dynamic Structures, aims to address the unique challenges posed by roller coaster wheel assemblies (bogies), specifically focusing on multiaxial fatigue topology optimization. Roller coaster bogies face complex multiaxial loading conditions and require specialized fatigue constrained optimization due to their intricate loading, operating conditions, and repetitive load time histories. Existing methodologies often overlook the intricacies of roller coaster engineering. They primarily concentrate on simpler loading cases or isolate different components into their own finite element analyses, neglecting the crucial aspect of how different components interact with one another. The main objective of this study is to reduce the volume of a roller coaster bogie while ensuring its structural integrity and potentially increasing its service life over the expected number of operational cycles.

Fatigue in materials is a phenomenon that arises when specific stress and strain concentrations surpass the material's fatigue endurance limit. This can result in the formation of cracks and a gradual deterioration of the material's structural integrity. High-cycle fatigue poses a considerable risk for structures subjected to cyclic loading, as it has the potential to culminate in abrupt and unexpected structural failures. In such cases, the cumulative effect of cyclic stresses over time can compromise the material's ability to withstand load-bearing demands, ultimately jeopardizing the safety and reliability of the entire structure.

To solve the complex multiaxial fatigue problem in roller coaster bogies, a multi-domain topology optimization is used, resulting in a solution that incorporates three discretely assigned materials. In total, 34.02% of the volume of the designable domains are removed from the bogie, resulting in a total volume reduction of 21.51%. The achieved service life of the bogies in this study reaches 991,100 cycles with minimal damage of 1.009E-6 accrued per cycle. The effectiveness of multiaxial fatigue solvers is further validated through a comprehensive analysis of three case studies, wherein material removal ranged from 25.34% to 34.62%, mirroring the results obtained in the bogie model. Static strength utilization and fatigue utilization values are used to verify proper fatigue optimization within the solutions.

Thesis has been successfully defended. Read more here: