Engineering design study of a titanium-fabricated primary rollover structure for a single-seater race car

This thesis explores the structural and manufacturing feasibility of a primary rollover structure (roll hoop) fabricated from welded titanium for a single-seater race car. The objective is to meet stringent FIA homologation requirements while minimizing weight and cost, ensuring driver safety, and introducing technological innovation. A systematic design methodology was adopted, starting with the definition of regulatory constraints and performance objectives, followed by concept generation and selection. Five manufacturing concepts—fabricated, cast, machined, additive manufactured, and CFRP—were compared using a weighted selection matrix. The fabricated titanium solution emerged as the most cost-effective and manufacturable option, despite a moderate weight penalty compared to additive manufacturing. Material selection was driven by specific strength, weldability, and formability, using Ashby charts and comparative analysis. Titanium alloys were identified as optimal, with a hybrid material strategy: Grade 9 for bent tubes, Grade 4 for formed sheets, and Grade 5 for machined components. This combination balances mechanical performance with manufacturing feasibility. The embodiment design phase produced multiple CAD layouts featuring dual main tubes connected by various reinforcement strategies, including truss structures, stamped or bent sheets, and extruded profiles. Preliminary Finite Element Method (FEM) analyses—linear static and buckling—were performed to screen concepts under scaled homologation loads. Results indicated similar global behavior across layouts, with main tubes and mounting bushings as critical components. Buckling was not a governing failure mode. A comprehensive nonlinear FEM model incorporating elastoplastic material behavior, weld seams, and realistic boundary conditions was developed for the most promising layout. Simulations under full homologation loads revealed that the initial design failed, primarily due to stress concentrations and plasticization at tube-to-bushing welds. Iterative reinforcements were introduced: thicker bushings, gussets, and finally a redesigned bushing with an integrated socket relocating welds to less critical regions. These modifications significantly improved structural integrity, reducing displacement and plastic strain, albeit with a 20.9% mass increase. A cost analysis confirmed that the fabricated titanium solution is over 50% cheaper than an additively manufactured counterpart, despite a slight weight increase, while meeting safety standards. The final design satisfies structural requirements and remains within acceptable weight and cost limits, validating the feasibility of a welded titanium roll hoop for high-performance racing. Future work includes experimental validation through material and weld testing, optimization of reinforcement geometry, and full-scale homologation tests. These steps will ensure compliance, reliability, and readiness for integration into the race car platform.