Computational analysis for improved design of an SAE BAJA frame structure

摘要

Baja SAE is an intercollegiate competition to design, fabricate, and race a small, single passenger, off-road vehicle powered by a 10 HP Briggs u26 Stratton 4-Stroke gasoline engine. All Baja SAE vehicles for the competition are powered by a small engine, thus large part of vehicle performance depends on the acceleration and maneuverability of the vehicle which is proportional to the weight of the chassis and rollcage. As weight is critical to achieve the greater performance of the vehicle, a balance must be found between the strength and weight of the rollcage to ensure the safety of the driver.The objective of the present research was to optimize the design of roll cage in compliance with the guidelines set by SAE and to perform the finite element analysis (FEA) for validating the design. Initially, a preliminary design of the rollcage was produced based on the rules of the competition and a 3-D model was generated using CAD. To study the effects of stress and deformation on the frame members, linear static frontal impact analysis was carried out using FEA techniques for different loading conditions on the rollcage model. The static analysis in this research is focused to obtain the optimum grid size for the rollcage structure. Modifications were done to the existing design to withstand the applied load based on the analysis results for the optimum mesh size. The design was considered to be safe if the generated roll-cage Von Mises stresses were less than the yield strength of the material and the deflections of the members were favorable enough for the safety of the driver. The research also presents different approaches to achieve the optimum design of the roll cage. The new design was subjected to FEA for validation.Dynamic analysis was also performed on the vehicle chassis to review the structural rigidity of the chassis frame. A full vehicle modeling was carried out for the equivalent mass distribution of the vehicle. An initial velocity of 6.7 m/s (15 mph) is ascribed to the full vehicle model to impact a fixed rigid wall to investigate the effects of dynamic stresses, energy, reaction forces and acceleration of the frame members in a worst case loading scenario. Different ways of mitigating the acceleration on the chassis are also discussed in this research for the driver safety.