Electric Bus Roof Frame Optimization With Different Materials and Thicknesses

On electric bus ceilings; Because high-mass energy storage systems are also positioned on the ceiling compared to traditional internal combustion engine bus roofs, it significantly affects both static and dynamic loads in the ceiling area. The carrying capacity, rigidity and weight optimization of the profiles under the batteries with high mass are critical design parameters. In this study, the ceiling carcass structure of an electric bus was analyzed with a systematic approach using the finite element method under different thickness scenarios and different material configurations. The main purpose of the study is to obtain a design configuration that will provide the balance between structural strength and weight while providing weight optimization in the ceiling carcass and to quantitatively examine the mechanical behavior of profile structures made of different materials under the same boundary and loading conditions. For this purpose, three different thickness scenarios were modeled. In Scenario-1, the main carrier body profiles and profiles carrying high-mass batteries are designed to be 3 mm thick and the other profiles are designed to be 2 mm thick and the maximum von Mises stresses are examined. In Scenario-2, it is the scenario where only the main carrier profiles are left at a thickness of 3 mm, and all remaining profiles are modeled as 2mm. In this scenario, it was observed that there was an increase in stress value, but the S460MC high-strength structural steel used was below the yield stress of 460 MPa; He states that the scenario has a significant potential in terms of weight optimization. In Scenario-3, it is the scenario where all profiles in the ceiling carcass have a wall thickness of 2 mm. In this scenario, it has been observed that stresses reach 200 MPa levels. Although it structurally showed a value below the yield limit, it was interpreted as a design close to the limit due to rigidity losses and potential fatigue risks. In the second stage of the study, the safety coefficient of the structure was examined using high-strength S460MC steel and X2CrN12 materials in the ferritic stainless-steel class on this scenario, taking Scenario-3, which is the lightest configuration, as a reference. Considering the stresses of approximately 205 MPa for S460MC structural steel and the yield strength of the material, it has been observed that it has an average safety of 2.4 for the same limit and loading conditions, while it has been observed that it has an average of 1.4 times the safety for the same limit and loading conditions based on the stress of approximately 230 MPa in X2CrNi12 material. In this case, it can be stated that the X2CrNi12 material, which is in the ferritic stainless-steel class, offers less safety in lightness studies.