Most of the Federal Motor Vehicle Safety Standards applicable to school buses do not specifically cover the cutaway type of buses assembled on ladder-type chassis, for which a production process is split into two stages. In the first stage, the chassis and cab section are assembled by automobile manufacturers. In the second stage, the vehicle is shipped to another company where the bus body and additional equipment are installed. Lack of strict structural standards for transit bus body builders necessitates the crashworthiness and safety evaluation of this category of vehicles. Such an assessment process is imperative since these transit buses are often used to transport disabled passengers.
A full scale crash test is considered the most reliable source of information regarding structural integrity and safety of motor vehicles. However, the high cost of such tests and difficulties in collecting data results in an increasing interest in the analytical and computational methods of evaluation. Theses methods allow for extensive safety studies once the finite element model is validated. A reliable analytical investigation can reduce the cost dramatically and allow faster introduction of the new solutions.
This thesis research work presents the procedure for development of a finite element (FE) model of a public transit bus and the results of its crashworthiness and structural integrity analysis. The finite element model was developed based on the geometry obtained by disassembling and digitizing all major parts of the actual bus. The FE model consists of 73,600 finite elements, has 174 defined property sets (groups of elements with the same features) and 23 material models. All parts are connected using different multi point constraints and special links with failure to model actual types of structural connections such as bolts and spot welds. LS-DYNA non-linear, explicit, 3-D, dynamic FE computer code was used to simulate behavior of the transit bus under different impact scenarios, such as frontal impact and side impact at various velocities.
