Dinesh Mohan, Sudipto Mukherjee and Anoop Chawla
Objectives
To prepare a geometric model of the BAL three-wheeler (as specified by the sponsor) for use in the latest version of the MADYMO (TNO) software for crash worthiness analysis.
To identify the most hazardous contact surfaces of the vehicle by performing computer simulations of crashes of the existing three-wheeler using an approximated 50 percentile dummy representing the Indian male for the following configurations:
Pedestrian impacts with front centre and front side at impact velocities of 10, 20 and 30 km/h.
Three-wheeler impact with rigid flat surface at velocities 10, 20, 30 km/h.
To modify the hazardous contact surfaces to minimise the injuries sustained by the pedestrian and the vehicle occupant in consultation with the sponsor.
To prepare a work plan for determining an alternate vehicle design of the three-wheeler (including finite element models) for further enhancement of safety.
Methods
The Software: The MADYMO 3-D Crash Victim Simulation software3 will be used to evaluate the crash properties of the TST and the modified TST structure in accidents with pedestrians and a rigid surface. Two setups will be used in this study. The first one represents a pedestrian dummy impacted by a TST front, as shown. The second one represents a TST with one driver and one passenger in a frontal impact with a rigid flat surface. In the TST-pedestrian simulations the model can be divided into two separate systems: one for the pedestrian dummy and one for the TST. In the TST-flat surface simulations, the model can be divided into three separate systems: one for the TST, driver dummy and passenger dummy, respectively.
The TST model will be made based on the dimensions of the vehicle and inertial properties supplied by BAL. All surfaces will be modelled as planes and ellipsoids simulating the real shapes of the TST. The model for the pedestrian, driver and passenger will be based on dimensions for a 50 percentile male approximated for Indian conditions.
Simulations - Phase I: The model developed as above will be exercised for impacts with a pedestrian and a rigid flat surface respectively at 10, 20 and 30 km/h. Assumed values will be used at this stage based on our experience and data available from literature. The MADYMO model gives the kinematics of the human beings during impact. Based on these kinematics the contact surfaces of the TST with the driver, passenger and the pedestrian will be determined. The MADYMO model also calculates the impact forces, displacements and decelerations of the various body parts undergoing impact. The body parts suffering unacceptable injury according to known biomechanical tolerance values will be selected for further analysis. The parameters generally used for this purpose are: head acceleration, chest acceleration, abdomen, pelvis and extremity impact forces. The tolerance limits used for analysis are: head acceleration of 150 g or maximum HIC of 1,000, a chest acceleration at the centre of gravity of 60 g or deflections of 500 mm, pelvis impact force of 10 kN, etc. The soft tissue structures are usually represented by a set of spring elements: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) and lateral collateral ligament (LCL) by one spring each, the medial collateral ligament (MCL) by two springs. For the relative elongation of knee ligaments a tolerance limit of 15% is used. However, the latest criteria available in scientific literature will be taken into account at the time the work is done.
The TST surfaces these body parts impact will be selected for alteration. These results will be discussed with the sponsors to determine the ones which are amenable for alteration in the first phase. BAL will be requested to provide IITD with the force-displacement characteristics of these selected surfaces/structures.
Simulations - Phase II: The model developed in Phase I will be changed to incorporate the actual physical properties of the TST as supplied by BAL. The simulations will be run again to determine the injury indices of the pedestrian, driver and passenger with the realistic properties of the TST. The worst injury causing surfaces will be short listed for analysis and alteration. Simulations will be run again as before to do sensitivity analyses. These will involve changing shapes and properties of surfaces for impacts at 10, 20 and 30 km/h impact velocities. Optimisation programmes will be run to minimise injuries and the best combination of impact surface properties will be selected for further analysis.
Simulations - Phase III: A discussion will be held with BAL at this stage to determine surfaces and structures that are amenable for alterations based on economic and manufacturing limitations. Further, it will be decided in these discussions which structures can be modified and which structures can be padded, etc. After finalising these issues the model will be run again to determine the improvements over the original design.
