Research Project

Safer Bus Design

Dinesh Mohan, Sudipto Mukherjee and Anoop Chawla

Project Details

Background
The head,thorax, pelvis, upper arms and the legs sustained severe injuries. Even at speeds below 25   m/h, when impacted directly, the leg suffers serious injuries. The head and chest injuries become  evere at higher velocities. The bumper height, bumper protrusion from the front pane and the  nclination of the front panel with the vertical are geometric factors influencing the injury severity. The force distribution characteristic of the panels is an influencing factor. The bumper has to avoid direct impact on both the pelvis and the knee and optimally designed bumper offset controls injury to the head and thorax, especially for side impacts.
In case of the frontal impact, tuning of the force deflection (F-δ) characteristics is critical for limiting injuries. Special materials when introduced between the stiffer chassis and the front frame, allow fixation of the front surface of the bus to the chassis to be transitioned to a larger local  surface area. This modifies the local F-δ characteristics. The number of such intervention sites has to be minimized as it increases the number of components and assembly steps.
It was shown that trends based on reconstruction of real life crashes could be reproduced with properly constructed rigid body models. Throw distance and injury measures like Head Injury Criterion (HIC)
were shown to have non-monotonic variation with vehicle speed. So designs can be optimized only for range of speeds.

Objective:
i) To reduce pedestrian – bus impact injury severity with focus on leg, pelvis, thorax and head through the re-design of a bus front vis-à-vis a base bus front design
ii) To evaluate injury severity in frontal and side impacts of 50th percentile pedestrian dummy at velocities up to 30 km/h.2.

Methodology:

The approach used in this study was to first evaluate the performance of an existing ALL bus (EAB) in pedestrian impacts by computer modelling using the MADYMO™ software, and then perform the same tests on a new ALL bus (NAB) design provided to IITD. The MADYMO™ software utilises force deflection properties of the respective impacting surfaces for calculation of all kinematic and dynamic parameters during an impact.

Summary:

In designing the safer bus front, it may be more efficient to optimise the front panel properties using the available sub-system test methods by computer simulation, then validate the modelling by actual laboratory tests. This should be followed by computer simulation models using the latest pedestrian dummies and the design finalised after conducting actual impact tests with pedestrian dummies.

Conclusion:

The pedestrian-bus impact simulations were performed using MADYMO™ software with a vehicle occupant dummy which is not a bio-fidelic pedestrian dummy. The model requires input of force deflection characteristics of bodies that come in contact during the impact. The bus sub segment characteristics
were measured at quasi-static strain rates. 
Head injury criteria (HIC) and other measures increase with increase in impact velocity for all the impact configurations.
Some simulations were run with the stiffness of the offset and middle positions interchanged.
In designing the safer bus front, it may be more efficient to optimise the front panel properties using the available sub-system test methods by computer simulation, and then validate the modelling by actual laboratory tests. This should be followed by computer simulation models using the latest pedestrian dummies and the design finalised after conducting actual impact tests with pedestrian dummies.

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