Dinesh Mohan
Objectives
The objectives of this project are as follows
To do a preliminary analysis of truck pedestrian accidents based on secondary data from Delhi hospitals
To develop mathematical tools and biomechanical data for modeling truck pedestrian impacts using the MADYMO simulation programme
To develop optimized design criterion for safer truck fronts at different impact velocities with pedestrian varying the following parameters
Height of bumper
Width of bumper
Bumper offset
Angle of bus front with vertical
Force deflection properties of truck front above bumper
Methodology
This work involved the following components.
Preparation of dummy model for use in MADYMO software.
Preparation of geometric models of truck types exisying in India.
Determination of quasi-static force-deflection properties of truck panels of existing types in India.
Collection of injury data for bus/truck - pedestrian impacts from Delhi hospitals.
Modeling of truck- pedestrian impacts for existing truck types.
Optimization for truck front properties using MADYMO.
Conclusion
Head, thorax, pelvis, upper arms and lower and upper legs of pedestrians could suffer severe injuries in case of impact with fronts of all models of trucks. Impact with current models of trucks on Indian roads could result in severe injury to the directly hit leg even at 25 km/h. At 35 and 45 km/h, head and chest could sustain fatal injuries besides the lower legs. Bumper at a height of pelvis could result in hip injuries.
Significant reduction in injuries could be achieved by altering geometry of truck front as well as the force - deflection characteristics. Bumper height, bumper offset from the front and angle of truck front with vertical are main geometric features of truck fronts influencing injuries. Bumper width influences injuries to a lesser extent but increasing bumper width leads to a reduction in all injuries simultaneously, unlike other geometrical factors which reduce some injuries at the cost of others. This effect of bumper width result from using ellipsoid - ellipsoid contacts for modeling pedestrian leg and bumper impact in MADYMO. This effect needs to be further analysed using alternate techniques.
Pelvis injuries could be avoided for a fifty percentile Indian male if the bumper is below 75 cms height from the top edge of the bumper. It should be made 70 cms for the safety of shorter people. However, this results in increase in force on the leg. In the this project we did not consider bumper heights below the knee of fifty percentile Indian male. However, this aspect deservers attention if the truck and car bumpers have to made at the same height.
Providing a bumper offset reduces injuries to the head and thorax in case of impacts with side of dummy. Most trucks on Indian roads have small offsets including few recently launched models. Our investigations indicate that these models are not safe for pedestrians. Our simulations indicate that a bumper offset of 20 -25 cms is required for a fifty percentile Indian male. This aspect should be further investigated considering differnet dimensions of pedestrians and impacts involving front of the dummy.
The simulations performed in this project predict injuries to the lower legs. This is supported by the data collected from Delhi hospitals. These injuries do not result from the direct impact of the bumper but from the subsequent impact with the bumper when the pedestrian is thrown away. However, the magnitude of this force cannot be considered accurate as this contact occurs later in simulation and by that time the cumulative error in calculations has become quite large.
The trucks with a bonnet in front have sharp edges at the top of the bonnet. This kind of truck is not recommended because it can cause severe injuries to the head. Model 2A has a flat front but also has a sharp edge at the head level. Further, these trucks have a soft grille (where the thorax hits) while the local stifness at the sharp edge (where the head hits) is quite high. This results in major portion of impact energy being taken by head and also in injuries to neck due to excessive bending.
Force on upper legs is primarily a function of the height of the bumper. However varying bumper height does not reduce the force below safety limits. It is required to make the bumpers less stiff for pedestrians hits by covering it with a soft rubber padding.
Since the dummy used in this project (although has 3D properties) is not validated for impacts with front of dummy, only few preliminary observations could be made. Frontal impacts result in higher value of HIC compared to side impacts. Head hits the grille before the thorax. Both legs suffer high forces unlike side impacts where only the leg directly hit by bumper undergoes high a high force. Upper arm force is not critical in case of frontal impacts.
