A support structure for a free motion head form impactor was designed and fabricated so that head impact testing could be performed inside a school bus and motor coach. The first stage in this design process was to analyze the current support structure which is being used for performing head impact testing inside passenger cars. It was observed that the size of current structure imposed limitations in using it inside a school bus and motor coach.
Available space inside the vehicle and the weight of the support structure were the two main constraints in the design process. Dimensions of the school bus and the motor coach were measured. Based on the measurements, preliminary models of the support structure were created using Solidworks. Provisions for fixing the structure onto the school bus and motor coach chassis were also modeled. A number of design iterations were made which enabled the motion of the impactor in three axes without having to necessarily move the support structure. Design iterations resulted in a compact and low weight support structure. The strength of the support structure was evaluated by finite element modeling of the structure. Stress analysis was performed using Solidworks Simulation.
Simulations were performed at different positions of the impactor and high stress concentration regions were identified.
Analytical modeling of the support structure was also performed. Based on the computer simulation results, the stress was analytically computed at specific points in the structure where it was expected to be high. Using the simulation and analytical results, slight design changes were made so that the structure is robust and compact. Once the structure was fabricated, preliminary tests were conducted using the support structure. A 3.5 kg headform was fired using the impactor fixed to the support structure. Strain gauges were attached to the structure at the high stress concentration regions and the strain readings were recorded. Experimental results were compared with the simulation and analytical results.
After the preliminary tests, the structure was moved inside the school bus. The headform was fired at different locations on the school bus windows which were considered to cause head injury during a school bus crash. Using the acceleration data collected from the head form, Head injury criterion (HIC) was computed and the locations which had high HIC values were identified. In order to improve the safety of the passengers, foams were attached to these locations and tests were performed again. It resulted in reduced HIC values and results were communicated to the school bus manufacturers. A similar procedure was adopted in carrying out the tests inside a motor coach.