Impact Attenuation System using a Passive Damper

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The goal of this work is to mitigate the degree of damage to passengers caused by automobile collisions. Crash phenomena involving road vehicles were investigated for the purpose of developing an impact attenuation design that can withstand speeds higher than the current specified range of up to 4 km/h (for a bumper). Different impact attenuation systems in the vehicle were studied with emphasis on the bumper modeling, analysis and design. A mathematical model for a bumper was developed. Simulation of impact of the bumper against a fixed barrier was performed. A passive friction element was introduced into the bumper system to improve on the attenuation of the impact and kinetic energy absorption capacity. A mathematical model of the bumper-damper system was formulated and used to simulate impact phenomena for a 1900 kg mass moving at a speed of 70 km/h (19.4 m/s), 17.5 times the speed of a typical design specification. The simulation revealed that the energy absorption capacity of the bumper was improved with the addition of a friction element. Design parameters for the friction damper were extracted from the results of the simulation. The extracted design parameters include stiffness, k, and coefficient of the damping, c, of the bumper. The use of the results from the simulation in the design of the bumper was pursued with success. Friction damper designs were proposed. Two of these designs were built and used in experiments to verify their effectiveness and to validate the simulation results. The experiments revealed that higher energy absorption could be achieved with the addition of a friction element to traditional bumpers. From simulation, it was observed that a combination of material stiffness and damping factors could influence energy absorption ability of the damper. It was observed that the addition of a friction element to an ordinary bumper-damper system with the new design parameters can improve its energy absorption capacity by 103.6 kJ, that is about 146 %. Additionally, it was also observed that the addition of the friction element to a traditional vehicle could increase the critical design speed from 4 km/h (1.11 m/s) to 14.9 km/h (4.1 m/s). It was concluded that a passive friction damper system could be used to attenuate road vehicle impact energy in collisions (of vehicles of mass similar to that of a typical sedan car) at speeds 3 times higher than the speed for which current conventional bumpers are designed to attenuate (i.e. 4 km/h).
A Dissertation submitted to the Department of Mechanical Engineering, Kwame Nkrumah University of Science and Technology In partial fulfillment of the requirements for the degree of Doctor of Philosophy