Impact Attenuation System Using a Passive Damper
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Date
2015-05-22
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Abstract
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
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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).
Description
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