Michalec, Christopher Ryan (2005-08). Development of an optimal impact energy absorber for highway crash cushions. Master's Thesis.
The objective of this research is to develop a new and efficient method of
absorbing a vehicle??s kinetic energy for highway safety crash cushions. A
vehicle that makes a direct impact with a rigid highway structure traveling at
highway speeds can be fatal for its occupants. Crash cushions are implemented
on roadways in front of these rigid structures with the intent to ??soften?? the
impact. The cushion will bring a vehicle to a stop at safe rates before it impacts
the rigid structure. The energy absorbing component of the crash cushion must
meet four main requirements. The cushion must reduce the vehicles speed at a
rate that does not allow the occupant to impact the vehicle interior at velocities
greater than 12 m/s. The cushion must then bring the vehicle to a complete stop
with deceleration rates below 20 g??s. A crash cushion must satisfy these
requirements for an 820 kg vehicle and a 2000 kg vehicle traveling at 100 km/hr.
Advanced design methodologies were applied to enable multiple,
innovative design concepts. These concepts made use of the deformation of
steel in structural pipe, structural angle, and structural plate to reduce the
velocity of a vehicle at a safe rate. Critical design parameters were identified
which allowed for efficient and effective numerical experiments to be conducted.
The data collected from these experiments were then validated when compared
to physical test data. After the data had been collected, each of the designs was
compared to one another in order to decide upon the best design. The design
selected was the deforming plate concept which makes use of steel plate
mounted in a fashion that created two arms that acted similar to two cantilever
beams. A wedge was forced beneath these arms deforming them upward. This design is effective because the deformation can be easily controlled by the
thickness of the plate, the moment arm created by the wedge, and the geometry
of the wedge. Steel plate is a readily available material that requires minimal
manufacturing for installation preparation making it cost-effective, and easy to
install. In the event of impact with the cushion, new parts will be inexpensive
and readily available. Being reusable, easy to repair and low in cost, the energy
absorbing concept presented herein is a cost effective alternative to existing
energy absorbing technology. Due to replaceable parts being readily available,
repair time and cost will be reduced compared to other designs that require new
parts to be fabricated for replacement. This will make for a competitive design.