The fuel efficiency and emission gas regulation of passenger cars are two important issues in these days. The best way to increase fuel efficiency without sacrificing safety is to employ fibre reinforced composite materials in the body of cars.
Although the role of the bumper is to absorb the collision energy, it usually satisfies the 5-mile collision regulation. If the car collides with the speed larger than 5-miles per hour, the bumper bracket, the engine and other parts of the car absorb the impact energy of the car through collapsing. In this case deceleration of the passenger usually becomes large because the bumper brackets and other parts of the car cannot absorb large impact energy of the car compared to bumper beam.
In this work, a new bumper that had two pads attached at the ends of the bumper was developed. The two pads were designed to hit the front two tires of the car when the bumper brackets collapse during the collision. When the pads of the bumper beam hit the rim of the tire after collapsing the tires, the tapered section at the end of the bumper beam that holds the pad was designed to buckle progressively, such that large energy should be absorbed.
In order to absorb characteristics of energy absorption of the bumper beam and other parts of the car, a small car with the polypropylene bumper beam was tested under collision at 30 miles per hour speed. During the collision test, the deceleration curve with respect to time was recorded and used to calculate the strength of the bumper beam and other parts of the car. On the basis of this calculation, the composite bumper beam was designed using ANSYS, a commercial finite element analysis package.
The four piece moulds for fabrication of the composite bumper beam was designed and used in manufacturing the prototype composite bumper beams. The majority of the composite bumper beam was made of glass fibre fabric epoxy composite material and the elbow section of the bumper was made of carbon fibre epoxy composite material in order to increase the strength of the elbow section.
The energy absorption capacity of the tapered sections at the ends of the bumper beam during buckling was analyzed by the finite element method and the test specimens prepared based on the analysis were tested with the Instron in order to determine the optimal value of the taper angle. The steel bumper beams with the same strength but heavier weight than the composite bumper beam were also manufactured to compare the performances between the composite bumper beam and the steel bumper beam.
Both the composite bumper beams and the steel bumper beams were equipped in small passenger cars and tested on the collision at 30 miles per hour speed. From the collision tests, it was found that the composite bumper beam that has 1/3 weight of the steel bumper beam absorbed more energy and reduced the maximum deceleration.
