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BACKGROUND
Many devices we use every day were designed to absorb and dissipate energy. Automobile braking systems dissipate the kinetic energy of a moving car into heat and noise as they bring the car to a stop. Bullet proof vests are designed to absorb and dissipate the kinetic energy of a very concentrated mass. Figure 1 shows layers of woven reinforcement fibers just before a bullet impacts.
Materials science and mechanical engineers are continually improving the design of bullet proof vests to make them less penetrable, lighter, and more comfortable. This project will let you become the materials science engineer. Your team will design and construct a cement composite to protect a fragile object from the destructive energy in a falling golf ball.
Figure 1. Many layers of woven material prove to be a good way to provide comfort and strength to bullet proof vests.
WHAT ARE WE SUPPOSED TO DO?
WHAT ARE WE SUPPOSED TO DO?
- Your team is to design and fabricate a cement composite onto which a projectile will be dropped from increasingly higher levels until the raw egg your composite is protecting gets smashed. Your design team will: Design a scheme for using the cement matrix and the reinforcement fibers.
- Prepare the reinforcement materials by separating, cutting, weaving, etc., in the mold provided.
- Mix the cement and water.
- Pour the cement into the mold.
- Test the composite after 30 min.
You may use the following materials in your cement COMPOSITE.
- hydraulic cement
- water
- 2 cotton balls
- 1 sheet of notebook paper
- 30 cm of cotton string
Figure 2. : Testing the composites will involve dropping a projectile
onto the composite from increasing heights until the egg is cracked
HOW WILL WE KNOW HOW WELL WE HAVE SUCCEEDED?
HOW WILL WE KNOW HOW WELL WE HAVE SUCCEEDED?
Your composite will be tested by placing it in the composite holder and dropping the projectile onto the compostie from an initial height of 30 cm. The drop height will be increased by approximately 15 cm after each successful drop. The drop is considered successful if the egg placed below the composite does not crack. Once you have placed your composite in the holder, you will not be allowed to adjust its position or touch it in any way. Your Performance Index (PI) will be determined by the number of drops for which your composite successfully protects the egg.
Hints: When your team is designing the arrangement of the reinforcement materials, visualize what will happen when the projectile strikes and where the maximum compression and tension may be in the composite.
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