Material Science

Topics: Glass, Materials science, Solid Pages: 8 (2271 words) Published: March 22, 2013
Material Science Open Book Test
Question 1
A) Car brakes are typically made using cast iron and weigh about 20 pounds. What other materials can be used to make brakes that would last long and weigh less? Cast iron is heavy material that use to make car brake and so it reduces the fuel efficiency of a car. There are other material can be used to make brakes less weigh and long life which is made from fiber-reinforced ceramic and this material is nearly indestructible. A typical metal brake weighs nearly 20 pounds. Which this ceramic the brake weighs can be less than around five pounds. There is a lot of weight savings to makes the cars accelerate faster, more maneuverable, reduces gas consumption. However, making the brakes which the ceramic is expensive and time consuming to make the brake, taking over long hours. Ceramic brakes also last longer than metal brakes, so there is no need to replace them as often.The secret behind the ceramic brakes is the special polymer. That polymer is also being used for repairs on space shuttle flights and in circuit boards

ABOUT CERAMICS: "Ceramic" applies to almost any inorganic, non-metallic material formed by heat, most commonly simple ceramics like the clays used in pottery, bricks and tiles, as well as cement and glass. However, single-ingredient simple ceramics tend to be very brittle and break easily. To make ceramics tough enough for a brake disc, and light enough to give it the reduced-weight advantage, the material is made as a composite, in which strands of carbon fiber -- which are highly resistant to stretching -- are embedded in the material. The fibers are woven into a disc shape before being doused with a liquid made of carbon and silicon. That liquid is then heated to convert it into a very tough ceramic known as silicon carbide. The finished surface resembles stone.

B) Dislocations are most significant in metals and alloys since they provide a mechanism for plastic deformation. Discuss why would metal behave as brittle materials without diclocation?

First, dislocations are most significant in metals and alloys since they provide a mechanism for plastic deformation, whish is the cumulative effect of slip of numerous dislocations. Plastic dislocations refers to irreversible deformation or change in shape that occurs when the force stress that caused it is removed. This because the applied stress causes dislocation motion that in turn causes permanent deformation. The palstic deformation is to be distinguished from elactic deformation, which is temperory change in shape that occur while a force or stress remain applied to a material.

In elastic deformation, the shape change is a result of strectching of interatomic bonds, however, no dislocation motion occurs. Slip can occur in some ceramics and polymers. First, slip explain why the strength of metal is much loweer than the value pradicted from the metallic bond. If slip occurs, only a tiny fraction of all of the metallic bonds across the interface need to be broken at any one time, and the force required to deform the metal is small. Second, slip provides ductility in metals. If no dislocation were present, an iron bar would be brittle and the metal could not be shaped by metalworking processes, such as forging, into useful shapes. Third, we control the mechanical properties of a metal or alloy by interfering with the movement of dislocations. An obstacle introduced into the crystal prevent a dislocations from slipping unless we apply higher force. Thus, the presence of dislocations helps strengthen metallic materials.

C) A titanium pipe used to transport a corrosive material at 400°C is found to fail after several months. How would you determine the cause for the failure?

Since a period of time at a high temperature was required before failure occured, we might first suspect a creep or stress-corrotion mechanism for failure. Microscopic examination of the material near the fracture surface...
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