mate 11

MLLDelaCruz, UP DMMME!

Intro to the World of Materials

MatE 11 | Lecture 02 AY 2014 - 2015

Structure and composition of materials (metals. polymers, ceramics and composite materials); properties and behavior in service conditions


What are Materials? substances out of which a thing

is or can be made


Materials Science & Engineering: What is It?

field devoted to understanding and controlling the performance of useful Materials

through the study of interrelationships between materials

synthesis, structure and properties


This is what Materials Engineering is all about

MLLDelaCruz, UP DMMME!Figure 1-1 Application of the tetrahedron of materials science and engineering to sheet steels for automotivechassis. Note that the composition, microstructure, and synthesis-processing are all interconnected and affectthe performance-to-cost ratio. (Car image courtesy of Ford Motor Company. Steel manufacturing image and car chassisimage courtesy of Digital Vision/Getty Images. Micrograph courtesy of Dr. A.J. Deardo, Dr. M. Hua, and Dr. J. Garcia.)

1-1 What is Materials Science and Engineering? 5

Thus, in this case, materials scientists are concerned with the sheet steels composition; strength; weight; energy absorption properties; and malleability (formability).

Materials scientists would examine steel at a microscopic level to determine if itsproperties can be altered to meet all of these requirements. They also would have to

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Figure 1-2 Application of the tetrahedron of materials science and engineering tosemiconducting polymers for microelectronics.

6 CHAPTER 1 Introduction to Materials Science and Engineering

consider the cost of processing this steel along with other considerations. How can weshape such steel into a car chassis in a cost-effective way? Will the shaping process itselfaffect the mechanical properties of the steel? What kind of coatings can be developed tomake the steel corrosion resistant? In some applications, we need to know if these steelscould be welded easily. From this discussion, you can see that many issues need to be con-sidered during the design and materials selection for any product.

Lets look at one more example of a class of materials known as semiconductingpolymers (Figure 1-2). Many semiconducting polymers have been processed into light emit-ting diodes (LEDs). You have seen LEDs in alarm clocks, watches, and other displays.These displays often use inorganic compounds based on gallium arsenide (GaAs) and othermaterials. The advantage of using plastics for microelectronics is that they are lightweightand flexible. The questions materials scientists and engineers must answer with applica-tions of semiconducting polymers are

What are the relationships between the structure of polymers and their electricalproperties?

How can devices be made using these plastics? Will these devices be compatible with existing silicon chip technology?

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This is what Mat E 11 is all about

PROPERTY = f (STRUCTURES)

= f (electronic structure)


Traditional Materials

Metal Ceramics Polymers


What are Metals?

q Any of a category of electropositive elements

q possess a shiny surface

q good conductors of heat and electricity


Looks familiar?

More than 80% of known elements are metallic!


What are Ceramic Materials?

Any of various hard, brittle, heat-resistant and corrosion-resistant materials

made by shaping and then firing an inorganic, nonmetallic mineral

Keramikos = BURNT STUFF


Types of Ceramics

Elemental Ceramics

Compound Ceramics

SiO2

SiC

Al2O3


What are Polymers?

many units

natural and synthetic compounds of high molecular weight

consisting of up to millions of repeated linked simple organic units PROPERTIES?


Explaining the POLYMER Concept

Ethylene

Polyethylene


Polyethylene

LDPE HDPE UHMWPE


TYPES OF POLYMERS

THERMOSETS

THERMOPLASTICS

ELASTOMERS


What are Composite Materials?

A combination of two or more materials

differing in form or composition


Classification of Materials

Ceramics and

glasses Polymers

Metals

Composites

Steel reinforced concrete

Cermets: (ceramic particles bonded together by metals)

CFRP/ GFRP

Steel-cord tires


Why mix two materials?


Structural Classification of Materials


Service Conditions

National aerospace plane

Figure 1-8Skin operating temperatures foraircraft have increased with thedevelopment of improved materials.(After M. Steinberg, ScientificAmerican, October 1986.)


September 11, 2001. Although the towers sustained the initial impact of the collisions,their steel structures were weakened by elevated temperatures caused by fire, ultimatelyleading to the collapse.

High temperatures change the structure of ceramics and cause polymers to meltor char. Very low temperatures, at the other extreme, may cause a metal or polymer to failin a brittle manner, even though the applied loads are low. This low-temperature embrit-tlement was a factor that caused the Titanic to fracture and sink. Similarly, the 1986Challenger accident, in part, was due to embrittlement of rubber O-rings. The reasonswhy some polymers and metallic materials become brittle are different. We will discussthese concepts in later chapters.

The design of materials with improved resistance to temperature extremes isessential in many technologies, as illustrated by the increase in operating temperatures ofaircraft and aerospace vehicles (Figure 1-8). As higher speeds are attained, more heatingof the vehicle skin occurs because of friction with the air. Also, engines operate more effi-ciently at higher temperatures. In order to achieve higher speed and better fuel economy,

Figure 1-7Increasing temperature normallyreduces the strength of a material.Polymers are suitable only at lowtemperatures. Some composites,such as carbon-carbon composites,special alloys, and ceramics, haveexcellent properties at hightemperatures.

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National aerospace plane

Figure 1-8Skin operating temperatures foraircraft have increased with thedevelopment of improved materials.(After M. Steinberg, ScientificAmerican, October 1986.)


September 11, 2001. Although the towers sustained the initial impact of the collisions,their steel structures were weakened by elevated temperatures caused by fire, ultimatelyleading to the collapse.

High temperatures change the structure of ceramics and cause polymers to meltor char. Very low temperatures, at the other extreme, may cause a metal or polymer to failin a brittle manner, even though the applied loads are low. This low-temperature embrit-tlement was a factor that caused the Titanic to fracture and sink. Similarly, the 1986Challenger accident, in part, was due to embrittlement of rubber O-rings. The reasonswhy some polymers and metallic materials become brittle are different. We will discussthese concepts in later chapters.

The design of materials with improved resistance to temperature extremes isessential in many technologies, as illustrated by the increase in operating temperatures ofaircraft and aerospace vehicles (Figure 1-8). As higher speeds are attained, more heatingof the vehicle skin occurs because of friction with the air. Also, engines operate more effi-ciently at higher temperatures. In order to achieve higher speed and better fuel economy,

Figure 1-7Increasing temperature normallyreduces the strength of a material.Polymers are suitable only at lowtemperatures. Some composites,such as carbon-carbon composites,special alloys, and ceramics, haveexcellent properties at hightemperatures.

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1-5 Environmental and Other Effects 15

new materials have gradually increased allowable skin and engine temperatures. NASAsX-43A unmanned aircraft is an example of an advanced hypersonic vehicle (Figure 1-9).It sustained a speed of approximately Mach 10 (7500 miles/h or 12,000 km/h) in 2004.Materials used include refractory tiles in a thermal protection system designed by Boeingand carbon-carbon composites.

Corrosion Most metals and polymers react with oxygen or other gases, partic-ularly at elevated temperatures. Metals and ceramics may disintegrate and polymers andnon-oxide ceramics may oxidize. Materials also are attacked by corrosive liquids, leadingto premature failure. The engineer faces the challenge of selecting materials or coatingsthat prevent these reactions and permit operation in extreme environments. In space appli-cations, we may have to consider the effect of radiation.

Fatigue In many applications, components must be designed such that the loadon the material may not be enough to cause permanent deformation. When we load andunload the material thousands of times, even at low loads, small cracks may begin todevelop, and materials fail as these cracks grow. This is known as fatigue failure. In design-ing load-bearing components, the possibility of fatigue must be accounted for.

Strain Rate Many of you are aware of the fact that Silly Putty, a silicone-(notsilicon-) based plastic, can be stretched significantly if we pull it slowly (small rate of strain).If you pull it fast (higher rate of strain), it snaps. A similar behavior can occur with manymetallic materials. Thus, in many applications, the level and rate of strain have to be considered.

Figure 1-9 NASAs X-43A unmanned aircraft is an example of an advanced hypersonic vehicle. (Courtesy ofNASA Dryden Flight Research Center (NASA-DFRC).)

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effects of temperature, fatigue, stress, and corrosion may be interrelated, and other

outside effects could affect the materials performance.


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