The Materials.pdf

Engineer On a Disk

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email: jackh@gvsu.edu

phone: (616) 771-6755

fax: (616) 336-7215

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1. TABLE OF CONTENTS

TABLE OF CONTENTS.......................................................................................................... 2

MATERIAL PROPERTIES ..................................................................................................... 4

TERMINOLOGY - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4

MICROSTRUCTURES - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4

IRONS AND STEELS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8

NONFERROUS METALS AND ALLOYS - - - - - - - - - - - - - - - - - - - - - - - - - - - 15

HEAT TREATING - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 16

PAUL JOHNSON NOTES FOR EGR 250 - - - - - - - - - - - - - - - - - - - - - - - - - - - 16

PRACTICE PROBLEMS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43

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Materials Information

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2. MATERIAL PROPERTIES

• Ideally materials are a microscopic matrix of small balls that form a larger solid. In reality the

atoms that make of solids fall into local pockets of well organized matrices. It is very rare to

find a solid that is made up of a single structure.

• If solids were made of single well organized molecules they would be significantly stronger.

But, small deformations and cracks weaken materials to the values we are more accustomed to.

• Material properties are a function of multiple factors. Primarily chemistry determines what

atoms are available to make up the structure. Also, the atoms are dispersed in a non-homoge-

nous mix.

• Solids typically fail because cracks form, and then quickly propagate through solids. It is the

chemistry and non-homogenous structure that can slow or stop these cracks. The composition

of the solid also determines how stiff it is.

2.1 TERMINOLOGY

• A basic list of terms commonly used are,

Brittleness - the tendency of a material to break before it undergoes plastic deformation

Ductility - the ability of certain materials to be plastically deformed without fracture (pull-

ing).

Elasticity - The ability to deform and return to the undeformed shape. This follows

Hooke’s law.

Hardness - the resistance to deformation and forced penetration

Malleability - the ability of a material to take a new shape when hammered or rolled.

Tensile Strength - the maximum tensile load that can be applied before a material fractures

Toughness - The ability to withstand cracking, as opposed to brittleness

Yield Strength - The load at which the material stops elastically deforming, and starts per-

manently deforming.

2.2 MICROSTRUCTURES

• To consider materials properly we must start with the basic atomic structure and then look at the

more macroscopic aspects, and how they are related to the microscopic components.

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2.2.1 Atomic Structures

• In an atom there are some fundamental ratios,

• Each atom is understood to have a basic structure with a nucleus and orbiting electrons.

• The nucleus is a combination of neutrons and protons.

• The number of protons and neutrons in an atom are equivalent and these determine the

atomic number. If there are additional neutrons in the nucleus this is called an iso-

tope.

• The mass of the atom is determined by the sum of the neutrons and protons (the electron

mass is much smaller).

• In a mole of material there are 6.023*10**23 atoms.

• How these components fit together is described in models,

Bohr model

- electrons have quantized energy levels

- electrons are discrete and orbit the nucleus

- a free electron has a negative energy level

Wave-mechanic model

- electron waves can behave like particles or waves

- an electron is described as an electron cloud

- electrons have energy levels including ground levels

- valence electrons are the outermost and most likely to be removed first

• The valences of electrons are determined with the ’spdf’ numbers.

• The basic atomic elements are listed in the periodic table. This is in sequence of the atomic

masses, as well as proton counts. It can also be used to determine similarities in properties by

proximity in the table.

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