Chapter 2 Properties of Materials

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Chapter 2Properties of Materials
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Properties of Materials

• Objectives
• Be able to describe the composition of matter.
• Be able to describe the components of an atom.
• Be able to describe how a type of element is
  determined.
• Be able to describe the four categories of
  chemical bonds.

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Properties of Materials

• Objectives
• Be able to describe the 4 states of matter.
• Be able to describe the components of an atom.
• Be able to describe nucleation of grains.
• Be able to describe the seven different crystal
  systems.
• Be able to describe properties of materials that
  are dependent on their crystal structure.

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Properties of Materials

• Objectives
• Be able to describe how materials are affected
  and respond to forces.
• Be able to describe material properties and
  methods of testing.
• Be able to discuss material defects and
  impurities.
• Be able to briefly discuss iron and steel
  manufacturing.
• Be able to briefly discuss nonferrous metal
  manufacturing.

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Properties of Materials

• Structure of Matter
• If the atomic structure, bonding structure,
  crystal structure, and their imperfections in the
  material are known, then the properties of the
  material can be determined.

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Properties of Materials

• Structure of Matter
• Matter is composed of atoms.
• Atoms are the smallest units of individual
  elements.
• Atoms are composed of protons, neutrons, and
  electrons.

Electron (- charge)
Proton ( charge) Number of Protons determine
type of element
Neutron (No charge)
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Properties of Materials

• Structure of Matter
• Atoms of the same element always have the same
  number of protons, but the number of neutrons in
  the nucleus may vary.
• Atoms can combine to form molecules.
• Molecules are the smallest identifiable unit of
  chemical compounds.

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Properties of Materials

• Chemical Compound molecule atoms are held
  together by chemical bonds.
• Four types of bonds
• Ionic
• Covalent
• Metallic, and
• Van der Waal

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Properties of Materials
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• Ionic Bonds
• Created between charged particles
• Metallic elements have more electrons than their
  most stable configuration.
• Other, nonmetallic elements become more sable
  with the addition of electrons to their atoms.
• In this case, atoms having more electrons will
  donate electrons to atoms needing electrons to
  create a stable configuration. When this occurs
  the atom with excessive electrons is called a
  donating atom.
• Donating atoms have more protons than electrons
  and possess a positive charge. Positive charged
  ion.
• Where as, those atoms accepting electrons acquire
  a negative charge. Negative charged ion.Sodium
  Chloride
• Resulting in charged particles attracted to each
  other by ionic bonds.
• Such bonds exist in Sodium Chloride, potassium
  chloride.

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Properties of Materials

• Covalent Bonds
• Bonds between elements that have too many
  electrons to be given off or too many to be added
  for ionic bonds to form.
• Electrons are shared to form more stable
  compounds.
• Shared electrons form covalent bonds.
• All organic and most bonded plastics involve the
  covalent bonds.

Shared electrons
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Properties of Materials
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• Metallic Bonds
• Always formed between metals
• All metals have an excess of electrons over their
  most stable configuration.
• Metallic theory Elemental metal atoms form
  electron Clouds, to which the nuclei are
  attracted, thus the metallic bond.

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Properties of Materials

• Van der Waal Bonds
• Asymmetrical atoms or molecules with a net polar
  moment in the charge.
• Know as London Forces or Polar Bonds.
• Do not exist by themselves.
• Compounds like helium, two protons, two neutrons,
  and two electrons which is a very stable gas
  atom. But, at approximately -425 oF helium is
  slowed and becomes asymmetrical forming a polar
  bond. At this temperature helium forms a solid
  due to the Van der Waal bond.

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Properties of Materials

• Material Properties often depend on the type of
  bonds in the material.
• Melting Point
• Boiling Point
• Optical Transparency
• Electrical Conductivity
• Thermal Conductivity
• Crystal Structure

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Properties of Materials

• All matter exists in one of four (4) states
• Gas,
• Liquid,
• Solid, and
• Plasma.
• In manufacturing it is important to know how
  materials transition from liquids to solids
  because these transitions are used in material
  removal, forging, and heat treatments.

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Properties of Materials

• Gaseous State
• A state of matter where the individual atoms or
  molecules have little or no attraction to each
  other.
• Atoms or molecules are in constant motion.
• This movement is the result of the energy in the
  material and a function of the heat stored within
  the atoms.
• These particles are continuously bouncing from
  one particle to another or the gas container
  walls.
• These collisions result in heat generation
  because of the energy in the material and is a
  function of the heat stored in the atoms.
• Compressing gases results in shoving particles
  closer together, more collisions, and higher
  temperatures and conversely.
• May be comprised of individual atoms or
  molecules.
• Many gases are diatomic molecules where two atoms
  bond to form an individual gas molecule, i.e.
  oxygen (O2), hydrogen (H2), nitrogen (N2).
• Very few items are manufactured from gases.
• Gases are used in process operations such as
  welding.

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Properties of Materials

• Boiling Point
• Gaseous State
• Temperature where the gas has been cooled to the
  point that molecules or atoms begin to bond to
  each other.
• When a gas has been cooled to its boiling point,
  then the heat of vaporization must be removed to
  transform the as to a liquid.
• Conversely, a liquid requires an addition of the
  same energy (heat of vaporization) to transform
  the liquid to a gas.

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Properties of Materials

• Liquid State
• Liquids lack a definite long-range crystalline
  structure.
• Particles are arranged randomly.
• Produces bonds of various lengths.
• Longer the bond the weaker and more susceptible
  to heat fracture reducing viscosity of the
  material.
• The more heat applied, shorter bonds will break.
• Rigid materials are not necessarily solids. Could
  be a very viscous liquid.
• Solids must possess a definite structure for
  Material scientists.

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Properties of Materials

• Solid State
• The material state which has a definite,
  long-range crystalline structure.
• Melting point of a solid is when a temperature is
  reached where the bonds between particles can no
  longer hold the particles together.
• If enough energy is provided to break one bond,
  then there is enough energy to break all the
  bonds, and a melting point has been established.
• All True solids have a definite melting point.
  This is a test of a solid.
• Glass is not a solid. It is a superviscous liquid
  at room temperature.

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Properties of Materials

• Nucleation of Grains
• Phenomenon when the temperature of a molten metal
  is lowered to the melting point and small
  crystals or nuclei are formed at many points in
  the molten liquid. The nuclei form individual
  crystals and start growing by adding more and
  more atoms from the liquid to the solid.

Nucleus
Atoms or molecules
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Properties of Materials

• Formation of grains in a solid
• Eventually, crystals or nuclei grow together
  forming grains in a solid.
• If the solid is maintained at temperatures just
  below the melting temperature, then the large
  grains will absorb the smaller grains in the
  solid.

Solid nuclei
Melted Material
Melt
Nuclei formed
Nuclei growth
Solidification (Nuclei grow together)
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Properties of Materials

• Crystal Structure
• Only seven different patterns or crystal systems
• Cubic
• Tetragonal
• Orthorhombic
• Rhombohedral
• Hexagonal
• Monoclinic
• Triclinic
• Fourteen modifications of these seven crystal
  structures can occur.

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Properties of Materials

• Additional Crystal Formations
• In addition to the fourteen previously identified
  crystal modifications, there exists material
  structures that overlap each other, i.e. diamonds
  have Cubic close pack (complex cubic) and
  graphite has Hexagonal close pack structures.
• Some crystals grow large enough to be see by the
  naked eye. But, most require the use of a
  microscope to identify the crystal structure.
• Regardless of the size the crystals will all have
  the same shape.
• Regardless of the size of the crystal, when
  broken, they will always break into smaller
  replicas of the large crystal.

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Properties of Materials

• Properties of materials are dependent on their
  crystal structure.
• Examples of numerous material properties
• Density,
• Ductility,
• Malleability,
• Ultimate tensile strength,
• Yield strength in tension,
• Elongation,
• Modulus of elasticity,
• Compression strength,
• Shear\strength,
• Impact strength, and
• Fatigue strength.

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Properties of Materials

• Strength Properties
• Materials vary greatly in the magnitude of forces
  they can withstand.
• Calculations for the forces and strengths of
  materials are published in American Institute of
  Steel Construction (AISC) Manual for Steel
  Construction, Structural Steel Detailing, and
  Design of Welded Structures.
• Forces applied to materials
• Stress defined as the load per unit cross
  section of area.
• Strain defined as the elongation of a specimen
  per unit of original length.

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Strength Properties

• Stress

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Strength Properties

• Strain

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Stress-Strain Diagram

• Elastic Region
• Proportional Limit
• Tensile Strength
• Rupture Strength
• Plastic Region
• Draw on Board

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Safety Factor

• Divide the yield strength by the design load of
  the object to determine the safety factor.

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Load Types

• Compression
• Shear
• Torsion
• Flexure

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Density

• density mass / volume
• More dense means more atoms per cubic inch.

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Specific Gravity

• SG Density of a Material / Density of Water
  (62.4 lbs/cubic foot or 1 gram/milliliter)

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Properties of Materials

• Surface Properties
• Hardness
• Plays an important part in manufacturing.
• Makes cutting tools dull very quickly.
• Tests
• Rockwell
• Brinnell
• Vickers
• Other Tests
• Tukon
• Shore Scleroscope
• Mohrs

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Time-Dependent Properties

• Impact
• Creep
• Fatigue

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Properties of Materials

• Testing of Materials
• Destructive Testing Parts damaged by testing
  methods.
• Nondestructive Testing- Parts not damaged by
  testing methods.

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Properties of Materials

• Defects and Impurities
• Defects are properties of material that alters
  or upsets the orderly arrangement of particles in
  the crystal.
• Point Defects
• Vacancies
• Holes
• Interstitials
• Substitutes
• Line Defects
• Plane Defects
• Inclusions

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Properties of Materials

• Iron and Steel
• Used in so many applications of manufacturing.
• Steel is produced from Iron ore.
• Reduction of the ore to produce iron and
• The conversion of the iron into steel.
• Steel is produced from iron because of the high
  carbon content of iron.
• Steel is generate for high-strength steel
  applications.
• Converters used in converting iron into steel.
• 1) Open Hearth Converter.
• 2) Bessemer Converter
• 3) Electric-arc Converter
• 4) Oxygen lance Converter
• Burns off Carbon in pig iron

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STEELS

• AISI/SAE designation system.
• First two numbers designate alloys
• Second two numbers designate of Carbon.
• See Table 2-3

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Properties of Materials

• Nonferrous Materials
• Aluminum- most abundant metal on the earth.
• Used mostly as an alloy.
• Huge electricity power requirement for
  production.
• Bayer Process
• Magnesium- noted for its light weight.
• Like aluminum requires huge electrical power
  consumption for production.
• Must be located near salt water.
• Copper- best commercially available electrical
  conductor.
• Bronze Brass
• Titanium- maintains its strength at high
  temperatures.
• More expensive and
• Difficult to machine