PHYSICAL
PROPERTIES
OF
MATERIALS
Chapter 3
PHYSICAL
PROPERTIES
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Density
Melting point
Specific heat
Thermal conductivity
Thermal expansion
Electrical properties
Magnetic properties
Resistance to oxidation
Resistance to corrosion
DENSITYMASS PER UNIT
VOLUME
Also called specific gravity
which expresses a material’s
density with respect to water
TABLE 3.1 PHYSICAL PROPERTIES OF SELECTED MATERIALS AT ROOM TEMPERATURE
TABLE 3.2 PHYSICAL PROPERTIES OF MATERIALS, IN
DESCENDING ORDER
• Titanium and
aluminum are
among the most
commonly used
metal for aircraft
and aerospace
applications
FIGURE 3.1 RATIO OF MAXIMUM YIELD STRESS TO DENSITY FOR SELECTED METALS.
FIGURE 3.2 SPECIFIC STRENGTH (TENSILE STRENGTH/DENSITY) AND SPECIFIC STIFFNESS (ELASTIC MODULUS/
DENSITY) FOR VARIOUS MATERIALS AT ROOM TEMPERATURE. (SEE ALSO CHAPTER 9.)
COMPOSITE MATERIALS HAVE
BECOME IMPORTANT FOR
THEIR HIGH SPECIFIC
STRENGTH AND STIFFNESS
Density
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High speed equipment
Textile machines
Printing press
Cameras
High weight desirable– Counterweights
– Flywheels
– Ballasts
– Golf clubs
Elevated temperaturesspecific strength & stiffness
• Turbines
• Automotive
• Jet engines
• Gas turbines
FIGURE 3.3 SPECIFIC STRENGTH (TENSILE STRENGTH/DENSITY) FOR A VARIETY OF MATERIALS AS A
FUNCTION OF TEMPERATURE. NOTE THE USEFUL TEMPERATURE RANGE FOR THESE MATERIALS AND
THE HIGH VALUES FOR COMPOSITE MATERIALS. MMC—METAL-MATRIX COMPOSITE; FRP—FIBERREINFORCED PLASTIC.
MELTING POINTDEPENDS ON
THE
TEMPERATURE
TO SEPARATE ITS
ATOMS
• Plastics have lowest
useful range
• Graphite and
refractory metals
have the highest
useful range
• Annealing
• Heat treating
• Hot-working
• Alloying has a minor effect on
specific heat
• Temperature rise in a work piece is
a function of the work done and of
the specific heat of the work piece
material
SPECIFIC
HEATTHE ENERGY
TO RAISE THE
TEMPERATURE
OF A UNIT
MASS BY 1
DEGREE
THERMAL
CONDUCTIVITY
• The rate at which heat flows
within and through a
material
• Metallically bonded materials
(metals) generally have a
higher conductivity
• Ionically or covalently
bonded materials (ceramics,
plastics) have poor
conductivity
• Cooling fins
• Cutting tools
• Die-cast molds to conduct
heat
THERMAL
EXPANSION
• Generally, the coefficient of
thermal expansion is inversely
proportional to the melting point
of the material
• Shrink fits utilize thermal
expansion and contraction-heat a
part often installed on a shaft,
install the part, let the part cool
and contract
• Thermal stress
• Cracking
• Warping
• Loosening
• Thermal fatigue results from
thermal cycling
• Thermal shock-cracks after just a
single thermal cycle
• Low expansion alloys-iron-nickel
alloys with low thermal-expansion
coefficients
ELECTRICAL
CONDUCTIVITY
ELECTRICAL
CONDUCTIVITY
• ELECTRICAL EQUIPMENT
• MACHINERY
• MANFACTURING
PROCESSSES
• UNITS: MHO/M OR MHO/FT
WHERE MHO IS THE REVERSE
OF OHM, THE UNIT OF
ELECTRICAL RESISTANCE
• ALLOYING OF METALS RAISES
THE CONDUCTIVITY
CONDUCTORS:
MATERIALS
WITH HIGH
ELECTRICAL
CONDUCTIVITY
• INSULATORS OR
DIELECTRICS:
MATERIALS WITH HIGH
ELECTRICAL RESISTIVITY
• ELECTRICAL RESISTIVITY
IS THE INVERSE OF
ELECTRICAL
CONDUCTIVITY
SUPERCONDUCTORS
• SUPERCONDUCTIVITY IS THE
PHENOMENON OF NEARZERO ELECTRICAL
RESISTIVITY THAT OCCURS IN
SOME MATERIALS OR
ALLOYS BELOW A CRITICAL
TEMPERATURE (OFTEN
ABSOLUTE ZERO)
• HIGH-POWER MAGNETS
• MRI-MAGNETIC RESONANCE
IMAGING
CORROSION
RESISTANCE
• CORROSION REFERS TO THE
DETERIORATION OF METALS
AND CERAMICS
• DEGRADATION REFERS TO
THE DETERIORATION OF
PLASTICS
• FOOD
• CHEMICAL
• PETROLIUM INDUSTRY
• MANUFACTURING
OPERATIONS
PITTING:
LOCALIZED
CORROSION
OF A
MATERIAL
SALT…CORROSION?
• CORROSION RESISTANT
MATERIALS:
• NONFERROUS METALS
• STAINLESS STEEL
• NONMETALLIC
MATERIALS
• STEEL & CAST IRON MUST
BE PROTECTED BY
COATINGS AND SURFACE
TREATMENTS
GALVANIC
CELL
• TWO ELECTRODES IN AN
ELECTROLYTE IN A CORROSIVE
ENVIRONMENT THAT
INCLUDES MOISTURE CAUSE
GALVANIC CORROSION
• STRESS-CORROSION
CRACKING
• OXIDATION-REMOVAL OF
MATERIAL BY CHEMICAL
REACTION