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Difference between Hardness and Toughness
Hardness
i. It is the property of the material to resist
scratching, abrasion, indentation orpenetration.
ii. Hardness of a material is stated relative to
the hardness of other material.
iii. Important in shafts, bearing whichever is
having relative motion.
Toughness
i. Ability of a material to withstand both elastic
and plastic deformation, shock and vibration.
ii. Toughness is measured in terms of the
energy a material can absorb before a actual
failure takes place.
iii. Important in structural members, machine
parts which are subjected to shock and
vibration. E.g. shafts, spring.
Difference:
The hardness of a metal limits the ease with which it can be
machined, since toughness
decreases as hardness increases Toughness is a combination of
high strength and medium
ductility. It is the ability of a material or metal to resist
fracture, plus the ability to resist failure
after the damage has begun. A tough metal, such as cold chisel,
is one that can withstand
considerable stress, slowly or suddenly applied, and which will
deform before failure.
Toughness is the ability of a material to resist the start of
permanent distortion plus the ability
to resist shock or absorb energy [31].
Brittleness
materialis brittle if, when subjected tostress, it breaks
without significant deformation (strain).
hebrittle strengthof a material can be increased bypressure.
Tensile strength
Tensile strength measures the force required to pull something
such as rope, wire, or a
structural beam to the point where it breaks.
Yield strength - The stress a material can withstand without
permanent deformation.
* Ultimate strength - The maximum stress a material can
withstand.
* Breaking strength - The stress coordinate on the stress-strain
curve at the point of rupture.
http://www.engineerszone.net/2010/11/difference-between-hardness-and.htmlhttp://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Brittle_strengthhttp://en.wikipedia.org/wiki/Brittle_strengthhttp://en.wikipedia.org/wiki/Brittle_strengthhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Brittle_strengthhttp://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Materialhttp://www.engineerszone.net/2010/11/difference-between-hardness-and.html
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Other mechanical properties of steel
Other mechanical properties of structural steel that are
important to the designer include:
Modulus of elasticity, E = 210,000 N/mm
Shear modulus, G = E/[2(1 + )] N/mm, often taken as 81,000
N/mm
Poisson's ratio, = 0.3
Coefficient of thermal expansion, = 12 x 10-6/C (in the ambient
temperature range).
Ductility
Ductility is a measure of the degree to which a material can
strain or elongate between the onset of yield
and eventual fracture under tensile loading as demonstrated in
the figure below. The designer relies on
ductility for a number of aspects of design, including
redistribution of stress at the ultimate limit state, bolt
group design, reduced risk offatiguecrack propagation and in
thefabrication processesofwelding, bending
and straightening. The various standards for the grades of steel
in the above table insist on a minimum
value for ductility so the design assumptions are valid and if
these are specified correctly the designer can
be assured of their adequate performance.
The long out of print Kellogg Design of Piping Systems calls for
this equation and it's the basis
for most span tables that you'll find in B31.3 engineering.
Sag = 17.1 * (w * (L^4) / (E*I) (inches)
w = weight per foot of pipe+liquid+insulation (lbs/ft)
L = pipe span (ft)
E = modulus of elasticty (psi)
I = moment of inertia (in^4)
Most span tables are based on a maximum deflection of 5/8",
which is intended to keep the
natural frequency of the span above 4Hz and therefore less
likely to resonate in the wind.
Oh and, temperature is a factor as it will affect your elastic
modulus, especially at high
temperatures.
http://www.steelconstruction.info/Fatigue_design_of_bridgeshttp://www.steelconstruction.info/Fatigue_design_of_bridgeshttp://www.steelconstruction.info/Fatigue_design_of_bridgeshttp://www.steelconstruction.info/Fabrication#Fabrication_processeshttp://www.steelconstruction.info/Fabrication#Fabrication_processeshttp://www.steelconstruction.info/Fabrication#Fabrication_processeshttp://www.steelconstruction.info/Weldinghttp://www.steelconstruction.info/Weldinghttp://www.steelconstruction.info/Weldinghttp://www.steelconstruction.info/Weldinghttp://www.steelconstruction.info/Fabrication#Fabrication_processeshttp://www.steelconstruction.info/Fatigue_design_of_bridges
