Introduction : Mechanical Metallurgy - PPT, Engineering, Semester Notes

: Introduction : Mechanical Metallurgy - PPT, Engineering, Semester Notes

``` Page 1

• The various engineering and true stress-strain properties
obtainable from a tension test are summarized by the
categorized listing of Table 1.1.
• Note that the engineering fracture strain e
f
and the %
elongation are only different ways of stating the same
quantity.  Also, the %RA and e
f
can be calculated from each
other.
• Note that the strength coefficient H determines the
magnitude of the true stress in the large strain region of the
stress-strain curve, and so it is included as a measure of
strength.
• The strain hardening exponent n is a measure of the rate of
strain hardening.
Page 2

• The various engineering and true stress-strain properties
obtainable from a tension test are summarized by the
categorized listing of Table 1.1.
• Note that the engineering fracture strain e
f
and the %
elongation are only different ways of stating the same
quantity.  Also, the %RA and e
f
can be calculated from each
other.
• Note that the strength coefficient H determines the
magnitude of the true stress in the large strain region of the
stress-strain curve, and so it is included as a measure of
strength.
• The strain hardening exponent n is a measure of the rate of
strain hardening.
Table 1.1  Materials Properties Obtainable from Tension Tests
Category Engineering Property True Stress-Strain
Property
Elastic
Constants
Elastic modulus, E
Poisson's ratio, ?
Strength
Proportional limit, s
p
Yield strength, s
y
Ultimate tensile strength, s
µ
Engineering fracture strength, s
ƒ
True fracture strength, s
f
Strength coefficient, H or K
Ductility
Percent elongation, 100 ?
ƒ
Reduction in area, %RA
True fracture strain, ??
ƒ
Energy Capacity
Resilience, ?u
r
Tensile toughness, u
t
True toughness, ?u
ƒ
Strain hardening Strain hardening
Ratio,  s
µ
/ s
?
Strain hardening
exponent, ?n
Page 3

• The various engineering and true stress-strain properties
obtainable from a tension test are summarized by the
categorized listing of Table 1.1.
• Note that the engineering fracture strain e
f
and the %
elongation are only different ways of stating the same
quantity.  Also, the %RA and e
f
can be calculated from each
other.
• Note that the strength coefficient H determines the
magnitude of the true stress in the large strain region of the
stress-strain curve, and so it is included as a measure of
strength.
• The strain hardening exponent n is a measure of the rate of
strain hardening.
Table 1.1  Materials Properties Obtainable from Tension Tests
Category Engineering Property True Stress-Strain
Property
Elastic
Constants
Elastic modulus, E
Poisson's ratio, ?
Strength
Proportional limit, s
p
Yield strength, s
y
Ultimate tensile strength, s
µ
Engineering fracture strength, s
ƒ
True fracture strength, s
f
Strength coefficient, H or K
Ductility
Percent elongation, 100 ?
ƒ
Reduction in area, %RA
True fracture strain, ??
ƒ
Energy Capacity
Resilience, ?u
r
Tensile toughness, u
t
True toughness, ?u
ƒ
Strain hardening Strain hardening
Ratio,  s
µ
/ s
?
Strain hardening
exponent, ?n
Modulus of Elasticity

•The slope of the initial portion of the stress-strain curve is
the modulus of elasticity, or Young’s Modulus.  The
modulus of elasticity is a measure of the stiffness of the
material.  It is an important design value.

•The modulus of elasticity is determined by the building
forces between atoms.  It is only slightly affected by
alloying.
Page 4

• The various engineering and true stress-strain properties
obtainable from a tension test are summarized by the
categorized listing of Table 1.1.
• Note that the engineering fracture strain e
f
and the %
elongation are only different ways of stating the same
quantity.  Also, the %RA and e
f
can be calculated from each
other.
• Note that the strength coefficient H determines the
magnitude of the true stress in the large strain region of the
stress-strain curve, and so it is included as a measure of
strength.
• The strain hardening exponent n is a measure of the rate of
strain hardening.
Table 1.1  Materials Properties Obtainable from Tension Tests
Category Engineering Property True Stress-Strain
Property
Elastic
Constants
Elastic modulus, E
Poisson's ratio, ?
Strength
Proportional limit, s
p
Yield strength, s
y
Ultimate tensile strength, s
µ
Engineering fracture strength, s
ƒ
True fracture strength, s
f
Strength coefficient, H or K
Ductility
Percent elongation, 100 ?
ƒ
Reduction in area, %RA
True fracture strain, ??
ƒ
Energy Capacity
Resilience, ?u
r
Tensile toughness, u
t
True toughness, ?u
ƒ
Strain hardening Strain hardening
Ratio,  s
µ
/ s
?
Strain hardening
exponent, ?n
Modulus of Elasticity

•The slope of the initial portion of the stress-strain curve is
the modulus of elasticity, or Young’s Modulus.  The
modulus of elasticity is a measure of the stiffness of the
material.  It is an important design value.

•The modulus of elasticity is determined by the building
forces between atoms.  It is only slightly affected by
alloying.
Measures of Yielding

• Yielding defines the point at which plastic deformation begins.
This point may be difficult to determine in some materials, which
have gradual transition from elastic to plastic behavior.  Therefore,
various criteria (depends on the sensitivity of the strain
measurements) are used to define yielding.
1. Proportional Limit - This is the highest stress at which stress is
directly proportional to strain.

2. Elastic Limit - This is the greatest stress the material can
withstand without any measurable permanent strain remaining on
the complete release of the load.

3. Yield Strength - This is the stress required to produce a small
(0.2% strain) specified amount of plastic deformation.
Page 5

• The various engineering and true stress-strain properties
obtainable from a tension test are summarized by the
categorized listing of Table 1.1.
• Note that the engineering fracture strain e
f
and the %
elongation are only different ways of stating the same
quantity.  Also, the %RA and e
f
can be calculated from each
other.
• Note that the strength coefficient H determines the
magnitude of the true stress in the large strain region of the
stress-strain curve, and so it is included as a measure of
strength.
• The strain hardening exponent n is a measure of the rate of
strain hardening.
Table 1.1  Materials Properties Obtainable from Tension Tests
Category Engineering Property True Stress-Strain
Property
Elastic
Constants
Elastic modulus, E
Poisson's ratio, ?
Strength
Proportional limit, s
p
Yield strength, s
y
Ultimate tensile strength, s
µ
Engineering fracture strength, s
ƒ
True fracture strength, s
f
Strength coefficient, H or K
Ductility
Percent elongation, 100 ?
ƒ
Reduction in area, %RA
True fracture strain, ??
ƒ
Energy Capacity
Resilience, ?u
r
Tensile toughness, u
t
True toughness, ?u
ƒ
Strain hardening Strain hardening
Ratio,  s
µ
/ s
?
Strain hardening
exponent, ?n
Modulus of Elasticity

•The slope of the initial portion of the stress-strain curve is
the modulus of elasticity, or Young’s Modulus.  The
modulus of elasticity is a measure of the stiffness of the
material.  It is an important design value.

•The modulus of elasticity is determined by the building
forces between atoms.  It is only slightly affected by
alloying.
Measures of Yielding

• Yielding defines the point at which plastic deformation begins.
This point may be difficult to determine in some materials, which
have gradual transition from elastic to plastic behavior.  Therefore,
various criteria (depends on the sensitivity of the strain
measurements) are used to define yielding.
1. Proportional Limit - This is the highest stress at which stress is
directly proportional to strain.

2. Elastic Limit - This is the greatest stress the material can
withstand without any measurable permanent strain remaining on
the complete release of the load.

3. Yield Strength - This is the stress required to produce a small
(0.2% strain) specified amount of plastic deformation.
(a)
Figure 1-13. (a) Typical stress-strain (type II) behavior for a metal showing
elastic and plastic deformations, the proportional limit P, and the yield
strength s
y
, as determined using the 0.002 strain offset method.
(b) Representative stress-strain (type IV) behavior found for some steels
demonstrating the yield drop (point) phenomenon.
(a)
(b)
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