Exam 3 Review Outline
I.
Mechanical Properties
A.
Engineering Stress and Strain
1.
Stress (σ) = (Force perpendicular to area)/(Initial Crosssectional Area)
2.
Strain (ε) = (Change in length)/(initial Length)
3.
Hooke’s Law
B.
Modulus of Elasticity
1.
Modulus (E) = σ/ε
2.
stiffer materials have larger modulus
C.
Types of Deformation
1.
Linear elastic Region
a.
Will completely regain its form when released
2.
Uniform Plastic Deformation
a.
Permanent deformation
b.
Area is maintained
3.
Nonuniform plastic deformation
a.
Necking
D.
Tensile Strength
1.
maximum stress that is achieved by a sample in the stressstrain curve
E.
True Stress & True Strain
1.
True Stress = (Force)/(Crosssectional area)
a.
After necking, true stress = (Force)/(Area of necked region)
2.
True Strain = l
N
((length at time t)/(initial length))
a.
After necking, true strain = l
N
((area at time t)/(initial area))
F.
Yield Strength
1.
stress where plastic deformation begins
2.
uses the offset method at a +Δε = .002
3.
welldefined yielding is a sudden drop in stress
a.
yield strength is the average stress at the lower yield point
G. Ductility
1.
%EL = (ℓ
f
 ℓ
0
)/ℓ
0
x 100
2.
%RA = (A
f
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 Fall '07
 Harris
 Materials Science, Tensile strength, Work hardening

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