# FE Review – Mechanics of Materials Resources - EF

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29 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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FE Review – Mechanics of
Materials
FE Review Mechanics of Materials 2
Resources

You can get the sample reference book:
www.ncees.org
– main site
http://www.ncees.org/exams/study_ma
terials/fe_handbook

Multimedia learning material web site:
http://web.umr.edu/~mecmovie/index.
html
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FE Review Mechanics of Materials 3

Normal Stress (normal to surface)

Shear Stress (along surface)
First Concept – Stress
FE Review Mechanics of Materials 4

Normal Strain – length change

Mechanical

Thermal

Shear Strain – angle change
Second Concept – Strain
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Material Properties

Hooke’s Law

Normal (1D)

Normal (3D)

Shear
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Material Properties

Poisson’s ratio
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Stress

Deformation
FF
P
L
A
E
δ
=

x
P
A
σ
=
F
σ
x
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Stress

Deformation
TL
J
G
θ
=

θ
J
ρ
τ
=
TT
max
Tc
J
τ
=
ρ
τ
τ
max
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Bending Stress

Stress

Find centroid of cross-section

Calculate I about the Neutral Axis
r
x
M
y
I
σ
=−
max
r
M
c
I
σ
=
M
M
σ
x
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Transverse Shear Equation
ave
V
A
τ
=
Average over entire cross-section
ave
VQ
Ib
τ
=
Average over line
V = internal shear force
b = thickness
I = 2
nd
moment of area
Q = 1
st
moment of area of partial
section
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Partial 1
st
Moment of Area (Q)
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Max. Shear Stresses on Specific
Cross-Sectional Shapes
Rectangular Cross-Section
max
3
2
V
A
τ
=
τ
Circular Cross-Section
max
4
3
V
A
τ
=
τ
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Max. Shear Stresses on Specific
Cross-Sectional Shapes
Wide-Flange Beam
max
web
V
A
τ

τ
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V & M Diagrams
dV
w
dx
=
V
M
dM
V
dx
=
FE Review Mechanics of Materials 22
Six Rules for Drawing V & M
Diagrams
1.w = dV/dx
The value
at any point in the beam is equal to the
slope
of the shear force
curve.
2.V = dM/dx
The value
of the shear force
at any point in the beam is equal to the slope
of
the bending moment
curve.
3.The shear force curve
is continuous unless there is a point force
on the
beam. The curve then “jumps” by the magnitude of the point force (+ for
upward force).
4.The bending moment curve
is continuous unless there is a point moment
on
the beam. The curve then “jumps” by the magnitude of the point moment
(+ for CW moment).
5.The shear force
will be zero at each end of the beam unless a point force is
applied at the end.
6.The bending moment
will be zero at each end of the beam unless a point
moment is applied at the end.
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FE Review Mechanics of Materials 23
Deflection Equation
2
2
d y
M
EI
dx
=
y = deflection of midplane
M = internal bending moment
E = elastic modulus
I = 2
nd
moment of area with
respect to neutral axis
To solve bending deflection problems (find y):
1.Write the moment equation(s) M(x)
2.Integrate it twice
3.Apply boundary conditions
4.Apply matching conditions (if applicable)
FE Review Mechanics of Materials 24
Method of Superposition
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Stress Transformation
Plane Stress Transformation Equations:
cos2 sin2
2 2
x y x y
n xy
σ
σ σ σ
σ
θ τ θ
+

= + +
sin2 cos2
2
x y
xy
nt
σ
σ
τ
θ τ θ
⎛ ⎞
⎜ ⎟
⎝ ⎠

=− +
τ
xy
σ
x
σ
y
FE Review Mechanics of Materials 26
Stress Transformation
Principal Stresses:
2
2
1,2
2 2
x
y
x y x y
p p
σ σ σ σ
σ
τ
⎛ ⎞
⎜ ⎟
⎜ ⎟
⎜ ⎟
⎝ ⎠
+ −
=
+ +
( )
tan 2
2
xy
p
x
y
τ
θ
σ
σ
=

⎛ ⎞
⎜ ⎟
⎝ ⎠
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FE Review Mechanics of Materials 27
Stress Transformation
Max Shear Stress:
1 2
max
2
p p
σ
σ
τ

=
1
max
2
p
σ
τ
=
2
max
2
p
σ
τ
=
FE Review Mechanics of Materials 28
Stress Transformation
Mohr’s Circle
σ
τ
C
(
)
,
x
xy
σ
τ−
(
)
,
y xy
σ
τ
R
τ
xy
σ
x
σ
y
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We have derived stress equations for four
x
P
A
σ
=
max
V
k
A
τ
=
FE Review Mechanics of Materials 30
x
M
c
I
σ = −
x
M
c
I
σ = +
Tc
J
τ
=
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Method for Solving Combined
1.Find internal forces and moments at
cross-section of concern.
2.Find stress caused by each individual
force and moment at the point in
question.
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Thin-Walled Pressure Vessels
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Column Buckling
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σ
Y
σ
Y
−σ
Y
−σ
Y
Failure occurs when:
1
p
Y
σ
σ>
where
σ
p1
is the largest principal stress.
if σ
p1
and σ
p2
have the same sign
1 2
p
p Y
σ
σ σ

>
if σ
p1
and σ
p2
have different signs
σ
p1
σ
p2
Maximum Shear Stress Theory
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σ
Y
σ
Y
−σ
Y
−σ
Y
Failure occurs when:
2 2 2
1 1 2 2
p
p p p Y
σ
σ σ σ σ

+ >
σ
p1
σ
p2
Maximum Distortion Energy
Theory
This theory assumes that failure
occurs when the distortion
energy
of the material is
greater than that which causes
yielding in a tension test.
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