2025 Fall
Solid Mechanics II
MEN23101
#00 Review of Statics
and Solid Mechanics I
Prof. KIM Sung Youb
(sykim@unist.ac.kr)
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I
2
(Statics)
(normal stress)
F
 = lim
A → 0 A
(shear stress)
P
 ave =
A
P
 ave =
A
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I
3
(State of Stress)
• Only six components of stress are required
to define the complete state of stress in 3D.
• Only three components of stress are required
to define the complete state of stress in 2D.
→ Stress is symmetric. Otherwise, the system rotates.
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I
4
(Stress-strain diagram(curve))
(Fatigue)
(Elastic vs. Plastic)
B: elastic limit
(yield stress)
Beyond B: Plastic
Endurance limit
of steel
Repeated loading
makes a material
weaker → fatigue
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I
5
(axial loading)
• From Hooke’s Law:

P
 = E
= =
E
AE
• From the definition of strain:
 =
(Poisson’s ratio)

L
• Equating and solving for the
deformation,
* E = Young’s Modulus or
PL
Modulus of Elasticity
=
(for steel, E ~ 200 GPa)
AE
 =−

lateral strain

=− y =− z
axial strain
x
x
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I
6
(Hooke’s law)
(Shearing strain)
 x  y  z
x = +
E
y = −
z = −
Shear stress
Shear strain
−
 x
E
+
E
−
 y  z
E
 x  y
E
−
E
−
E

+ z
E
E
 xy = G  xy  yz = G  yz  zx = G  zx
 xy = G  xy  yz = G  yz  zx = G  zx
* k = Bulk Modulus or
Modulus of Compression
Computational
Advanced
Nanomechanics Lab
Review of Solid Mechanics I (Torsion)
7
(Terminology)
Shaft
Torque (twisting couple) T [N‧m]
Polar moment of inertia J [m4]
Angle of twist
(Important relations)
Tc
T
and  =
J
J

Tc
 max = max =
G
JG
 max =
=
TL
JG
Computational
Advanced
Nanomechanics Lab