Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
MOLDFLOW KOREA 1995.8
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical ConceptUNIT
SI kg m sec N Pa
Metric kg mm sec kgf kgf/cm2
English lb in sec lbf psi
mass length time force pressuremass length time force pressure
Examples for UNIT
SI Metric English
Force
Pressure
1 N1 N 9.8 N4.448 N
0.102 kgf 1 kgf1 kgf0.453 kgf
0.225 lbf 2.206 lbf 1 lbf1 lbf
1 MPa1 MPa 0.1 MPa 6.9 kPa
10.2 kgf/cm2
1 kgf/cm1 kgf/cm22
0.07 kgf/cm2
145 psi 14.22 psi 1 psi1 psi
Pa = N / mPa = N / m2 2 psi = lb / in psi = lb / in22
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
P ( N or kgf )
A ( m2 or cm2 )L
L
Stress : S = P / A Strain : / LLUnit : N/m2 = Pa (kgf/cm2 ) Unit : %
Stress & Strain
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Tensile Strength = Stress at Yield
Tensile Strength = Stress at Break
Elastic Plastic
Proportional Limit
Elastic Limt
Break Point
Yield Point
E
Ductile FractureDuctile Fracture
Brittle Fracture Brittle Fracture
Strain-Stress Curve (1)
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Stress-Strain Curve (2)
Material-A
Material-B
• E =
Toughness Material A > Material B
Strength & Stiffness Material A < Material B
Strain Energy ;
Toughness
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Examples for Tensile Properties
Tensile Strength (73F,lb/in2)
AcetalABSNylonPolycarbonatePolyethylenePolyesterPMMAPPOPolypropylenePolystyrenePolysulphonePVC
104 - 88 - 128 - 101 - 68 - 108 - 118 - 104 - 65 - 119 - 105 - 9
0.50.2 - 0.50.2 - 0.40.30.02 - 0.2
0.3 - 0.40.40.20.4 - 0.60.40.3 - 0.6
Modulus (73F,b/in2X106)
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Poisson's Ratio () H / H L / L
Poisson's Ratio
H
L
L
H
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical ConceptExamples for Poisson's ratio
탄소강 알루미늄콩크리트유리Rubber
Most Crystalline & Glassy Polymer
Eng. Plastics
0.28 - 0.29 0.33 0.19
0.250.49 - 0.50
0.25 - 0.33
0.35 - 0.40
Principal Stress =Max. Normal Stress
Normal Stress
Shear Stress
Shear Stress is zero on this SurfaceSurface
Principal Stress
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mohr Circle
x
y
x
yx y+yx
y
11
+
-
y
x'xy x'y'
xy
x'y'
x
x'
22
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Principle Stress
prin-1xyxyxy
prin-2xyxyxy
xy
xy
[Example ]
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
1. Von Mises Stress
( Shell Element )
V.MISES > Y
Criterion for Yield
V.MISES
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
2. Tresca Criterion
| max min | tresca =
-
11
max
tresca > Y
Criterion for Yield
+
22
Shear Stress
l
= / l Shear Rate
Shear Stress
G
= Shear force / Area = G
## Shear Modulus
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Shear Stress
Shear Modulus =
0.5 - 0.6 X Tensile Modulus
@ Von-Mises ; 0.6 Tresca ; 0.5
위의 결과는 Yield Point 기준
P P
전단면
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Bending Stiffness
MM
y
x
Compression
Tension
Neutral Axis
Flexural Rigidity
= E I
@ E : Tensile Modulus@ I : Moment of Inertia
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Moment
P
Ymax
L
( Max. Moment & Stress )Position A
M = P LSmax = M / ZYmax = PL3/3EI
M : MomentI : Moment of InertiaSmax : Max. StressYmax : Max. Deflection Z : = I / C
C
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical ConceptExamples for Moment with Various Boundary condition
LLL
PP PP PP
M A X I M U M S T R E S S
1 1/81/4 M A X I M U M S T R E S S P O S I T I O N
at Supportat Center & Supportat Center
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical ConceptMoment of Inertia
Moment of Inertia
Deflection
yNeutral Axis I = A y2 dA
100100 100100
274 274 36.5 36.5
4600 4600 2.17 2.17
wt
h
r
w=101.6, t=3.18, r=4.76, h=22.22
L
L
L
LL
LL
L
L
LL
LL
LL
L
1 0.59 0.55 0.331 0.59 0.55 0.33
0.66 0.51 0.91 0.910.66 0.51 0.91 0.91
Thickness = L/4
Examples for Moment of Inertia
100 wt 78 wt 34 wt 50 wt100 wt 78 wt 34 wt 50 wt
78 wt 63 wt 63 wt 63 wt78 wt 63 wt 63 wt 63 wt
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
T2 L L
Coefficient of Thermal Expansion
T1 L
CV = L / LT2 - T1
( Unit : mm/mm/degC )
Sthermal = CV X E)T2X ( T2 - T1 )
HeatingHeating
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Examples for Coefficient of Thermal Expansion
Coefficient of Thermal Expansion (x10-5,in/in/C)
AcetalABSNylonPolycarbonatePolyethylenePolyesterPMMAPPOPolypropylenePolystyrenePolysulphonePVC
8.19.08.36.512.06.07.05.25.86.05.410.0
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Creep ( under Load control )
AP
PA
RE
NT
MO
DU
LU
S
TIME (HOURS)
High Temperature
l
t = 0 t = hour
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
l1
l2
l1 = l2
AP
PA
RE
NT
MO
DU
LU
S
High Temperature
TIME (HOURS)
Stress Relaxation ( Under Displacement Control )
t = 0
t = hour
Examples for Tensile Creep Modulus
Applied Load (lb/in2)
AcetalABSNylonPolycarbonatePolyethylenePolyesterPPOPolypropylenePolystyrenePolysulphonePVC
Creep Modulus (73F,b/in2X103)
1 hr 1000 hr100 hr
15001000150030001000100015001000150040001000
390295160345 50440430165135350330
250210100310 25380320 65 10310180
280255115320 30400400 90 20320280
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Cyclic Loading
Fatigue Failure ( S-N Curve )
Load
Time
Cycle
Load (kg/mm2 )
103 104 105 106 100
400
300
200
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Load ( lb/in2 )
Cycle102 103 104 0
6000
3000
9000
12000
105
Examples for Fatigue Data
106 107
AcrylicAcetalPCPVCABS
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Loa
d (
kg)
& E
ner
gy (
kg.
m)
Time (msec)
Load Energy
Velocity = m/secWeight = kg
Plastics
Impactor
Impact Resistance ( Dynamic Failue )
For
ce (
N)
Time (sec)
tL)1 tL)2
Impact Load
Static Load
Factor of Impact
1. Stiffness 2. Mass 3. Course & Velocity
If TL > (5-6) Tn ,
Loading Type = Static( @ Tn : Natural Frequency )
Impact (continued)Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Impact (continued)
1. Elastic Deformation higher than Yield Strength 2. Permanent Deformation3. Tearing4. Fracture
Failure Type
Rapid Deformation1. Fast Loading Rate2. Rate Sensitivity of Mechanical Properties
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Coefficient of Friction
W
N
F
Friction Force)
F = N
@ : Corfficient of Friction (Static) N : Normal Force : Angle of Friction
When Max. Angle with no sliding
S
S
Examples for Coefficient of Friction
AcetalNylonPolycarbonatePolyethylene (LD)Polyethylene (HD)PETPTFEPVCPVDC
Steel on Polymer Polymer on Polymer
s k0.140.370.600.270.180.290.100.450.68
0.130.340.530.260.100.280.050.400.45
-0.42 -0.330.120.270.040.500.90
-0.35 -0.330.110.200.040.400.52
s k
s : Static Friction Coefficientk : Kinetic Friction Coefficient
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Hardness
PP - Indentation Test
- Stiffness
- Wear & Scratchif Hardness-A >> Hardness-B ( ex. Steel >> Polymer )
Abrasive Wear
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Mechanical ConceptMechanical ConceptMechanical ConceptMechanical Concept
Wear
V V
Abrasive WearAbrasive Wear Adhesive WearAdhesive Wear
Abrasive Resistance
PE, PSABS, PPAcetal, Nylon, PC, PVC,PPO