Mechanical Concept

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


P ( N or kgf )

A ( m2 or cm2 )L

L

Stress : S = P / A Strain : / LLUnit : N/m2 = Pa (kgf/cm2 ) Unit : %

Stress & Strain


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)


Stress-Strain Curve (2)

Material-A

Material-B

• E =

Toughness Material A > Material B

Strength & Stiffness Material A < Material B

Strain Energy ;

Toughness


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)


Poisson's Ratio () H / H L / L

Poisson's Ratio

H

L

L

H


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


Mohr Circle

x

y

x

yx y+yx

y

11

+

-

y

x'xy x'y'

xy

x'y'

x

x'

22


Principle Stress

prin-1xyxyxy

prin-2xyxyxy

xy

xy

[Example ]


1. Von Mises Stress

( Shell Element )

V.MISES > Y

Criterion for Yield

V.MISES



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


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


Bending Stiffness

MM

y

x

Compression

Tension

Neutral Axis

Flexural Rigidity

= E I

@ E : Tensile Modulus@ I : Moment of Inertia


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 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


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


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


Creep ( under Load control )

AP

PA

RE

NT

MO

DU

LU

S

TIME (HOURS)

High Temperature

l

t = 0 t = hour



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


Cyclic Loading

Fatigue Failure ( S-N Curve )

Load

Time

Cycle

Load (kg/mm2 )

103 104 105 106 100

400

300

200



Load ( lb/in2 )

Cycle102 103 104 0

6000

3000

9000

12000

105

Examples for Fatigue Data

106 107

AcrylicAcetalPCPVCABS


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



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


Hardness

PP - Indentation Test

- Stiffness

- Wear & Scratchif Hardness-A >> Hardness-B ( ex. Steel >> Polymer )

Abrasive Wear



Wear

V V

Abrasive WearAbrasive Wear Adhesive WearAdhesive Wear

Abrasive Resistance

PE, PSABS, PPAcetal, Nylon, PC, PVC,PPO

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Mechanical Concept