rushabh workshop presentation

8/2/2019 Rushabh Workshop Presentation

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Rushabh J. Vora, Dr. I. A. Ashcroft and Dr. R. Hague

21/12/2005

Presented by: Rushabh J. Vora

Depth Sensing Indentation of

Polymeric Materials


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Contents

Introduction

Objectives

Experimental Technique

Study of cure kinetics and time dependent behaviour Investigation of viscoelastic/viscoplastic behaviour and

determination of suitable test parameters

Finite element Analysis (FEA) and Atomic force microscopy(AFM)

Conclusions


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Introduction

Rapid Prototyping (RP)

Stereolithography (SL)

Ageing and non-uniform mechanical properties.

DSI technique.

Application to polymers.

Sensitivity to stress state and strain rate.


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Objectives

Investigation of mechanical properties of an epoxy basedSL7580 using DSI technique.

Investigation of viscoelastic/viscoplastic behaviour anddetermination of suitable testing parameters

To investigate curing of the SL resin and relate this to themechanical properties.

To generate comparative mechanical data using standardtest methods such as uniaxial compressive, tensile and

creep tests and dynamic mechanical thermal analysis(DMTA).


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Objectives

Finite element modelling is used to increase understandingof DSI of polymers.

AFM is used to study the surface roughness, non-uniformities and indentation impression.


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Stereolithography (SL) process

SL7000 from 3D system

The photopolymer usedin the current research isSL7580, which isproduced by RenShapeSolutions, the tooling unitof Huntsman advancedmaterials(www.huntsman.com)


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Sample preparation

Post-processing technique

Group A: - Stereolithography samplescleaned with TPM (Tri-propylene GlycolMonomethyl Ether)

Group B: - Stereolithography samplescleaned with TPM and U.V post cured for90 minutes.

Group C: - Stereolithography samples treated with Methanol.

Group D: - Stereolithography samples treated with Methanoland U.V post-cured for 90 minutes.


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DSI Technique

Experimental set-up for DSI

A Nanotest 600 from Micro Materialswas used for the DSI tests.

Loads ranging from 5 to 100mNwere used and loading rate, dwell

time and unloading rate were allvaried independently.


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Study of time-dependent behaviour of SL7580

SL7580 samples treatedwith methanol and U.V postcured for 90 minutes.

0

500

1000

1500

2000

2500

30003500

4000

4500

0 5 10 15 20 25

Weeks

Plasticdepth(n

m)


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Time (weeks)

0 5 10 15 20 25 30

Hardness(MPa)

0

50

100

150

200

250

SL 7580 samples treated with methanol

SL 7580 samples treated with methanol and U.V postcured for 90 min

Time (weeks)

0 5 10 15 20 25 30

Indentationmodulus(GPa)

0

1

2

3

4

5

SL 7580 samples treated with methanol

SL 7580 samples treated with methanol and U.V postcured for 90 min


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Time (weeks)

0 5 10 15 20 25

Hardness(GPa)

0

20

40

60

80

100

120

140

160

180

200

SL 7580 samples treated with T.P.M

SL 7580 samples treated with T.P.M and U.V postcured for 90 min

Time (weeks)

0 5 10 15 20 25

Indentationmodulus(GPa)

0

1

2

3

4

5

SL 7580 samples treated with T.P.M

SL 7580 samples treated with T.P.M and U.V postcured for 90 min


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Cure kinetics of SL7580

-6

-4

-2

0

2

46

8

10

12

14

0 50 100 150 200 250 300 350

Temperature (0

C)

mW

Heating

rates

Differential Scanning Calorimetry (DSC) tests

Dynamic DSC plots at 3, 7, 10 and 15 0C/min


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Cure kinetics of SL7580

Dynamic heating runsT

T

T

H

dTdT

dH

1

0

Isothermal runst

t

0

H

dtdt

dH

T

T

T

0

dTdT

dHH

n)1(k

dt

d

nth order mechanistic model

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250

Temperature (0C)

n

n

-12

-10

-8

-6

-4

-2

0

0 50 100 150 200 250

Temperature (0C)

Ln(K)(1/se

c)

ln (K)


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0

50

100

150

200

250

0 1 2 3 4 5 6

Time (weeks)

Hardness(MPa)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

D

egreeofcure

Hardness (MPa)

Degree of cure

0

50

100

150

200

250

0 5 10 15 20 25

Time (weeks)

Hardness(MPa)

0

0.1

0.2

0.30.4

0.5

0.6

0.7

0.8

0.9

1

Degre

eofcure

Hardness (MPa)

Degree of cure

Standardization chart: Relation between hardness (MPa) and degree of cure.

Cure kinetic parameters for SL7580

Kinetic constants

k = 3.36*10-5 sec-1n = 2.8

)1ln(n)kln()dt

dln(


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Cure kinetic parameters for SL7580

bx

0 aeyy

Kinetic parametersy0 = -46.55,

a = 123.7 and

b=0.6503Degree of cure

0.0 0.2 0.4 0.6 0.8 1.0

H

ardness(MPa)

40

60

80

100

120

140

160

180

200

220

240

Indentation hardness vs. Degree of cure

Degree of cure

In estigation of iscoelastic beha io r of


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0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000

Displacement (nm)

Load(mN)

0.5 mN/sec

2 mN/sec

0.1 mN/sec

Load-displacement plots at different loading rates andconstant unloading rate.

When no dwell period is applied theunloading curve shows a nose or

bowing which increases with loading

rate.

This compromises the application ofthe standard data analysis methods

developed for metals.

Investigation of viscoelastic behaviour ofSL7580

Investigation of viscoelastic behaviour of


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0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000

Displacement (nm)

Load(mN)


0.1mN/sec

0.5mN/sec

2mN/sec

Load-displacement plot at constant loading rate anddifferent unloading rates

The bowing effect also increaseswith decreasing unloading rate.

Assumption of purely elastic

behaviour during unloading is

incorrect and the viscoleastic

behaviour must be accounted for

before extracting meaningful

mechanical properties.



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0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500

Displacement (nm)

Load(mN)


Load-displacement plots with different dwell periods.

No dwell

60s dwell

180s dwell

300s dwell

Loading rate 2mN/sec

Unloading rate 0.1mN/sec

Elastic unloading can be

achieved by the addition of a

suitable dwell period at maximum

load prior to unloading.

However, data obtained is still a

function of the non-uniform stress

state and the test rate.



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0

5

10

15

20

25

0 400 800 1200 1600 2000 2400 2800 3200

Displacement (nm)

Load(mN)


No dwell

60 s dwell

180 s dwell

300s dwell

Multiple load cycles reloaded to same maximum loadafter different dwell periods

It can assumed that if the

unloading and reloading curves

follow the same path then the initial

portion of the unloading curve is

elastic.



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0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500

Displacement (nm)

Load(mN)


1 mN/sec 0.1 mN/sec

0.5 mN/sec

Multiple load cycles reloaded to same maximum load at differentloading rate

Dwell 180sec



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0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500

Displacement (nm)

Load(mN)

0

100

200

300

400

500

600

700

0 50 100 150 200

Time (sec)

Displacement(

nm)


0.1 mN/sec

0.5 mN/sec

2 mN/sec

Load-displacement plots with differentloading rates and fixed unloading rate (0.5mN/sec).

2mN/sec

0.5mN/sec

0.1mN/sec

Creep curves for 180s after differentloading rates

Dwell 180sec



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1500

2000

2500

3000

3500

4000

0 0.5 1 1.5 2 2.5

Loading rate (mN/sec)

Inden

tationmodulus(MPa

40

50

60

70

80

90

100

110

120

130

Indentationhardness(MPa)

Indentation modulus (Mpa)

Indentation hardness (Mpa)

Indentation modulus and hardness at differentloading rates.


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Atomic force microscopy (AFM) Study

VEECO Dimension 3100 AFM


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Atomic force microscopy (AFM) Study

Centre Edge

AFM images of Centre and Edge of unpolished sample

Investigation of non-uniform mechanica


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Investigation of non uniform mechanicaproperties

0

50

100

150

200

250

300

-1 1 3 5 7 9

Time (Weeks)

Indentationhardness(MPa)

Group C (Centre)

Group C (Edge)

Time (Weeks)

0 2 4 6 8 10

Hardness(MPa)

50

100

150

200

250

300

Group D (Centre)

Group D (Centre) SL samples treated with methanol.Group D (Center)

Group D (Edge)

SL samples treated with methanol and U. V postcured for 90 min.


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0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16

True Strain (%)

Truestress(MPa)

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

True strain (%)

Truestress(MPa)

Bulk mechanical testing

Tensile tests 100mm/min

10mm/min

1mm/min

0.1mm/min

High temperature (600C)

100mm/min

10mm/min

1mm/min

0.1mm/min

Room temperature

B lk h i l i


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Compressive tests


0

20

40

60

80

100

0 5 10 15 20 25

Strain (%)

Compressivestre

ss(MPa)

IncreasingTest rate

Compressive stress vs. strain at room temperature.

0

20

40

60

80

100

0 2 4 6 8 10 12

Test rates (mm/min)

Yieldstress(MPa)

Compression Tests

Tensile Tests

Comparison between compressive and tensileyield stress at room temperature.

B lk h i l i


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Tensile creep experimental set up

Creep tests

Creep constants

B=7.35e-12

m=4.2763m

ss BDorn relation

B lk h i l t ti


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DMTA

@ Displacement 0.001, 0.005,

0.01, 0.05, 0.1, 0.15 mm

@ Frequencies 1, 2, 5, 10, 100 Hz

Dynamic Properties vs Temperature

0.0E+00

2.0E+08

4.0E+08

6.0E+08

8.0E+08

1.0E+09

1.2E+09

1.4E+09

1.6E+09

1.8E+09

2.0E+09

0.0 20.0 40.0 60.0 80.0

Temperature (C)

Mo

dulus(Pa)

0.000

0.050

0.100

0.150

0.200

0.250

0.300

T

anDelta


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Finite element modelling

8 Node Quad Elements

Conical indenter with same area to depthratio as Berkovich indenter

Spherical indenter with 50 m radius


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Linear Mohr-coulomb Material Model


Fi i l d lli


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Displacments in X-direction Compression stresses in X-Direction

C l i


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Conclusions

The DSI technique has been used to characterise the mechanical behaviour of an

epoxy SL resin with respect to time under various environmental and loading conditions.

A kinetic cure model has been applied to the resin and a good correlation between

the predicted degree of cure and mechanical properties has been demonstrated.

Viscoelastic/viscoplastic behaviour has been observed in the DSI load-unload plots,

which is dependent on loading/ unloading rates and dwell period at maximum load.

FEA can be used to increase understanding of material behaviour under indentation.

C t t


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Rushabh J Vora

PhD student

Wolfson School of Mechanical and Manufacturing Engineering

Loughborough University

[email protected]

Contact

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