EXPERIMENTAL INVESTIGATION AND MODELING OF … · 4 Institute of Polymer Mechanics 23 Aizkraukles...
Transcript of EXPERIMENTAL INVESTIGATION AND MODELING OF … · 4 Institute of Polymer Mechanics 23 Aizkraukles...
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EXPERIMENTAL INVESTIGATION AND MODELING
OF NONLINEAR VISCOELASTIC PLASTIC
BEHAVIOR OF POLYIMIDE
A. Aniskevich
Institute of Polymer Mechanics, University of Latvia
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Europe, Latvia, Riga …
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Outline
• Introduction and objective of the research
• Experimental details
• Our results
• Acknowledgments
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Institute of Polymer
Mechanics
www.pmi.lu.lv
23 Aizkraukles Str., Riga, LV-1006, Latvia
Since 1963
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Our research group
• Long-term deformability of polymers and composites;
• Prediction of the durability and deformability;
• Environmental effects.
Prediction of long-term
deformability
Nano-modified composite
matrixes with improved properties
Environmental effects on
deformability
Products made from
recycled plastic
Composite materials with
biomimetic solutions
Technology of fiber-
reinforced polymer-matrix
composites
Development of profiled
grips
Potted anchor with
wedged insert
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Our research group
• 2 Dr. Habil. Sc.
• 11 Dr. Sc.
• 2 PhD students.
• 2 MSc.
• 2 Master course students.
• 1 Bachelor course student.
• 3 engineers.
Total 23
In 2011:
• 9 journal papers published
or in press.
• 15 conference presentations.
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Journal Mechanics
of Composite Materials
The bimonthly journal is issued since 1965.
Since the first issue the Journal has been
translated into English and now it is issued by
Springer Science+Business Media, Inc.
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Conference on Mechanics
of Composite Materials
Since 1965, the Institute has organized 17 conferences.
The number of participants is ca. 150 scientists.
The XVII Conference was held May 28 - June 1, 2012.
May 2012
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Introduction: Polyimide films
• Tensile strength and initial tear resistance
• Exceptional toughness and resistance to cutthrough and abrasion
• Flame and heat resistanceSpeaker Cones
Pressure-Sensitive Tape
Bar Code Labels Flexible Heater
Flexible display
Hard disk drives
Flexible Circuits
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Research objective and tasks
• The aim of the present study is to perform a detailed analysis of
strains arising in creep and recovery tests.
– for this purpose elastic and ultimate tensile characteristics of
the material have to be obtained,
– inelastic contribution in deformability of PI should be
investigated,
– deformability of the film should be modelled.
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Tested material
• Upilex® S UBE industries
Tested specimens had a strip shape of 30 mm width.
Thickness 130 mm.
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• Standards EN ISO 527-1,
EN ISO 527-2, and ASTM D 638
• Test temperature 202°C,
• 3 - 5 specimens tested
• Testing machine Zwick 2.5
Quasistatic tension tests
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Quasistatic tension tests
Comparison of Upilex S stress-strain typical diagrams for two strain
rates – slow: e’ 10–5 and fast: 10–2 s–1.
Elastic modulus
Ultimate stress
and strain
Yield point
0
50
100
150
200
250
0 5 10 15 20
σ, M
Pa
ε, %
σ(ε)
Upilex - slow
Upilex - fast
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Strength and ultimate strain
209
227
100
120
140
160
180
200
220
240
3.3E-05 6.7E-02
σ, M
Pa
e', s-1
Strength
1514
10
11
12
13
14
15
16
17
3.3E-05 6.7E-02
ε, %
e', s-1
Limit strain
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Elastic modulus
4.865.515.42
5.82
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
3.3E-05 6.7E-02
E, G
Pa
e', s-1
E-Modulus
ε=1-1.5%
ε=0.5-1.0%
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Yield point determination
• Secant or Offset (0.2%)
• Tangent
σ (ε) + secant
0
20
40
60
80
100
120
140
160
180
200
0.0 1.0 2.0 3.0 4.0 5.0ε, %
σ,
MP
a
Upilex: № 74 @ 800 mm/min
Elastic
Yield (offset)
Yield point
σ (ε)
0
50
100
150
200
250
0 5 10 15ε, %
σ,
MP
a
Upilex: № 74 @ 800 mm/min
Tangents
Yield point
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Yield stress and strain
2.56 2.73
3.58 3.76
0.00.51.01.52.02.53.03.54.0
3.3E-05 6.7E-02
ε, %
e', s-1
Yield strain ε
Yield ε (offset)
Yield ε (tangent)
115139
178
208
0
50
100
150
200
250
3.3E-05 6.7E-02
s, M
Pa
e', s-1
Yield stress σ
Yield σ (offset)
Yield σ (tangent)
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Creep tests
• Dead weight loading
• Four loading sections
• Lever with two arms with 1:10
ratio
• Maximal load about 1 kN
• Strip shape specimens
• Grip-to-grip distance was 75 mm
• Gauge length was about 50 mm
for longitudinal strain and 30 mm
for transverse strain
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Strain measurement
Stress
Stress
Thin film
specimenStrainStrain
Strain
Strain
t
e11
e22
Files
PC
Testedspecimen
Photocamera
Strain vs. time graph
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Strain measurement
Program interface.
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Experimental determination of the
viscoelastic properties
Strain = Elastic + Viscoelastic (non) linear + Plastic
σ(ε)
0
50
100
150
200
250
0 10 20 30 40 50ε, %
σ, M
Pa
Kapton HN - slow
Kapton HN - fast
Upilex - slow
Upilex - fast
Creep testsQuasistatic tests
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Creep tests
0
1
2
3
4
5
6
0 5000 10000t, s
e,
%
12 MPa 25 MPa 50 MPa75 MPa 100 MPa 125 MPa150 MPa
Creep curves for Upilex S at different stress levels, 3 h tests.
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Creep isochrones
Deviates from linear!
0
20
40
60
80
100
120
140
160
0 1 2 3 4 5 6
σ, M
Pa
ԑ, %
Isochrones
t=10s
t=1200s
t=10800s
t=10s
t=1200s
t=72000s
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Quasi elastic modulus
In creep loading (10 sec) and recovery unloading (10 sec).
Loading and unloading coincide.
Upilex is linear elastic up to 75 MPa.
0
1
2
3
4
5
6
7
8
0 50 100 150 200
E, G
Pa
s, MPa
Upilex(load)
Upilex(unload)
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Creep tests
Creep (3 h) and long-term recovery
(one week) test for stress 150 MPa.
Upilex creep 150 MPa
0
1
2
3
4
5
6
7
0 5 10 15ln(t)
e,
%
foto U35
(unload-week)
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Non recoverable strain
Non recoverable strain 20 h (active : passive = 1:7).
Upilex reveals viscoelastic behavior (no residual strain) up to s = 75 MPa.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 50 100 150 200
enre
c,
%
s, MPa
Non recoverable strain 20 h af ter 3 h creep
Upilex
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Creep modeling
• Elastic
• Viscoelastic
non linear
• Plastic
( , ) ( ) ( , ) ( , ),crel ve plt t te s e s e s e s
( ) ,el Ee s s
( )1 exp ,ve
n
iii
a tA
E
s se
1 2( ) exp( ),a s s
( , ) .pl
mj b
jj
t c te s s
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Creep modeling
10 100 1 103
1 104
1 105
0
1
2
3
4
5
6
Time, s
Str
ain
, %
Experimental and
calculated creep curves for
Upilex S for 7 stress levels
from 12 till 150 MPa.
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Creep modeling
Construction of the generalized curve.
Dots — experiment.
103
105
107
109
1011
0.01
t, s
J.10
0, M
Pa
5.10-3
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Creep modeling
Calculated curves of creep (a) and creep recovery (b) (solid lines). Dots —
experiment, dashed lines — reversible strains (elastic and viscoelastic
components). σ = 150 (1), 125 (2), 100 (3), 75 (4), 50 (5), and 25 (6) MPa.
10 100 10 103 4
6
5
4
3
2
1
ecr, %
1
2
3
a
t , s
4
5,6
b
10 100 10 103 4 5
10
2
1
1
2
erec, %
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Conclusions
• Elastic, viscoelastic, and plastic components of material
deformation were experimentally separated and determined.
• In creep tests, the threshold load σ = 75 MPa was determined on
exceeding which irreversible strains arose in the material.
• Creep behavior of the films was described successful. The
calculations were carried out on the basis of the STS principle.
• The nonlinear viscoelastic component was separated from the
general strain of the material by approximating the experimental
data on the accumulation of irreversible strains during loading.
ECCM 15, June 24-28, 2012, Venice, Italy
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Acknowledgment
European Regional Development Fund Project:
• ―Support to international cooperation projects on the
physicomechanical investigation of polymer composite
materials‖
Agreement No. 2010/0201/2DP/2.1.1.2.0/10/APIA/VIAA/005
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