Recently, a hyperelastic-viscoplastic constitutive model was developed for PET and the noncrystallizing copolymer PETG (R. B. Dupaix, Ph.D. thesis, MIT, 2003). The materials were found to behave very similarly under monotonic loading conditions and the single constitutive model was able to capture both materials’ behavior. However, differences were observed upon unloading, and it is expected that additional differences would be observed under more complex loading conditions. Here their behavior is investigated under nonmonotonic loading conditions, specifically under load-hold conditions. The model of Dupaix and Boyce (R. B. Dupaix, Ph.D. thesis, MIT, 2003) is modified to include Ahzi’s upper-bound model for strain-induced crystallization [Ahzi et al., Mech. Mater., 35(12), pp. 1139–1148 (2003)]. The crystallization model is adapted to include criteria for the onset of strain-induced crystallization which depend on strain rate and level of deformation. The strain-rate condition prevents crystallization from beginning prior to the deformation process slowing significantly. The level-of-deformation condition delays crystallization until the material has deformed beyond a critical level. The combined model demonstrates differences in behavior between PET and PETG during complex loading situations, indicating its ability to capture the fundamental criteria for the onset of strain-induced crystallization.

1.
Dupaix
,
R. B.
, 2003, “
Temperature and Rate Dependent Finite Strain Behavior of Poly(ethylene terephthalate) and Poly(ethylene terephthalate)-glycol above the Glass Transition Temperature
,” Ph.D. thesis, MIT.
2.
Ahzi
,
S.
,
Makradi
,
A.
,
Gregory
,
R. V.
, and
Edie
,
D. D.
, 2003, “
Modeling of Deformation Behavior and Strain-induced Crystallization in Poly(ethylene terephthalate) above the Glass Transition Temperature
,”
Mech. Mater.
0167-6636,
35
(
12
), pp.
1139
1148
.
3.
Kattan
,
M.
,
Dargent
,
E.
, and
Grenet
,
J.
, 2002, “
Three Phase Model in Drawn Thermoplastic Polyesters: Comparison of Differential Scanning Calorimetry and Thermally Stimulated Depolarisation Current Experiments
,”
Polymer
0032-3861,
43
(
4
), pp.
1399
1405
.
4.
Dargent
,
E.
,
Grenet
,
J.
, and
Auvray
,
X.
, 1994, “
Thermal Behaviour of Drawn Semi-crystalline Poly(ethylene terephthalate) Films
,”
J. Therm. Anal.
0368-4466,
41
, pp.
1409
1415
.
5.
Salem
,
D. R.
, 1992, “
Development of Crystalline Order during Hot-drawing of Poly(ethylene terephthalate) Film: Influence of Strain Rate
,”
Polymer
0032-3861,
33
(
15
), pp.
3182
3188
.
6.
Ajji
,
A.
,
Guevremont
,
J.
,
Cole
,
K. C.
, and
Dumoulin
,
M. M.
, 1994, “
Orientation, Mechanical, and Thermal Characterization of Drawn PET
,” in
Annual Technical Conference-ANTEC, Conference Proceedings
, pp.
1421
1423
.
7.
Mahendrasingam
,
A.
,
Martin
,
C.
,
Fuller
,
W.
,
Blundell
,
D. J.
,
Oldman
,
R. J.
,
Harvie
,
J. L.
,
MacKerron
,
D. H.
,
Riekel
,
C.
, and
Engstrom
,
P.
, 1999, “
Effect of Draw Ratio and Temperature on the Strain-induced Crystallization of Poly (ethylene terephthalate) at Fast Draw Rates
,”
Polymer
0032-3861,
40
(
20
), pp.
5553
5565
.
8.
Middleton
,
A. C.
,
Duckett
,
R. A.
,
Ward
,
I. M.
,
Mahendrasingam
,
A.
, and
Martin
,
C.
, 2001, “
Real-time FTIR and WAXS Studies of Drawing Behavior of Poly(ethylene terephthalate) Films
,”
J. Appl. Polym. Sci.
0021-8995,
79
, pp.
1825
1837
.
9.
Bergström
,
J. S.
, and
Boyce
,
M. C.
, 1998, “
Constitutive Modeling of the Large Strain Time-dependent Behavior of Elastomers
,”
J. Mech. Phys. Solids
0022-5096,
46
(
5
), pp.
931
954
.
10.
Boyce
,
M. C.
,
Socrate
,
S.
, and
Llana
,
P. G.
, 2000, “
Constitutive Model for the Finite Deformation Stress-strain Behavior of Poly(ethylene terephthalate) above the Glass Transition
,”
Polymer
0032-3861,
41
(
6
), pp.
2183
2201
.
11.
Lee
,
E. H.
, 1969, “
Elastic-plastic Deformation at Finite Strains
,”
ASME J. Appl. Mech.
0021-8936,
36
, pp.
1
6
.
12.
Anand
,
L.
, 1979, “
On H. Hencky’s Approximate Strain Energy Function for Moderate Deformations
,”
ASME J. Appl. Mech.
0021-8936,
46
, pp.
78
82
.
13.
Doufas
,
A. K.
,
McHugh
,
A. J.
, and
Miller
,
C.
, 2000, “
Simulation of Melt Spinning Including Flow-induced Crystallization Part I. Model Development and Predictions
,”
J. Non-Newtonian Fluid Mech.
0377-0257,
92
, pp.
27
66
.
14.
Arruda
,
E. M.
, and
Boyce
,
M. C.
, 1993, “
Evolution of Plastic Anisotropy in Amorphous Polymers during Finite Straining
,”
Int. J. Plast.
0749-6419,
9
(
6
), pp.
697
720
.
15.
Arruda
,
E. M.
, and
Boyce
,
M. C.
, 1993, “
A Three-dimensional Constitutive Model for the Large Stretch Behavior of Rubber Elastic Materials
,”
J. Mech. Phys. Solids
0022-5096,
41
(
2
), pp.
389
412
.
16.
de Gennes
,
P.-G.
, 1979,
Scaling Concepts in Polymer Physics
,
Cornell University Press
, Ithaca, New York.
17.
Doi
,
M.
, and
Edwards
,
M. F.
, 1986,
The Theory of Polymer Dynamics
,
Oxford University Press
, New York.
18.
Llana
,
P. G.
, and
Boyce
,
M. C.
, 1999, “
Finite Strain Behavior of Poly(ethylene terephthalate) above the Glass Transition Temperature
,”
Polymer
0032-3861,
40
(
24
), pp.
6729
6751
.
19.
Vigny
,
M.
,
Aubert
,
A.
,
Hiver
,
J. M.
,
Aboulfaraj
,
M.
, and
G’Sell
,
C.
, 1999, “
Constitutive Viscoplastic Behaviour of Amorphous PET During Plane-strain Tensile Stretching
,”
Polym. Eng. Sci.
0032-3888,
39
(
12
), pp.
2366
2376
.
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