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Thongwichean T. a, Phalakornkule C. b and Chaikittiratana A. b
Finite Element Analysis for Thermoforming Process of Starch/
Biodegradable Polyester Blend
aRajamangala University of Technology Srivijaya Rattaphum
College bKing Mongkut’s University of Technology North Bangkok
INTRODUCTIONBioplastics is derived from
renewable resources and could be degraded more easily than petroleum-based plastics.
Starch-based bioplastics is one class of bioplastics. which can be further divided into three categories.
1. thermoplastic starch materials; modified starch with
plasticizing additives. 2. blends of starch and
biodegradable plastics.3. plastics whose monomers are
biochemically derived from starch
3. Elastic-plastic material models were used to capture the compressive
behaviour of the material.
The objective of study 1. Develop a simple computational
modelling using finite element techniques in order to predict the mechanical behaviour of a starch/
biodegradable plastic blend. 2. The mechanical behaviour testing
of thin sheet means of compression tests at temperatures ranging from 363 to 393 K and at strain rates of 0.1 and
0.5 s-1.
Experimental WorkMaterialsThe polymer in this study was
tapioca starch-EnpolTM blend, provided by DES Co.Ltd.
(Thailand). EnpolTM is a fully biodegradable aliphatic polyester resin developed by IRe Chemical Ltd. (Seoul, Korea). The ratio of tapioca starch to EnpolTM was
50:50 by weight
Samples preparation
Twin screw extruder.HAAKE Polylab, Rheomex CTW 100P
Thin strips of extruded tapioca starch- EnpolTM blend.
12 mm.
2 mm.
12 mm.
Specimen dimension of 12x12x2 mm
Plot of endothermic melting vs. temperature
Differential Scanning Calorimeter test
Mechanical Testing In order to determine the
mechanical deformation behaviour of the biodegradable material, the uniaxial compression tests were
performed at various temperatures ranging from 363 K to 393 K with strain rates of 0.1
and 0.5 s-1. The compression tests were carried out according to ASTM D695 using an universal
testing machine equipped with a temperature control chamber
Instron model 5567
4 mm.
Compressing plattens
Stack of small thin samples
Compressing load
Compression test arrangement
Plot of compressive engineering stress vs.
engineering strain at different temperatures and strain rates.
0
10
20
30
40
50
60
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6
Compression Engineering Strain
Co
mp
res
sio
n E
ng
ine
eri
ng
Str
es
s (
MP
a)
90 องศาเซลเซ�ยส 90 องศาเซลเซ�ยส100 องศาเซลเซ�ยส100 องศาเซลเซ�ยส110 องศาเซลเซ�ยส110 องศาเซลเซ�ยส120 องศาเซลเซ�ยส120 องศาเซลเซ�ยส
έ = 0.1 s-1έ = 0.5 s-1
έ = 0.5 s-1
έ = 0.1 s-1έ = 0.5 s-1έ = 0.1 s-1έ = 0.5 s-1
έ = 0.1 s-1
363 K 0.5 s-1
363 K 0.1 s-1
373 K 0.5 s-1
373 K 0.1 s-1
383 K 0.5 s-1
383 K 0.1 s-1
393 K 0.5 s-1
393 K 0.1 s-1
0
5
10
15
20
25
30
35
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Compression True Strain
Co
mp
ress
ion
Tru
e S
tres
s (M
Pa)
90 องศาเซลเซ�ยส100 องศาเซลเซ�ยส110 องศาเซลเซ�ยส120 องศาเซลเซ�ยส
363 K 0.5 s-1
373 K 0.5 s-1
383 K 0.5 s-1
393 K 0.5 s-1
Plot of compressive true stress vs. true strain at different
temperatures.
Sheet thermofor
ming
Sheet thermoforming test arrangement
Specimen after the sheet thermoforming process
Finite Element SimulationMaterial Model
Since the deformation behavior was found to be temperature
dependence, strain rate insensitive with no strain hardening after yield,
thus it was modeled with a standard isotropic elastic-perfectly plastic material model inbuilt in a
commercial finite element package ABAQUS 6.5 .
Material's Properties for elastic-perfectly plastic material model.
Temperature (K)
Young's
Modulus (MPa)
True Yield stress (MPa)
363 484.387 28.307373 380.168 23.757383 341.897 20.313393 314.767 17.293
0
5
10
15
20
25
30
35
40
45
50
55
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Compression Engineering Strain
Co
mp
ress
ion
En
gin
eeri
ng
Str
es
s (M
Pa)
ทดสอบท�� 90 องศาเซลเซ�ยส ทดสอบท��100 องศาเซลเซ�ยส ทดสอบท��110 องศาเซลเซ�ยส ทดสอบท��120 องศาเซลเซ�ยส
แบบจำ�าลองท�� 90 องศาเซลเซ�ยส แบบจำ�าลองท�� 100 องศาเซลเซ�ยส แบบจำ�าลองท�� 110 องศาเซลเซ�ยส แบบจำ�าลองท�� 120 องศาเซลเซ�ยส
363 K Data
373 K Data
383 K Data
393 K Data
363 K Simulation
373 K Simulation
383 K Simulation
393 K Simulation
Comparison between experimental data and finite
element simulation with elastic-perfectly plastic material model.
A finite element model was developed to simulate the matched
mould thermoforming process at 393 K described in section 2.5 using a finite element package ABAQUS 6.5. The process was
symmetrical and thus one-half of the system was modeled. 2-D shell
elements (S8) were employed incorporating with the isotropic elastic-perfectly plastic material
model.
Finite element simulation of thermoforming process.
Distribution of the specimen's final thickness predicted by
the finite element simulation.
Distribution of Von Mises' stress in the moulded specimen
predicted by the finite element simulation.
0
200
400
600
800
1000
1200
1400
0 2 4 6 8 10 12
Displacement (mm)
Lo
ad
(N
)
การทดลอง แบบจำ�าลองอ�ลาสติ�ก- เพอร�เฟคล�พลาสติ�ก
DataFE Simulation
Comparison between the compressing load measured
during the forming process and the prediction from the
simulation.
Conclusion 1. It was found that
temperature of 393 K and strain rate of 0.5 s-1 gave the most
satisfying condition for the sheet stamping process.
2. It was found that the Elastic–Perfectly Plastic model described reasonably well the
behavior of the material. 3. The 2D Finite element
simulation of a sheet stamping thermoforming process with
Elastic–Plastic material model can give good representation of the real thermoforming process.
END