Analysis of the nonlinear behavior of bio-based polymers reinforced with flax fibers

L. Rozite and R. Joffe Luleå University of Technology, S-97187 Luleå, SWEDEN

The Objective of this study was to analyze nonlinear behavior of flax fiber bio-based polymers composites. Influence of moisture also has been analyzed.

Acknowledgment

Financial support by EU sixth framework programme project “New class of engineering composite materials from renewable resources”, BIOCOMP. Specimens were supplied by Tecnaro (Germany).

17th International Conference on Mechanics of Composite Materials, May 8 – June 1, 2012, Riga, Latvia

www.ltu.seroberts.joffe@ltu.se

Materials

Scanning electron microscope images for PLA-NF10 (left), Lignin/FL30 (middle) and for comparison viscose fiber composite PLA-VF5 (right)

Summary

Material model was developed assuming that possible sources of the observed behavior may be microdamage related stiffness reduction, nonlinear viscoelasticity as well as viscoplasticity. The model was rewritten in an incremental form where stress is a function

of strain to simulate strain controlled tests. The simulated stress-strain curves in tensile test showed satisfying agreement with experimental data. Increase of moisture level in material decreases mechanical properties of composite.

Damage Visco-elastic Visco-plastic

td

d

gdSgd VP

t

,2

010max

Material model

Notation Matrix Fibers/length/ weight fraction

PLA-NF10 PLA Flax/1 mm/10%

Lignin/FL30 Lignin Flax/1mm/30%

PLA-VF5 PLA Viscose/2 mm/5%

Mechanical behaviorStress-strain curves

0

5

10

15

20

25

30

35

0.00 0.01 0.02 0.03 0.04 0.05

Strain (mm/mm)

Str

ess

(MP

a)

PLA-VF5

PLA-NF10

LIGNIN/FL30

PLA-NF10

0

5

10

15

20

25

30

35

0.00 0.01 0.02 0.03 0.04 0.05

Strain (mm/mm)

Str

ess

(MP

a)

RH =34%

RH=66%

RH (%) Material E, (GPa) εmax, (%) σmax, (MPa) εfail, (%) σfail, (MPa)

34

PLA-NF10 3.05 (0.11) 1.50 (0.05) 29.5 (1.0) 4.1 (0.6) 25.4 (1.5)

PLA-VF5 2.35 (0.06) 1.40 (0.05) 26.8 (0.4) 2.8 (0.6) 21.4 (1.2)

LIGNIN/FL30 6.54 (0.41) 0.40 (0.01) 22.1 (1.2) 0.8 (0.3) 21.1 (1.5)

66

PLA-NF10 2.60 (0.24) 1.41 (0.03) 26.1 (0.2) 2.6 (0.7) 21.8 (1.0)

PLA-VF5 2.30 (0.08) 1.37 (0.03) 25.0 (0.1) 2.9 (0.9) 17.3 (0.8)

LIGNIN/FL30 5.99 (0.16) 0.41 (0.01) 20.3 (0.1) 1.3 (0.4) 18.8 (0.3)

E Damage

Lignin FL30, RH=66%

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

5 10 15 20 25

Stress (MPa)

No

rmal

ized

mo

du

lus

max

0max

E

Ed

Visco-plasticityLignin FL30, RH=34%

0

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000

Time (s)

Str

ain

(%

)

16 MPa

15,5 MPa

15 MPa

14 MPa

12 MPa

Lignin FL30, RH=34% (m=0.6)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 0.2 0.4 0.6 0.8 1 1.2 1.4t/t*

Str

ain

(%

)

16 MPa

15,5 MPa

15 MPa

14 MPa

Visco-elasticityLignin FL30, RH=34%

0

0.2

0.4

0.6

0 2000 4000 6000 8000 10000

Time (s)

Str

ain

(%

)

16 MPa

15.5 MPa

15 MPa

14 MPa10 MPa

6 MPa

SimulationStress-strain curves

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1 1.2

Strain (%)

Str

ess

(MP

a)

experimental curves

modeling curve

elastic response