Moisture Simulation Model for Polymer Composites

OBJECTIVES

• Develop 3D finite element model for moisture absorption of fiber-reinforced polymer composites.

• Perform case studies for glass fiber-reinforced polymer composites over long time periods.

• Validate the simulation results with the analytical and experimental results.

FINITE ELEMENT MODELING & SIMULATION

FINITE ELEMENT RESULTS

CONCLUSIONS AND FUTURE WORK• Simulation results match well with 1D analytical results,

which validates the finite element model.

• Results are presented for both 2D and 3D models.

• Study polymer composites moisture evolution under complex environments.

• Evaluate the effects of temperature and humidity on polymer composites moisture behavior subjected to long time exposure.

ACKNOWLEDGEMENTS

Student(s): Zhen Huo Mechanical & Aerospace Engineering Department

Faculty Advisor(s): Dr. K. Chandrashekhara, Mech. & Aero. Engineering Dept. Dr. Thomas Schuman, Chemistry Dept.

This project is funded by Bell Helicopter Inc. and Intelligent Systems Center.

GOVERNING EQUATIONS

X=0 X=1.7703 mm

B.C.=SATURATION

Face B.C. is

applied

Diffusivity (D11) 4.44158E-5 mm2/h

Saturation concentration 4170 ppm

Half thickness 1.7703 mm

ABAQUS 2D half modeling ABAQUS 3D half modeling

where c is moisture concentration, t is time span, n is outward normal to S. J is concentration flux and is given by:

where s is solubility, ∅ is the normalized concentration, which equals c/s, ks is “soret effect” factor, providing temperature gradient driven diffusion; kp is the pressure stress factor,

providing pressure gradient driven diffusion; θz is absolute zero temperature.

ABAQUS 3D half modeling moisture content after 168 hours

D11= 4.44158E-5 mm2/h; D22= D11 / 2; D33 = D11 / 4

ABAQUS 2D half modeling moisture content after 168 hours

INTRODUCTION

• Composite materials degrade due to environmental exposure such as moisture diffusion, thermal spike, UV, and thermal oxidation.

• Moisture absorption of composites decreases the strength and stiffness, degrade the fiber/matrix interface strength, swell and plasticize the resin lowering its glass transition temperature.

• The relative degree of degradation is related to chemistry of the reinforcement and matrix as well as the exposure time.

• The determination of moisture concentration profile through the thickness of the composite structure requires the knowledge of 3D moisture diffusion coefficients.

FINITE ELEMENT RESULTS (CONT. )

Convergence study with half modeling after 168 soaking

hours

Aspect ratio effects study with half modeling using

50 nodes mesh

VARIANCE STUDY

2D half modeling moisture content results comparison

after 168 hours

3D half modeling moisture content results comparison

after 168 hours

VALIDATION

0 0.02 0.04 0.06 0.080

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

X position to the midpoint of whole length (inch)

Mo

istu

re C

on

ten

t (%

)

10 nodes mesh30 nodes mesh50 nodes mesh

0 0.02 0.04 0.06 0.080

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

X position to the midpoint of whole length (inch)

Mo

istu

re C

on

ten

t (%

)

ASPECT RATIO 2.8ASPECT RATIO 10ASPECT RATIO 20

0 0.02 0.04 0.06 0.080

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

X position to the midpoint of whole length (inch)

Mo

istu

re C

on

ten

t (%

)

1D analytical solution2D finite element half model

0 0.01 0.02 0.03 0.04 0.05 0.06 0.070

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

X position to the midpoint of whole length (inch)

Mo

istu

re C

on

ten

t (%

)

1D analytical solution3D finite element half model