Slide 1 © CSIR 2006 Etienne K.Ngoy, I. Campbell, R. Paskaramoorthy School of Mechanical,...

© CSIR 2006 www.csir.co.za

Etienne K.Ngoy, I. Campbell, R. PaskaramoorthySchool of Mechanical, Industrial, and Aeronautical Engineering

University of the Witwatersrand

Modeling and Prediction of the Modeling and Prediction of the Environmental Degradation of Environmental Degradation of

Fiber Reinforced PlasticsFiber Reinforced Plastics


OUTLINEOUTLINE

IntroductionThis Analysis ContributionConclusion


INTRODUCTIONINTRODUCTION

What is the environmental degradation?MotivationLiterature reviewObjective


What is the Environmental Degradation ?What is the Environmental Degradation ?


Environmental DegradationEnvironmental Degradation

Wide spread use of FRP materials

Large variety of service environments

Temperature and humidity, energetic

radiations, chemicals

Change of Material properties

Mechanical properties, colors,

brittleness, cracks…

interaction


Discoloration and flaking of a pipe surface by uv (1), Inner of a pipe attacked by chemicals. The glass surface tissue hanging from the walls where the resin has been removed by the chemical (2), Advanced corrosion on the surface of a pipe by UV and humidity. The structural laminate becomes exposed, which looks like dry glass, with no resin bonding it together (3) (SASOL)

1 2

3


Environmental DegradationEnvironmental Degradation

Wide spread use of FRP materials

Large variety of service environments

Temperature and humidity, energetic

radiations, chemicals

Change of Material properties

Mechanical properties, colors,

brittleness, cracks…

interaction


In practice any change affecting the material properties relative to the initial desirable properties is called degradation


MotivationMotivation


Rational utilization

Design optimization

Economic assessment

Safe utilization

Equipment maintenance

Good understanding of the environmental degradation effects.

The availability of reliable method for quantification and prediction of environmental effects.

Modeling

Requests

Motivation


Literature ReviewLiterature Review


Literature ReviewLiterature Review

The Complexity of the environmental Degradation process:

- Interaction between many physical, chemical and mechanical processes not easy to model.


No general or accurate predictive model has been available so far:

- modeling efforts focus on the characterization of effects and mechanism. - Only partial models based on particular process and environment - Accelerated prediction method based on Arrhenius law

Literature ReviewLiterature ReviewLiterature ReviewLiterature Review


Exposure in the real service environment - Standard lifetimes are determined based on statistical data resulting from long term exposure in real service environment. - Implies that test lasts many years and must be conducted for each particular combination of environment and material



Extended utilization slowed down in many fields.

Catastrophic failure reported in the industry. “However there have been a small but significant number of

international failures witch have caused concerns. Cases of tanks containing demineralized water in particular at 700C failing catastrophically are reported.” (SASOL 2000).



ObjectivesObjectives

Provide a comprehensive model of the environmental degradation of fiber reinforced plastics including the chemical degradation, the ultraviolet rays attack, the temperature and humidity effects, and the stress corrosion.

Provide a short term test method for environmental degradation of mechanical strength of FRP composites


THE CONTRIBUTIONTHE CONTRIBUTION

The theoretical approach.Environmental degradation models.Prediction method.Simulation in laboratory.


Theoretical ApproachTheoretical Approach


Basis of the Theoretical ApproachBasis of the Theoretical Approach

All FRP degradation results in one of the following effects :Chemical: Chemical links density modification caused

by either a chemical attack, a thermal attack or a ultra violet rays attack.

Physical: cohesion forces deterioration or plasticization caused by either moisture absorption or by temperature variation.

Mechanical: Stress state modification.


DefinitionsDefinitions

Ld: index of chemical linkage density degradation.

Cf: index of cohesion forces degradation.env: index of environmental stresses.


The Analysis of the Environmental The Analysis of the Environmental Degradation process and ModelingDegradation process and Modeling

Temperature T

Moisture, m

Chemicals C0

UV Rays, IUV

Ld

Cf

env

Stiffness Matrix Stress state

EffectsEnvironmental

causes

Degradation

Ed

Rheology


Modeling ProcessModeling Process

Rheology = f(T, m, C0, IUV, Ed, env).


Environmental Degradation ModelsEnvironmental Degradation Models



Partial model of uv rays caused degradation.General model of stiffness matrix degradation.General environmental degradation model

involving stress corrosion.


Model of ultraviolet rays caused Model of ultraviolet rays caused degradationdegradation

nabs

UV

d kIdt

dL


Environmental Degradation of Environmental Degradation of the Material Stiffness.the Material Stiffness.General Model General Model

Where t = time, and 0 are constants depending on the material and environmental conditions.

tTCd edt

dE00


Environmental Degradation. The Environmental Degradation. The Stress Corrosion General Stress Corrosion General Model. Model.

Where ε is the strain and t’ = time of strain application.env (t) is the degradation function measuring

environmental degradation history.

'

'

''' dtdt

tdttCttenvt

t


Prediction Method in three stepladder Prediction Method in three stepladder


Prediction MethodPrediction Method

Exposure at constant environment.Monitoring the chemical structures change or

Measurement of the stress relaxation time or creep rate.

Determination of the degradation parameters based on the mathematical model.


Simulation in LaboratorySimulation in Laboratory



Chemical degradation of the Stiffness Matrix The model shows good accuracy but the precision needs improvement due to instrumental methods used

Stress Corrosion


Correlation Between the Model and Correlation Between the Model and Experimental ValuesExperimental Values

y = 0.0457x - 1.9291

R2 = 0.9734

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000 2500

Ed (Raman Intensity)

Te

nsil

e S

tre

ng

th (

MP

a)

R2=0.973




Stress Corrosion


Relaxation under stresses only and under Relaxation under stresses only and under stress corrosionstress corrosion

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 1000 2000 3000 4000 5000 6000

Relaxation time (secondes)

Stre

ss in

dex

(vol

ts)

relaxation under chemical degradation and mechanical stress

relaxation under mechanical stress only


Environmental Degradation Factor on the Environmental Degradation Factor on the Stiffness Matrix.Stiffness Matrix.

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 1000 2000 3000 4000 5000 6000

Degradation time (secondes)

Env

ironm

enta

l fun

ctio

n

'

'

''' dtdt

tdttCttenvt

t




Stress Corrosion


CONCLUSIONCONCLUSION

A theoretical analysis of the environmental degradation process based on the transformation of the material rheology has been suggested.

Two comprehensive mathematical models have been derived for the chemical degradation and for the stress corrosion.

The simulation of these models in laboratory showed good correlation with experimental data.


AcknowledgementAcknowledgement

We wish to acknowledge the support from: Denel DST/NRF Centre of Excellence in Strong Materials ESKOM THRIP CSIR


THANK YOUTHANK YOU

Slide 1 © CSIR 2006 Etienne K.Ngoy, I. Campbell, R. Paskaramoorthy School of Mechanical,...

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