1. Slide 1 © CSIR 2006 www.csir.co.za Etienne K.Ngoy, I. Campbell, R. Paskaramoorthy School of Mechanical, Industrial, and Aeronautical Engineering University of the Witwatersrand Modeling and Prediction of the Environmental Degradation of Fiber Reinforced Plastics

2. Slide 2 © CSIR 2006 www.csir.co.za OUTLINE  Introduction  This Analysis Contribution  Conclusion

3. Slide 3 © CSIR 2006 www.csir.co.za INTRODUCTION  What is the environmental degradation?  Motivation  Literature review  Objective

4. Slide 4 © CSIR 2006 www.csir.co.za What is the Environmental Degradation ?

5. Slide 5 © CSIR 2006 www.csir.co.za Environmental 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… propertiescolors, interaction

6. Slide 6 © CSIR 2006 www.csir.co.za 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) 12 3

7. Slide 7 © CSIR 2006 www.csir.co.za Environmental 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… propertiescolors, interaction

8. Slide 8 © CSIR 2006 www.csir.co.za  In practice any change affecting the material properties relative to the initial desirable properties is called degradation

9. Slide 9 © CSIR 2006 www.csir.co.za Motivation

10. Slide 10 © CSIR 2006 www.csir.co.za 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

11. Slide 11 © CSIR 2006 www.csir.co.za Literature Review

12. Slide 12 © CSIR 2006 www.csir.co.za Literature Review  The Complexity of the environmental Degradation process : - Interaction between many physical, chemical and mechanical processes not easy to model.

13. Slide 13 © CSIR 2006 www.csir.co.za  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 Review

14. Slide 14 © CSIR 2006 www.csir.co.za  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 Literature Review

15. Slide 15 © CSIR 2006 www.csir.co.za  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). Literature Review

16. Slide 16 © CSIR 2006 www.csir.co.za Objectives  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

17. Slide 17 © CSIR 2006 www.csir.co.za THE CONTRIBUTION  The theoretical approach.  Environmental degradation models.  Prediction method.  Simulation in laboratory.

18. Slide 18 © CSIR 2006 www.csir.co.za Theoretical Approach

19. Slide 19 © CSIR 2006 www.csir.co.za Basis 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.

20. Slide 20 © CSIR 2006 www.csir.co.za Definitions  L d : index of chemical linkage density degradation.  C f : index of cohesion forces degradation.   env : index of environmental stresses.

21. Slide 21 © CSIR 2006 www.csir.co.za The Analysis of the Environmental Degradation process and Modeling Temperature T Moisture,  m Chemicals C 0 UV Rays, I UV LdCfLdCf   env Stiffness MatrixStress state Effects Environmental causes Degradation EdEd Rheology

22. Slide 22 © CSIR 2006 www.csir.co.za Modeling Process  Rheology = f(T,  m, C 0, I UV,  E d,  env ).

23. Slide 23 © CSIR 2006 www.csir.co.za Environmental Degradation Models

24. Slide 24 © CSIR 2006 www.csir.co.za Environmental Degradation Models  Partial model of uv rays caused degradation.uv rays  General model of stiffness matrix degradation.matrix  General environmental degradation model involving stress corrosion.corrosion.

25. Slide 25 © CSIR 2006 www.csir.co.za Model of ultraviolet rays caused degradation

26. Slide 26 © CSIR 2006 www.csir.co.za Environmental Degradation Models  Partial model of uv rays caused degradation.uv rays  General model of stiffness matrix degradation.matrix  General environmental degradation model involving stress corrosion.corrosion.

27. Slide 27 © CSIR 2006 www.csir.co.za Environmental Degradation of the Material Stiffness. General Model  Where t = time,  and  0 are constants depending on the material and environmental conditions.

28. Slide 28 © CSIR 2006 www.csir.co.za Environmental Degradation Models  Partial model of uv rays caused degradation.uv rays  General model of stiffness matrix degradation.matrix  General environmental degradation model involving stress corrosion.corrosion.

29. Slide 29 © CSIR 2006 www.csir.co.za Environmental Degradation. The Stress Corrosion General Model.  Where ε is the strain and t’ = time of strain application.  env (t ) is the degradation function measuring environmental degradation history.

30. Slide 30 © CSIR 2006 www.csir.co.za Prediction Method in three stepladder

31. Slide 31 © CSIR 2006 www.csir.co.za Prediction 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.

32. Slide 32 © CSIR 2006 www.csir.co.za Simulation in Laboratory

33. Slide 33 © CSIR 2006 www.csir.co.za Simulation in Laboratory  Chemical degradation of the Stiffness Matrix The model shows good accuracy but the precisionaccuracyprecision needs improvement due to instrumental methods used  Stress CorrosionCorrosion

34. Slide 34 © CSIR 2006 www.csir.co.za Correlation Between the Model and Experimental Values R 2 =0.973

35. Slide 35 © CSIR 2006 www.csir.co.za Simulation in Laboratory  Chemical degradation of the Stiffness Matrix The model shows good accuracy but the precisionaccuracyprecision needs improvement due to instrumental methods used  Stress CorrosionCorrosion

36. Slide 36 © CSIR 2006 www.csir.co.za Relaxation under stresses only and under stress corrosion

37. Slide 37 © CSIR 2006 www.csir.co.za Environmental Degradation Factor on the Stiffness Matrix.

38. Slide 38 © CSIR 2006 www.csir.co.za Simulation in Laboratory  Chemical degradation of the Stiffness Matrix The model shows good accuracy but the precisionaccuracyprecision needs improvement due to instrumental methods used  Stress CorrosionCorrosion

39. Slide 39 © CSIR 2006 www.csir.co.za CONCLUSION  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.

40. Slide 40 © CSIR 2006 www.csir.co.za Acknowledgement We wish to acknowledge the support from:  Denel  DST/NRF Centre of Excellence in Strong Materials  ESKOM  THRIP  CSIR

41. Slide 41 © CSIR 2006 www.csir.co.za THANK YOU