Slide 1 © CSIR 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

Slide 2 © CSIR OUTLINE  Introduction  This Analysis Contribution  Conclusion

Slide 3 © CSIR INTRODUCTION  What is the environmental degradation?  Motivation  Literature review  Objective

Slide 4 © CSIR What is the Environmental Degradation ?

Slide 5 © CSIR 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

Slide 6 © CSIR 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

Slide 7 © CSIR 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

Slide 8 © CSIR  In practice any change affecting the material properties relative to the initial desirable properties is called degradation

Slide 9 © CSIR Motivation

Slide 10 © CSIR 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

Slide 11 © CSIR Literature Review

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

Slide 13 © CSIR  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

Slide 14 © CSIR  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

Slide 15 © CSIR  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

Slide 16 © CSIR 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

Slide 17 © CSIR THE CONTRIBUTION  The theoretical approach.  Environmental degradation models.  Prediction method.  Simulation in laboratory.

Slide 18 © CSIR Theoretical Approach

Slide 19 © CSIR 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.

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

Slide 21 © CSIR 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

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

Slide 23 © CSIR Environmental Degradation Models

Slide 24 © CSIR 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.

Slide 25 © CSIR Model of ultraviolet rays caused degradation

Slide 26 © CSIR 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.

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

Slide 28 © CSIR 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.

Slide 29 © CSIR 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.

Slide 30 © CSIR Prediction Method in three stepladder

Slide 31 © CSIR 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.

Slide 32 © CSIR Simulation in Laboratory

Slide 33 © CSIR 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

Slide 34 © CSIR Correlation Between the Model and Experimental Values R 2 =0.973

Slide 35 © CSIR 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

Slide 36 © CSIR Relaxation under stresses only and under stress corrosion

Slide 37 © CSIR Environmental Degradation Factor on the Stiffness Matrix.

Slide 38 © CSIR 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

Slide 39 © CSIR 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.

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

Slide 41 © CSIR THANK YOU