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Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase

Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase. K. N. E. Verghese. Advisor: Dr. J. J. Lesko. Materials Engineering and Science Program Virginia Tech. January 19th 1999. Outline for Presentation. Introduction: What is a Sizing? Materials Used

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Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase

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  1. Durability of Polymer Matrix Compositesfor Infrastructure: The Role of the Interphase K. N. E. Verghese Advisor: Dr. J. J. Lesko Materials Engineering and Science Program Virginia Tech January 19th 1999

  2. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Acknowledgements

  3. What is a Sizing? A thin film applied to the surface of the carbon before impregnation with the matrix material. Phenoxy Particulate Sized K-90 PVP Sized

  4. Why do Sizings Affect Properties? • Processability- • Sizings protect the brittle carbon fiber • Sizings affect the wettability of the carbon fiber • The Interphase (0-1 m)-Causes changes in damage initiation and propagation. • Interdiffusion results in a concentration profile or a mechanical property profile. • Changes in stochiometry of the matrix reactants.

  5. Why do Sizings Affect Properties? • Matrix Plasticization (0-1 m)- An Interphase with no gradients. • Results from a sizing that has diffused to such an extent that no gradients exist. • Fiber/Matrix Adhesion (0-100 nm)- Causes changes in interfacial properties like shear strength. • Results from a sizing that is physically or chemically bonded to the fiber while interacting strongly with the matrix.

  6. Influence of the Interface in Fiber Reinforced Composites Interfacial Shear Strength (ISS) (ksi/MPa) Interfacial Failure Mechanism Fiber Tensile Strength (ksi/MPa) Transverse Tensile Strength (MPa) Fiber Tensile Modulus (ksi/GPa) Material AU-4 34K/234.4 520/3585 5.4/37.2 18 Friction AS-4 34K/234.4 520/3585 9.9/68.3 34.2 Interfacial AS-4C 34K/234.4 520/3585 11.8/81.4 41.2 Matrix Epon 828/ m-PDA Matrix 525/3.6 13/89.6 ----- ----- ----- Ref: M. S. Makhukar and L. T. Drzal, Proc. Fifth Tech. Conf. of the American Society for Composites, 1990, 849 - 858.

  7. 0° Tensile/ Compression Modulus (GPa) 0° Tensile/ Compression Strength (MPa) Shear Modulus/ Strength (±45) (GPa/MPa) 90° Tensile Modulus/ Strength (GPa/MPa) Interfacial Failure Mechanism Material AU-4 130/130 1403/679 9.1/37.2 8.9/18.0 Friction AS-4 138/126 1890/911 6.2/72.2 9.7/34.2 Interfacial AS-4C 150/153 2044/1174 6.0/97.5 10.3/41.2 Matrix Influence of the Interface in Fiber Reinforced Composites Continued…. Ref: M. S. Makhukar and L. T. Drzal, Proc. Fifth Tech. Conf. of the American Society for Composites, 1990, 849 - 858. M. S. Makhukar and L. T. Drzal, JCM Vol. 25 1991, pp.932-957 M. S. Makhukar and L. T. Drzal, JCM Vol. 25 1991, pp.958-991 M. S. Makhukar and L. T. Drzal, JCM Vol. 26 1992, pp.936-968

  8. Spool Load Cell Sizing Bath Motorized Nip Rollers Interphase and Interface Formation The sizing life cycle must be tracked to fundamentally understand and predict interphase and interface formation. Fiber Preform

  9. Structure - Property Effects of Cross-link Density Tear strength, fatigue life toughness Static Modulus Hardness Tensile Strength Property Hysteresis. Permanent Set, friction coefficient Cross-link density

  10. Interphase Micromechanics Broken Fiber Tensile Load

  11. The Approach

  12. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  13. C H O C H C H O 3 O H O H 3 3 ( ) O C H C H C H O C C C H C C H C C O C H C H C H O 2 2 2 n 2 2 2 C H Vinyl Ester Mn ­ 700 - 1200 g/mol 3 Reactive groups only at chain ends. C H C H 2 Vinyl ester Resins 140-150°C styrene benzoyl peroxide The distance between crosslink junctions is one factor controlling toughness. Higher Mc leads to tougher materials.

  14. 20% styrene 28% styrene 35% styrene 0.87  0.12 730g/mol “irreg” 0.72  0.11 0.63  0.11 840g/mol “irreg” 0.94  0.03 0.87  0.09 0.76  0.05 0.97  0.05 840g/mol “reg” 0.92  0.03 0.79  0.09 1.03  0.07 0.96  0.12 0.82  0.07 1050g/mol “irreg” 1120g/mol “reg” 1.51  0.17 1.40  0.12 1.24  0.1 1200g/mol “reg” 2.02  0.07 1.94  0.02 1.52  0.06 Fracture Toughness for Resin Fracture toughness ---K1c (MPa-m.5) ASTM D5045-91 Molecular weights are from proton NMR. Courtesy: Ellen Burts and Dr. H. Li

  15. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  16. K-17 Mn = 14k Tg 107C K-90 Mn = 1.2M Tg 170C N ( ) C H C H x 2 O H C H O C H 3 3 ( ) O H C O C H C H C H O C H O n 2 2 C H C H 3 3 Sizing Materials • Poly(vinylpyrrolidone) (Brittle Thermoplastic) tensile strength for K90 = 62 MPa strain to failure = 0.9% Tg = 180°C (DSC) • Polyhydroxyether • (Tough Thermoplastic ?) Mn = 19k Tg 97C tensile strength = 55 MPa strain to failure = 40-100% Tg = 97°C (DSC)

  17. P(t) R= -1 and 10 Hz fatigue limit for Phenoxy fatigue limit for PVP Unsized Fully Reversed Fatigue Test Results of Cross-ply Laminates 50 Run-out 40 Applied Stress (ksi) 30 Phenoxy Sizing 20 PVP-k17 Sizing fatigue limit for Unsized 10 100 1,000 10,000 100,000 10,000,00 10,000,000 Number of Cycles

  18. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  19. CH CH 3 3 CH CH 2 2 CH CH 3 3 CH CH 3 3 CH CH 2 2 CH CH 3 3 CH CH 3 3 CH CH CH CH 2 2 2 2 CH CH (CH ) 3 3 2 2 Poly(hydroxyether) Sizing Materials Unmodified Poly(hydroxyether) OH HO C O CH O C OH x Modified Poly(hydroxyether) OH HO C O CH O C OH COOH x Poly(hydroxyether ethanolamine) OH OH HO C O CH N CH O C OH OH x

  20. Bilayer Resin Matrix Interphase Sizing Material Preparation of sizing/matrix bilayers Fiber in Matrix Fiber Cross section cut and microtomed (room temp. or cryo)

  21. Tapping mode (phase) images of bilayer cross-sections a) Carboxy modified poly(hydroxyether) sizing and Vinyl ester b) Poly(hydroxyether ethanolamine) sizing and Vinyl ester

  22. Nano-indentation Courtesy: Dr. M. A. F. Robertson

  23. Carboxy functional Polyhydroxyether Indentation profile across a carboxy functional poly(hydroxyether)/vinyl ester cross section 140 Plastic Deformation Elastic Deformation 130 Carboxy functional Polyhydroxyether 120 110 Vinyl Ester Depth (nm) 100 Vinyl Ester 10 0 -30 -20 -10 0 10 20 30 m) m Distance Relative to Interface (

  24. Indentation profile across a poly(hydroxyether ethanolamine)/vinyl ester cross section 140 Plastic Deformation Elastic Deformation 130 Polyhydroxyether ethanolamine 120 110 Vinyl Ester Depth (nm) 100 10 Vinyl Ester Polyhydroxyether ethanolamine 0 -30 -20 -10 0 10 20 30 m Distance Relative to Interface ( m)

  25. F F/2 F/2 Grips Network drop Fiber Interfacial Shear StrengthsMicrodebond Test Materials Fiber: AS-4 Matrix: 700 g/mol vinyl ester with 30 wt. % styrene cured with 1.1 wt. % Benzoyl peroxide, 130°C/20 min.,N2 IFSS (MPa) Sizing None 28±8 Poly(hydroxyether) 43.6±8.7 Carboxylic acid modified poly(hydroxyether) [MPE] 52.6±4.7 Poly(hydroxyether ethanolamine) [PHEA] 22 Poly(vinylpyrrolidone) [PVP] 33.8±6.5 Phosphine oxide modified polyester urethane 56.7±7.5 Courtesy: I. C. Kim and Dr. T. H. Yoon, Korea

  26. Run Out Unsized R=-1 Fatigue Response at 10Hz on Notched Specimens Poly(hydroxyether ethanolamine) Sized Composite Compression Strength: -48.6 ksi Modified poly(hydroxyether) Sized Composite Compression Strength: -54.3 ksi 50 Modified Poly(hydroxyether) Sizing 40 Poly(hydroxyether ethanolamine Sizing Run Out for modified poly(hydroxyether) 30 Applied Stress (ksi) Run Out for poly(hydroxyether ethanolamine) Run Out for Unsized 20 10 100 1000 10000 100000 1000000 10000000 Number of Cycles

  27. Dynamic Modulus Curves for Modified Polyhydroxyether Sized Composites

  28. 45 Experimental Data 40 34 ksi:17209 cycles S-N Curve Fit Residual Strength Stress Levels 35 Applied Stress (ksi) 37 ksi:2998 cycles 30 31 ksi:143767 cycles y = 54300*(a+b*(log10(x)^c)) a = 0.02256 25 b = -0.0215 c = 0.0132 20 100 1000 10000 100000 1000000 Number of Cycles Residual Strength Test Levels for MPE Sized Composites

  29. Residual Strength Curves on MPE Sized Composites 1.2 @ 37 ksi or 0.67 1 @ 34 ksi or 0.6 @ 31 ksi or 0.56 0.8 Normalized Stress 0.6 3 specimens for 2 specimens for 2 specimens for 0.4 each level each level each level 0.2 0 100 1000 10000 100000 1000000 Number of Cycles

  30. The MRLife Philosphy

  31. Modified Polyhydroxyether Sizing Data Prediction for Modified Polyhydroxyether (h = 2) Polyhydroxyether ethanolamine (PHEA) Sizing Data Prediction for PHEA (h = 1.1) Preliminary Fatigue Performance Predictions (MRLife) 50 Run Out 40 Applied Stress (ksi) 30 20 h = Coefficient related to the bonding condition of the fiber in Xu and Reifsnider’s micro-mechanical compression model. 1< h<2 for the debonded and well bonded conditions respectively 10 100 1000 10000 100000 1000000 10000000 Cycles to Failure (Log N)

  32. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  33. LMWVE/Phenoxy Sizing LMWVE/Unsized LMWVE/G' HMWVinylester/Phenoxy LMWVE/Polyurethane Recent Work 50 Run Out 40 Applied Stress (ksi) 30 20 LMWVE stands for low molecular weight vinyl ester HMWVE stands for high molecular weight vinyl ester 10 100 1000 10000 100000 1000000 10000000 Number of Cycles (log cycles)

  34. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  35. Sized Carbon Fiber Creels Pultrusion Die (T=200 C) Residence Time is <1 min. Cured Composite Resin Dip Bath Residence Time is 10 minutes Schematic of Pultrusion Line

  36. Tensile Strength of Pultruded Composites

  37. Longitudinal Flexure Strength Strength

  38. Short Beam Shear Strength of Pultruded

  39. Composite Material: Low spread AS4 fiber sized with Modified polyhydroxyether in Derakane 411-350 resin 340 Experimental Data Model Prediction 320 300 280 260 240 220 200 Tensile Strength Comparison between Model and Experimental Data

  40. Outline for Presentation • Introduction: What is a Sizing? • Materials Used • Results obtained thus far • Mechanical properties of laminates • study #1 • study #2 • study #3 • pultruded composites • Thermo-mechanical experiments • dynamic mechanical analysis of resin and composites • Environmental Durability • hygrothermal aging of resin and composites • Proposed work for the future • Acknowledgements

  41. Cooperativity Model • Intermolecular interactions and constraints • Segments move in a cooperative motion • Degree of cooperativity - temperature dependence oflog(aT) z = 6 log(aT) Glassy State Tg Tg/T “Relaxation Phenomena in Polymers” Shiro Matsuoka

  42. Concept of Cooperativity * 20 15 increasing n 10 • equilibrium • bulk polymers T 5 log a 0 -5 -10 -0.05 0.00 0.05 0.10 0.15 (T-T )/T g g * D. J. Plazek and K. L. Ngai, Macromolecules, 24, 1222 (1991).

  43. Vinyl Ester Resins Vinyl Ester Styrene Calculated Measured T T DSC g g D C T p Oligomer Weight Content M M Onset End g c c (J/g°C) (g/mol) (%) (g/mol) (g/mol) (DSC,°C) (DSC,°C) (°C) 700 20 292 300 136 164 152 0.269 700 35 359 569 124 145 136 0.244 1200 20 417 812 115 133 125 0.322 1200 35 513 969 110 126 118 0.298

  44. Dynamic Loss Modulus Vinyl Ester (Mn = 1200g/mol, 20% Styrene)

  45. 4 2 0 -2 -4 Glassy State -6 0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 Fragility (cooperativity) plot for vinyl ester resins 20% 700g/mol William-Landel- Ferry equation 35% 700g/mol 20% 1200g/mol 35% 1200g/mol ) T log(a n = d(logaT)/d(Tg/T)|Tg fragility (cooperativity) Tg / T

  46. Cooperativity versus molecular weight between crosslinks 94 1200, 20% 92 700, 20% 90 88 86 84 n, fragility 82 80 78 1200, 35% 76 700, 35% 74 72 0.002 0.003 0.004 1/Mc (mol/gram)

  47. Fracture toughness versus normalized domain size

  48. Master Curve - Matrix Tg = 137°C log E ’ (MPa) log waT log w 107°C - 164°C, 3 °C steps, second heat

  49. Master Curve - Composite Tg = 123°C log E ’ (MPa) log waT log w 93°C - 219°C, 3 °C steps, Phenoxy sizing, second heat

  50. DMA - damping of composites G’ PVP Phenoxy 1 Hz, second heat

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