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Fire Resistive Materials: Adhesion

Fire Resistive Materials: Adhesion. Performance Assessment and Optimization of Fire Resistive Materials NIST July 14, 2005. Microstructure Experimental 3-D Tomography 2-D optical, SEM Confocal microscopy Modeling 3-D Reconstruction Parameters Porosity Pore Sizes Contact Areas.

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Fire Resistive Materials: Adhesion

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  1. Fire Resistive Materials: Adhesion Performance Assessment and Optimization of Fire Resistive Materials NIST July 14, 2005

  2. Microstructure Experimental 3-D Tomography 2-D optical, SEM Confocal microscopy Modeling 3-D Reconstruction Parameters Porosity Pore Sizes Contact Areas Properties (all as a function of T) Thermal Heat Capacity Conductivity Density Heats of Reaction Adhesion Pull-off strength Peel strength Adhesion energy Fracture toughness Equipment TGA/DSC/STA Slug calorimeter Dilatometer Blister apparatus Environmental Interior Temperature, RH, load Exterior Temperature, RH, UV, load Performance Prediction Lab scale testing ASTM E119 Test Real structures (WTC) Materials Science-Based Studies of Fire Resistive Materials

  3. Adhesive Performance of FRMs Why should we care? • Opportunity: Recent events have demonstrated the importance of in-service adhesive performance in the ability of FRM to protect steel. • What can we learn about existing adhesive properties of FRM?

  4. What is Gc energy to create a unit of surface area units: J/m2 How do we measure adhesion? • Want a geometry independent property. • Adhesive Fracture energy, Gc How do we measure Gc?

  5. P w 2a Experimental: Schematic and Theory Assumptions: Thin, stretching membrane, loaded elastically and at a point Eh: Film Tensile Rigidity (modulus, E, · thickness, h)

  6. P w 2a Experimental: Schematic and Theory Load-based equation (P) displacement-based equation (w)

  7. Experimental Set-Up: Load suspended from center of specimen N kg

  8. WTC Material

  9. Experimental: Shaft-Loaded Blister Test for WTC Material Mechanically driven shaft attached to Instron Shaft attached To instron P Rigid substrate Film is on the underside Of stand w h coating Mirror to view film Stand to hold sample Kai Tak Wan and Yiu-Wing Mai, International Journal of Fracture, 74, 181-197 (1995) E: Young’s Modulus

  10. WTC Sample P Fire Retardant Material (3/4”) Primer The mechanical properties of the film are estimated from: Steel E (Pa) = 2 * 10^11 h (m) = 0.05 *10^-3 Adhesion Promotor E (Pa) = 3 * 10^9 h (m) = 0.20 *10^-3 and: 2 mil steel For a bending plate: Ecomposite = v2E1 +v2E2

  11. Experimental: Shaft-Loaded Blister Test 54 % of the samples were entirely debonded when received G = 17.3 +/- 12.8 J/m2

  12. Fire Retardant Coatings

  13. Testing of Adhesive Joints:Introduction to Sub-Critical Adhesive Fracture Testingand the Wedge Test (m/s) (m/s) (m/s) Wedge Test: v v v Log Crack Velocity, 10-10 a (t = 0) Crack Driving Energy, G (J/m (J/m (J/m ) 2 v-G curves will tell you: -rank order of adhesive -failure mechanisms -engineering design parameters a (t >0)

  14. v-G Curve Reveals Mechanisms of Adhesive Failure at the Crack-Tip: Regions I, II, III Increasing Aggressiveness of Environment Region III: stress controlled (m/s) III v Crack Velocity, v (m/s) II v* Region II: diffusion to crack tip Log Crack Velocity, Region I: stress-dependent chemical reaction I I I Crack Driving Energy, G (J/m2) GTh Crack Driving Energy, Crack Driving Energy, Crack Driving Energy, G (J/m (J/m (J/m ) ) ) 2 Region II

  15. (m/s) (m/s) (m/s) v v v Log Crack Velocity, GTh Crack Driving Energy, G (J/m (J/m (J/m ) 2 Application of Sub-Critical Adhesion Testing: Residual Stress (σr) in Coatings σr arise due to CTE mismatch or processing Data from wedge test

  16. Constant-Load Subcritical Blister Test Measure debond easily with micrometer!

  17. Fire Resistive Coating Cold Rolled Steel Substrate

  18. Screening Tool for Different Coatings Bonded to Cold Rolled Steel at 100% r.h. & RT A DCB A SLBT B SLBT Epoxy DCB C D

  19. “Soft” vs. “Hard” Coating, low humidity vs. high humidity High (95%) RH Low (1%) RH “Hard” coating performs better than “Soft” coating! Coatings perform better at low humidity

  20. FRC DCB : Tensile Residual Stress is reduced by moisture absorption Reduction in residual stress leads to improved durability Increase humidity and reduced residual stress

  21. FRM’s. • Modern Adhesion testing methods can give LRFD parameters. • These parameters are environmentally sensitive. • (increasing RH can either increase or decrease performance.) What about Temp and UV? Rate effects? • What about the existing test methods? • Can we modify existing test methods?

  22. Adhesion Tests: Ideal • Ideal Adhesion Test: • Simple, cheap, fast, easy to perform • Grounded in fundamental mechanics and material science- LFRD guidance • Includes modes- opening, in-plane shear, torsion, mixed, • Could include environmental and rate dependence. How far are the test from idea?

  23. Current FRM Standards: • ASTM E759 (Effect of Deflection) Deflect 1/120 or 1 inch. • ASTM E736 (Cohesive/Adhesive) 12 Ft • ASTM E760 (Effect of Impact) 60 lb from 4 ft. Concrete 12 Ft

  24. Advantages: Quick, easy, Cheap Practical Pass/Fail guidance Disadvantages: Highly dependent on sample preparation Specific to situation tested (geometry, speed, etc) Little or no design guidance Current Empirical Methods:

  25. w P  a P P Quantitative Adhesive Test Methods: Beam, JKR and Peel Measure G and E JKR Test Beam Test, ex. Wedge Test At equilibriumG =W P Peel Test(s) Blister Test 2a

  26. Fundamental Mechanics • Advantages: • Link to fundamental mechanics and material science properties G • Results are independent of geometry/sample preparation. • Gives LFRD guidance • Disadvantages: • Expensive • Require equipment • Time consuming

  27. Fundamental Mechanics DCLB Peel Tests Blister Tests JKR Empirical, Practical Pull off Lap Shear Impact Deflection w P  a P P Current Methods:

  28. General Approach: • Simple Test, • Fast, easy, inexpensive to perform • Calibrate. • Can be calibrated against fundamental mechanics and material science • Rate, strain and environmental dependence • Round robin

  29. Prototype: Steel • Bending, twisting, stretching will produce known strains at the interface (different modes) • Stress can be calculated from first principles and calibrated with known adhesion geometries. • Visually evaluated, or calibrated. • Can give both rate and environmental performance. • Never have to touch the material FRM

  30. Summary • Current methods for evaluating the adhesion performance are pass/fail. • Modern adhesion testing methods present the ability to give design guidance for FRMs. • It appears possible to build a close to “ideal” adhesion test for FRMs. • Simple, cheap, fast, based in mechanics, calibrated by NIST.

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