# Presentation: 489845

## Fire Resistive Materials: Adhesion

- Performance Assessment and Optimization of Fire Resistive Materials
- NIST
- July 14, 2005

## Materials Science-Based Studies 

*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

**Materials Science-Based Studies **
**of Fire Resistive Materials**

- _Environmental_
*Interior*
- Temperature, RH, load
*Exterior*
- Temperature, RH, UV, load

- _Performance Prediction_
- Lab scale testing
- ASTM E119 Test
- Real structures (WTC)

## 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?

## How do we measure adhesion?

- Want a geometry independent property.
- Adhesive Fracture energy,  Gc
- How do we measure Gc?

## Experimental: Schematic and Theory

- Assumptions: Thin, stretching membrane,
- loaded elastically and at a point

*Eh*: Film Tensile Rigidity (modulus, *E*, · thickness, *h*)

## Experimental: Schematic and Theory

**Experimental: Schematic and Theory**

- Load-based equation (*P*)

- displacement-based equation (*w*)

## Experimental Set-Up:

*N* kg

- Load suspended
- from center of
- specimen

## WTC Material

## Experimental: Shaft-Loaded Blister Test for WTC Material

*P*

*h*

- Kai Tak Wan and Yiu-Wing Mai,
*International Journal of Fracture*, 74, 181-197 (1995)

- E: Young’s Modulus

- coating

- Rigid substrate

- Mechanically driven
- shaft attached
- to Instron

- Shaft attached
- To instron

- Stand to hold sample

- Film is on the
-  underside
- Of stand

- Mirror to view
-  film

*w*

## WTC Sample

- P

- Fire Retardant Material (3/4”)

- Primer

- 2 mil steel

- For a bending plate:

- 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:

*E*composite = *v*2 *E*1 +*v*2 *E*2

## Experimental: Shaft-Loaded Blister Test

- 54 % of the samples were entirely debonded when received

**Experimental: Shaft-Loaded Blister Test**

- G = 17.3 +/- 12.8 J/m2

## Fire Retardant Coatings

## Testing of Adhesive Joints:Introduction to Sub-Critical Adhesive Fracture Testingand the Wedge Test

- Wedge Test:

*a* (*t *>* *0)

*a* (*t *= 0)

*v*-G curves will tell you:
-      -rank order of adhesive
-      -failure mechanisms
-      -engineering design parameters

- Log Crack Velocity,

*v*

- (m/s)

- Crack Driving Energy,

- (J/m

- )

*v*

- (m/s)

- (J/m

*v*

- (m/s)

*G*

- (J/m

- 2

- 10-10

## v-G Curve Reveals Mechanisms of Adhesive Failure at the Crack-Tip: Regions I, II, III

*v**

- Region II: diffusion to crack tip

- Region III:
- stress
- controlled

*G*Th

- Region I: stress-dependent
-  chemical reaction

- Crack Driving Energy,

- (J/m

- )

- I

- Crack Driving Energy,

- (J/m

- )

- I

- II

- Log Crack Velocity,

*v*

- (m/s)

- Crack Driving Energy,

*G*

- (J/m

- 2

- )

- I

- III

- Increasing
- Aggressiveness of
- Environment

- Crack Velocity, *v* (m/s)

- Crack Driving Energy, G (J/m2)

- Region II

## Application of Sub-Critical Adhesion Testing: Residual Stress (σr) in Coatings

*σ*r arise due to
- CTE mismatch or processing

***Data from wedge test***

## Constant-Load Subcritical Blister Test

- Measure debond easily with micrometer!

## Fire Resistive Coating

- Cold Rolled Steel
-  Substrate

## Screening Tool for Different Coatings Bonded to Cold Rolled Steel at 100% r.h. & RT

- Epoxy DCB

**Screening Tool for Different Coatings ****Bonded to Cold Rolled Steel at 100% r.h. & RT**

- A SLBT

- B SLBT

- A DCB

- D

- C

## “Soft” vs. “Hard” Coating, low humidity vs. high humidity

**“****Soft****” vs. “****Hard****” Coating,**** low humidity vs. high humidity**

- “Hard” coating performs better than “Soft” coating!
- Coatings perform better at low humidity

**High (95%) RH**

**Low (1%) RH**

## FRC DCB :

- Increase humidity and reduced residual stress

- Tensile Residual Stress is reduced by moisture absorption
-  Reduction in residual stress leads to improved durability

## 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?

## 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?**

## Current FRM Standards:

- ASTM E759 (Effect of Deflection)

**12 Ft**

**Deflect 1/120 or 1 inch.**

- ASTM E760 (Effect of Impact)

**12 Ft**

**Concrete**

**60 lb from 4 ft.**

- ASTM E736 (Cohesive/Adhesive)

## Current Empirical Methods:

**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

## Quantitative Adhesive Test Methods: Beam, JKR and Peel Measure G and E

**JKR Test**

- At equilibrium* *G* =W*

**Beam Test, ex. Wedge Test**

**Blister Test**

- 2*a*

*P*

**Peel Test(s)**

## 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

## Current Methods:

**Fundamental Mechanics**
- DCLB
- Peel Tests
- Blister Tests
- JKR

**Empirical, Practical**
**Pull off**
**Lap Shear**
**Impact**
**Deflection**

## 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

## Prototype:

**Steel**

**FRM**

- 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*

## 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.