Laminates to Investigate Crack Behavior at Elastic/Viscous Interfaces Presented by: Sean Landwehr Advisor: Prof. Rod Trice
Feb 05, 2016
Processing of Alumina/Glass Laminates to Investigate Crack Behavior at Elastic/Viscous Interfaces
Presented by: Sean LandwehrAdvisor: Prof. Rod Trice
Background on Crack Behavior
No Crack deflection
Crack Deflection
A crack can either deflect at an interface or go straight through it.
Crack
What is Known About Crack Deflection
He and Hutchinson looked at elastic material interfacesFound crack deflection regime to be dependent on ratio of fracture energies and elastic mismatch.
He, Evans, & Hutchinson, Int. J. Solid Structures, 31 [24] 3443-3455 (1994)
2
2
1
Deviation From He and Hutchinson
Trice found He and Hutchinson was not applicable to a BN/Si3N4 system.
The 1000°C sample showed much crack deflection.
Trice R.W. et al., J. Amer. Cer. Soc., 89[9] 2502-8 (1999)
Link to Glassy Phase
Well below Tg, crack goes straight through the glassy phaseAround Tg, the crack is blunted by the glassy phase
Glassy Phase
BN
Crack
Primary Objective
Investigate crack behavior at elastic/viscous interface Under what conditions is crack
deflection observed
Possible uses: Energy absorption material Maximize energy absorption by tailoring
viscosity to temperature and strain rate
Looking at Elastic/Viscous Interface
Simple structure is neededElastic material needs to be brittle and linear elasticElastic material needs to have constant material properties through the viscous temperature range of glassViscous material must have a wide range of viscositiesProperties of the viscous material need to be well characterized.
Choosing the Alumina/Glass Laminate
Laminate Simple structure
Alumina Well characterized Brittle Linear elastic Good mechanical stability Easy to tape cast
Alkali zinc phosphate (AZP) glass
Well characterized Wide range of viscosities Low glass transformation
range (starts ~400°C)
Al2O3
Al2O3
Al2O3
Al2O3
AZP Glass
AZP Glass
AZP Glass
General Approach to Making the Laminate
Tape cast the alumina using an aqueous based slurryBurnout binder and fully densify aluminaSpray glass, and heat treatLaminate
Tape Casting Slurry
Mill together: 17.4 wt% DI Water 0.8 wt% D-3005 (dispersant) 81.8 wt% Alcoa A-16SG (alumina
powder)
Filter slurry through 50m screen to remove large particles10% of slurry weight added in active binder is added
Alumina Sheet Fabrication
Tape Casting Process
Lay down a sheet of mylar with a silicone coatingSet a blade gap of 600mSet motor speed to 1 cm/sPour slurry behind blade
Alumina Sheet Fabrication
Sintering of Alumina
Put green tape samples in between porous alumina substratesBurnout/Sinter according to this schedule: Ramp at 600°C/h to 250°C Ramp at 60°C/h to 600°C Ramp at 250°C/h to 1600°C Hold for 3h Cool at 600°C/h to 25°C
Alumina Sheet Fabrication
Shrinkage Effects
Green tape thickness is ~350m Fired thickness is ~280m, which is ~19% shrinkageLength dimensions shrink ~17% upon firing
Alumina Sheet Fabrication
Spraying AZP GlassExperimental glass from Corning, courtesy of Dr. MorenaReacted Powder Mixed in 1g AZP to 10mL isopropanol20 “passes” are made with the sprayer, letting spray dry after every 10 passes
Preparation of Glass Interface
Forming Glass LayerHeat glass-covered alumina up to 550°C Keep at temperature for 5 hours to remove bubbles form the melted glassFurnace cool, to avoid thermal shock20 “passes” yields ~20m glass layer
Preparation of Glass Interface
Glass Powder
Alumina Sheet
Alumina Sheet
Glass Layer
55
0 °C
/5h
Layering of the Laminate
Stack up glass covered alumina, so that layers of glass and alumina alternatePlace between 2 cordierite setters, and put a brick on top of itHeat up furnace to 550°C and hold for 2 hours, furnace cool
Brick
SettersLaminate
The Laminate
Glass wets both sheets of alumina well.Glass is adhering to the surfaces of both alumina pieces
Problems with Alumina
Waviness, and curvature in alumina sheets made lamination difficult
Problems with Lamination
Problems with AZP Glass
Bubbles cause gaps in the glass layer
Problems in Lamination
Alumina AZP Glass Layer
Gaps in AZP Glass Layer
Conclusions
Alumina/AZP Glass laminates can be madeThe glass can be sprayedFlatter alumina sheets are needed for laminationBubbles in the glass also need to be removed
Future Work
Trouble making very flat alumina sheets Refine tape casting procedure Resolve setter difficulties Use pre-made alumina sheets
Trouble removing the bubbles out of the glass Use vacuum to remove bubbles Refine spray process
Acknowledgements
Roland Bruyns for his help with tape casting and making alumina sheetsDr. Robert Morena from Corning for helping with glass issues during the projectProf. Trice and the faculty at Purdue for putting up with me this summer