Lecture Friday will be a broadcast of makeup lecture held today 12pm in the New Media Classroom atte

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Lecture Friday will be a broadcast of make-up
lecture held today 1-2pm in the New Media
Classroom attend either lecture or view at your
leisure
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Strengthening of Ceramics
depends on crack geometry (including radius of
curvature)
crack length
Fracture toughness
dependent on cracks
independent of cracks
Stress intensity factor
Need to focus on cracks
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Strengthening of Ceramics

• Process to eliminate cracks (internal)
• Polish to eliminate surface cracks
• Blunt crack tip
• Anneal (heat treat) to eliminate randomly
  distributed internal stresses
• Quench (a silicate glass) to induce compressive
  stress on surface
• Ion exchange to induce surface compressive stress

once crack penetrates compressive region,
material shatters explosively
Na
K
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Strengthening of Ceramics

• Transformation toughening
• Cool ZrO2 cubic ? tetragonal ? monoclinic
• Modify with CaO cubic ? tetragonal ?
  monoclinic cubic
• Rapid cooling tetragonal ? monoclinic is
  slow obtain tetragonal cubic

crack catalyzes tetragonal ? monoclinic
transition increase in volume upon transition DV
places compressive stress on crack (closes it)