Lecture 7 Flashcards
what does ceramics mean in greek?
Potter’s clay, pottery from the greek word kermaos
How are ceramics defined?
inorganic materials that are made in high temp
What are the durability types?
Chemical
Mechanical
Thermal
ceramics are resistant to…
ALMOST all acids, alkalis,
and organic solvents. Not affected by O2
the durability of ceramics is evidenced by their…
strength and hardness
hardness makes ceramic materials very resistant to…
abrasion.
Technical Ceramics
- Oxides-based: silicate and non-silicate oxide ceramics (alumina,
zirconia, etc.) - Non-oxides: carbides, borides, nitrides, silicides.
-Composites: Particulate reinforced, combinations of oxides/nonoxides.
Traits of Brittle Fracture
limited dislocation mobility
No appreciable plastic deformation
Crack propagation is very fast
The crack propagates nearly perpendicular to the direction of the applied stress
Crack often probates by cleavage
Examples of brittle and ductile fracture
- Very ductile - soft metals (e.g., Pb, Au) at room temperature, glasses at high temp
- Moderately ductile fracture - typical for ductile metals
- ## Brittle fracture - cold metals, ceramics
What are the failure mechanisms for Polycrystals?
Transgranular (pass through grains)
- Rough surface everywhere
Intergranular (along grain boundaries)
-Rough surface of many flat faces
strength specimen depends on the
size of major flaws,
what is the Weibull modulus?
describe the scatter degree of strength data.
- higher Weibull Modulus (m) value implied a narrower distribution of fracture stresses and higher reliability.
how do u test ceramic mechanical properties?
bending test
stress at fracture using bending test is known as the…
flexural
strength, modulus of rupture, fracture strength, or the bend
strength.
applied stress is amplified at the
tips of micro-cracks, voids, notches,
surface scratches, corners are called…
stress raisers
