At least Nishi took off the blindfold unlike the school heads!
Jarlath said:
What do they use for their saucers that it didn't snap?
Maybe aluminum oxide or boron carbide (both used in body armor plates that protect against rifle rounds)? Boron nitride is supposedly pretty strong as well. It probably wouldn't be boron carbide because it is naturally a very dark gray while the other two ceramics are usually white, more like a typical saucer. :-)
I commend Darj for maintaining her bearing; as they say, everybody get's scared--it's how you deal with it that is important! There's also "it's better to be lucky than to be good!"
At least Nishi took off the blindfold unlike the school heads!
Maybe aluminum oxide or boron carbide (both used in body armor plates that protect against rifle rounds)? Boron nitride is supposedly pretty strong as well. It probably wouldn't be boron carbide because it is naturally a very dark gray while the other two ceramics are usually white, more like a typical saucer. :-)
I commend Darj for maintaining her bearing; as they say, everybody get's scared--it's how you deal with it that is important! There's also "it's better to be lucky than to be good!"
Both are brittle though. Hard but brittle (these two properties often come hand in hand). Great for stopping a bullet, but will shatter easily when dropped.
Both are brittle though. Hard but brittle (these two properties often come hand in hand). Great for stopping a bullet, but will shatter easily when dropped.
Yes, that's why the rifle plates are usually have a layer of more resilient material on the outside, and you have to inspect them periodically. As long as you stay in the elastic deformation region of the stress-strain curve (i.e. below the yield strength), it shouldn't break though, and Aluminum oxide ceramic has an ultimate tensile strength of around 250 MPa (compressive strength is much higher), about 8 to 10 times that of an average porcelain material and higher than the yield strength of some lighter metal alloys.
Yes, that's why the rifle plates are usually have a layer of more resilient material on the outside, and you have to inspect them periodically. As long as you stay in the elastic deformation region of the stress-strain curve (i.e. below the yield strength), it shouldn't break though, and Aluminum oxide ceramic has an ultimate tensile strength of around 250 MPa (compressive strength is much higher), about 8 to 10 times that of an average porcelain material and higher than the yield strength of some lighter metal alloys.
Hidden because of length
Ceramics fracture way before they reach their tensile strength.
There's usually no plastic deformation region of the stress-strain curve for ceramics. It's just one steep straight line until it abruptly terminates with material failure (the failure/fracture point). Ceramics don't "yield" so much as shatter.
(Or in other words, the entire region is elastic deformation, with no clear yield point. And it fractures at like 0.1% strain with widely-varying measured stress depending on how you align the sample. Or it just straight up breaks in the grips before the test even starts. One may instead use a four-point bend test to determine the tensile strength indirectly, and you can good reproducible results that way, but the figures you get are mostly only useful for, say, load-bearing considerations for building structures. Not for predicting impact resistance.)
Unless it's one of those funny ceramic fibers, or a composite material with both ceramics and other materials in the same matrix (this include bioceramics glued with protein fibers), which I don't think rifle plates are made out of yet (though the top-secret proprietary coatings might be a different story).
You want fracture toughness. This varies considerably depending on the purity of the ceramic and the manufacturing process (defects play a big role), and also depending on how you measure the "fracture". IIRC most oxide/carbide ceramics have them in the single digit MPa*m^(1/2) range (yes there's the weird square root meter there in the unit, because crack size is factored in). Most ceramic rifle plates are under 5 MPa*m^(1/2).
You can also sort of measure or calculate the fracture strength of the above materials, but it's kinda hard to define a useful measure of such (one will, IIRC, get values from tens to hundreds of MPa for the above ceramics depending on how the test is conducted), which is why it is preferred to use fracture toughness with the weird square root meter unit (it tells you how likely the cracks will propagate).
Thanks as always for posting these 4-panel comics and their translations. It's much appreciated. Been reading them for years and they never cease to make me laugh. Keep it up!
Also, that saucer saved her life. Thank goodness for carbon coating!
It's nice to have tea by the pool every once in a while, right?Truly it is huh!But it's a little bright out, so it does have its draw-backs...Whoah!?
I made a mistake with the water-melon
!!* Inner heart
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