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What kind of materials fracture?
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Many things can fracture. Everything from baseball bats to windows to
bones. |  |
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Many structures are made of steel and/or concrete, and both of
these materials can fracture.
Civil Engineers use both steel and concrete, so they must be concerned with
fracture. |
| In steel, fracture is often ductile and may be due to
fatigue.
A fatigue crack is caused when a
cyclic load (*) is applied. You are applying a cyclic load to a soda
can tab when you push it back and forth to break the tab off of the soda
can.
"Ductile fracture" means that the part of the material which is cracking is
also deforming (its shape is changing). Think of pulling a piece of silly
putty into two pieces: as you pull it apart, it deforms until you have
created two new pieces. |
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 | On the other hand, concrete fracture is brittle. Brittle
fracture means there is no deformation around the crack; the very grains of
the material are separating, or cracking themselves.
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Concrete is the material of choice for many, many
structures: buildings, bridges, dams, to name a few. Concrete offers many
advantages: low cost, good weather and fire resistance, good
compressive strength (*), and
excellent formablility (*). Concrete
is bad in tension and therefore prone to cracking. Also, it's behavior
is not so predictable.
But what is concrete?
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