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Try this cracking
experiment!
If there is something wrong in the material that might make it easier for
cracks to start, we call that a flaw.
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| Like a piece of paper, for example -- it has a
flaw, a tear, right in the middle.
Find a piece of paper and put a tear in it just like this. |
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Now grab the paper on each side of the tear, like this.
Pull. What happens?
Nothing. Your crack should not have grown. |
| But now pull on it like this.
What happens?
Your crack grows and the paper tears. |
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So now we've learned that for a crack to grow, it matters how you apply the
force. |
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