Why is packing tape nearly impossible to tear when intact, but easily shreds if you cut the slightest nick into it?

Question

Why is packing tape nearly impossible to tear when intact, but easily shreds if you cut the slightest nick into it?

In: 6079

Answer 1

Stress concentration, if you cut a slit in a paper and applied pressure to it, all the stress that used to go through the material at the slit line can’t anymore and needs to find another path. It will flow throw the nearest material connection it can find, and since slits usually end at a single sharp point, all that stress that used to pass a whole line now passes throw a point, creating a spike of high stress that passes the failure point of the material, and so the paper will tear.