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

It’s a material property known as fracture toughness, the ability of a material with an existing defect to resist failure. Polymers have low values (approx 1-2) whilst materials that have to perform with defects present like aerospace metals have a much higher value (40-100).

Source: I’m a materials engineer!