In tensile test, why is it necessary to state the gage length when reoporting the percentage of elongation?

Answer 1

Typically, when a part starts to fail, it does not elongate uniformly over its entire length. Instead, most of the elongation occurs over a relatively small portion of the length, with the rest of the material elongating relatively little. The percentage elongation for a given amount of strain will therefore depend on the length of the sample.

Answer 2

The tensile strength vs elongation curve may not be linear.