Copper Yeild Strength

The yield point for Copper alloys is not sharply defined. As a result
it tends to be reported as either a 0.5% extension under load or as
0.2% offset.

Most commonly the 0.5% extension yield strength of annealed material
registers as approximately one-third the tensile strength. Hardening
by cold working means
the material becomes less ductile, and yield strength approaches the
tensile strength.