Full definition
Stress at which a material begins to deform permanently (elastic limit). Design limit for most mechanical components. Typical values (Sy): 1045 HR steel 530 MPa, 4140 T steel 655 MPa, 6061-T6 aluminum 276 MPa, 304 stainless steel 205 MPa. Designing with working stress ≤ Sy/SF ensures operation within the elastic zone and prevents permanent set.