stresses is they are those stresses remaining
in a solid body under zero external
force (gravity excluded). Residual
stresses are formed when portions of a
material undergo nonuniform, permanent
dimensional changes. Such
changes usually result from plastic deformation,
but may also be caused by
localized expansion or contraction of
the metal lattice. Plastic deformation
may be induced by large temperature
gradients as often occur in welding,
quenching, or rapid heating, as well as
during the forming process.