The yield strength or yield point of a material is defined in
engineering and materials science as the stress at which a material
begins to deform plastically. Prior to the yield point the material
will deform elastically and will return to its original shape when
the applied stress is removed. Once the yield point is passed, some
fraction of the deformation will be permanent and
non-reversible.
In the three-dimensional space of the principal stresses
(σ1,σ2,σ3), an infinite number of yield points form together a
yield surface.
Knowledge of the yield point is vital when designing a component
since it generally represents an upper limit to the load that can
be applied. It is also important for the control of many materials
production techniques such as forging, rolling, or pressing. In
structural engineering, this is a soft failure mode which does not
normally cause catastrophic failure or ultimate failure unless it
accelerates buckling.
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