Actually, permanent set can occur well before the yield strain. Viscoelastic flow occurs as soon as the elastic limit is exceeded, i.e., anywhere after the linear portion of the stress-strain curve. Most of that viscoelastic flow that occurs prior to yield is generally recoverable with time --- but not all of it. That which is not recoverable is permanent set.
Today, the pace of innovation in the manufacturing industry is faster than ever before, but at the same time engineers are under increased pressure to get concepts to market quickly. Development teams must make fast and accurate decisions during the conceptual stage of design.