Britannica Sources used in this answer

What is the difference between elastic strain and plastic strain in a metal rod?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram of a zinc-lead blast furnace system showing ore and coke entering through charge hoppers, with labeled furnace, air preheater, blower, taphole for slag and lead bullion, and a connected lead-splash condenser using rotors to separate and cool lead and zinc, with pathways for molten metals and off-gas. — metallurgy A zinc-lead blast furnace and lead-splash condenser. This technology is utilized mainly for producing zinc while managing both lead and zinc from raw materials, a technique that was highly influential in 20th-century smelting.

In metallurgy, the distinction between elastic and plastic strain in a metal rod is defined by how the material responds to an applied load and whether it returns to its original shape upon unloading.1

Elastic Strain: When a metal rod is lightly loaded, the strain is proportional to the stress. In this regime, the rod elongates as the load increases, but it will shrink back to its original size once the load is removed. This reversible deformation typically accounts for 0.1 to 1 percent of the strain at the point of yielding.1
Plastic Strain: If the load exceeds the yield stress, the metal undergoes plastic deformation. In this state, strain increases more rapidly than stress, and the atomic structure undergoes permanent displacement. Consequently, when the load is removed, the rod does not return to its original dimensions, leaving a residual elongation. This permanent deformation is a hallmark of ductility and can reach 20 to 40 percent or more in many alloys before rupture.1

Would you like to learn more about how crystal structures influence these deformation processes?