plastically

Plastically is an adverb used to describe something that happens in a plastic manner, particularly with respect to plastic deformation. In materials science, to deform plastically means to undergo a permanent change in shape or size when the applied stress exceeds the material's elastic limit. Unlike elastic deformation, which is reversible when the load is removed, plastic deformation remains.

The threshold is often defined by the yield strength or yield point of the material; beyond this, dislocations in crystalline solids move, allowing permanent shape change. In metals, plastic deformation occurs primarily by dislocation glide and climb; in polymers and viscoelastic materials, permanent deformation can arise from chain slippage and rearrangement. In geological contexts, rocks can deform plastically at high temperatures and pressures, enabling ductile flow in the earth's mantle.

The term also appears in discussions of plasticity theory, a branch of continuum mechanics that models the irreversible response of materials to stress. Plastic flow is often rate-dependent in materials exhibiting viscoplasticity and creep, so the word plastically can imply time-dependent or rate-sensitive deformation. Plastically referring to shaping a material is common in manufacturing processes such as rolling, forging, extrusion, and stamping, where the material is intended to be permanently reshaped.

Examples include steel workpieces that are bent, clay that retains a pressed shape, and ice that deforms plastically under long-term stress. The concept is distinct from elasticity and from brittleness, which involve little to no plastic deformation before failure.