Plasticity

Plasticity is a material’s ability to retain deformation after an applied stress exceeds its elastic limit. It distinguishes permanent shape change from reversible elastic deformation.

Yield strength: The stress at which a material begins to deform plastically. It marks the threshold beyond which plastic deformation begins.
Stress: Internal force per unit area within a material under load. Plastic deformation begins when stress reaches a material-dependent threshold.
Metal forming: Manufacturing processes that shape metals through plastic deformation. Processes such as forging and rolling deliberately exceed yield strength to create parts.
Viscoelasticity: Time-dependent material behavior combining elastic recovery with viscous flow. Unlike ideal plasticity, viscoelastic deformation depends on loading time and may partly recover.
Dislocation: A line defect in a crystal lattice where atomic arrangement is disrupted. Dislocation motion lets crystalline materials deform permanently without breaking every atomic bond at once.
Strain: A measure of deformation expressed relative to an object's original dimensions. Plasticity describes the permanent component of strain after unloading.
Forging: A process that shapes metal by compressive forces, often using a hammer or press. Forging relies on plastic flow to form strong components without removing material.
Viscoplasticity: A constitutive behavior in which plastic deformation depends on both stress and deformation rate. It extends plasticity to materials whose permanent flow changes with loading speed.
Slip system: A crystallographic plane and direction along which dislocations move during plastic deformation. The available slip systems determine how readily a crystal can yield.
Elasticity: The ability of a material to recover its original shape after a load is removed. Elastic deformation is recoverable; plastic deformation remains after unloading.

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