Which term denotes the slow, permanent deformation of a material under a sustained mechanical stress?

• A. Density
• B. Creep
• C. Design for process
• D. Creosote

Answer: (B)

Creep is slow, permanent deformation under sustained mechanical stress. When a constant load is applied, the material’s internal structure allows dislocations and atoms to move bit by bit, causing shape to change gradually over time. The deformation remains after the load is removed, which is why it’s called permanent. The rate at which creep happens depends on temperature and the level of stress—hotter conditions and higher stresses accelerate the process. In engineering practice, creep matters for components that hold loads for long periods, so designers consider the three stages: an initial rapid response that slows down, a steady-state deformation, and eventually accelerating deformation toward failure. The other terms—density (mass per volume) and creosote (a wood preservative)—don’t describe this time-dependent deformation, and design for process refers to manufacturing planning rather than material behavior.