Time-dependent deformation under sustained load – what is it called? The slow, continuous extension of a material under a constant applied load, increasing with time, is known as:

Introduction / Context:
Many engineering materials exhibit time-dependent deformation under sustained stress or load. Recognizing the correct term and its implications is essential for long-term serviceability checks in structures, pavements, pressure vessels, and high-temperature components.

Given Data / Assumptions:

• Load is essentially constant over time (dead load).
• Temperature and moisture may influence the rate but not the basic definition.
• Elastic strain occurs immediately; additional strain accumulates gradually.

Concept / Approach:
Creep is the progressive, time-dependent increase in strain at a constant stress level. It occurs at room temperature in materials like concrete, polymers, and wood, and at elevated temperatures in metals (e.g., turbines, boilers). Yielding is an instantaneous plastic deformation when stress exceeds yield strength; fracture is sudden failure; stress relaxation is the decrease of stress under constant strain; work hardening refers to strengthening due to plastic deformation.

Step-by-Step Solution:
Identify the loading condition: constant load → constant stress (approximately) in many applications.Observe deformation behavior: strain increases with time under unchanged load → definition of creep.Match with terminology: select “Creep”.

Verification / Alternative check:
Concrete codes include creep coefficients to predict long-term deflection; metal creep curves show primary, secondary, and tertiary creep stages under constant stress and temperature.

Why Other Options Are Wrong:

• Yielding is immediate under rising load, not time-dependent at constant load.
• Fracture is a failure mode, not necessarily time-dependent under constant sub-yield load.
• Stress relaxation assumes constant strain, not constant stress.
• Work hardening describes material evolution under plastic strain cycling, not time-dependent extension under constant load.

Common Pitfalls:
Confusing creep with shrinkage (moisture-related volume change) in concrete; creep requires sustained stress, while shrinkage occurs without load.

Final Answer:
Creep