Time-dependent deformation under constant tensile stress The phenomenon describing the slow, progressive increase of strain in a material subjected to a steady (constant) tensile stress over time is called:

Introduction / Context:
Materials often display time-dependent behavior. Under constant stress, some continue to deform gradually, a process relevant to metals at high temperature, polymers at ordinary temperatures, and concrete under sustained loads. Understanding terminology helps interpret long-term serviceability and durability.

Given Data / Assumptions:

• Constant tensile stress (sustained load).
• Observation of strain increasing with time.
• Material within service stress levels (not immediate fracture).

Concept / Approach:

Creep (or creeping) is the time-dependent increase in strain under sustained stress. The classical creep curve includes primary (transient) creep with decreasing rate, secondary (steady-state) creep with nearly constant rate, and tertiary creep culminating in failure. Temperature, humidity (for concrete/wood), and stress level significantly influence creep rate and magnitude.

Step-by-Step Solution:

Verification / Alternative check:

Concrete codes include creep coefficients to estimate additional deflection under sustained loads. Metallurgy handbooks present creep rupture curves as time-to-failure vs stress at a given temperature, reinforcing the definition.

Why Other Options Are Wrong:

• Yielding: Instantaneous plastic deformation at yield; not a slow time-dependent strain under sub-yield stresses (except viscoplastic contexts).
• Breaking: Final failure; does not describe the progressive deformation stage.
• None of these: Incorrect because “creeping” precisely names the phenomenon.
• Ratcheting: Progressive plastic strain under cyclic asymmetric loading, not constant stress.

Common Pitfalls:

• Confusing creep with shrinkage (stress-free volume change) in materials like concrete.
• Assuming creep is only a high-temperature metal issue; it also affects polymers and cementitious materials.

Final Answer:

creeping.