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How does creep deform a material that remains under a constant load for a long time?

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Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).
mechanics of solids Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).

In the context of the mechanics of solids, creep is defined as the slow, permanent, and continuous deformation of a material that occurs under a constant load over a long period of time.12

When a material is subjected to prolonged stressā€”at levels below those required to cause instantaneous fractureā€”it undergoes a gradual change in dimensions, known as creep strain. This behavior is a form of elasticoviscous deformation, where the material yields continuously in a viscous manner while under a constant applied load.12

This phenomenon is observed in various materials, including metals, crystals, ice, soil, and rocks at depth. In ductile materials, this process involves flow mechanisms such as intracrystalline slip, intercrystalline motion (crushing and fracture), and recrystallization. Because creep is time-dependent, engineers often use mathematical techniques to extrapolate data from shorter tests to predict how a material will behave over much longer durations, such as thousands of hours.12