CREEP

Creep (or cold flow) is the time-dependent part of strain resulting from stress.
Creep occurs when a plastic part is subjected to a load for a longer period of time.
High temperature can be an accentuating factor.
Raw materials manufacturers usually provide creep data in the form of curves for specific stresses (psi); they are called strain vs. time curves.
The following diagram shows the strain/time curves for an ABS material.