Phenomenological Creep Failure Models

This chapter presents a brief survey of the phenomenological aspects of creep, fracture, and failure properties. Phenomenologically, it is represented by a regime of constant strain rate, known as secondary creep rate or steady‐state creep rate for a constant stress and temperature. Mechanical tests for characterization of materials are essentially divided into two basic groups: creep tests and strength tests. Creep studies should fundamentally be made at constant stress rather than at constant load. For stresses of engineering importance, creep failure is invariably preceded by a tertiary stage attributable to the development of cavities and cracks, as well as necking. The fatigue behavior of high‐temperature alloys and the design‐related aspects of creep‐fatigue are very complex. One of the most common assumptions in strength testing for rate‐sensitive materials that include all crystalline solids at elevated temperatures is that constant stress creep tests can provide results comparable to those obtained from constant strain rate tests.