Figure 2.

Representative load history during fatigue loading. Progression of cumulative clamp-to-clamp strain is characterized by a continuously increasing, triphasic pattern (denoted by Primary, Secondary, and Tertiary phases), with inflection points 1 and 2 that mark the transition from one phase to the next. Stiffness increases initially in early fatigue life, leading to a relatively stable level for an extended duration of loading, until reaching the end stages when stiffness declines at an accelerated rate. [Color scheme can be viewed in the online issue, which is available at http://www.interscience.wiley.com]