Elevated-temperature fatigue interactions in engineering materials

Abstract

The development of failure at elevated temperature under transient loading conditions can be a complex process. In addition to the operation of the basic fatigue mechanism, which often initiates a dominant surface crack, other time-dependent processes operate to a varying degree. These include creep deformation and fracture processes, metallurgical changes, and environmental effects. In failures controlled by the dominant crack these processes can markedly alter both crack-initiation and crack-growth rates. It is shown that effects on crack growth are usually limited to an order of magnitude change, the important factor being their effect on the crack-tip displacement. Serious acceleration of failure can occur when internal fracture damage due to creep processes directly contributes to crack advance. This is analogous to plastic instability in low-temperature failure. A study of the development of failure can provide a new basis for the design of components in elevated-temperature service.