The use of damage concepts in component life assessment

The damage concepts introduced by Kachanov several decades ago have rarely been used in practical application, in spite of their simplicity. Because there are no alternatives of note to Kachanov's ideas, this paper re-examines the basic premises involved in damage concepts, with a view to deriving results which will be credible to those responsible for component life management. This has led to possible schemes for economical data acquisition as well as to simplified life assessment procedures which are described in the paper. For metallurgically stable materials, long term creep strain and rupture data can be described simply in terms of two material constants and the results from short term tests for initial creep rates and strength. These data are all bounded by a single term beta which depends on the stress level in relation to the short term strength. Examples are given for stiffness and strength reductions caused by damage. A simple relationship between current strain rate and remaining life should be of use in routine plant measurements.