Continuum damage

Abstract

This chapter covers continuing irreversible material damage caused by mechanical loading and environmental features. This results eventually in unacceptably high rates of change in component damage leading to rupture. The term damage could result from cavity formation (ω), micro cracks (a) and gross deformation (δ), for example, and be strain (ε) or age (t) induced. Some or all of these forms of damage could be accelerated by creep at temperatures above about 0.3 T _m, as well as by other processes such as fatigue, corrosion, spalling, irradiation. These features are depicted in Fig. 5.1, together with their stochastic nature which is inevitable. Typical lifetime expectations could be hours to decades of years but, expressed in terms of life fractions, the form of the schematic is much the same for different situations. The designer’s task is to provide for a safe life using Codes as guidelines. The operator’s task is to seek a useful life by extending the design life, to do so with a minimum of interruptions in the operation and with close bounds on failure probabilities. In some cases, e.g. combined high temperatures and high loadings, Codes do not exist. In all cases, there is likely to be a shortage of (even) bulk materials behaviour data. Laboratory tests from which these data are obtained are often performed outside the regimes of component operation.