scope:

In surveying an area as amorphous as simplified inelastic analysis methods, a systematic approach is advised. The choice of the system should be designed to provide guidance to the investigator. The approach taken here is based partly upon failure mode classification, in concert with the underlying theme of the ASME Boiler and Pressure Vessel Code. The classifications of failure can be described in terms of mechanistic observations, in order to focus attention on the quantities that are to be measured or calculated. For example, time-dependent and time-independent structural instability calculations involve large deformation and, although the general complexity can be greatly reduced in any number of ways, the ability to treat geometric nonlinearity is desirable. Creep-rupture life can be conservatively estimated for some structures through elastic analysis; those structures for which such estimation is not possible, because of a design feature that prevents the redistribution of stress, can sometimes be redesigned to alleviate this difficulty. Other designs may not be amenable to this simplified treatment. Creep-fatigue interaction and strain accumulation, because of the necessity of establishing inelastic strain ranges and cyclic additions, also lie in the intermediate regime where one is less certain of the advantages of simplified methods.