Application of notch strain techniques to elastic-plastic and elastic-plastic-creep behaviour of complex structures

Notch strain techniques have been widely applied to simple notch components and geometries to predict both elastic-plastic and creep strains along with associated stresses. However, the real benefit of such methods ought to be in their application to more complex structures with stress concentration features such as notches under multi-axial stress states. Aero-engine casing structures are a typical example of such a complex component in which optimum design is critical for weight savings and appropriate stiffness behaviour but where notch features may lead to localized plastic strains and hence damage. This article examines the performance of a number of notch strain techniques for the prediction of the elastic-plastic and creep notch stress and strain responses of a complex aero-engine casing structure. In addition, a modelling methodology involving a combination of (a) linear elastic and limit load analyses of a simplified global model and (b) linear elastic analysis of detailed local models is developed to demonstrate how approximate notch predictions of elastic-plastic and elastic-plastic-creep notch stresses and strains in complex structures can be obtained without recourse to the more significant computational expense of global (fine mesh), non-linear (incremental), and time-dependent elastic-plastic-creep analyses.