No abstract

This paper describes general techniques for predicting notch stresses and strains under elastic-plastic and creep conditions. A linear interpolation method, usually used in creep analysis, is adapted for use in predicting elastic-plastic stresses and strains and the Neuber and the Molski-Glinka methods, usually used in elastic-plastic analyses, are adapted to predict peak creep stresses at notches in components. The accuracy of the methods is assessed by comparing predictions based on them with results obtained from elastic-plastic and creep finite element analyses.

This paper describes general techniques for predicting multiaxial notch stresses and strains under elastic-plastic and creep conditions. The Neuber method, which is often used in elastic-plastic analysis, has been adapted and extended for predicting creep equivalent notch stresses and strains, based on a time-stepping integration scheme. A linear interpolation method, often used in creep analysis, is adapted and extended for predicting elastic-plastic equivalent stresses and strains. Then notch principal stresses and strains are obtained by applying plasticity theory in combination with assumptions concerning the ratios of the stress or strain components. The accuracy of the predicted equivalent and principal stress and strain values are assessed by comparing predictions based on them with results obtained from finite element analyses.

A number of key aspects of the three-dimensional finite element (FE) modelling of spline couplings for fretting and fatigue assessment are discussed. The primary issue addressed is the development of an efficient and accurate modelling technique for non-symmetric shaft loading of the couplings, which is an important mode of loading for fretting fatigue assessment. An improved method is presented for implementing an axial modification of the contact geometry, commonly referred to as barrelling, which is also important for fretting fatigue assessment of splines.

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.