Finite element investigation of the incremental deformation of components
Many components in conventional and nuclear power plants and chemical plants are likely to be subjected to 'severe' loading conditions, i.e. loads which would cause cyclic plastic straining and/or incremental deformation (i.e. ratchetting). For operating temperatures above the creep threshold, creep strain also occurs, which may exacerbate the ratchetting of components. If ratchetting occurs, the components may fail either due to excessive deformation so that the components cannot function properly or due to incremental collapse. For simple component geometries, loadings and material behaviour models, the mechanism of ratchetting and the behaviour of components are well understood and analytical solutions (closed form or simplified model) are available. However, for components with complicated stress distributions, loading and material behaviour, the mechanisms of ratchetting are not fully understood and closed form solutions, in general, cannot be obtained. An understanding of the mechanisms of ratchetting is important as an aid to the design process and to apply bounding techniques. Also information on the effect of the material ratchetting phenomena on the ratchetting of components is still scarce. Components with different geometries and loading conditions have been analysed by using the finite element method. The results have been used to investigate ratchetting mechanisms and to obtain ratchet strain data. The effects of complete stress redistributions due to creep have also been investigated. The effects of material ratchetting on the behaviour of components were also investigated. Comparison between experimental results, for a component made of lead alloy material, and finite element predictions, using simple and sophisticated material behaviour models, is also presented. The results show the improvement in accuracy which is possible if more realistic material behaviour models are used.