5.1. Introduction

Progressive plastic deformation design checks (PD-DC) deal with the failure mode progressive plastic deformation, also called ratchetting and inadaptation, with regard to cyclic application of actions and short-time response, i.e. excluding creep effects. This design check often uncovers clearly singular features of structural behaviour under the influence of repeated actions.

Three basic types of responses of structures to cyclic actions are shown in Figs. 5.1 5.3.

Figure 5.1: (a) Elastic shakedown after one action cycle; (b) Elastic shakedown after infinitely many cycles with one-sided plasticity; (c) Elastic shakedown after infinitely many cycles with two-sided plastic deformation.

Figure 5.3: Progressive plastic deformation (ratchetting).

Figs. 5.1a c show examples of shakedown to linear-elastic behaviour.

Fig. 5.1a shows an example of a shell with a local structural perturbation source subjected to one single-amplitude cyclic proportional combination of actions, an example where the structure shakes down to linear-elastic behaviour in one action cycle. The stress path at the critical point is shown in the deviatoric map, with the shakedown trajectory shown as the thick line. From the initially stress-free state, represented by the point 0 in the origin, a proportional increase of actions up to their maximum value results for a linear-elastic model in a linear-stress path, up to in the deviatoric map. The stress path for the linear-elastic ideal-plastic model deviates from this straight line at the intersection with the circle, representing the yield limit, remains at the circle and ends in . Unloading is linear-elastic; the deloading path is parallel to...