Plastic instability of mechanical bulging process for Zircaloy-4 cladding tube based on localized necking criterion

Plastic instability of mechanical bulging process, different from the traditional tube hydroforming, is developed for Zircaloy tube based on localized necking criterion. Based on the observation of published experiments of bulging, an elementary analyzed model of plastic deformation is proposed and applied for examining the variation of bulging process and its limitation. The developed model comprises two deformation regions, one is bulged part with friction effect and the other is flattened part but without friction effect. All mentioned process parameters, such as contact friction, material properties (strain hardening exponent and normal anisotropy), and process geometries conditions (tube radius and thickness), are taken into account for in such mechanical bulging model. Plastic instability in bulging is examined using localized necking criterion based on the proposed model. A published experiment was initially used to verify the present model. Then, the effects of process parameters on the variation of bulging limit are investigated. The developed model allowed us to better understand the failure mechanism through the localized necking criterion, and also can be defined as a sign of fracture for a bulged tube. Moreover, a proposal will be made to examine the limitation of bulging for practical needs.