On Damage and Crack Initiation of Zircalloy-made Structural Components
Sponsor: Massachusetts Institute of Technology (MIT)
The Zircaloy-4 exhibits a mild strength differential response under compression as compared with tension. Because of the well-known twinning-slip mechanism usually activated in compression after yielding in HCP metals, distortional hardening is required to define plastic flow throughout fracture. A general pressure-dependent asymmetric yield function with the first invariant to the Cauchy stress tensor and the third invariant to the deviator stress tensor is considered to model the pressure-sensitive response and the Strength Differential (SD) effect in HCP polycrystal materials. The proposed macroscopic yield function provides results that are in good agreement with experiments. The onset of fracture and subsequent crack propagation in upsetting tests is also investigated. The results show that failure is controlled by material properties and friction between contact surfaces of specimens and experimental setup. In addition, the concept of a fixed cutoff value for negative stress triaxiality condition is analyzed. It turns out that the specimen fails differently from what is observed experimentally when a constant cutoff value is set. However, a cutoff stress triaxiality function yields a more realistic fracture pattern consistent with tests.
Status: Completed