Shear cracks of Zircaloy tube during cold pilgering: experimental investigation and numerical modeling

Cold pilgering process is a seamless tube forming technology, in which the metal is subjected to a series of small incremental deformations. It has been extensively applied for the manufacturing of cladding tube in nuclear reactors, due to high dimensional accuracy and favorable texture evolution. Notwithstanding, the pilgered tubes showed a kind of shear cracks similar to those obtained during low-cycle shear fatigue experiments. To confirm it, a novel low-cycle shear fatigue experiment was designed, in which the shear stress amplitude was obtained from a tracking point in the inner surface of the pilgered tube through finite element model (FEM). Additionally, a theoretical model was established based on the experimental results to predict fatigue life during the cold pilgering process. Through this model, the effects of Q value, side relief, and friction coefficient on the safety factor during cold pilgering were investigated. The results showed that with the increase of Q value, and the decrease of the difference between the friction coefficients of the inner and outer surfaces, the safety of cold pilgering tube could be improved by decreasing the tendency of shear cracks.