Theoretical and experimental study of cold pilgering

This study deals with the pilgering of Zircaloy 4 cladding tubes. During the last pilgering pass, surface defects may appear in a little quantity but of a great potential noxiousness. In order to foresee this damage, a previous thesis was dedicated to the turning of mechanical model. Its major limits were: - the use of isotropic plasticity behaviour law although the material is highly textured and mechanically anisotropic. The mechanical model has then been modified so that an anisotropic behaviour of a Hill quadratic type be accepted. The anisotropy has been experimentally quantified over the upstream stages of the pilgering process line, throughout the six Hill parameters. An original method for the measurement of shear parameters has been set up using the shearing of cylindrical bars coming from the tube wall. The Lebensohn and Tome model was used to predict the mechanical properties over the whole process line; - the difficulty to take account, using a predictive manner, the shear buckling within the radial-longitudinal tube plane, although its importance had been proved. This obstacle has been cancelled with the building of an upper boundary model. This model has been enhanced with the calculation of the mandrel horizontal stresses using the slab method. Along with these developments, a series of numerical simulations with 3D finite elements allowed a better understanding of this complex process of cold deformation. The information obtained from these simulations showed it was necessary to reconsider some of the hypothesis from the analytical model. We concentrated on the building and the validation of an new 3D modelization of the last pilgering pass getting of the approximations showed to be the most questionable by the simulation. (author)