Exprimental and numerical study of mechanical influence of cyclic flaring and sinking (CFS) method to produce strong copper tubes

In this research, a novel severe plastic deformation (SPD) method entitled cyclic flaring and sinking (CFS) is presented for producing of the fine-grained copper tubes. Finite element simulation has determined the influence of design parameters. CFS process includes two different flaring and sinking half-cycles. At flaring half cycle, the flaring punch with two stepped regions is pressed into the tube. Shear and normal tensile strains are applied as a result of the existence of shear zones and increase in the tube diameter. In the second half cycle, the tube is then pressed to sinking die that applies same shear strains and normal compression strain so that the initial diameter of the tube is achieved and high plastic strain is applied. This process can be run periodically on the tube to exert more strain and consequently finer grain size and ultimately achieve better mechanical properties. The true stress-strain curve of pure copper tubes was studied in different cycles. Results show the increasing strength in upper cycles if the yield and ultimate strength were significantly increased to 185 Mpa, and 285 Mpa, respectively from the initial values of 120 Mpa, and 180 Mpa. On the other hand, the elongation to failure was decreased after the process. The average hardness along thickness has reached to 127Hv after eleven cycles from 96 Hv.