Experimental and numerical study of formability in stainless steel 304 tube by hydroforming process

In this paper, with the aim of providing a new test pattern for empirical prediction of FLD of 304 stainless steel tube, firstly numerical investigation of hydro-bulging process with various load paths and die geometries has been performed on strain path and plastic instability. Study on geometry of dies has been performed by varying die corner radius (R) and bulging length (W). Here, effect of axial feeding on strain ratio (β) has been studied. In this condition, by increasing of W, strain ratio (β) tends to value of zero that this situation is independent to boundary condition. By increasing of die corner (R) in free loading condition, reduction of β occurs and the strain path approaches to plane strain state; while in loading with axial feeding condition, increasing of R has neglect able effect on strain path and ratio. In loading with axial feeding condition, increase in axial feeding strain ratio (β) is reduced drastically. From the simulated tests, number of 10 tests with distributed loading path on strain diagram was selected for empirical study. Meshed tubes are loaded controllably until tearing and the FLCs have been drawn using strains which were obtained near tearing locations.