et al.2 demonstrated that, for approximately linear strain paths, the FLC predicted splitting failures adequately. Currently, the main feedstock of tubular blank However, the situation for a tube hydroformed commaterial for tube hydroforming is derived from slit ponent may be very different from that for a conventional steel coil, which has been roll formed and electric sheet metal stamping. This complexity is a consequence of resistance welded (ERW). From ERW tubular blank, the strains introduced by the various stages of processing, a number of intermediate processing stages such starting from the original parent coil through tube manuas prebending and preforming may be necessary to facture to the component. The series of strains involved achieve the final formed component. The end result may render the original sheet forming limit curve inaccurate is a component that may have experienced afor complete forming analysis. In the conventional electric complex strain path history. The traditional forming resistance welded (ERW) tube manufacturing process, the limit (strain) curve (FLC) is inherently affected by mechanical characteristics of the original strip may be non-linear strain paths; hence, a suitable alternative altered by a wide range of induced strains. The predominant forming limit criterion has been studied and is cold working effects, highlighted by Kato and Aoki,3 are: proposed for complex tube hydroforming processes.longitudinal bending, from uncoiling/levelling; transverse The criterion proposed is the forming limit stress plane strain bending, owing to roll forming; and compressive curve (FLSC), which is theoretically independent of strains caused by subsequent sizing of the tube to fix its strain path and prestrain history. The methods diameter. These straining effects mean that the original sheet used to generate the FLC and FLSC for tubular FLC cannot be used with confidence to predict splitting blanks are described, and prebending is used as an during any subsequent process. example to demonstrate how complex tubular Kergen and Lescart4 have suggested an experimental component forming operations, and subsequent method to obtain an FLC for ERW tubular blanks. This formability, may be evaluated through use of the involves applying internal pressure to a blank contained FLSC.I&S/1514 within die tooling that represents a double cone. The strain mode is varied by controlling the tube end constraint, andAt the time the work was carried out Mr Darlington and Professor this approach has been claimed to provide linear deformation Parker were at the EPSRC Engineering Doctorate Centre -Wales, paths. However, this technique has limitations in that biaxial

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