Forming mechanism of double-layered tubes by internal hydraulic expansion

摘要

In this paper, the hydro-expanding principle for a double-layered tube is set out in detail. The force state of a double-layered tube was analyzed during the process of hydro-forming. The stress and strain for the inner and outer tubes were evaluated using theories of elasticity and plasticity. By using the relation of deformed compatibility of hoop strain, suitable conditions of hydraulic expansion and variable range of hydro-expanding pressure are given, and formulae of hydro-expanding pressure related to residual contact pressure are derived. The results are applicable to cases where the inner tube is both thin-walled and thick-walled.