Experimental verification of the influence of normal stress on the formability of thin-walled 5A02 aluminum alloy tubes

Abstract

Several forming limit theory models, which considering the effect of through-thickness normal stress, have been established based on the classical plastic instability theory and M–K approach respectively. Moreover, finite element analysis of influence of normal stress on the deformation behavior of double-sided hydroforming has been carried out by several researchers. However, the systematic experimental works have not yet been conducted to verify these proposed forming limit theory models and the numerical results. In this paper, in order to verify the influence of normal stress on the formability of thin-walled tubes, a special experimental setup was designed and manufactured for double-sided tube hydroforming. The normal stress can be introduced through the internal and external pressure. Then 5A02-O aluminum alloy tubes with outer diameter of 63mm and nominal thickness of 2mm were bulged freely and in a square-section die cavity under different external pressures. It is shown that the homogeneous plastic deformation ability of the tube before necking occurrence has hardly any dependence on the normal stress, which only influence the fracture morphology and fracture strain on the crack. This investigation reveals that the normal stress induced by double-sided pressures only has an effect on the fracture behavior of the dense sheet or tube metals and has no practical significance in the metal forming production.