Effects of mechanical property parameters on wrinkling behavior of thin-walled tubes in hydroforming process

In tube hydroforming, some controllable wrinkles can be used to improve the formability of tubes, so as to obtain the tubular parts with large expansion ratio and relatively uniform wall thickness. In this paper, finite element analysis and experimental research with 5052 aluminum alloy and 304 stainless steel tubes are used to investigate the effects of mechanical property parameters on wrinkling behavior of thin-walled tubes for hydroforming application. The numerical simulation results show that the effect of elastic modulus is very small and ignorable, but the initial yield stress and tangent modulus of tubes have an obvious effect on their wrinkling behavior. Tubes with higher initial yield stress and lower tangent modulus tend to possess three axisymmetric wrinkles within the lower internal pressure range. Moreover, it is found that the ratio of initial yield stress to flow stress of the tubes, σ_s/σ_f, is a significant factor to their wrinkling behavior. Three axisymmetric wrinkles could be produced on the tubes with higher σ_s/σ_f under a lower internal pressure. All of these were verified by the experimental results of 5052 aluminum alloy and 304 stainless steel tubes, whose wrinkles obtained under wrinkling internal pressure of 1.8 p_s and 1.2 p_s can be flattened completely in the calibration stage. These research findings are extremely meaningful to get controllable wrinkles for different kinds of tubes.