Results in Materials (Jun 2020)
Effect of bulge ratio on the deformation behaviour and fracture location during welded steel tube hydroforming process
Abstract
A drawing quality welded steel tube with outer diameter of 57.15 mm and thickness of 1.6 mm was used in this study. These tubes were hydroformed at bulge ratio (or L/D ratio) of 1, 2 and 3 to achieve different strain paths. It was observed that the tubes after hydroforming fractures in the base metal near the weld for L/D = 1 whereas for L/D = 2, 3 the fracture occurs in the base metal opposite to the weld which was a novel observation. The experimental and simulated strain paths for two extreme L/D ratios of 1, 3 were analysed. It was found that the maximum value of major strain was found at the base metal for all L/D ratios, however, its location and subsequent fracture depends upon L/D ratio. Therefore, to investigate this anomaly, the detailed FE analysis was carried out by varying the ratio of strain hardening exponent between base and weld metal and by introducing the thickness imperfection in the tube. The FE analysis predicts the trade-off between the material inhomogeneity and thickness imperfection leading to fracture at specific location for both L/D. The present study concludes that the relative sensitivity of thickness imperfection versus material inhomogeneity is dictated by the tube bulge ratio.
