Evaluation of Tube Materials for Tube Hydroforming

摘要

The transverse properties of two commercial hydroforming tubes with different D/t ratios were obtained using the newly developed Ring Hoop Tension Test (RHTT). It has been found that (1) the transverse properties of these tubes are different from the sheet properties and from the tube longitudinal properties; (2) work hardening during tube making can change the material behavior significantly, especially for small D/t ratio tubes, and tube flattening can cause additional changes in the transverse properties of tubes. The most interesting finding was a marked loss of elongation after tube making in the higher strength steel used to make the smaller tube. Also of significance was the change in properties associated with flattening for the flattened transverse strip tensile test; and (3) transverse tube properties, especially the yield strength and elongation, vary around the tube circumference; higher yield strengths were observed at the 180° position and near the edges of the strip. It is very clear that tensile properties are changed when the sheet is subjected to roll forming, and that they depend on test specimen orientation. Properties are further changed if specimens are subjected to flattening.