Three kinds of micro-sample thicknesses(0.4 mm

0.5 mm and 0.6 mm)and three kinds of chamfer radii(0.5 mm

0.8 mm and 1.0 mm)of the original main pipe material were taken as the research objects to analyze the influence of restraint intensity in hydraulic bulging test

and to build a correlation model of yield strength

tensile strength and hydraulic bulging elongation.The fitting error of yield strength and tensile strength and the dispersion of hydraulic bulging elongation were studied.The results show that with the gradual increase of microspecimen thickness

the peak load increases obviously

while the peak displacement generally decreases

but the overall curve trend changes little.With the gradual decrease of the microsample chamfer radius

the peak displacement decreases obviously.The test stability is best under the test conditions of microsample thickness 0.5 mm and chamfer radius 1.0 mm.