The identification of strain-stress curve for 5049 aluminum based on tube hydraulic bulging test

Benny Endelt,Shu Yan,Bin Zhang,Karl Brian Nielsen,Yang Zhao,Lihui Lang

doi:10.25518/esaform21.4067

Abstract

Tube hydraulic bulging tests with fixed-end conditions are carried out to explore tubular material characteristics for 5049 aluminium. Tube diameter at the center of specimen and pole thickness under different internal pressures are recorded during forming process. Based on experimental data, two types of theoretical models using membrane mechanics and total strain theory are applied to determine the flow stress curve of tubular specimens. A tension specimen is cut from the same tube along longitudinal direction and strain-stress curve is fitted by a universal tensile test. In order to test their accuracy, obtained material parameters from three methods are imported into a finite element model (FEM) and its predicted results are compared with bugle height measured from experiments. The comparison shows that the flow stress curve of 5049 aluminium tube can be identified by these three methods and simulated results from total strain model has a better agreement with experimental measures compared with the other two methods.

Highlights

Tube hydroforming process can form tubular material into various components and is widely utilized in the automotive industry and civil engineering as it can reduce vehicles and structures weight and decrease production cost
Tube hydraulic bulge test is an advanced method to evaluate the tubular material properties under complex stress state, in which the collected experimental data like internal fluids pressure and bulge height is fitted to analytical models for this process and the constitutive parameters can be determined[2]
A big progress is made by Fuchizawa et al.[4] who assume the tube wall is formed under plane stress state and derive the stress formulas along circumferential and axial direction

Summary

Introduction

Tube hydroforming process can form tubular material into various components and is widely utilized in the automotive industry and civil engineering as it can reduce vehicles and structures weight and decrease production cost. Tube hydraulic bulge test is an advanced method to evaluate the tubular material properties under complex stress state, in which the collected experimental data like internal fluids pressure and bulge height is fitted to analytical models for this process and the constitutive parameters can be determined[2]. The derivation of force equilibrium for small element at bulge top along radial direction neglects tube wall thickness, which reduces the accuracy of analytical models. An analytical model based on total strain theory is developed to determine materials parameters using experimental measures. It considers the change of tube wall in the force equilibrium equation and introduces the plastic flow rule, which can increase its prediction accuracy. Based on the geometrical relationship, the curve radius along the axial direction can be written as: the circumferential radius at the tube pole is describe as below: Where R0 is the initial tube outer radius, L0 is the length of tube deformation and h is the bulge height at tube pole

Strain analysis

Stress analysis

Results and discussion

Conclusion