Accurate characterization of circumferential uniaxial hardening and efficient modeling of biaxial hardening for anisotropic aluminum alloy tubes

Determining comprehensive anisotropic parameters for thin-walled tubes is extremely challenging due to the curved surface geometry, causing constitutive modeling and applications to lag significantly behind those for sheets. Although a segment ring expansion test (SRET) has been established to enable precise measurement of the circumferential normal anisotropy coefficient r ₉₀, limitations remain in modeling the biaxial tensile hardening of anisotropic aluminum alloy tubes (Cui et al., 2025). In this paper, a novel pyramid-segment ring expansion test (PRET) method was first developed to determine the σ ₉₀- ε ₉₀ curve of tubes through mechanical analysis. Quantitative relationships between test parameters and stress state were established to produce a uniform, near-uniaxial stress state, and its high accuracy was verified, with a measurement error of only 1.6%. Then, the predictive characteristics of the Barlat89 model are analyzed to clarify the effects of the model coefficients and exponent. Based on theoretical analysis and testing conditions, a hybrid calibration strategy was proposed to model biaxial tensile hardening. Then, experimental tests on 6061 and 5B02 aluminum alloy tubes confirmed distinct anisotropies in hardening and flow under uniaxial and biaxial states. After precisely quantifying their anisotropies, a chain of relationships was established for the Barlat89 model, linking anisotropic parameters to model coefficients and exponent and to prediction accuracy, thereby comprehensively revealing how different calibration strategies and material characteristics affect prediction performance. Results show that the hybrid calibration strategy reduces the average error from 2.9% to 0.7% for 6061 tubes and from 7.0% to 2.8% for 5B02 tubes under M = 8 compared with (Cui et al., 2025), and benefiting from lower M -sensitivity, yields stable predictions over a wide range of M . Thus, an efficient modeling approach was established for anisotropic aluminum alloy tubes by synergistically integrating a novel test method, a simpler yield criterion, and a flexible modeling concept. It not only predicts the load-displacement response of the PRET but also precisely describes the biaxial hardening behavior in finite element (FE) simulation, thereby significantly enhancing the simulation accuracy for strain distribution and tube geometry in the biaxial tension test. These can contribute to high-precision simulations of load matching and deformation behavior during the axisymmetric forming processes of aluminum alloy tubular components, which primarily involve biaxial tension.