Integrated multi-scale framework for predicting deformation and damage in hot bulging of Ti-6Al-4V alloy: Experiments, modelling, and simulation

Abstract

Accurate prediction of metal bulging forming requires a multi-scale material model that fully describes material flows, microstructures, and forming limits under a plane stress state, as well as a precise bulging control method to maintain constant strain rate throughout the forming process for reliable forming limit data. However, research integrating all these aspects into a unified prediction framework remains limited. This study analyzes the hot bulging of Ti-6Al-4V alloy via experiments, modelling and simulations. Frictionless gas bulging tests were conducted under various temperatures (800–900 ℃), strain rates (0.001–0.1 s⁻¹) and axial length ratios (1, 1.5, 2). A pressure loading model was developed to ensure a constant strain rate across bulging process, with 90.73 % accuracy. Based on bulging tests and post-bulging microstructural observations, a physically based constitutive model with a plane stress state damage mechanism was established, accurately predicting microstructure, macroscopic flows and forming limits. The prediction accuracies for stress-strain curves and average grain size were 91.77 % and 93.40 %, respectively, with the predicted forming limit curves aligning well with experimental data. The validated constitutive model was applied in finite element simulations. The thickness distribution and damage positions from the simulations closely matched the experimental results, which confirmed the reliability of the finite element framework. Finally, optimal bulging conditions were identified via finite element simulations for improved deformation uniformity within 700–900 ℃ and 0.0001–1 s⁻¹. According to this, a large complex tubular component was successfully formed. By integrating an experimental–theoretical–computational framework, this study provides an effective approach to bridge fundamental research and industrial application, offering insights into the multiscale deformation damage mechanisms and practical control during sheet metal forming.