Formability and failure mechanisms of ultra-thin TA2 titanium sheets in microchannel hydroforming: Effect of thickness-to-grain-size ratio

Abstract

The forming limit behavior of ultra-thin TA2 titanium sheets under microchannel hydroforming is critically affected by the ratio of sheet thickness (t) to grain size (d). In this study, the impact of varying t/d ratios on formability was systematically evaluated using an integrated experimental and finite element (FE) methodology. Forming limit curves (FLCs) were determined for sheets with t/d ratios spanning 1 to 5.21. The results indicate a pronounced decrease in the plane-strain forming limit for t/d values below 5.21, correlating with heightened susceptibility to localized thinning and fracture, particularly at microchannel bends and corners. To address the limitations of direct FLC measurement at low t/d, a hybrid experimental-numerical framework was introduced, enabling virtual FLC prediction. Strain path analysis and FE simulations identified the upper corner regions of the microchannel as most prone to failure, characterized by thickness-direction thinning exceeding 20% under plane strain conditions. The proposed approach establishes a direct relationship between microstructural state, deformation mode, and failure, offering a robust strategy for optimizing process parameters and structural integrity. These findings advance the design and manufacture of ultra-thin titanium components for energy and microfluidic applications, including fuel cell bipolar plates.