Comparison of damage behavior of AA2024–T4 under quasi-static hydraulic and electro-hydraulic forming

The aim of the thesis is to investigate high-speed forming processes and the particular attention given to the damage mechanism during plastic deformation in the forming process. Electro-hydraulic forming (EHF) and quasi-static hydraulic (QS) processes were used to form 1.2mm thick AA2024-T4 sheets. To identify the damage at the limit of forming process, many sheets were formed with different energy, up until the fracture was observed at the top of the conical shape. The velocity measurement was performed using PDV system for EHF process. The specimens at the forming limit were chosen for microstructural characterisation using SEM and micro tomography to quantify the damage in various sections of the specimen. The maximum velocity of 174.6 ms-1 and a maximum strain rate of 938 s-1 was achieved during the EHF process. The strain, void fraction (Vf) and hardness were plotted to investigate the difference between EHF and QS forming process. The main mechanism responsible for the ductile damage in AA2024-T4 is void nucleation, growth, and coalescence of intermetallic particles. Due to strain hardening mechanism influenced by strain accumulation, the hardness of the QS was increased by 27.7% and 28.5% for EHF specimen. EHF specimens have a higher number of small voids present at high and low strain deformation zones. Strain localisation, combined with microstructural heterogeneity is identified to be responsible for the final failure. The formability of the EHF process is observed to be better than the QS forming process.