Fracture Prediction Of Aluminum Alloy Tube Hydroforming Based On GTN Damage Model

Hydroforming of aluminum alloy tubes is an advanced manufacturing technologyof structure lightweight, which has been widely used. However, due to poor formabilityof aluminum alloy at room temperature, burst is one of the main defects inhydroforming of aluminum alloy tubes. The macroscopic response and the microscopicstructure of material have an essential relation, the ductile fracture of metal materialusually includes void nucleation, growth and coalescence. Micromechanics damagemodel can reflect the process of accumulation of material damage and fracture ofmaterial. Micromechanics damage model has been widely applied for the analysis andprediction of ductile fracture. The research on fracture prediction of tube hydroforminghas an important significance on application of tube hydroforming technology.In this paper, damage evolution of the uniaxial tensile specimens of5A02aluminum alloy was observed by scanning electron microscopy (SEM), the originalvoid volume fraction, the critical void volume fraction and the void volume fraction atthe final failure were preliminarily identified, the damage parameters of GTN modelwere determined by the finite element inverse method, which combined the uniaxialtensile experiment and finite element numerical simulation,.The finite element numerical simulation of tube bulging based on GTN damagemodel was carried out when the both ends of tubes were fed or free. Burst pressure werepredicted in tube bulging in which the void volume fraction at the final failure as a tubeburst criterion. The influence of damage evolution on wall thickness thinning, thebulging height and ultimate strain were analyzed. The results show that, with the growthof the void volume fraction, the bulging height will increase and wall thickness willdecrease.The bulging experiments of5A02aluminum alloy tube were conducted when theboth ends of tubes were fed or free. Burst pressure were compared with the tube burstpressure predicted, and the strains of the highest bulging point were analyzed, and theforming limit diagram of tube bulging was established.The damage fracture behavior of T-shape hydroforming was researched based onGTN damage model. The influences of internal pressure and feed on damage evolutionwere analyzed, and the influences of stress triaxiality and equivalent plastic strain on thevoid volume fraction were also studied.