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    Enhancing formability of Ti-6Al-4V cylindrical cups by pulsating hydroforming process: Experimental, numerical and microstructural investigations
    (Elsevier - Division Reed Elsevier India Pvt Ltd, 2024) Ozturk, Osman; Aydin, Mevlut; Gokcepinar, Omer Faruk; Ilbeyli, Harun Mert; Korkmaz, Habip Gokay; Yapan, Yusuf Furkan; Dilmec, Murat
    Ti-6Al-4V alloy sheet is an engineering material that is widely used due to its superior properties such as high strength-to-density ratio besides high temperature and corrosion resistance. However, its low formability at room temperature limits its wider applications. In this study, a cylindrical cup was hydroformed using a female die to examine how the pulsating effect would result under frictional conditions. Initially, finite element simulations were performed to design a proper die geometry. Next, forming tests were run on Ti-6Al-4V blanks under pressure increased monotonically and with pulsation, and microstructural analyses were performed on the formed specimens. The effects of pulsation frequency, amplitude, and base pressure on the formability were investigated. The nose radius/thickness ratio, maximum thinning, bursting pressure, and die-filling ratio measured on the specimens formed under monotonic and pulsating loadings were compared, and the improvement in the formability was demonstrated. An increase of 38.5 % in bursting pressure occurred and the nose radius of the part was decreased up to 30 % with pulsating loading. The die-filling ratio was improved from 87.9 % to 95.3 % with optimized pulsation parameters. The underlying microstructural reasons for the improved formability were elaborated using XRD, SEM, and TEM analyses.
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    Formability improvement in Ti-6Al-4 V sheet at room temperature by pulsating hydraulic bulging: experimental and numerical investigations
    (Springer London Ltd, 2023) Ozturk, Osman; Korkmaz, Habip G.; Atas, Gurkan; Aydin, Mevlut; Turkoz, Mevlut; Toros, Serkan; Dilmec, Murat
    Ti-6Al-4 V sheets possess limited formability at room temperature due to low ductility with almost no strain hardening. Pressure pulsation during hydroforming may bring significant improvement as an alternative to the widespread solution hot forming. However, much uncertainty exists on the deformation mechanism and effects of pulsating on difficult-to-form materials. In this study, the effect of pulsating pressure on the hydraulic bulge test was investigated to increase the limited formability of the Ti-6Al-4 V sheet at room temperature. Experimental results of thickness distribution and bulge height obtained from the bulge tests were compared with the finite element simulation results. The results show that the tests with pulsation allow a higher thickness reduction with a slightly more homogenous thickness distribution. Pulsation causes a delay in the material's failure resulting in a 15.4% increase in the dome height with a 17% increased burst pressure compared to monotonic loading. The underlying microstructural phenomena of increased formability were elaborated using dislocation estimations, fracture surface analysis, and hardness. Test results suggest that pulsation improves formability by 47% in terms of maximum elongation due to stress relaxation.