Effects of Nonconstant Strain Rate on Forming Limit and Efficiency in High Pressure Pneumatic Forming of Ti-Alloy Components

A process with gas pressure up to 70MPa is introduced, which is called High Pressure Pneumatic Forming (HPPF), comparing to superplastic forming (SPF) with pressure lower than 5MPa. HPPF process can be used to form tube blank at lower temperature with high energy efficiency and also at higher strain rate than SPF. With Ti-3Al-2.5V Ti-alloy tube, the potential of HPPF was studied through experiment in the temperature range of 700~850°C. To know the formability of the Ti-alloy tube, HPPF experiments of a large expansion tube and a square cross-section tube were carried out at different temperature and pressure. The limit expansion ratio and limit radius were measured to evaluate the forming limit of Ti-3Al-2.5V tube within HPPF. The results show that the lower the pressure, the better formability and the lower efficiency. At a constant pressure, the strain rate increases exponentially with bulging time during the free bulging procedure, but decreases exponentially during the small corner calibration. Through EBSD pictures, the deformation mechanism of the corner forming process in HPPF was analyzed. Because of a nonconstant strain rate deformation state and complicated stress and strain state during HPPF, the microstructure at the transition zone of the components are also nonhomogenous, but the grains are refined to a certain extent. Key words: HPPF, Ti-3Al-2.5V, limit expansion ratio, corner forming

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Forming Limit and Loading Path of Mg-Alloy Tube Bulging

Materials Science Forum ◽

10.4028/www.scientific.net/msf.488-489.637 ◽

2005 ◽

Vol 488-489 ◽

pp. 637-640

Author(s):

Gang Liu ◽

Stephan Jäger ◽

Klaus Siegert

Keyword(s):

Internal Pressure ◽

Strain Rate ◽

Expansion Ratio ◽

Mg Alloy ◽

Loading Path ◽

Forming Limit ◽

Small Range ◽

Inner Pressure ◽

Alloy Tube ◽

Az31 Mg Alloy

The paper researched formability ability of AZ31 Mg-alloy tube by hot pneumatic bulging. FEM simulations were carried out to reveal the effect of internal pressure changing on bulging process and forming limit. Several loading paths with different pressure changing were used in the simulations. From the research, the original expansion ratio of diameter using a bilinear loading path, namely the internal pressure was increased linearly, is only 22%, and bursting occurs quickly. With a step-like loading path, namely the internal pressure is increased step by step, among the steps, the pressure is kept constant, and the strain rate of bulging can be kept into a small range. Thus the deformation around the hoop direction is more even than the linear loading path, and than bursting can be postponed. During bulging, the inner pressure should be lowered with the increase of diameter to keep the strain rate in a small range around a constant value. Through optimization of loading path, the forming limit can be enhanced obviously so that the expansion ratio of diameter can be increased to 25.1%.

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Acquisition and Evaluation of Theoretical Forming Limit Diagram of Al 6061-T6 in Electrohydraulic Forming Process

Metals ◽

10.3390/met9040401 ◽

2019 ◽

Vol 9 (4) ◽

pp. 401 ◽

Cited By ~ 2

Author(s):

Min-A Woo ◽

Woo-Jin Song ◽

Beom-Soo Kang ◽

Jeong Kim

Keyword(s):

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Forming Limit Diagram ◽

Forming Limit ◽

Forming Process ◽

Electrohydraulic Forming ◽

Al 6061 ◽

Shpb Test ◽

Strain Rate Hardening ◽

Free Bulging

The current study examines the forming limit diagram (FLD) of Al 6061-T6 during the electrohydraulic forming process based on the Marciniak–Kuczynski theory (M-K theory). To describe the work-hardening properties of the material, Hollomon’s equation—that includes strain and strain rate hardening parameters—was used. A quasi-static tensile test was performed to obtain the strain-hardening factor and the split-Hopkinson pressure bar (SHPB) test was carried out to acquire the strain rate hardening parameter. To evaluate the reliability of the stress–strain curves obtained from the SHPB test, a numerical model was performed using the LS–DYNA program. Hosford’s yield function was also employed to predict the theoretical FLD. The obtained FLD showed that the material could have improved formability at a high strain rate index condition compared with the quasi-static condition, which means that the high-speed forming process can enhance the formability of sheet metals. Finally, the FLD was compared with the experimental results from electrohydraulic forming (EHF) free-bulging test, which showed that the theoretical FLD was in good agreement with the actual forming limit in the EHF process.

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Progress on High Pressure Pneumatic Forming and Warm Hydroforming of Titanium and Magnesium Alloy Tubular Components

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.2456 ◽

2014 ◽

Vol 783-786 ◽

pp. 2456-2461 ◽

Cited By ~ 3

Author(s):

Gang Liu ◽

Yong Wu ◽

Jian Long Wang ◽

Wen Da Zhang

Keyword(s):

High Pressure ◽

Temperature Field ◽

Magnesium Alloy ◽

Thickness Distribution ◽

Expansion Ratio ◽

Mg Alloy ◽

Ti Alloy ◽

Warm Hydroforming ◽

Corner Filling ◽

Tubular Components

Complex structural tubular components of Titanium and Magnesium alloy can be obtained at a certain temperature by high pressure pneumatic forming (HPPF) with gas medium or warm hydroforming with pressurized liquid medium. At 800°C, through experimental research on HPPF of TA18 Ti-alloy tube with expansion ratio of 50%, the influence of axial feeding on thickness distribution of the workpiece was studied. Using reasonable loading curve, the component with large ratio can be formed with a small thinning ratio as 13% with total axial feeding amount of 40mm. At 850°C, HPPF experiments of TA18 Ti-alloy component with square section were carried out. The influence of gas pressure on thickness distribution and corner filling process were analyzed. The larger the pressure, the sooner the displacement changes at the corner, and the shorter corner filling term. At pressure of 30 MPa, small corner with the relative corner radius of 2.0 can be obtained within 168s. For Mg-alloy tubular part, warm hydroforming with non-uniform temperature field was studied. By using reasonable axial temperature field and loading path, the maximum thinning ratio of Mg-alloy tubular component with expansion ratio of 35% was reduced from 21.6% to 11.6%.

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Warm hydroforming of magnesium alloy tube with large expansion ratio

Transactions of Nonferrous Metals Society of China ◽

10.1016/s1003-6326(09)60419-2 ◽

2010 ◽

Vol 20 (11) ◽

pp. 2071-2075 ◽

Cited By ~ 10

Author(s):

Gang LIU ◽

Ze-jun TANG ◽

Zhu-bin HE ◽

Shi-jian YUAN

Keyword(s):

Magnesium Alloy ◽

Expansion Ratio ◽

Alloy Tube ◽

Large Expansion ◽

Warm Hydroforming

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Warm hydroforming of magnesium alloy tube with large expansion ratio within non-uniform temperature field

Transactions of Nonferrous Metals Society of China ◽

10.1016/s1003-6326(12)61739-7 ◽

2012 ◽

Vol 22 ◽

pp. s408-s415 ◽

Cited By ~ 10

Author(s):

Gang LIU ◽

Wen-da ZHANG ◽

Zhu-bin HE ◽

Shi-jian YUAN ◽

Zhe LIN

Keyword(s):

Temperature Field ◽

Magnesium Alloy ◽

Expansion Ratio ◽

Uniform Temperature ◽

Alloy Tube ◽

Large Expansion ◽

Uniform Temperature Field ◽

Warm Hydroforming

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Mechanical Response of Future Combat Systems (FCS) High-Energy Gun Propellants at High-Strain Rate

10.21236/ada402939 ◽

2002 ◽

Author(s):

Michael G. Leadore

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

Mechanical Response ◽

High Strain ◽

High Energy ◽

Future Combat Systems ◽

Gun Propellants

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Effect of High Strain Rate on Adiabatic Shearing of α+β Dual-Phase Ti Alloy

Materials ◽

10.3390/ma14082044 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2044

Author(s):

Fang Hao ◽

Yuxuan Du ◽

Peixuan Li ◽

Youchuan Mao ◽

Deye Lin ◽

...

Keyword(s):

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Damage Tolerance ◽

Shear Bands ◽

Dual Phase ◽

Ti Alloy ◽

Hopkinson Pressure Bar ◽

Β Phase ◽

Schmid Factor ◽

Pressure Bar

In the present work, the localized features of adiabatic shear bands (ASBs) of our recently designed damage tolerance α+β dual-phase Ti alloy are investigated by the integration of electron backscattering diffraction and experimental and theoretical Schmid factor analysis. At the strain rate of 1.8 × 104 s−1 induced by a split Hopkinson pressure bar, the shear stress reaches a maximum of 1951 MPa with the shear strain of 1.27. It is found that the α+β dual-phase colony structures mediate the extensive plastic deformations along α/β phase boundaries, contributing to the formations of ASBs, microvoids, and cracks, and resulting in stable and unstable softening behaviors. Moreover, the dynamic recrystallization yields the dispersion of a great amount of fine α grains along the shearing paths and in the ASBs, promoting the softening and shear localization. On the contrary, low-angle grain boundaries present good resistance to the formation of cracks and the thermal softening, while the non-basal slipping dramatically contributes to the strain hardening, supporting the promising approaches to fabricate the advanced damage tolerance dual-phase Ti alloy.

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