http://repositorium.sdum.uminho.pt/bitstream/1822/53320/1/art18.pdf

Mechanical characterization and constitutive parameter identification of anisotropic tubular materials for hydroforming applications

Tube hydro-bulging test is a specialized method to obtain the mechanical properties of tubes when they are deformed under bi-axial stress states. However, the normal stress cannot be ignored in double-sided tube hydroforming process. In order to investigate the mechanical properties of anisotropic thin-walled tubes under three-dimensional stress state, an analytical model for stress component calculation for fixed-end tube under internal and external pressures was proposed. Furthermore, the equivalent stress and the equivalent strain were derived using the Hill 1948 yield criterion through plastic increment theory. A thin-walled AA5052-O aluminum alloy tubes were bulged under different external pressures using a dedicated testing apparatus for double-sided tube hydro-bulging tests. Then, hardening curves considering anisotropy were obtained for each external pressure condition, respectively. It is shown that the strain hardening exponent of AA5052 tube shows a slight increase with the increasing external pressure, and the external pressure of 85 MPa has little or no effects on the hardening behavior of tubes. Moreover, the anisotropy has a little effect on the strain hardening exponent, but has an obvious influence on the strength coefficient of the AA5052 tube. Therefore, for the measurement of the AA5052 tube’s mechanical properties under three-dimensional stress state, the effect of external pressure can be ignored but the anisotropy of tubes must be considered.

Determination of mechanical properties of anisotropic thin-walled tubes under three-dimensional stress state

Cryogenic deformation behavior of 6061 aluminum alloy tube under biaxial tension condition

Constitutive parameter identification of CB2001 yield function and its experimental verification using tube hydroforming tests

In the present study, the Johnson-Cook damage model is proposed as a comprehensive damage criterion to predict all types of probable failures in tube hydroforming process. Also, the Johnson-Cook ma...

A comprehensive damage criterion in tube hydroforming

The flow stress, used to describe the plastic deformation behavior of thin-walled tube, is one of the most important parameters to ensure reliable finite element simulation in the tube hydroforming process. In this study, a novel approach of on-line measurement based on digital speckle correlation method is put forward to determine flow stress of thin-walled tube. A simple experimental tooling is developed and free-bulged tests are performed for 304 stainless steel and H62 brass alloy tubes. An analytical approach is proposed according to the membrane theory and the force equilibrium equation. The developed method is validated by means of FE simulations. The results indicate that the present method is acceptable to define the flow stress in the tube hydroforming process.

Determination of flow stress of thin-walled tube based on digital speckle correlation method for hydroforming applications.

In this article, tube hydroforming along with stamping, a compound forming technology of thin-walled tube using stamping and hydroforming processes, was presented to cut forming costs, reduce numbe...

Investigation of tube hydroforming along with stamping of thin-walled tubes in square cross-section dies

Liquid impact forming (LIF) is a new type of composite forming method based on tube hydroforming (THF) and stamping forming. It has high efficiency and low energy consumption, with no need for external pressure source, so LIF has good development prospect and application value in the field of lightweight and integrated manufacturing. In order to investigate LIF technology, the generation mechanism of the internal pressure was analyzed in this paper. Firstly, based on the theory of the liquid volume compression, the change law of the cavity volume of metal thin-walled tubes was analyzed according to size parameters of the tube and dies during the forming process. The mathematical relationship between the internal pressure in the tube cavity and clamping parameters (clamping speed and clamping height) was obtained under the impact load. Then, the theoretical maximum internal pressure Pmax1 was discussed under different die cavities. Furthermore, the relationship between the internal pressure in the tube and the clamping time under different die cavities with a same clamping speed was obtained according to the transient dynamic analysis by ANSYS Workbench. At the same time, the simulated maximum internal pressure Pmax2 and the calculational maximum internal pressure Pmax were acquired under different die cavities. In addition, the LIF experiments were performed using a simple and suitable device to verify the calculational maximum internal pressures under die cavities with different side lengths. Through the comparison of the calculational and experimental maximum internal pressures, it is not difficult to find that the values of both showed a good agreement and the maximum deviation is 10.27%. The research results indicate that the theoretical equation of internal pressure of metal thin-walled tubes based on LIF is reliable, and it will lay a good foundation for further study.

Investigation of the generation mechanism of the internal pressure of metal thin-walled tubes based on liquid impact forming

The utility model provides a thin-walled metal tube impacting and hydraulic expansion device. The bottom ends of center blind holes in the two ends of a liquid supply bolt are communicated with the outer wall through a radial hole. The liquid supply bolt penetrates through a thin-walled metal tube and the two ends of the liquid supply bolt both extend out. Sealing plugs are arranged at the two ends of the liquid supply bolt in a sleeved mode and are plugged into openings of the thin-walled metal tube. Large center step holes of positioning covers are arranged in the openings of the thin-walled metal tube in a sleeved mode so that the liquid supply bolt can extend out of small center step holes of the positioning covers, nuts are screwed at the two ends of the liquid supply bolt, and the positioning covers squeeze the sealing plugs so that the sealing plugs can be attached to the thin-walled metal tube and the liquid supply bolt. One end of the liquid supply bolt is connected with an L-shaped tube through a control valve, and the other end of the liquid supply bolt is connected with a liquid container in a sealed mode through another control valve. An upper template and a lower template of a die frame are fixedly provided with an upper die and a lower die respectively, the thin-walled metal tube is arranged between the upper die and the lower die, when the device is used, the left control valve and the right control valve are opened, liquid is injected into the liquid container so that the thin-walled metal tube is filled with liquid, the control valves are closed, a stamping head of a press machine moves downwards, the upper die and the lower die are closed, and hydraulic expansion is achieved. The device is easy and convenient to use, high in efficiency, simple in structure and low in cost.

Thin-walled metal tube impacting and hydraulic expansion device

The invention relates to an impact hydraulic expansion device for a metal thin-wall tube and a using method thereof. The bottom ends of center blind holes at two ends of a liquid supply bolt are communicated with an outer wall through radial holes. The liquid supply bolt penetrates through the metal thin-wall tube, the two ends of the liquid supply bolt extend out and are sleeved with sealing plugs, and the sealing plugs are plugged into pipe openings of the metal thin-wall tube. The pipe opening of the metal thin-wall tube is sleeved with a large hole of a center step hole of a locating cover, the liquid supply bolt extends out of a small hole, nuts are screwed in two ends of the liquid supply bolt, and the locating cover extrudes the sealing plugs to adhere to the metal thin-wall tube and the liquid supply bolt. One end of the liquid supply bolt is connected with an L-shaped pipe through a control valve, and the other end of the liquid supply bolt is in sealed connection with a liquid container through another control valve. An upper die and a lower die are fixed on an upper formwork and a lower formwork of a die frame respectively, and the metal thin-wall tube is placed between the upper die and the lower die. The using method comprises the steps of opening a left control valve and a right control valve, pouring liquid into the liquid container, filling the metal thin-wall tube with the liquid, closing the control valves, descending a pressing machine stamping head, and closing the upper die and the lower die to achieve hydraulic expansion. The impact hydraulic expansion device is simple, convenient, practical, high in efficiency, simple in structure and low in cost.

Huiping Liang

Papers

Determination of flow stress of thin-walled tube based on digital speckle correlation method for hydroforming applications.

Investigation of tube hydroforming along with stamping of thin-walled tubes in square cross-section dies

Investigation of the generation mechanism of the internal pressure of metal thin-walled tubes based on liquid impact forming

Thin-walled metal tube impacting and hydraulic expansion device

Impact hydraulic expansion device for metal thin-wall tube and using method thereof