| Metal tubular components,with excellent properties such as light weight,good formability and the ability of impact energy absorption,have higher and higher usage rate,as the automobile,aviation and shipbuilding industries develop rapidly.Therewith,more precise forming is required.Small or medium diameter seamless tube is generally obtained by cold rolling,cold drawing or extrusion processing.There is a distribution along the specific direction of the texture,resulting in the performance of the tube varying in different directions,i.e.anisotropic,which has a great impact on deformation behavior of the tube.However,the tube's unique hollow structure,makes a much more complex mathematical analysis compared with the plate.In this study,the existence of anisotropy in small diameter metal tubes was confirmed by the experimental method,and two methods that characterized anisotropy were introduced.Then,a variety of anisotropy models were set up in the software ABAQUS to explore the effects of anisotropy on the bending and necking properties of tubes.Finally,the behavior of slightly larger diameter tubes in the ring hoop tension test,which characterized their circular deformation ability,was discussed.The main contents of the study include the following aspects:(1)The mechanical properties and true stress-strain curves were obtained by uniaxial tension test for tubes including two kinds of materials(1Cr18Ni9Ti/5A03)and three kinds of diameters(?8/10/12mm)and a uniform wall thickness of 1mm.The inner and outer diameters of the deformed tubes were measured at different elongations.By calculating the circumferential strain values inside and outside of the tubes,the two strains were found to be unequal.The difference was obvious under the small elongation,and decreased gradually with the elongation increasing.This showed that deformation was not uniform throughout the tubes,i.e.the tubes were not isotropic.(2)The contractile strain ratios of the inner and outer sides of the tubes,CSR_d and CSR_D,were calculated by using the parameters measured in the macroscopic uniaxial tensile test.Based on the hypothesis of isotropy in rotative surface while anisotropy in thickness,the finite element anisotropy models that considered only CSR_D or considered only CSR_d,and the layered anisotropy model that considered both CSR_D and CSR_d,were defined in ABAQUS to evaluate the performance of tubes in uniaxial tension test.By comparing the simulation results with the experimental results,the optimal anisotropy model was chosen.(3)Based on the definition method of the selected anisotropy model,the finite element models of rotary bending of tubes were defined.The effect of anisotropy on the deformation behavior during tube bending was analyzed by comparison with the results of isotropic model simulation and the experimental results.(4)The method,which gave the plastic strain ratios along different directions of X65steel tube with diameter of 40mm and wall thickness of 4mm according to the original texture information of measured by XRD and a virtual experiment frame,was introduced.Then,the data was quoted in this paper to establish the anisotropic finite element model of tube necking process based on Hill48 anisotropic yield criterion.The feasibility of using this method to characterize the anisotropy of tubes and the effect of anisotropy on tube necking was analyzed.(5)A new method of hoop tension test,hoop tension with unconstrained gauge-sections,was proposed,and investigated by using the 1Cr18Ni9Ti tube with diameter of 34mm and wall thickness of 2mm.Combined analysis of experiment,theory and finite element method discussed the advantages and disadvantages of the new method,as well as the deformation features of the ring specimen,in contrast with the conventional hoop tension test with frictional gauge-sections. |
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