Contractile Strain Ratio Research Articles

An insight into texture evolution and tailoring during multi-pass cold pilgering of high-strength titanium alloy tubular materials

The high-strength titanium alloy tubular materials are extensively applied in aviation and aerospace industries, wherein the mechanical properties, subsequent formability and in-service performance of the tube are strongly dependent on the texture variation. Cold pilgering has been a favorable fabrication technology for hard-to-deform tubes, however, the coupling effects of inherently low symmetric and complex multi-pass thermal-mechanical histories led to the significant diversity of the texture evolution of high-strength titanium alloy tubular materials. The traditional methods which mainly dependent on the Q value and deformation degree adjusting are difficult to achieve the precise tailoring of texture in multi-pass cold pilgering process. In this work, to break the limitation of the traditional method, by taking into account the mechanical properties iterating in each pass and the texture inheritance in recrystallization annealing process, a numerical computation platform for texture evolution prediction during multi-pass cold pilgering of titanium alloy tube was firstly established. The accuracy and reliability of the platform was verified by the 3-pass cold pilgering experiment and texture characterization. Secondly, the crucially effect of the initial texture was deeply explored in this work, the results indicated that the desired radial texture would be enhanced only when the Q value and area reduction ratio (AR) exceed the corresponding threshold under the specific initial texture, in which the tensile twinning was the vital deformation mode for the grain rotation and texture evolution. Thirdly, the quantitative correlation between processing conditions and finished radial texture intensity fRD was established which comprehensively introduced the Q value, AR and initial texture intensity. In contrast to the accuracy of 59.4% based on the single factor Q value and 75.1% based on double factor of Q value and AR, the prediction accuracy of the quantitative correlation established in this work upgraded to approximate to 95%. Finally, taking the contractile strain ratio (CSR) as the index to reflect the macro anisotropy mechanical properties, the bonds that unite the processing conditions, fRD and CSR were also built.

Influence of Texture on Mechanical Properties of Titanium Alloy Tubes

Mechanical properties and texture of tube material formed in the process of tube production were studied. Texture in tubes was estimated by contractile strain ratio (CSR) according to requirements of the standard for tubes. Mechanical properties depend on CSR. Optimal values of mechanical properties were determined: ultimate strength, yield strength and relative elongation which provide CSR values within 1.3...3.5. The texture was evaluated in the process of tube manufacture. An increase in radial component of the texture leads to an increase in CSR. At high CSR values up to 3-3.5, tubes often do not withstand process tests for flattening and bending. Correction of CSR values is required. It was shown that an increase in ductility of tubes increases the value of CSR.

Effects of the crystallographic texture on the contractile strain ratio of Ti–3Al–2.5V tubing

The contractile strain ratio (CSR) is an important property and a quality control factor of cold-worked and stress-relieved Ti–3Al–2.5V tubing. In this work, the CSR values of three thin-walled Ti–3Al–2.5V tubing samples were obtained by uniaxial tensile tests, and the crystallographic textures of the tubing samples were characterized by orientation distribution functions (ODFs) which were determined on the basis of a series of pole figures obtained by X-ray diffraction. A quantitative method is proposed for exploring the correlation between the CSR values and the ODF data of the tubing samples, including the following steps: Firstly, taking advantage of the ODF data, the volume fraction (V%) of crystallites that lie within a certain range of Euler angles (φ1, Φ, φ2) can be calculated, and the calculation is performed on each set of Euler angles (φ1, Φ, φ2). Secondly, each V% is resolved into an effective fraction in the orientation of the ideal radial texture {0002}〈10\overline 10〉 corresponding to the Euler angles of (0, 0, 0), and the equivalent radial texture (ERT) is obtained as the sum of all such effective fractions. Thirdly, similarly to the previous step, the equivalent tangential texture (ETT) is calculated. The CSR will be related to the ratio of the ERT to the ETT, named the equivalent texture ratio (ETR). The CSR values of the tubing samples are 1.38, 1.96 and 2.19 and their ETR values are 1.33, 1.72 and 1.87, respectively. In particular, the CSR and the ETR of the tubing with a random distribution of the basal poles in the radial–tangential plane are both unity. It is found from the above data that the CSR increases approximately linearly with the ETR. Since the three-dimensional orientations of crystallites and the orientation distributions throughout the Euler space are taken into account in the calculations of the ETR, the proposed method can be used for predicting and explaining the mechanical anisotropy of Ti–3Al–2.5V tubing more accurately.

Deformation-based joining for high-strength Ti-3Al-2.5V tubular fittings based on internal roller swaging

Deformation-based joining presents efficient, reliable and environmentally friendly advantages widely applying in the pipeline system. Internal roller swaging (IRS), one of deformation-based joining ways, is an inner expanding spinning process with characteristics of sheet-bulk forming, and it has the potential to fabricate high-strength tubular joining components with better high-pressure resistance and sealing performance. Taking a high-strength Ti-3Al-2.5V titanium alloy (TA) tube as the case material, this study combines explicit and implicit finite element (FE) modeling with experimental validating to explore the deformation mechanisms of the IRS process. By using the digital image correlation method (DICM) based uniaxial tension, the contractile strain ratio (CSR) of the TA tube was obtained to describe its anisotropy. By analyzing the mechanism of IRS, the motion equations of three rollers were deduced in the forming process, and a simplified 3D FE model for the IRS process was developed. Based on the FE simulation and analysis, the inhomogeneous flow deformation behaviors of TA tube in the IRS process were investigated by subdividing the deformation areas of the tube. Then, the material flow features of TA tube in the IRS process were explored by analyzing the axial displacements of the tube and observing its flow localization by means of optical microscope. Finally, the forming quality of the tubular joining components can be accurately designed and controlled by revealing the relationship between the swaging depth and the axial elongation and the relationship between the swaging depth and the contact shear stress. It is concluded that this incremental deformation-based joining process has obvious superiority to fabricate high-strength TA tubular joining components, and their reliability can be effectively enhanced by accurately controlling the swaging depth.

Texture evolution and controlling of high-strength titanium alloy tube in cold pilgering for properties tailoring

Abstract As one of the preferred fabrication technologies for high-strength titanium alloy tubes, cold pilgering has unique advantages of large deformation, fine surface, and close dimensional tolerance since materials are incrementally experiencing compressive stress states dominated local loading throughout entire rolling process. However, both complex external loading history and low symmetric hexagonal close-packed (HCP) crystal structure induce heavy crystallographic reorientation of polycrystalline significantly influencing formability and performance of titanium tubular products. How to achieve a bespoken tailoring of texture related properties is still a challenge. Accordingly, taking high-strength Ti-3Al-2.5 V tubes as the case material, this study focuses on the tube texture evolution and the texture controlling guidelines for properties tailoring in cold pilgering. By coupling validated and verified three dimensional finite element (3D-FE) model and viscoplastic self-consistent (VPSC) crystal plasticity model, a macro-meso scaled computation platform is established to predict the inhomogeneous deformation flow and texture evolution during pilgering. Then the tube texture evolution characteristics along rolling process with three typical initial textures are investigated, and the correlation between texture evolution and spatial inhomogeneous deformation allocation is explored, in which the deformation history is fully featured by strain vector, viz., strain ratio α and equivalent plastic strain ee as well as ratios of wall thickness thinning to outer diameter reduction (total Q value and transient Q value). Taking the contractile strain ratio (CSR) as the most important indicator for evaluating the texture and properties, the effect of final texture features of the tube on its tensile mechanical properties is revealed, and then the texture controlling guidelines for properties tailoring of the tube are proposed. To obtain the desired near radial texture and the reasonable CSR, the different pass rolling specifications can be considerably designed to coordinate the spatial strain components based on reasonable range of total Q value and ee, then the rolling tools can be designed for further fine tuning of the transient Q value and strain ratio α.

Tooling design–related spatial deformation behaviors and crystallographic texture evolution of high-strength Ti-3Al-2.5V tube in cold pilgering

Cold pilgering has been considered as the preferred rolling fabrication technology for difficult-to-deform tubular materials such as high-strength titanium alloy tubes. However, the tooling geometry may induce complex deformation and significantly influence crystallographic texture which is closely related to the dimension assuring and properties tailoring of tube products. In this study, taking high-strength Ti-3Al-2.5V tubes as the case material, the tooling design–related spatial deformation behaviors and crystallographic texture evolution of tube in cold pilgering are focused. A macro-meso scaled computation platform is established by combining the three-dimensional finite element (3D-FE) model with the viscoplastic self-consistent (VPSC) crystal plasticity model to predict both the inhomogeneous macrodeformation and microtexture evolution in cold pilgering. Two basic tooling parameters in pilgering, viz., E1 representing exponent of roller groove curve and mandrel curve and E2 representing exponent of groove clearance, are chosen as the design variables. The cold pilgering under different tooling parameters are simulated and analyzed. The results show that (1) The rolling force decreases with the increase of E1 , while the effect of E2 on the rolling force is not significant, and smaller E1 and larger E2 have advantage for preventing surface defects of the tube product; (2) The E1 of 2.8 and E2 of 2.0 are more conducive to the wall thinning–dominated deformation of tube; (3) Taking the contractile strain ratio (CSR) as an indicator for characterizing crystallographic texture–related mechanical properties, the appropriate values of E1 and E2 for desirable radial texture of tube product are obtained.

Wall Thinning Characteristics of Ti-3Al-2.5V Tube in Numerical Control Bending Process

A finite element (FE) model for the numerical control (NC) bending of Ti-3Al-2.5V titanium alloy seamless tube is established, considering the variation in the contractile strain ratio (CSR) and elastic modulus (E). The wall thinning characteristics of Ti-3Al-2.5V tube under different geometric and process conditions were investigated. The results showed that the CSR-E variation can change the wall thickness, but has no remarkable effect on the change characteristics. The reasonable parameter ranges are as follows: a bending-radius range not less than 1.5 times the outer diameter, a bend angle up to 180?, and a mandrel extension of 0–3 mm. The friction coefficient between the pressure die and the tube should be in the range of 0.20–0.35, and between the bending die and the tube should be in the range of 0.05–0.15. As long as the performance meets the requirements, the relative push-assistant speed should be as small as possible.

An analytical springback model for bending of welded tube considering the weld characteristics

Predicting springback is important for improving the precision of tube bending forming. Compared with a homogeneous tube, the springback of a welded tube is more complex owing to the uneven material properties and geometric characteristics. An analytical springback model for welded tube bending was established according to the static equilibrium condition, with the aim of improving the prediction accuracy for the welded tube springback. In this model, the continuous variations of the weld material properties and the anisotropic parameter (contractile strain ratio), as well as the effect of the weld position were considered. Using the model, the springback angles of a QSTE340 welded tube in numerical control bending were predicted. Comparisons with experimental results suggest that this springback model can accurately predict the springback angle and present higher prediction accuracy than the existing models. In addition, the influence of description exactitude about the weld material property on the prediction accuracy was analyzed. The results suggest that the continuous weld material model adopted can significantly improve the prediction accuracy, and the improvement degree varies with the position of weld during bending. Finally, the effects of the mechanical properties matching between the weld and parent metal and the geometric parameters of the welded tube on the springback were determined using the established springback model.

Section Flattening in Numerical Control Bending Process of TA18 High Strength Tube

Section flattening is an inevitable physical phenomenon in the forming process of tube bending, and severe section flattening will affect the reasonable assembly of the tube fittings, and therefore restricts its wide application. Finite element (FE) model for numerical control (NC) bending of titanium tube considering the variation law of contractile strain ratio (CSR) and the Young's modulus (E) was established in the present paper. The section flattening behaviors of TA18 tube under different geometric conditions and different process conditions were investigated. The results show that considering the variation law of CSR-E can change the cross-section, which has no remarkable influence on the change law. The reasonable range of geometric and process parameters are obtained, which provides a basis for studying the forming prediction and controlling the final precision for the NC bending of TA18 tube.

Quasi-Static and Dynamic Properties of Ti-3Al-2.5V Titanium Alloy Tubes

This paper aimed to study the quasi-static and dynamic properties of Ti-3Al-2.5V titanium alloy seamless tubes. The extrusion billets were hot extruded, and then multipass cold rolled into tubes with outside diameter of 6mm, 8mm, 12mm respectively, and wall thickness of 0.5mm, 0.6mm, and 0.9mm respectively. The quasi-static properties were investigated by MTSTM testing system at strain rate of 10-3 s-1, while dynamic compression properties by Split Hopkinson Pressure Bar system at strain rate of 3000±200 s-1. The results show that the values of contractile strain ratio of the tubes are between 1.34 and 1.77. The quasi-static yield strength of the tubes is above 765MPa, which is 75 ∼ 80% of that of commercial Ti-6Al-4V plates. The dynamic plasticity of the tubes is comparable to commercial Ti-6Al-4V plates, while the dynamic strength of the tubes is only 50∼60% of that of commercial Ti-6Al-4V plates.

Texture Development of Ti-3Al-2.5V Titanium Alloy Tubes

Abstract The anisotropy, which is one of key mechanical properties of Ti-alloy tubes, is usually described in terms of the contractile strain ratio (CSR) macroscopically and dependent on the micro texture evolution. In order to understand the variation of CSR, the texture evolution of Ti-3Al-2.5V titanium alloy tubes was studied by Electron Back-Scattered Diffraction (EBSD). The results show that the basal poles of the α-phase incline from the radial direction to circumferential direction and stabilize around 45° between these two directions, and the strongly preferred orientation of the β-phase is observed with the increase of axial plastic strain. This change of texture decrease the CSR values rapidly in the initial stage, then they decrease slowly until stabilizing in the final stage. The simple model between CSR and texture quantity parameter f is modified by incorporating the texture component in the axial direction. Comparison with experiment shows that the modified model is in better agreement with the experimental values than the simple model.

Variation of contractile strain ratio of Ti–3Al–2.5V tubes and its effects in tubes numerical control bending process

The rapid development of high-technology fields, such as aviation and aerospace engineering, leads to the increased demand for lightweight and high-strength bent tubes due to their desirable properties. However, these tubes are of clear anisotropy. The anisotropy of tubes is usually described in terms of the contractile strain ratio (CSR). The current method to determine CSR can only be applied to cases of small uniform plastic deformation. This makes it difficult to obtain the variation in CSR during the plastic forming processes in which large plastic deformation usually occurs. Considering that the circumferential strain and axial strain can be directly and continuously obtained using the Digital Speckle Correlation Method (DSCM), this study proposed a new method based on the DSCM for determining CSR values over a large deformation range. Using this method, small gage lengths can be flexibly adopted to obtain a uniform plastic deformation as large as possible. To improve the precision of the method, elastic deformation was compensated theoretically, and varied values of Young's modulus with deformation were adopted. Using this method, the CSR of Ti–3Al–2.5V (ASTM Gr. 9) titanium alloy seamless tubes, which are typical anisotropic tubes, was observed varying with plastic deformation in that it decreased rapidly in the initial stage, then decreased slowly until stabilizing in the final stage. The variation can be expressed approximately as a second-order decay equation. The results of this study also show that the variation of CSR is sensitive to the values of Young's modulus and Poisson's ratio, therefore, varied values of Young's modulus and reliable Poisson's ratio should be adopted to improve precision. By embedding the variation in CSR with deformation into the finite element (FE) simulation for the numerical control (NC) bending of Ti–3Al–2.5V seamless tubes, the predication accuracy for the thinning degree of wall thickness, the flattening degree of the cross-section, and the springback angle can all be improved.

A constitutive model for anisotropic tubes incorporating the variation of contractile strain ratio with deformation

The contractile strain ratio (CSR) is an important index measuring the anisotropy of tubes. The values of CSR vary non-linearly with the amount of plastic deformation. However, up to now, there are no constitutive models which are able to take this variation into account. In order to obtain the actual deformation characteristics and improve the prediction capability for plastic deformation processes of anisotropic tubes, this study developed an elasto-plastic constitutive model based on Hill׳s 48 anisotropic yield function. In this constitutive model, the variation in CSR with plastic deformation was considered. A user material subroutine VUMAT incorporating the constitutive model was developed based on ABAQUS/Explicit platform. The comparisons between the finite element (FE) simulations and experiments for uniaxial tension, uniaxial compression and numerical control (NC) bending process of Ti–3Al–2.5V titanium alloy anisotropic tube, show that this constitutive model is reliable. The simulation accuracy was improved and the plastic deformation characteristics could be better described for the anisotropic tubes by using this constitutive model.

Effect of Recrystallization on Tensile Behavior, Texture, and Anisotropy of Ti‐3Al‐2.5 V Cold Pilgered Tubes

AbstractThe recrystallized volume fraction of Ti 3Al 2.5 V seamless tubes is measured using electron BackScatter diffraction (EBSD) after annealing under various conditions. Standard tensile tests and contractile strain ratio (CSR) measurements are carried out in order to analyze the effect of recrystallization on the tensile behavior and the anisotropy of the tubes. The tensile tests show anomalous yield‐point phenomena, which become stronger when the recrystallized fraction is increased. CSR value changes through recrystallization, from 0.8 in the cold worked stress relieved (CWSR) state to 1.1 in the fully recrystallized structure. Orientation distribution functions (ODFs) calculated from X‐ray data reveal a decay in the intensity of the crystallographic texture as recrystallization advances. This can explain the tendency toward isotropy when complete recrystallization is achieved.

Effect of Annealing Temperature on Texture and Creep Anisotropy in Ti3Al2.5V Alloy

Effect of annealing temperature is investigated on texture and creep anisotropy in a thinwalled tubing of titanium alloy. Creep anisotropy is studied under equibiaxial loading using internally pressurized tubing superimposed with axial load while monitoring in-situ the time variations of both hoop and axial strains. Relatively weak hoop direction in the cold-worked material became stronger following complete recrystallization. The analyses of the data reveal that the anisotropy parameter, P which is the contractile strain ratio for testing along hoop direction increases from around 0.6 for the cold-worked material to around 1.5 following complete recrystallization. Results indicate that planar isotropy should occur following annealing at around 800K. Work on the effects of annealing on the textures and deformation microstructures is in progress. We summarize here results from some of our earlier work on a different lot of Ti3Al2.5V tubing in the recrystallized states where the ODFs were used in conjunction with crystal slip models to predict creep anisotropy.

Effect of c/a-Ratio on Crystallographic Texture and Mechanical Anisotropy of Hexagonal Close Packed Metals

Hexagonal close packed metals exhibit highly anisotropic mechanical properties, a thorough knowledge of which is a primary requisite for predictability of the dimensional changes in service as well as formability characteristics. We summarize our work on the effects of c/a-ratio on preferred orientations and the resulting anisotropic mechanical properties. Zr and Ti alloys are considered to represent low c/a-ratio while Mg alloy (AZ31B) was chosen as ideal; these materials were available in tubing form. Pure zinc sheet was used to represent high c/a-ratio. Distinct differences are noted in the basal pole distributions, and crystallite orientation distribution functions derived from the pole distributions were combined with crystal slip models to predict the mechanical anisotropy parameters. While in all cases the uniaxial yield stresses were evaluated along the RD and TD, the contractile strain ratios (CSR) were determined using grided tensile samples fabricated from sheets of Zircaloy and Zinc. The experimental results correlated with slip predictions based on predominant prism and basal slip modes respectively in Zicaloy and Zn. For Mg alloy, either pyramidal slip or a combination of basal and prism slip modes exhibited good agreement with the experimental results. In addition, the anisotropic creep behavior of thin-walled Zircaloy tubing is considered. Excellent agreement is noted, in recrystallized Zircaloy tubing, between the experimental creep locus and model predictions based on prism slip dominance. However, distinct deviations are noted in Ti3Al2.5V alloy albeit electron microscopy of deformed tubing revealed dislocations on prism ({10.0}) planes with Burgers vectors along .

SANDVIK Ti-3Al-2.5V GRADE 9

Abstract Sandvik Ti-3Al-2.5V Grade 9 titanium-aluminum alloy offers excellent corrosion resistance, especially to chloride media, and has a high strength-to-weight ratio, which is especially suitable for use in aerospace applications. Tubing can be produced having a CSR (contractile strain ratio) that enhances the fatigue endurance limit. This datasheet provides information on composition, physical properties, elasticity, tensile properties, and bend strength as well as fatigue. It also includes information on corrosion resistance as well as forming, machining, and joining. Filing Code: TI-109. Producer or source: Sandvik.

Influence of manufacturing process on the in-reactor creep anisotropy of stress-relieved Zircaloy-2 cladding

A procedure to determine the axial/radial and circumferential/radial contractile strain ratios (the R and P factors respectively in the Backofen-modified von Mises-Hill yield criterion) from post-irradiation dimensional measurements of Zircaloy-2 cladding of BWR fuel rods, tie rods and water rods was developed and has been described previously (S.H. Shann and L.F. van Swam, Creep anisotropy of Zircaloy-2 cladding during irradiation, Trans. SMiRT-11, Vol. C, 1991). The present study employs the procedure to determine the anisotropy factors R and P for textured cold-worked stress-relieved (CWSR) Zircaloy-2 cladding fabricated by various manufacturing processes. The analysis indicates that the cladding manufacturing process can have a pronounced effect on the anisotropy of irradiation-induced creep. Cladding types with identical yield and ultimate tensile strengths but fabricated by different manufacturing processes have different values of R and P during in-reactor creep.

Creep anisotropy of Zircaloy-2 cladding during irradiation

A procedure is described to determine the axial-radial and circumferential-radial contractile strain ratios (the R and P factors in the Backofen modified von Mises-Hill yield criterion) from post-irradiation dimensional measurements of Zircaloy-2 of boiling water reactor fuel rods, tie rods and water rods. Values for R and P have been determined for textured cold-worked stress-relieved (CWSR) Zircaloy-2 cladding. A sensitivity study was performed to evaluate the effects of measurement uncertainties on the derived values of R and P and on the engineering application of the model to predict the in-reactor deformation of CWSR Zircaloy-2 cladding.

Contractile strain ratios of textured cp-titanium (Grade II) sheet

The mechanical anisotropy and strain localization were investigated on cp-titanium sheet using grid analysis method which yielded the transverse contractile strain ratios (R,P), formability parameter (B), and critical strains to necking and fracture. Crystallographic texture pole figures were determined using X-ray diffraction (XRD) techniques from which crystallite orientation distribution functions (CODFs) were derived. The anisotropy and formability parameters were evaluated using CODF in conjunction with crystal plasticity models, and are correlated with experimental results.