Thin-walled Aluminum Alloy Tube Research Articles

Optimizing Pure Shear Experiment to Properly Characterize the Shear Properties of Thin-Walled Aluminum Alloy Tubes

Optimizing Pure Shear Experiment to Properly Characterize the Shear Properties of Thin-Walled Aluminum Alloy Tubes

Bending forming of lightweight large diameter thin-walled aluminum alloy aviation tube

To improve the forming quality of lightweight aviation tubes, the influence of different tube specifications, forming requirements and process parameters on bending forming of large diameter thin-walled (LDTW) LF2M aluminum alloy tubes (AATs) was studied. A finite element analysis model for LDTW AAT bending was established and verified. The results show that with the increase of mandrel extension length [Formula: see text], the wall-thinning ratio tends to increase. With the increase of [Formula: see text], the overall wall-thickening ratio decreases. With the increase of [Formula: see text], the ovality decreases first and then increases. The bending radius has a great influence on wall thickness variation. It has great significance to guide the bending forming of lightweight LDTW aluminum alloy aviation tube.

In-situ EBSD observation of texture evolution and lattice rotation behavior in shear deformation of thin-walled aluminum alloy tubes

As shear stress plays a significant role in the deformation of tubular parts with complex shapes, investigation of the microstructue evolution of tubes under the shear stress state is beneficial to understanding the shear deformation mechanism and promoting the prediction accuracy of numerical simulation. In this paper, the shear experiments were conducted on thin-walled 5052 aluminum alloy tubes. The texture evolution and lattice rotation behavior of the tube during shear deformation were studied using in-situ electron back scatter diffraction (EBSD) technology. It is shown that the initial Cube texture remains stable, while a new Rot. Copper texture is formed in the shear deformation zone. The grains with the orientation of <100> parallel to the axial direction (AD) tend to stabilize, while several low-angle grain boundaries (LAGBs) are formed inside the grains with unstable initial orientations. Notably, the orientations of adjacent grains are more similar after shear deformation, and the high-angle grain boundaries (HAGBs) gradually transform to LAGBs showing the characteristics of polycrystalline cooperative deformation. By analyzing the lattice rotation mechanism under shear stress, it is found that the shear stress promotes the lattice rotation to a stable orientation parallel to the direction of the shear stress. This research provides theoretical guidance for predicting the forming of tubular parts with complex shapes.

Study on Joining for Thin-Walled Aluminum Alloy/Steel Tubes by Electromagnetic Flanging Process

A structure for joining thin-walled 6061-T6 aluminum alloy tube (outer tube) and Q195 steel tube (inner tube) by electromagnetic flanging process was proposed. The formation process, mechanical properties, failure modes, and morphology of the joint were investigated. The results showed that the outer tube impacted the inner tube, the flanges of the prefabricated holes on the outer tube were embedded into the prefabricated holes of the inner tube under the action of Lorentz force, and thus the mechanical locking joint was obtained. There were two tensile failure modes for the joints: Pull-out and fracture. Specifically, when the discharge energy was relatively high, the failure mode changed from pull-out to fracture. Combining the results of tensile tests and morphology observations, the maximum loads of the joints increased with the discharge energy. However, excessive discharge energy would lead to the brittle fracture of the inner tube, which was not beneficial to the service. Better discharge energy and the maximum load of the joint at this discharge energy were obtained.

Experimental study on the impact resistance of hollow thin-walled aluminum alloy tubes and foam-filled aluminum tubes (6063-T5)

This paper presents a study on the axial impact resistance of hollow thin-walled aluminum alloy tubes and aluminum foam-filled thin-walled tubes. 15 hollow thin-walled aluminum alloy tubes and 15 thin-walled aluminum alloy tubes filled with aluminum foam were tested under drop hammer impacts. The process of the impact, the failure modes of the specimens, the time history curves of impact forces, and the vertical deflections were recorded in the test. The effects of impact velocity, aluminum alloy wall thickness, cross-sectional width, and aluminum foam on the performance of the hollow and aluminum foam-filled thin-walled aluminum alloy tubes were discussed. In addition, a finite element model was established to simulate the test considering the strain rate effect of aluminum alloy and aluminum foam. The results showed that both hollow and foam-filled thin-walled aluminum alloy tubes were damaged to different degrees. Under the same impact energy, the damage of the foam-filled thin-walled aluminum alloy tube was less severe than that of the hollow thin-walled aluminum alloy tube; under the axial impact load of the drop hammer, the most effective way to improve the impact resistance of the hollow and foam-filled thin-walled aluminum alloy tubes was to increase the wall thickness of the outer thin-walled aluminum alloy tube, while the effect of increasing the cross-sectional size of the outer thin-walled aluminum alloy tube on the impact resistance of the specimen is less significant. The peak impact force, vertical deflection and the duration of impact forces are most sensitive to the impact velocity.

Performance of hollow and aluminum foam-filled multi-cell thin-walled aluminum alloy tubes (6063-T5) under axial impact

This study investigates a new form of multi-cell thin-walled structures under axial impact. Eighteen multi-cell thin-walled aluminum alloy tubes were tested under drop hammer impacts. Nine of the specimens were hollow tubes and the other nine specimens were aluminum foam-filled multi-cell thin-walled aluminum alloy tubes. This paper presents the entire duration of the impact including the time history curves of forces and vertical displacement. The influence of impact velocity, wall thickness and aluminum foam on the impact resistance of multi-cell thin-walled aluminum alloy tubes were discussed. Then, the energy dissipation performance of multi-cell thin-walled structures tested in this study and single-cell thin-walled structures tested in prior research is compared. The results show that the foam infill improves the energy dissipation capacity of the multi-cell thin-walled aluminum alloy tubes, but the specific energy absorption (the energy absorbed per unit mass) decreases. Although the specific energy absorption is reduced, using foam infill is still an effective method to improve energy dissipation capacity without increasing the size of the member. Compared with the single-cell thin-walled aluminum alloy tubes, the specific energy absorption of the multi-cell thin-walled aluminum alloy tubes is higher by 7.35%–55.51%, which means that multi-cell thin-walled columns are a better energy absorption component compared with single-cell columns.

Circumferential pure shear test of thin-walled aluminum alloy tubes

In order to obtain the pure shear deformation characteristics along the circumferential direction of tubes, a circumferential shear test for thin-walled tubes is proposed in this paper. The experimental device consists of a tubular sample and two cylindrical mandrels with shear plates. The torque along the circumferential direction was applied to the tubular sample by the two shear plates to make the pre-set shearing zone of the sample under a circumferential pure shear stress state. The two cylindrical mandrels support the inner wall of the tube to avoid buckling so that the pure shear stress state can be maintained during the whole deformation process. A 5052 aluminum alloy tube with an outer diameter of 50 mm and a wall thickness of 1.2 mm was used in the test. It is shown through simulation and experiment that shear deformation is concentrated in the pre-set shearing zone. This test can be used to obtain the circumferential pure shear stress-strain relationship.

In Situ Formation of Laser-Cladded Layer on Thin-Walled Tube of Aluminum Alloy in Underwater Environment.

The first study of thin-walled aluminum-alloy tubes with underwater-laser-nozzle in situ melting technology was carried out. The study mainly covered the influence of the water environment on the laser melting process, melting appearance, geometric characteristics, microstructure, regional segregation and microhardness. During the transfer of the cladding environment from air to water, the uniformity of the cladding layer became poor, but excellent metallurgical bonding was still obtained. The dilution rate (D) decreased from 0.46 to 0.33, while the shape factor (S) increased from 4.38 to 5.98. For the in-air and underwater samples, the microstructure of the melting zone (MZ) and the cladding zone (CZ) were columnar dendrites and equiaxed grains, respectively. In addition, the microstructure of the overlapping zone (OZ) was composed of columnar dendrites and equiaxed grains. The underwater average grain size was smaller than that of in-air. In addition, the water environment was beneficial for reducing the positive segregation in the columnar dendrite region. Compared with the in-air cladding sample, the precipitated phases in the OZ of the underwater cladding sample reduced. Under the combined action of grain refinement and precipitated phase reduction, the microhardness value of the underwater OZ was higher than that of the in-air OZ.

Bending deformation prediction in a welded square thin-walled aluminum alloy tube structure using an artificial neural network

Bending deformation prediction in a welded square thin-walled aluminum alloy tube structure using an artificial neural network

Underwater wire-feed laser deposition of thin - Walled tubular structure of aluminum alloy

Thin-walled aluminum alloy tube of underwater laser in-situ deposition technique was carried out for the first time, and the influences of laser powers, wire feeding speeds and shielding gas flow rates on the deposition appearance, geometry characteristics, microstructure and microhardness of single track deposited layer were investigated. As the laser power increased, the height of deposited region (DR) and deposition angle decreased, but the height of fusion region (FR) and the width increased. Besides, the deposition appearance became better firstly and then worse. With the wire feeding speed increased, the height of DR, width and deposition angle increased, but the height of FR decreased. In addition, the deposition appearance was greatly improved. As the shielding gas flow rate increased, the height of DR and deposition angle decreased, but the height of FR and width increased. Besides, the deposition appearance deteriorated. The microstructure of FR and DR were columnar dendrites and equiaxial dendrites, respectively. With wire feeding speed increased, the microstructure had a tendency to refine and average microhardness value gradually increased. However, as the laser power and shielding gas flow rate increased, the microstructure became coarse gradually and average microhardness value gradually decreased.

Numerical and experimental studies on thin-walled aluminum alloy tube hydroforming using differential lubrication method

In this paper, it was analyzed that the friction forces that affected the material flow were influenced by the friction coefficient and the load path of internal pressure and feeding in T-shaped tube hydroforming process. Therefore, a novel differential lubrication method was proposed to adjust the material flow through changing the friction coefficient in the asymmetric zone in the T-shaped tube besides the loading path design method. The differential lubrication zones in T-shaped tube were divided, and a method called intermediate semiring differential lubrication was designed. The effects of differential lubrication and traditional uniform lubrication methods on the wrinkle, height of branch tube and wall thickness distribution of the T-tube were investigated under the same loading path of internal pressure and axial feeding. Meanwhile, the differential lubrication methods were also simulated under the different loading paths of the internal pressure and axial feeding. The differential lubrication experiments of T-shaped tubes hydroforming were carried out with fluorosilicone grease and PEFT film as lubrication medium. The simulation and experimental results showed that the differential lubrication method more effectively avoided wrinkles in the back zone of the main tube, increased the height of branch tube and weakened the thickening than the traditional uniform lubrication method. And it was a promising way to improve the formability of T-shaped tube hydroforming and reduced the over-reliance on the loading path.

Investigation on influence of mandrel shape on shear stress in pure shearing test of thin-walled aluminum alloy tubes

A novel testing method of pure shear loading for tubes is proposed in this paper. A special designed tubular sample and two semicircle mandrels are used in this test. The interface between the two half tube on the whole tube zone of the sample is under shearing deformation with relative movement of the two mandrels, and the middle point of the shearing zone is under a pure shearing stress state. The influence of friction condition between the two mandrels caused by the relative movement of the mandrels was analyzed. Three different friction conditions of semi-circle mandrels were used in the simulation and the relation between the loading force and mandrel displacement was obtained. It is shown the friction force has very small influence on the loading force. This shearing test can be used to get the shearing property of tubes, also, it is a testing method of tubes except the axial and circumferential direction.

Push-bending method development of thin-walled tube with relative bending radius of 1 using sectional elastomers as mandrel

It is important for the thin-walled tube with relative bending radius of 1 to be bent with mandrel in order to avoid the defects such as wrinkling and cross-section distortion. In this paper, a novel push-bending method using sectional elastomers as mandrel was proposed to form the 5A02 thin-walled aluminum alloy tube with relative bending radius of 1 and 90° bending angle. Cylindrical polyurethane rubber (CPR) with shore hardness of 80A was chosen as the sectional elastomers. The influence of diameter (d), thickness (t), total length (L), and arrangement of CPR filler on the push-bending deformation of tube was first explored by means of simulations and experiments. According to the simulation results, 5A02 thin-walled aluminum alloy tube with relative bending radius of 1 was successfully fabricated with the sectional CPR as mandrel in the self-developed equipment of push-bending. The experimental results were in good agreement with the simulation results. The optimum parameters of CPR filler in push-bending process were obtained as follows: 37 mm diameter, a piece of CPR with 20 mm thickness contacted with the punch, and other 12 pieces of CPR with 10 mm thickness.

Sequential multi-objective optimization of thin-walled aluminum alloy tube bending under various uncertainties

Combining the design of experiments (DOE) and three-dimensional finite element (3D-FE) method, a sequential multi-objective optimization of larger diameter thin-walled (LDTW) Al-alloy tube bending under uncertainties was proposed and implemented based on the deterministic design results. Via the fractional factorial design, the significant noise factors are obtained, viz, variations of tube properties, fluctuations of tube geometries and friction. Using the virtual Taguchi's DOE of inner and outer arrays, considering three major defects, the robust optimization of LDTW Al-alloy tube bending is achieved and validated. For the bending tools, the robust design of mandrel diameter was conducted under the fluctuations of tube properties, friction and tube geometry. For the processing parameters, considering the variations of friction, material properties and manufacture deviation of mandrel, the robust design of mandrel extension length and boosting ratio is realized.

Characterization of Multiaxial Stress-Strain Response of Tube Metal from Double-Sided Hydro-Bulging Test Based on Hosford’s 1979 Yield Criterion

To further explore the characterization of the multiaxial stress-strain responses of anisotropic tube metal from double-sided hydro-bulging tests, an analytical model for the equivalent stress and equivalent strain calculation was derived based on Hosford’s 1979 yield criterion. Furthermore, thin-walled 5052-O aluminum alloy tubes were used to conduct the bulging experiment with an external pressure of 85 MPa. After the experimental data were substituted into the above analytical model, the Voce equation was used to fit the equivalent stress-strain relationship. It is concluded that the stress versus strain curves of the 5052-O tubes are strongly dependent on the loaded stress states, the adopted yield criteria, and the anisotropy coefficients. The external pressure of 85 MPa had little or no effect on the stress versus strain curves of the tubes, but the locations of the multiaxial stress versus strain curves were lower than that of the uniaxial stress versus strain curve. Moreover, the curve from Hosford’s 1979 yield criterion not only had a higher saturation stress and material constant value than the curve from Mises and Hill’s 1948 yield criteria but also had a dependence on the anisotropy coefficient.

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

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.

Investigation into wrinkling behavior of thin-walled 5A02 aluminum alloy tubes under internal and external pressure

In order to investigate the wrinkling behavior of thin-walled tubes under complex stress states, a dedicated experimental setup was designed and manufactured. In this experimental setup, the internal pressure, the external pressure and the axial feeding of left and right punches were coupled together through accurate closed-loop servo control. Thin-walled 5A02 aluminum alloy tubes were pushed into the die cavity under different internal pressures or under the combined actions of internal and external pressures with the same amount of axial feeding. Meanwhile, the wrinkle formation, as well as the stress state, was predicted numerically using the FEA Abaqus/Explicit solver. It has been found that the number and shape of wrinkles are strongly dependent on the internal pressure when only internal pressure is applied to the inner surface of the tube. Furthermore, the wrinkle formation is closely related to the inhomogeneous stress distribution induced by local bending and axial displacement. Moreover, the shape of wrinkles can be fitted effectively using the GaussAmp function when the internal pressures of 1.2ps, 1.6ps and 1.8ps (ps represents the initial yield pressure for the tube) are applied. In addition, the effect of external pressure has been discussed under three cases and it is shown that the wrinkling behavior exhibits hardly any dependence on the external pressure for the constant pressure difference. Finally, the formation of middle wrinkle can be prevented by higher external pressure both for the constant internal pressure and the variable internal pressure.

Deformation Characterization of Friction-Stir-Welded Tubes by Hydraulic Bulge Testing

In this article, the large-diameter thin-walled aluminum alloy tubes were produced using a hybrid process combining friction-stir welding (FSW) and spinning. For this novel process, rolled aluminum alloy sheets with a thickness about 2–3 times the wall thickness of target tube, were FSW to form cylinders, and then the cylinders were subjected to spinning to get thin-walled aluminum alloy tubes. Both experimental and simulation study were conducted to investigate the deformation characterization of the FSW tube during hydraulic bulge testing, and the stress and strain states and thickness distribution of the FSW tube were investigated. It was found that the common defects of FSW tube can be significantly improved by specific welding devices. The ductility of the tube is considerably improved with nearly two times higher bulge ratio than as-spun tube after annealing treatment at 300°C. But the annealed tube still shows a high nonuniform wall thickness distribution due to the inhomogeneous deformation characteristics. With increasing deformation of the tube, the gap between the hoop and axial stress for the weld and base metal (BM) decreases. However, the hoop and axial stress of the weld are always greater than those of the BM at the same pressure.

Experimental verification of the influence of normal stress on the formability of thin-walled 5A02 aluminum alloy tubes

Several forming limit theory models, which considering the effect of through-thickness normal stress, have been established based on the classical plastic instability theory and M–K approach respectively. Moreover, finite element analysis of influence of normal stress on the deformation behavior of double-sided hydroforming has been carried out by several researchers. However, the systematic experimental works have not yet been conducted to verify these proposed forming limit theory models and the numerical results. In this paper, in order to verify the influence of normal stress on the formability of thin-walled tubes, a special experimental setup was designed and manufactured for double-sided tube hydroforming. The normal stress can be introduced through the internal and external pressure. Then 5A02-O aluminum alloy tubes with outer diameter of 63mm and nominal thickness of 2mm were bulged freely and in a square-section die cavity under different external pressures. It is shown that the homogeneous plastic deformation ability of the tube before necking occurrence has hardly any dependence on the normal stress, which only influence the fracture morphology and fracture strain on the crack. This investigation reveals that the normal stress induced by double-sided pressures only has an effect on the fracture behavior of the dense sheet or tube metals and has no practical significance in the metal forming production.

Optimal design of process parameters of rotary-draw bending process for thin-walled rectangular tube of aluminum alloy

The rotary-draw bending process of thin-walled rectangular tube is a complex process with the interaction of many factors. The wrinkling may be produced if the process parameters are inappropriate. So, here, based on finite element numerical simulation, and taking the clearances and the frictions between tube and dies as the optimal design variables and the wrinkling height as the optimal objective, the optimization design for rotary-draw bending process of thin-walled rectangular 3A21 aluminum alloy tube has been carried out by using sequential quadratic programming method. Then, the recommended values of the clearances between mandrel, wiper die and bending die and tube, and the friction coefficients between pressure die, mandrel and wiper die and tube are obtained. The achievements of this study are significant to reduce the manufacturing cost and increase efficiency and bending quality.