Bimetallic Tubes Research Articles

Energy absorption, deformation and crushing behavior of bi-metallic tubes with different cross-sectional shapes under axial loading

Thin walled tubes because of their lightweight, economic manufacturing and efficient energy absorption characteristics are widely used in safety applications contemporaneously many researchers have investigated the behavior of thin-walled metallic tubes with the different cross section under identical test conditions for assessing its effectiveness in crashworthiness. This paper presents the deformation and energy absorption characteristics of bi-tubular tubes along with several different cross-sectional shapes whose base was set as the boundary condition whereas in reference to the axis of the tubes the load was applied at the opposite end with the help of a rigid wall. The analogy of double-walled tubes with different cross-section alters the deformation modes substantially and resulted in significant increase in the energy absorption capacity over bi-metallic tubes as an effect of stress wave propagation. The overall results divulge that the proposed geometry can be a good alternative due to stabilized deformation mode in safety applications such as a locomotive, automotive industries.

Square concrete-filled stainless steel/carbon steel bimetallic tubular stub columns under axial compression

This paper is an attempt to study the mechanical behavior of square concrete-filled bimetallic tubular (CFBT) stub columns subjected to axial compression. The bimetallic tubes in the CFBT columns in this research comprised an outer layer made of stainless steel and an inner layer made of carbon steel. 200-mm square carbon steel tubes (wall thickness tsc = 3.30 mm) were manufactured first, then the bimetallic tubes were fabricated by cladding the carbon steel tubes with stainless steel sheets. In the experimental program, fourteen CFBT columns and two conventional concrete-filled steel tubular (CFST) counterparts were tested to failure under axial compressive loading. The test parameters included the stainless steel grade (Grade 316, 304, and 202), wall thickness of the stainless steel tube layer (tss = 0.84, 1.32, and 1.88 mm), and cube compressive strength of concrete (fcu = 54.5, 68.4, and 80.5 MPa). A finite element analysis (FEA) model was established and validated against the experimental measurements. The failure mode and mechanical behavior of the square CFBT stub columns were then investigated and compared with those of the conventional CFST columns. Finally, the ultimate loads obtained from the experiments were compared to those predicted by the available design codes.

Structural analysis of absorber tube used in parabolic trough solar collector and effect of materials on its bending: A computational study

The maximum deflection of a Parabolic Trough Solar Collector (PTSC) absorber tube is a result of the circumferential non-uniformity in temperature distribution and self-weight. This non-uniformity in temperature is a factor of incoming solar flux distribution as well as material property of the absorber tube. The present work focuses on structural analysis of absorber tube used in PTSC and the effects of variations of material. Multiphysics platform, namely thermal-fluid analysis and structural analysis has been made in this regard. The computational investigation has been carried out on Schott PTR70 2008 receiver and Therminol VP1 as the Heat Transfer Fluid (HTF). Evacuated annular space along with specular and non-grey nature of glass cover which is semi-transparent to the input flux has been modeled to obtain better accuracy in results. The materials investigated are steel, copper, aluminum and various laminated composites like bimetallic (Cu-Fe) and tetra-layered laminate (Cu-Al-SiC-Fe), which are subjected to different mass flow rate of HTF at the absorber tube inlet with constant heat flux on the absorber tube outer surface. It is found that the change in the material of the absorber tube has a negligible effect on the amount of heat transferred to the HTF, but it has a significant effect on the bending due to thermal expansion as well as due to self-weight. Steel absorber tube is generally used, but its lower thermal conductivity results in poor circumferential temperature distributions. Copper has better thermal characteristics, but higher self-weight and lower mechanical strength compared to steel. So a combined effect of these properties is utilized in bimetallic tube, which results in a decrease in maximum deflection by 7–15% as compared to steel. As the self-weight of the absorber tube plays a vital role in deflection, therefore a tetra-layered laminate absorber tube having lower weight and improved temperature distribution results in a decrease in maximum deflection by 45–49% as compared to steel.

Fabrication and characterization of a bimetallic Al/Cu tube using the tube sinking process

In this work, two types of bimetallic tubes were fabricated from aluminum alloy and pure copper using the tube sinking process. The joint quality of the bimetallic tubes was evaluated using the so-called push experiment to determine the bonding shear strength. In addition, different microstructural studies were conducted in order to study the interface character of the layers. It was found that the bonding shear strength of the aluminum-clad copper was slightly higher than that of the copper-clad aluminum. Also, the former exhibited lower bonding shear strength variation than the latter. The discontinuous intermetallic components were detected at the latter interface for both types of bimetallic tubes. Also, it was interesting to note that a relatively thick aluminum oxide layer was found to be formed partially at the copper-clad aluminum tube layer interface. Signs of the cold pressure welding mechanism based on the film theory were indicated in aluminum-clad copper, whereas localized oxidation and wear phenomenon between the aluminum and copper layers deteriorated the bonding strength in copper-clad aluminum.

A new approach for manufacturing copper-clad aluminum bimetallic tubes by friction stir welding (FSW)

A new method is developed for manufacturing bimetallic tubes from pure Copper and 6061-T6 Aluminum tubes by Friction Stir Welding (FSW). The tubes were successfully joined by this new method. Then, the effect of welding parameters such as rotational speed and traverse speed on surface quality, hardness profile, macro and micro-structure and shear strength of the samples was investigated. Experimental results showed that copper and aluminum to be blend much better when bimetallic tubes are manufactured by FSW compared to other methods such as Severe Plastic Deformation (SPD). Furthermore, incorporating high rotational speeds during welding results in generation of excess heat, thus reducing weld surface quality and strength of copper and aluminum tube joints. According to the results, samples welded at rotational speed of 710rpm and traverse speed of 60mm/min presented the highest shear strength.

Interface microstructure evolution and mechanical properties of Al/Cu bimetallic tubes fabricated by a novel friction-based welding technology

In this study, a novel friction-based welding technology was proposed for fabricating Al/Cu bimetallic tubes. The frictional heat and radial pressure during the friction-based welding process are used to achieve the metallurgical bonding between Al and Cu tubes in a rapid and efficient way. Successful joints indicate that this technology has the potential for fabricating bimetallic tubes. Microstructure evolution, bonding mechanism and mechanical properties of Al/Cu bimetallic tubes were also analyzed. Results reveal that columnar α-Al, intermediate transition layer and intermetallic compounds (IMC) are identified at the rotational speed of 950rpm. While the rotational speed is decreased to 95rpm, only solid-state diffusion occurs at the interface which results in three IMC layers, Al2Cu, AlCu, and Al2Cu3. The thickness of the Al2Cu is more significantly affected by the rotational speed than that of AlCu and Al2Cu3. Maximum hardness is observed at the reaction layer due to the formation of IMC. The appearance of intermediate transition and thick Al2Cu layer weakens the bonding strength of bimetallic tubes. The joints are fractured at the reaction layers, and the fracture exhibits typical brittle characteristic. Three crack propagation paths are observed at the interface of Al/Cu bimetallic tubes.

Concrete-filled bimetallic tubes (CFBT) under axial compression: Analytical behaviour

Concrete-filled bimetallic tubes (CFBT) could be recognized as a type of steel-concrete composite members, and have the potential to be applied in engineering structures. A three-dimensional finite element analysis (FEA) model is established to further study the axial compressive behaviour of circular CFBT stub columns in this paper. The preciseness of the FEA predictions is evaluated by comparison with experimental results collected from ten CFBT column specimens tested in a companion paper (Ye et al., 2016) [15]. Good agreement is obtained between the FEA predictions and the test results in terms of failure pattern, load versus deformation response, ultimate strength, and strain development of the two steel tube layers. In light of the FEA results, the stresses of concrete and steel, as well as the interactions and load distribution between different components of the composite section are investigated. Finally,parametric study is performed and a simplified model is proposed to be used to calculate the ultimate strength of circular CFBT stub columns.

EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

A Generalized Dependence for Convective Heat Transfer in Horizontal Bundles of Finned Tubes with Free Air Convection

Results of a study of free convective heat transfer in two-, three-, and four-row horizontal in-line bundles of bimetallic finned tubes with coefficient of finning 16.8 are presented. The steps in the breakdown in the tubular sheets correspond to the applicable standardized steps in air-cooled heat exchangers with cross step S1 = 58–76 mm, and values of the longitudinal step S2 in the range 58–100 mm correspond to each value of S1. A generalizing equation for calculating the average convective heat-transfer coefficient, taking into account geometric parameters studied in the range of Reynolds numbers from 20000 to 70000, is obtained. Through the use of the dependence, it has become possible to design a wide range of gas–liquidtype heat exchangers for different purposes that function in free convection regimes.

Concrete-filled bimetallic tubes under axial compression: Experimental investigation

This paper presents the experimental results of axial compression tests on concrete-filled bimetallic tubes (CFBT). The cross section of the bimetallic tube is composed of an outer layer made of stainless steel and an inner layer made of carbon steel. A total of 12 specimens with a circular cross section were tested under axial compression. The test parameters included the thickness of the stainless steel tube layer (tss=0–1.36mm) and the compressive strength of the infilled concrete (fcu=21.1–42.8MPa). Test results showed that, the two layers of the bimetallic tube worked well together, and the CFBT specimens exhibited ductile characteristics. The influence of the parameters on the failure mode, load versus deformation relationship, axial compressive strength, and strain development of the tested specimens were investigated. Finally, the feasibility of three existing design codes for predicting the axial compressive strength of CFBT under axial compression was evaluated.

Experimental investigation on bimetallic tube compositions for the use in latent heat thermal energy storage units

Based on the high energy density of phase change materials, latent heat thermal energy storage devices can play an important role in the future energy market. Therefore, the latent heat thermal energy storage technique is an interesting technology for industrial applications (e.g. batch processes) and power cycles. A key technology for such a storage device is the design of the heat exchanger tube, because the heat transfer rate by charging and discharging is the limiting factor based on the low thermal conductivity of the phase change material. The heat exchanger tube material used for such an application should have a high thermal conductivity and also a high mechanical resistance. Such a behavior can be found in a combination of different materials. The present paper deals with the design of such a heat exchanger tube composition consisting of a plain steel tube and an aluminum tube where fins can be attached. A novel bimetallic tube composition will be presented and compared with three common compositions. First, the mechanical stability of the bimetallic compositions was determined. Additionally a creep test of the used aluminum under operation conditions for a storage device using sodium nitrate as phase change material confirmed the utilizability for the operation in a latent heat thermal energy device.One of the main challenges for the compositions under investigation is based on the different thermal expansion coefficient for aluminum and steel, which results in different strain and creeping tendencies of the aluminum at operation temperature of the storage system, which is up to 340°C. A good heat transfer from the heat transfer fluid through the steel tube to the storage material around the fins can only be guaranteed through a close and stable connection between the two tubes. Compared to former solutions the fin circumference and the fin design are independent from the connection to the steel tube and allows individual arrangements of tubes and high packing densities.The experimental investigations have shown that the novel bimetallic tube composition is able to compensate these different strains and is capable to guarantee a stable connection between the steel and the aluminum tube. This high pressure and high temperature resistant bimetallic heat exchanger tube is easy to assemble and may play a key role for the development of thermal energy storages and other heat exchanging processes.

Explicit expression for temperature distribution of receiver of parabolic trough concentrator considering bimetallic absorber tube

The portion of the absorber tube facing the trough surface receives the concentrated sun-rays and the other side of the absorber tube receives the sun-rays directly. Consequently, the temperature of the absorber tube is non-uniform across the circumference which leads to differential expansion of the material of the tube. Thus, the tube experiences compression and tension in its different parts. This may lead to bending of the tube. In literature, the temperature of the absorber tube is computed using CFD software which take large computational time. Thus, in the previous work, an explicit analytical expression was derived for finding the distribution of absorber’s temperature and it was found that the temperature gradient across the circumference of the absorber tube can lead to significant bending. Thus, in the current work, a bimetallic tube has been studied that can reduce the temperature gradient and an explicit analytical expression is derived for finding the temperature distribution of a bimetallic absorber tube. The study of the effects of thicknesses and material selection of the inner and outer layer of bimetallic tube on temperature distribution is a must for choosing right materials and dimensions. The appropriate thicknesses and materials of inner and outer layers can be found out from the current work. The issue of whether to use high conducting material on outside or inside has also been addressed in the current work and concluded that the material with higher thermal-conductivity should be used as outer layer of the bimetallic tube to minimize the non-uniformity across the circumference. It is also concluded that for Schott-2008-PTR70-receiver, 126°, 135° and 139° respectively are the appropriate rim-angles for trough’s aperture-width=3m, 6m and 9m corresponding to minimum non-uniformity across the circumference. 72°, 100° and 112° respectively correspond to maximum solar-flux at the absorber tube.

Analysis of Manufacturing Bimetallic Tubes by the Cold Drawing Process

Drawing processes apply to obtain the bimetallic tubes from the different metals and alloys, combined in the solid state, which significantly affects the specificity of this process. The manufacturing of bimetallic tubes by drawing process depends on many factors which include: preparation of the surface of materials joined in the solid state, the geometric parameters of the working tool, technological parameters of the drawing process (drawing speed, type of lubricant, the use of back pull etc.). Generally, the cold drawing process of producing the bimetallic tubes refers to metals which have high ductility (copper, aluminum, etc.). The tube sinking (tube drawing without a mandrel) of bimetallic tubes together with joining them at the interface of the two metal in the solid-state is applied for tubes of the diameter range between 6 to 20 mm and based on of the reducing the diameter of the tube. However, a slight increase of wall thickness ca. 0.05 ÷ 0.10 mm can appear, which is not dangerous phenomenon in case of producing the bimetallic tubes by joining in the solid-state. The aim of the research was to investigate the technology of tubes drawing process from non-ferrous metal, drawing process of bimetallic tubes and the production of bimetallic tubes in layers composition: cooper Cu-ETP - brass CuZn37 and CuZn37 brass - copper Cu-ETP in the tube sinking process. The research program included: production of bimetallic tubes with a different composition (Cu- ETP-CuZn37 and CuZn37-Cu-ETP) and a different percentage of the cross-section components; analysis of changes of tube wall thickness and the layer composition of the bimetallic tube, based on measurements on the workshop microscope; analysis of the material flow in the process of the bimetallic tubes production based on the measurements results of a profilograph CP-200.

The Influence of the Components of the Bimetallic Tubes for the Way of Deforming in the Hollow Drawing Process

Processes for producing bimetallic tubes can be divided for: producing the bimetallic tubes in the cold process, with preheating or with the heat treatment after each pull. First method relates to the metal with high ductility (copper, copper alloys, aluminum, aluminum alloys, zinc, etc.), second to the metals or bi-metal components, in one of which has significantly different plastic properties from the second for example: low-carbon steel, high alloy steel, etc. One of the methods for the production of bimetallic tubes is hollow cold drawing process. In this process the wall thickness is changed, which means the wall becomes thicker, the wall becomes thinner or remains unchanged. The aim of the research was to determine the effect of the influence of the share of components of bimetallic cooper tube species M1E, and the copper tube - species M63 in the arrangement M1E - M63 and M63 - M1E in the tubes hollow drawing process for the distribution and size of deformation of the individual layers. The research program included:- production of the bimetallic tubes by hollow drawing with a different percentage of the cross-section components and with a variable arrangement of layers,- determination of the size and distribution of true strain of the individual layers on the cross-section of bimetallic tube,- determination of replacement/equivalent strain for the deformable wall of the bimetallic tube,- evaluation of the usability of the graph of changes in thickness of the tube wall in the hollow drawing process for the drawing process of the bimetallic tubes.

Examine bi-metallic rectangular thin walled tube under different trigger mechanisms

Examine bi-metallic rectangular thin walled tube under different trigger mechanisms

Experimental Study of Aerodynamic Resistance of Staggered Equilateral Banks of Tubes with Spiral Aluminum Fins

Aerodynamic resistance of six four-row tube banks in isothermal air cross-flow is studied. The banks assembled from full-scale bimetallic tubes, the aluminum fins of which are rolled on a bearing steel tube with a diameter of 12 mm and a wall thickness of 1.25 mm. The tube spacing in the bank lattices was varied from 28 to 50 mm. The resistance of the banks is stratified depending on the spacing of the tubes even though they are geometrically similar. The experimental data are generalized by a single similarity equation in the Reynolds number range 2000–10000. Tight (compact) tube banks have the maximum thermal efficiency.

Experimental and Numerical Investigation of a Cu–Al Bimetallic Tube Produced by ECAP

ABSTRACTIn this paper, a new application of equal channel angular pressing (ECAP) for fabrication of Cu–Al bimetallic tubes is presented. For the evaluation of ECAP effects, the microstructure and micro-hardness of samples are considered. To investigate of bonding properties of Cu–Al tubes, optical microscopy and shear strength testing were used. In addition, the effect of friction coefficient and thickness on applied force was evaluated by numerical analysis. The results from the experiments indicated that the hardness of Cu and Al increased by 156.8 and 129%, respectively. Also, the average Cu grain size after three passes fell from 62.5 to 11.2 µm. Finally, Cu and Al tubes were well interconnected as a bimetallic tube at higher passes.

Material-based design of the extrusion of bimetallic tubes

Using finite element and polycrystalline plasticity modeling, we explore the influence of die design and material behavior on the extrusion of bimetallic tubes. Three distinctly different extrusion designs are introduced and evaluated based on a range of macroscopic and microstructural criteria: die and punch stress, interface roughness, peak forming loads, and strain and crystallographic texture heterogeneities across the tube thickness. We find that an extrusion die design proposed here that differs from the conventional one is better for reduction of peak forming load satisfying objectives of the traditional design. However, when the design is more constrained and considerations of strain and microstructural heterogeneities and gradients are made part of the design criteria, we show that one die design promotes such gradients while the other minimizes them. In all three designs, large disparities in flow stress and hardening rate (>3 times) lead to larger interfacial strain gradients. These findings provide basic die designs that can be used to evaluate the degree and locations of strain and texture gradients across the tube thickness.

Preliminary Investigations on Preparation of Cu-Al Bi-Metallic Tubes Using Swaging-Diffusion Method

Bi-metallic tubes (BMTs) combine performance advantages of two different tubes and are usually used in particular conditions where corrosion resistance is important. Traditionally, BMTs are manufactured by plastic processes such as extrusion, explosive welding/cladding, hydroforming and even combinations thereof. However, rotary swaging, which is commonly used to produce tubes, was seldom mentioned when preparing BMTs. In this work, Cu-Al BMTs were achieved using swaging-diffusion method (SDM). The effect of process on formability of BMTs are investigated. The experimental results indicate that with the increasing of deformation, metallurgical bonding layer, which is more desirable than mechanical bonding layer, can be achieved. And the metallurgical bonding layer will thicken to 2μm after diffusion. Besides, some failures produced in the swaging process are presented.

Vibration Reliability of Finned Tube Banks in Air Coolers

A procedure based on the effective diameter proposed by the author is presented for analysis of vibration indicators of heat-exchange bimetallic finned tubes (BFT) in a forced transverse flow of air. It is indicated that in characteristic operating regimes, tube bundles formed from BFT have a significant reserve of vibration reliability, and there is no danger of their failure owing to eddy separation and formation of an aerodynamic wake beyond the tubes.