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• Flow condensation was conducted for an expanded axial micro-fin aluminum tube. • R-32, R-454B, R-454C, R-455A, R-1234yf, and R-1234ze(E)) were tested. • High-glide refrigerant blends have heat transfer coefficient degradation up to 30 %. • Equivalent saturation temperature drop method was used for refrigerant comparison. Environmental regulations have driven the development of refrigerants with low global warming potential (GWP). To design heat exchangers using these new refrigerants, data are needed concerning the heat transfer coefficient and pressure drop in two-phase flow. Another change is the increasing use of aluminum tubes rather than copper tubes to reduce heat exchanger cost. Hence, this study presents an experimental investigation of flow condensation using an expanded axial micro-fin aluminum tube with a fin-tip diameter of 5.96 mm. The experiments included single compounds R-32, R-1234yf, and R-1234ze(E), zeotropic mixtures with low glide (R-454B), and zeotropic mixtures with high-glide (R-454C and R-455A). Experiments were conducted at condensation temperatures ranging from 40 °C to 50 °C, reduced pressures ranging from 0.21 to 0.55, and mass fluxes ranging from 150 to 350 kg/(m2 s). Data obtained for these refrigerants constitute one of the first reports for high-glide refrigerants using axial micro-fin aluminum tubes. An evaluation of heat transfer degradation of zeotropic mixtures due to mass transfer resistance at the liquid/vapor interface is presented. This information can be used to design heat exchangers for next generation air conditioning and refrigeration systems. [ABSTRACT FROM AUTHOR]

• Single- and two-phase frictional pressure losses in stainless steel smooth tubes (5.5 and 8.5 mm) and six aluminium straight inner-grooved profiles have been experimentally studied on ammonia. • The adequacy of existing correlations and approaches has been validated. • A new correlation has been proposed for the frictional pressure losses in inner-finned tubes. The experimental study of single-phase and two-phase frictional pressure losses has been performed with ammonia flow in stainless steel smooth tubes (internal diameter of 5.5 mm and 8.5 mm) and six straight inner-grooved aluminium tubes with different nominal diameters (7.15 to 13.3 mm), length (0.45 to 2.0 mm) and thickness (0.35 to 0.8) of fins. Single-phase test boundary conditions correspond to Reynolds numbers of 1000 to 20,000. Two-phase tests have been carried out at saturation temperature of 45 to 65 °C, mass velocity of 50 to 210 kg· m −2s−1 and vapour quality of 0.1 to 0.9. Comparison of obtained test data with the existing frictional losses approaches shows that the Blasius model is appropriate to single-phase flows in smooth tubes, and Müller-Steinhagen and Heck's (1986) model is most accurate in predictions of two-phase frictional losses in smooth tubes. Existing approaches of single-phase frictional pressure loss predictions in the pipes and channels with longitudinal fins (Carnavos, 1980; Edwards and Jensen, 1994) are not adequately suited to the ammonia test points obtained in the considered straight inner-grooved tubes. A new semi-empirical model has been proposed, based on generalisation around the revealed geometric dimensionless factor, which accurately describes friction pressure losses in the considered inner-finned profiles. The simplest homogeneous model for defining two-phase friction pressure losses, using McAdams et al.'s (1942) recommendation for mixture dynamic viscosity definition and a new model of single-phase friction factor, best fit both quantitatively and qualitatively to ammonia two-phase test points in most of the considered straight inner-grooved tubes. [ABSTRACT FROM AUTHOR]

• Ammonia condensation has been experimentally studied in 8 mm and 11 mm tubes. • A new phenomenological model has been proposed for ammonia condensation. • The lowest condensation HTCs characterise the downstream flow. The paper proposes the experimental study of ammonia condensation in aluminium tubes with 8 mm and 11 mm internal diameters. The new study aimed to compare and extend the existing ammonia in-tube condensation data. The lines were tested mainly in horizontal configuration at mass velocities of 20 to 160 kg·m−2s−1, saturation temperature of 35 to 65 °C and inlet vapour quality of 0.1 to 0.9. Shah (1979), laminar-laminar Dobson and Chato (1998), and Cavallini et al. (2001) models predict well ammonia condensation HTCs at mass velocities of 120 to 160 kg·m−2s−1. A new phenomenological model has been proposed for the mass velocities of 20 to 120 kg·m−2s−1, predicting the test data with an accuracy of ±20 %. Similar ammonia condensation HTCs have been obtained for horizontal and upstream flows at a mass velocity above 120 kg·m−2s−1. The lowest condensation HTCs at the considered boundary conditions characterise the downstream configuration of an in-tube condenser at a mass velocity below 120 kg·m−2s−1. However, inclining the ID 8 mm tube by 15° from the normal substantially increases the condensation HTCs by 10 to 30 %, depending on vapour quality. At the inclinations of 15 to 45° from the horizontal line toward the downstream flow, the condensation HTCs exceed the ones of horizontal flow by 10 to 15 % at the vapour quality of <0.5 and low mass velocity of 80 kg·m−2s−1. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a key technology for the individualized and resource-efficient production of structural components. Recent developments in manufacturing technologies enable improved quality of additively manufactured components and therefore they become more and more important in lightweight constructions. An example is the substitution of solid material by porous lattice structures. Those embedded lattice structures lead to highly weight-efficient structures. Most recent investigations focus on numerical and experimental studies to describe the mechanical behavior of lattice structures. In this paper, a method to determine analytical expressions for the axial stiffness properties of lattice structures is presented. The displacement method and direct stiffness method are used to derive symbolic parameter-dependent formulas for the axial stiffnesses and effective Young's moduli for f2cc,z, and bcc unit cells. Furthermore, an empirical approach based on Finite Element simulations is presented to describe the stiffness reduction for non-embedded or rather free lattice structures. The results are further validated by physical experiments. Stereolithography is used for specimen production. f2cc,z, and bcc lattice structures are embedded in thin-walled rectangular aluminum tubes and tested under compression load. Furthermore, lattices without a surrounding tube are tested. The analytical and empirical solutions are in good agreement with the experimental and numerical results. [ABSTRACT FROM AUTHOR]

How did humans become clever enough to live in nearly every major ecosystem on earth, create vaccines against deadly plagues, explore the oceans depths, and routinely traverse the globe at 30,000 feet in aluminum tubes while nibbling on roasted almonds? Drawing on recent developments in our understanding of human evolution, we consider what makes us distinctively smarter than other animals. Contrary to conventional wisdom, human brilliance emerges not from our innate brainpower or raw computational capacities, but from the sharing of information in communities and networks over generations. We review how larger, more diverse, and more optimally interconnected networks of minds give rise to faster innovation and how the cognitive products of this cumulative cultural evolutionary process feedback to make us individually "smarter"—in the sense of being better at meeting the challenges and problems posed by our societies and socioecologies. Here, we consider not only how cultural evolution supplies us with "thinking tools" (like counting systems and fractions) but also how it has shaped our ontologies (e.g., do germs and witches exist?) and epistemologies, including our notions of what constitutes a "good reason" or "good evidence" (e.g., are dreams a source of evidence?). Building on this, we consider how cultural evolution has organized and distributed cultural knowledge and cognitive tasks among subpopulations, effectively shifting both thinking and production to the level of the community, population, or network, resulting in collective information processing and group decisions. Cultural evolution can turn mindless mobs into wise crowds by facilitating and constraining cognition through a wide variety of epistemic institutions—political, legal, and scientific. These institutions process information and aid better decision‐making by suppressing or encouraging the use of different cultural epistemologies and ontologies. Human creativity does not solely rely on our individual cognitive abilities, but instead emerges from the recombination of ideas, practices, and approaches that result from social interactions and idea exchanges in large, diverse populations. These population‐level processes, which operate over generations, influence not only on our tools, technologies, and languages, but also key aspects of our culturally‐evolved cognition, such as our epistemologies and ontologies. [ABSTRACT FROM AUTHOR]

Insufficient research has been conducted on the pressure losses resulting from secondary air flow through tubular channels in indirect evaporative coolers, as well as the phenomenon of water drift. This study aims to methodically examine the impact of distinct heat exchanger tube structures (such as tube shape, tube material, and tube diameter) and various operating conditions (such as tube length, wind speed, and spray water flow rate) on the airflow resistance and water drifting phenomenon in the secondary air channel of a tubular indirect evaporative cooler. The experimental results indicate that the resistance increases quadratically with wind speed and is directly proportional to the tube length and spray water volume. Furthermore, it is found that flat oval tubes demonstrate greater resistance when compared to round tubes, the maximum increase is 288.97 %, whereas PVC tubes exhibit lower resistance when compared to aluminum tubes, the reduction is 13.51–29.46 % for a 25 mm tube diameter, and the reduction is 0.33–6.54 % for a 20 mm tube diameter. Additionally, the study reveals that water drifting increased as the wind speed and spray water flow rate increased. A multivariate fitting model of resistance was established to optimize the performance of the indirect evaporative cooler through a comprehensive analysis of each factor. This study provides valuable guidance on reducing the airflow resistance of the indirect evaporative cooling system, minimizing water drift, and enhancing overall efficiency. [ABSTRACT FROM AUTHOR]

This study investigates flange fracture formation in unconventional incremental radial extrusion. This manufacturing technique involves using rings with a gradually increasing inside diameter for constraining the free flow of material in the radial direction. As a result, the shaped flange has a constant thickness and a significantly larger diameter than that formed using the standard extrusion process conducted without the use of rings. EN AW 6060 aluminum alloy tube sections were used as the billet material, and the extrusion process was conducted under cold forming conditions at ambient temperature. For the determination of material fracture initiation, a new method was proposed involving the analysis of strain, strain rate and values of the normalized Cockcroft–Latham fracture criterion integral. The main advantage of the new method is that it allows for the prediction of fracture initiation via only FEM results analysis, i.e., it is not necessary to carry out additional experiments aimed at calibrating or determining limit parameters of a given material. It was shown that the occurrence of differences in the distribution of the above-mentioned parameters coincided with flange fracture initiation. [ABSTRACT FROM AUTHOR]

This work aims to explore crashworthiness of square aluminum/CFRP tubes with different hybrid schemes under quasi-static axial loading condition, and maximize their crashworthiness by performing multi-objective discrete robust optimization design. In the present study, metal/CFRP hybrid tubes with two hybrid schemes and their corresponding individual tubes are manufactured. The crushing process and crashworthiness indictors of all specimens are experimentally investigated under quasi-static axial crushing load. According to the experimental results, the AC hybrid tubes, made of outer aluminum square tube and internally adhered CFRP layers, show excellent energy-absorbing characteristics. Subsequently, numerical simulations are performed for the AC hybrid tubes to further investigate the effects of aluminum wall thickness, CFRP layer number and ply orientation on the energy-absorbing characteristics. It is found that the total energy absorption increases with the increasing tubal wall thickness of aluminum and CFRP layer, and ply orientation makes great contribution to the overall deformation modes and energy-absorbing characteristics of AC hybrid structures. Finally, a multi-objective discrete robust optimization has been conducted to optimize AC hybrid structures for the optimal crashworthy performance. [ABSTRACT FROM AUTHOR]

In order to further explore the forming limits of thin-wall tube necking and thickening, and obtain sufficient thickness of the tube in the thickening area, local electric pulse-assisted forming experiments were carried out to study the effects of current intensity and feed speed on the necking and thickening forming of thin-wall tube. The experimental results show that with the increase in current intensity, the temperature in the forming area of the tube increases, and the forming load for necking and thickening decreases. However, with the increase in feed speed, the overall forming load for necking and thickening increases in general, and the smaller feed speed is more conducive to forming. Taking into account the forming efficiency and electrode loss, the corresponding forming process window is obtained for the manufacturing of good parts. That is, during the necking stage, the current intensity shall not be less than 300 A, and the feed speed shall not exceed 10 mm/min. During the thickening stage, the current intensity should not be less than 1400 A, and the feed speed should not exceed 1 mm/min. The target part is finally formed, with an average wall thickness of 5.984 mm in the thickening zone and a thickening rate of 303.2%. [ABSTRACT FROM AUTHOR]

This article proposes a biomimetic multilayer foam-filled structure (BMFS) that mimics the microstructural characteristics of biological structures such as human bone and whale baleen. The lateral compression performance of such structures is investigated using experimental and numerical analyses. The proposed structure consists of three layers of aluminum foam with different densities filled in several concentric circular aluminum tubes. The test includes a solid design (Design-1) and a hollow design (Design-2). A series of quasi-static compression tests and finite element simulations are conducted, and the results show that BMFS exhibits a more advantageous sequential collapse deformation pattern for practical use. An energy absorption analysis of each layer shows that the energy absorption ratio of the foam layer reaches 85%. Comparing Models 1–3 of the two designs shows that the energy efficiency decreases, and the work efficiency increases, as the foam density increases. In addition, the interaction between the tubes and foams enhances the energy absorption properties of the structure. The parameter study shows that the energy absorption characteristics of Design-2 are insensitive to the diameter of the tube. The SEA of Design-1 increases with the thickness of Tube-1. [ABSTRACT FROM AUTHOR]

Round-end aluminum alloy tube concrete columns had good durability and were very economical, but the low strength and elastic modulus of aluminum alloy led to the need for improvement in performance. This paper proposes carbon fiber reinforced plastic (CFRP) strip reinforced round-end aluminum alloy tube concrete (CREAC) columns and investigates their mechanical properties under axial compression loads. A total of eight specimens were tested, including seven CFRP reinforced specimens and one control specimen. The effects of the width, spacing, and number of layers of CFRP strips on the axial compression performance of CREAC under the same amount of CFRP were studied. The experimental results indicate that the main failure modes of the specimen are the buckling of round-end aluminum alloy tubes and the fracture of CFRP strips. The CFRP strip can significantly improve the ultimate bearing capacity of the specimen, with a maximum increase of 15.3% in the test range. When the amount of CFRP is the same, as the number of CFRP strips decreases, the bearing capacity and ductility deteriorate. Increasing the width and thickness of CFRP strips significantly improves ductility. On the basis of the validated finite element model, parameter analysis was conducted, and the calculation method for stability coefficients was fitted. A calculation method for axial compression bearing capacity suitable for CREAC was proposed, with a maximum error of less than 1% between the predicted results and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the effect of burnishing on the surface hardness, selected surface roughness parameters and material ratio of tubes made of an EN AW-6060 aluminum alloy after welding. The prepared specimens were subjected to a 141-TIG welding process, after which the surfaces to be burnished were given a finishing turning treatment with DURACARB's CCGT09T302-DL cutting insert to remove the weld face. After the turning process, the surface finish treatment was carried out by rolling burnishing, for which Yamato's SRMD burnishing tool was used. The surface hardness, selected surface roughness parameters and material ratio were then measured. An analysis of the results showed an increase in hardness in the surface layer, as well as an improvement in the analyzed surface roughness parameters and the material ratio of the native material and the weld. [ABSTRACT FROM AUTHOR]

In each industry, compromises have to be made when choosing materials. Lower-density materials have a significant advantage in the automotive sector, especially due to rising fuel prices, since weight reduction can lower overall fuel consumption. The advantageous properties of metal foams, such as low density, high specific strength, and excellent energy absorption, should be researched and exploited in as many areas and ways as possible. This research aims to perform and evaluate the bending tests of ex situ functional metal foams: aluminum alloy matrix (AlSi7Mg) was used, which was filled with Ø2.5-3.0 mm lightweight expanded clay aggregate particles and surrounded by thin-walled aluminum tubes (AlMgSi0.5) with a wall thickness of 2 mm and an outer diameter of Ø32 mm. Empty tubes, foam-filled tubes (with and without structural epoxy adhesive) and metal matrix syntactic foams were compared based on their flexural strength and energy absorption capacity. Quasi-static three-point bend tests were carried out up to 25 mm deflection. The foam-filled tubes with epoxy adhesive showed an average of 6% increase in flexural strength compared to the foam-filled tubes without adhesive and a 145% increase compared to the metal matrix syntactic foams. [ABSTRACT FROM AUTHOR]

The article deals with an innovative, but not widely used type of joining of aluminum pipes through experiments. The joints are formed by plastic forming. The process is carried out in one step using the principle of pipe expansion, in order to bring the mating surfaces of the two pipes into a suitable position for the subsequent joining, which is created by means of plastic instability and simultaneous pressure flanging. Experimental tests were carried out with the tools designed to create most suitable joints. The length of the plastically formed pipe sections involved in the joint, the angle of the sharpened pipe ends, and the thickness of the formed joints were analyzed. One of the main goals of this study is to determine the proper joining parameters, such as tool distance or edge tapering for further investigations. As per the test results, it can be stated that the technology is suitable for joining aluminum tubes in a cost-effective way, and based on the promising strength results, further investigations will be conducted. [ABSTRACT FROM AUTHOR]

To enhance the concrete confinement ability of circular-ended aluminum alloy tubes, carbon fiber reinforced polymer (CFRP) was bonded onto the tube surface to form CFRP confined concrete columns with circular ends (RCFCAT). Eight specimens were designed with number of CFRP layers and section aspect ratio as variables. Axial loading test and finite element analysis were carried out. Results showed CFRP delayed buckling of the aluminum alloy tube flat surfaces, transforming inclined shear buckling failure into CFRP fracture failure. Specimens with aspect ratio above 4 experienced instability failures. Under same cross-section, CFRP increased axial compression bearing capacity and ductility by up to 30.8% and 43.4% respectively. As aspect ratio increased, enhancement coefficients of bearing capacity and ductility gradually decreased, the aspect ratio is restrictive when it is less than 2.5. CFRP strengthening increased initial axial compression stiffness of specimens by up to 117.9%. The stiffness decreased gradually with increasing aspect ratio, with most significant increase at aspect ratio of 4. Strain analysis showed CFRP bonding remarkably reduced circumferential and longitudinal strains. Confinement effect was optimal at aspect ratio around 2.0. The rationality of the refined FE model established has been verified in terms of load displacement curves, capturing circular aluminum tube oblique shear buckling, concrete "V" shaped crushing, and CFRP tearing during specimen failure. The parameter analysis showed that increasing the number of CFRP layers is one of the most effective methods for improving the ultimate bearing capacity of RCFCAT. [ABSTRACT FROM AUTHOR]

The finned-tube heat exchanger is the core part of an air conditioning system. Its heat exchange performance directly affects the energy consumption and efficiency of the air conditioner. The shortage and rising price of copper have led to increasing replacement of copper tubes with aluminum tubes in finned-tube heat exchangers. This paper studies two kinds of such heat exchangers, one consisting of copper tubes and aluminum fins and the other consisting of aluminum tubes and aluminum fins. The influences of the different base tube materials on heat transfer are compared and analyzed in terms of heat transfer strength and cost per unit heat transfer. The results show that the heat transfer and heat transfer coefficient increase with increasing inlet wind speed. Under different inlet wind speeds, the heat transfer and heat transfer coefficient of the finned-tube heat exchanger with aluminum tubes are 4%–12% and 7%%–9% lower than those of an identically structured heat exchanger with copper tubes, respectively. The aluminum-aluminum exchanger achieves 67% higher heat transfer than that of the copper-aluminum exchanger at only 8% of the cost. These results are significant for guiding the development and application of finned-tube heat exchangers. [ABSTRACT FROM AUTHOR]

Forming tubes with various bending radii without changing the bending dies is much easier for the 3D free bending forming (FBF) process. In the 3D-FBF process, different bending radii were realized by adapting the eccentricities of the bending dies. The accuracy of the U-R curve is crucial for the precision forming of complex bending components. In this study, the U-R relation curve of the Al alloy tube with a specific friction coefficient, fixed geometry size, clearance between tubes, and bending die was fitted first based on the forming results of AA6061-T6 tubes under different eccentricities. Second, the U-R relationship curve based on the experiment is used to propose the U-R relationship's mathematical formula based on many hypotheses. Finally, the modified U-R mathematical formula was applied in the finite element (FE) simulation and the actual FBF experiments for the AA6061-T6 Al alloy complex shape space bending members. The U-R relationship curve's reliability was verified by comparing the simulation and experimental results. The results obtained from the modified U-R relationship align well with the FE modeling results and can be directly applied to the bending process for the intended components. [ABSTRACT FROM AUTHOR]

The present study employed the ABAQUS numerical simulation method to analyze the forward flow forming of 7075 aluminum alloy tubes using power staggered spinning compression materials. Subsequently, a power staggered spinning experiment was conducted to analyze the microstructure and mechanical properties. The simulation results revealed that increasing the spinning temperature led to a decrease in the limit thickness reduction per pass while increasing range, as well as enhanced deformation along the wall thickness direction. At 400 ℃, favorable forming properties were observed with minimal plastic strain occurring in the inner layer when thickness reduction is below 10%. These findings indicate that an escalation in total thickness reduction resulted in refined and uniform grain distribution along the wall thickness direction, accompanied by improved hardness (up to 178.6 HV) due to synergistic effects from fine grain strengthening, strain strengthening, and dispersion strengthening induced by second particles. [ABSTRACT FROM AUTHOR]

Thermoelectric generators (TEGs) are devices that produce electricity due to the temperature difference between their cold and hot surfaces. The enhanced heat transfer from the cold surfaces of TEGs can increase their electricity efficiency. In this research, an experiment was arranged to study the direct and indirect contact of cooling water on the cold surfaces of the TEGs series and its results on their electricity efficiency. In this experiment, cooling water was flowing inside an aluminum tube with a rectangular cross-section. By changing the slope of the pipe, mixed convection was created in the cooling water. The results showed that the electrical efficiency of the TEGs was higher in the conditions of indirect contact as well as opposing mixed convection. In one of the results, the maximum electricity generation in indirect contact is 48 mW at pipe slop of 30 ∘ to 35 mW at pipe slop of 90 ∘ , more than direct contact. Since the connection of cold surfaces of TEGs happens indirectly through expensive metal plates such as copper and aluminum, therefore, the results of this research can be useful in the economic evaluation and improvement of such devices. [ABSTRACT FROM AUTHOR]

This study investigates the performance and design of high‐strength circular concrete‐filled double‐skin aluminum tubular (CFDAT) columns under axial loading. A new fiber element (FBE) model incorporating a new lateral confinement model is developed that considers the confinement effects and material nonlinearities. A new strength degradation factor is proposed for determining the postpeak behavior of the confined concrete in CFDAT circular columns. Existing experimental results are used to validate the accuracy of the predicted ultimate strength and axial load‐strain (P−ε) curves of CFDAT columns under axial loading. A comparison of the predictions of the ultimate strength and P−ε curves of CFDAT columns using the proposed lateral confinement model is made against the prediction using the three‐dimensional finite element modeling and the existing lateral pressure model of CFDAT columns proposed by other researchers. The performance of the CFDAT columns under axial loading is investigated using a detailed parametric study. The accuracy of existing empirical formulas given in various design standards for conventional concrete‐filled steel tubular columns as well as given by another researcher in predicting the ultimate strength of CFDAT columns is examined. Finally, a simple design formula is proposed and validated against the experimental and numerical results obtained from this study. It is found that the proposed FBE model and the simplified model developed in this study can accurately predict the performance of CFDAT columns under axial loading. [ABSTRACT FROM AUTHOR]

This work aims to research the oblique lateral crushing behavior of CFRP/AL hybrid tubes under different parameter configurations. First, a finite element model was established based on the maximum stress criterion and the traction‐separation law. The reliability of the numerical models for pure aluminum, pure composite, and hybrid tubes was verified by rigorous comparison with experimental data, respectively. Second, the influence of loading conditions and geometric characteristics on crashworthiness were studied. The results show that the damage modes of the hybrid tube under oblique lateral loading are mainly concentrated in the horizontal and vertical ends, specifically in the form of plastic hinge and fiber, matrix fracture. The CFRP layers has positive effect on improving the specific energy absorption (SEA). High ratio thickness of aluminum tubes can effectively improve the energy absorption (EA) and crush force efficiency (CFE). It is found that the sandwich structure is not conducive to resist lateral crushing, while the CFRP without external constraints can absorb more impact energy. Highlights: The oblique lateral crushing behavior of CFRP/AL hybrid tube was studied.A numerical simulation method was proposed and verified.The effects of loading angle, fiber layers and AL thickness were studied.The hybrid ratio and hybrid method were designed and discussed. [ABSTRACT FROM AUTHOR]

The crashworthiness of embedded composite structures that couple carbon fiber reinforced plastic tubes and aluminum honeycomb (CFRP-AH) was assessed through quasi-static compression tests and finite element simulation. Experimental results show that CFRP tubes tilt, when the AH fits with the CFRP tubes is not tight enough. With an increasing number of embedded CFRP tubes, the CFRP-AH composite structures are found to have a larger mean crush force (MCF) and specific energy absorption (SEA). Among the four experimental groups, CFRP-AH composite structures in Group S3, which used a larger size of CFRP tube, are found to have significantly improved energy-absorbing performance, and SEA of S3-t25 is improved by 576% compared with that of the pure AH S3-t0 without tubes. The S2 group's CFRP tube is tilted, which used a smaller size, and the structure is improved to obtain the NS2 structure, so that only tearing deformation occurs in the AH-CFRP structure's CFRP tube. The SEA of NS2-t25 was improved by 29.70% over S2-t25 and 22.83% over S3-t25, which has the best energy absorption characteristics among the filled tube structures. [ABSTRACT FROM AUTHOR]

In the hydroforming process of a thin-walled tubular component with multiple local bulges, the bulge in the middle position is almost impossible to be formed with a conventional one-step hydroforming process because of the difficult axial feeding. To solve this problem, a novel method is proposed by preforming wrinkles using selective induction heating at different positions of tube blank to aggregate materials in advance for the subsequent hydroforming of tubular component with multiple local bulges. In this paper, the wrinkling behavior of 5052 aluminum alloy tube blank under different conditions and the deformation behavior of the wrinkled tube blank in subsequent hydroforming process of tubular component with three bulges are analyzed. It is shown that the existence of wrinkles is beneficial to increase the ultimate expansion ratio of the tube blank. Moreover, the instability behavior of multiple wrinkles on 5052 aluminum alloy tube blanks under different conditions was investigated by experiments. The process parameters for prefabricating two or three wrinkles, including temperature, spacing between wrinkles, and internal pressure, were determined through a detailed experimental investigation. Finally, the defects including splitting and undercut that occur in the hydroforming of tubular component with three bulges are analyzed, and the thin-walled tubular component with three bulges was hydroformed successfully using a wrinkled tube blank obtained under the process parameters of 250 °C, 4 mm, 5.5 MPa/350 °C, 10 mm, 2 MPa/400 °C, 6 mm, 1.33 MPa. These results provide insights for the manufacturing of tubular component with multiple local bulges from hard-to-form materials. [ABSTRACT FROM AUTHOR]

An accurate constitutive model lays an analytical foundation for the thin-walled tube plastic joining process. This study obtained the best-fitted constitutive model to accurately simulate the steel/aluminum thin-walled tubes cracking during plastic joining. The process of establishing the constitutive model comprises three parts: 1) The flow stress model of AA6061 was determined by comparing the fit of seven flow stress models and experiments, and the model parameters were calibrated using a genetic algorithm. 2) A method combined with experiment and simulation was adopted to obtain the failure parameters in the ductile fracture criterion. 3) Combinations of different ductile fracture criteria and yield criteria were implemented into the VUMAT subroutine to simulate uniaxial tension. The constitutive model of AA6061 was determined based on the comparison of simulation and experiment. Subsequently, the constitutive model was applied to the cracking prediction of the steel/aluminum thin-walled tube plastic joining process. The predicted cracking was compared with the experimental cracking. Finally, the cracking risk areas were evaluated by the forming limit diagram. The results indicated that the Voce-Swift model could better reflect the trend of AA6061 flow stress and the genetic algorithm could effectively improve the Voce-Swift model fitting accuracy. The uniaxial tensile simulation suggested that the Cockcroft-Latham criterion combined with the Hill48 anisotropic criterion could accurately predict the fracture of AA6061. Moreover, the steel/aluminum joint simulation cracking matched very well with the experiment, which verified the validity of the constitutive model in predicting cracking during the plastic joining process. Finally, the aluminum/aluminum joint simulation result proved that the risk of cracking in the upper tube was more significant than in the lower tube. The AA6061 tube with poor plasticity should be the lower tube to improve the formability of the steel/aluminum joint. [ABSTRACT FROM AUTHOR]

Aluminum foams have recently received special attention due to their peculiar mechanical properties. For example, their energy absorption capacity in crash events and low density are very desirable characteristics for several applications. Actually, the energy absorption of aluminum foams is even magnified when they interact with aluminum tubes or when tubes are filled with aluminum foams. Since the automotive industry constantly demands light materials with high strain energy absorption capacity to reduce fuel consumption and fulfill safety requirements, aluminum foams are an excellent alternative to satisfy such demands. This work shows, by numerical simulations of reduced and full vehicle models, the usefulness of aluminum foams incorporated in a car structure when subjected to "35 mph Frontal Barrier Impact Test", according to the Federal Motor Vehicle Safety Standard No 208 (FMVSS). Foam was used to dramatically improve load capacity and crush displacement. Thus, dash panel intrusions and acceleration gradient were reduced, increasing the vehicle safety performance. Finally, it is shown that foams can be beneficial in electric vehicle development by increasing load capacity. [ABSTRACT FROM AUTHOR]

Fiber metal laminate (FML) is gaining increased interest among researchers in designing thin-walled tubes as an efficient energy absorber. The combination of aluminum tube and fiber-reinforced polymer (FRP) as an FML hybrid tube has successfully demonstrated enhanced crashworthiness performance of structures. Previous studies reported FML hybrid tubes employing a single type of FRP composite material as the laminate material. Investigations on the effect of stacking sequences of multiple types of FRP composite as laminate materials are limited and mostly focused on sandwich structures. This study aims to investigate the effect of reinforcement material as a laminate layer and stacking sequences on the crashworthiness characteristics of aluminum-FRP hybrid tubes under quasi-static axial compression loading. The crashworthiness characteristics and the failure behavior of aluminum monolithic tube, aluminum-single FRP material, and aluminum-multi FRP material hybrid tubes are tested and compared. Glass FRP (GFRP) demonstrates great potential as a laminate material for aluminum tube compared with carbon FRP (CFRP). Aluminum-GFRP and aluminum-GFRP-CFRP hybrid tubes exhibit a 26.4 % and 66.9 % increase in energy absorbed, respectively, compared with the monolithic aluminum tube. The specific energy absorption and crushing force efficiency of the aluminum-GFRP-CFRP hybrid tube show minimal reductions of 4.9 % and 6.2 %, respectively. GFRP is the better choice of laminate material for aluminum tubes compared with CFRP. Multiple FRP laminates show a larger crashworthiness enhancement of FRP hybrid tubes in achieving better crashworthiness performance of the energy absorber. These findings imply that the selection and stacking sequences of laminate material are vital in tailoring the performance of the hybrid tubes toward efficient energy absorbers. [ABSTRACT FROM AUTHOR]

A combination of multi-physics numerical simulation and experiment was conducted to study the magnetic pulse compaction technology driven by two aluminum tubes of tungsten copper powder. Then, the effects of different process parameters on the density and uniformity of the compact were studied by tuning the thickness of the pack and driver tubes and the gap between them. Results show that the density of compact is the highest when the thickness of the driver tube is 1.0 mm. More energy is consumed for force conduction as the thickness of the pack tube increases. Thus, the density of the compact is the highest when the thickness of the packer tube is 0.8 mm. The speed of the driver tube impacting the pack tube also increases with the rise in the gap. Accordingly, the compaction density with the gap of 1.5 mm is the highest under the same other parameters. [ABSTRACT FROM AUTHOR]

A structure for joining 6061T6 aluminum alloy tube and AZ31B magnesium alloy shaft via the magnetic pulse crimping process was proposed. The forming process, mechanical properties, failure modes, and corrosion behaviors of the joint were studied. The results showed that the enormous Lorentz force drove the wall of aluminum alloy tube to move towards the groove of magnesium alloy shaft at high velocity, thus realized mechanical locking and formed joint. Through torsion tests, it was found that the mechanical properties of the joint with different process parameters varied. There were two failure modes for joint: torsional separation and torsional crack. Specifically, discharge time, groove angle, and discharge energy for torsional crack were, respectively, 1, 90°, and 28 kJ and 3, 90°, and 25 kJ. The maximum torque was up to 961.99 N·m under discharged twice, 90° groove angle, and 25-kJ discharge energy. Through neutral salt spray corrosion tests, it was found that the maximum torque only decreased by 28.03% after corrosion for 192 h. It indicated that the corrosion resistance of joint was good relatively. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to study the effect of various materials on the performance of vortex tube. Beforehand, the recent progresses in the improvements on the performance of vortex tube (VT) and its efficiency, a literature survey has been discussed. The present work reports vortex tube performance augmentation considering four different materials vortex tubes and their orifice. The thermophysical properties of the material was considered to analyse the performance of vortex tubes for various materials. It was found that the aluminium vortex tube and its orifice achieved the highest performance among all the rest of the materials. The highest cold and hot temperature separation magnitude for Al VT and Al Vortex generator is 24 °C and 50 °C at an inlet pressure of 5 bar. The vortex tube of various materials had exact dimensions and specifications for an "apple to apple" comparison. Results show that the specific heat, thermal diffusivity, and thermal conductivity were the significant properties that affect the thermal performance of the VT. Furthermore, exergy analysis was done for the Al vortex tube and its orifice to predict the quality of available energy. It shows that high exergy destruction is found in hot regions for a high cold mass fraction. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement in tubes is widely applied in various industrial processes. The traditional method of heat transfer enhancement is to insert radial fins to expand the internal surface area and destroy the flow. However, there is a flue gas corridor in the central area of the tube, and the cost of expanding the inner fin is high. A centrally symmetrical bent extruded aluminum fin was developed to enhance the heat transfer in the tube. An experimental platform was constructed to test the performance of inner finned tubes and explore the process of combining extruded aluminum inner fin with steel tube. The bent extruded aluminum fins with two side fins extending to the central axis possesses the best comprehensive heat transfer performance. The heat transfer correlation of the optimal fin structure is Nu = 0.864Re0.4275Pry 0.3818(Pry/Prw)-0.1004. With low cost and strong heat transfer performance, the bent extruded aluminum inner fin tube will gain wide applications in the engineering field. [ABSTRACT FROM AUTHOR]

Aluminum closed cell foam blocks are created with a volume of 1 inch3 which consist of aluminum foam parts shielded with part of aluminum tube and in some types reinforced with inner aluminum tubes. Blocks have been made to overcome some existing problems in metallic foam used to protect some applications parts from impacts as a sacrificial part. Metallic foam has three main categories sandwich panels, filled tubes and corrugated sheets. Quasi-static compression tests have been applied on 12 blocks with different shapes and compared with pure aluminum foam blocks as a reference. Results display the enhancement of mechanical properties of blocks like yield strength (SY), crushing strength (Sc) and densification strength (Sd), compression at strain 70%, as well as absorbed energy (area of compression under the curve). The highest value for yield strength (5.87 MPa) was registered for Finger phalanxes cube block (FP—0.1 Sq.). While the highest value for densification strength (21.7 MPa) was registered for spine cylinder block (SV8—0.17 C25). The registered results for samples apparent the highest value for energy dissipation density (Edd) is 40.52 J/in3 (91% enhancement) and crushing strength (8.61 MPa) was registered for Finger phalanx cylinder block (FP—0.17 C25). The lowest value for Edd is 14.16 J/in3 (less than pure aluminum foam block value by 33%), SY = 0.42 MPa, Sc = 3.21 MPa, and Sd = 4.46 MPa, registered for thin wall Ear canal cylinder block (EC8—0.075 C26.5). Best mechanical properties had been achieved for Finger phalanx cylinder block (FP—0.17 C25) and spine cylinder block (SV8—0.17 C25). [ABSTRACT FROM AUTHOR]

In the research of drone wireless charging, the lightweight design of the wireless charging device has a large impact on the overall performance of the drone. To realize the lightweight, the tubular coil, which caused by high‐frequency excitation to produce skin effect in the conductor becomes a way to optimize the weight of the receiver coil. This paper proposes an aluminum tube with a thin copper layer plated on the surface as a drone receiver coil and landing gear. This solution can not only replace the original bracket but also be lightweight and obtain high coupling coefficient. Experiments show that this novel receiver can receive power up to 30 W at 250 kHz excitation source with 78% average transmission efficiency and has good antimisalignment ability. This new tubular coupler is more suitable for the demand of lightweight wireless charging for drones. [ABSTRACT FROM AUTHOR]

Experimental studies of free-convective heat exchange between single-row bundles of bimetallic tubes with spiral rolled aluminum fins of different heights (2–14.6 mm) and a vertical air flow created by an exhaust shaft with adjustable height H = 0.52, 1.16, and 2.12 m are presented. The tubes were layed out with a constant relative transverse spacing σ1 = 1.14 (6 pipes). The data of measurements were used to calculate the average reduced heat transfer coefficient, which ranged from 0.78 to 17.30 W/(m2∙°C) at Rayleigh numbers (19–360)·103. A similarity equation is obtained for describing the dependence of heat emission of single-row bundles with different fin heights in a free convection regime on the relative height of the bundle–shaft system. It is found that intensification of free convection of air by installing an exhaust shaft above the bundle of tubes allows one to increase the heat emission intensity by 2.3 times. Expressions are obtained for determining the energy and aerodynamic efficiencies of the bundle–shaft system. The optimal height of finning (about 8 mm) for bundles of studied tubes with an exhaust shaft was determined. [ABSTRACT FROM AUTHOR]

To meet the requirement of lighter weight and better performance in tube hydroforming, one of the most important tasks is to accurately predict the forming limit of thin-walled tubes under nonlinear loading paths. This work established the M-K+DF2012 model, a combination of the M-K model and the DF2012 ductile fracture criterion, for the forming limit prediction of thin-walled tubes under nonlinear loading paths. In this model, the failure of the groove is determined by the DF2012 criterion, and the corresponding strains in the uniform region are the limit strains. The limit strains of an AA6061 aluminum alloy tube under a set of linear loading paths and two typical nonlinear loading paths were tested. Parameter values of the M-K+DF2012 model for the tube were determined based on the experimental limit strains under linear loading paths, and the limit strains under the two nonlinear loading paths were predicted. Then the strain-based forming limit diagram (ε-FLD) and the polar effective plastic strain FLD (PEPS-FLD) of the tube under different pre-strains were predicted and discussed. The results show that the limit strains of the tube are obviously path-dependent, and the M-K+DF2012 model can reasonably capture the limit strains of the tube under both linear and nonlinear loading paths. The predicted ε-FLD shows a strong dependence on the pre-strain, while the predicted PEPS-FLD is weakly strain path-dependent and almost path-independent on the right-hand side for the AA6061 tube. [ABSTRACT FROM AUTHOR]

In recent times, particularly in applications used to build various structures for construction purposes or machines, solid sections have been gradually replaced by hollow sections due to their attractive features such as being light weight and having high specific strength. In the present investigation, an attempt was made to investigate, in detail, the flexural capability of aluminium hollow tubes (AHTs) with square cross-sections. The objective of the investigation was to study the influence of stress concentration on the flexural behaviour of the hollow tube. The stress concentration factor considered in this investigation was holes of various cross-sections and quantities. Three-point bending tests with concentrated loads were conducted on specimens of a hollow tube with different stress concentrations such as circular holes, multiple circular holes, square holes and perforations. The load was applied manually during the bending test with appropriate increments. The bending test was carried out on specimens with support spans of 110, 130, 170 and 200 mm. The output measures of the study were maximum bending load, deflection and flexural stiffness. The output measures were analysed in detail in order to recommend the type and nature of stress concentration in a hollow tube applied to structural applications to ensure the safest workability. The flexural stability of the tube was analysed by experimental and numerical procedures, and the results were validated using an analytical approach. It was found that the results of all the approaches complement each other with a low significance of error. AHTs with a circular hole, multiple circular holes and perforations were observed to have better flexural stability than other AHTs such as AHTs with square hole and plain AHTs. [ABSTRACT FROM AUTHOR]

An AA6061 aluminum alloy tube was fabricated by compacting machining chips via thermomechanical consolidation, including hot pressing and hot extrusion. The microstructure evolution and formation of oxide particles were investigated in correlation to tensile mechanical properties. It was found that fine Al/Mg oxide particles were formed due to the fracture of oxide layers on the chips and the reaction between Mg and Al2O3 during hot extrusion. The oxide particles inhibited the growth of recrystallized α-Al grains, leading to the formation of a microstructure consisting of coarse elongated grains with sizes of 420 μm and fine equiaxed grains with sizes of 10 μm. After T6 heat treatment, a microstructure with finer grains (grain sizes: 34 μm) formed due to further recrystallization induced by residual strain. The tensile mechanical properties testing results indicated that a good combination of strength (296 MPa) and ductility (7.6%) was achieved in the T6 heat treated samples, which were likely attributed to the high-quality inter-chip bonding, as well as the fine oxide particles which were small enough that further crack nucleation and growth around them were inhibited during tensile deformation. For the purpose of comparison, the microstructure and mechanical properties of the as-extruded and T6 heat treated samples produced by hot extrusion of the cast ingot of AA6061 aluminum alloy were also investigated. The lower tensile strength of solid-state recycled tube sample might be associated with the consumption of Mg atoms by the oxidation reaction, leading to the lower density of β″ precipitates in precipitation strengthening. [ABSTRACT FROM AUTHOR]

The smaller the relative bending radius of the bent tube, the more difficult the tube blank is to be bent. In this paper, the push-bending process for the aluminum tube with a relative bending radius of 0.9D was analyzed through simulation. There was tangential tensile stress concentration occurring at the front endpoint of tube intrados, which increased the risk of cracking. That is because the bending tube's extrados moves less angular distance than its intrados by the uniform lubrication method, causing excessive deformation of the cross-section. Therefore, a differential lubrication method using the lubricant with a larger friction coefficient at intrados and the lubricant with a smaller friction coefficient at extrados was proposed to increase the angular velocity of the tube's extrados. It was found that the differential lubrication method helped avoid excessive thinning at the front endpoint of tube intrados through simulations. Furthermore, push-bending experiments of 5A02 aluminum alloy with a relative bending radius of 0.9D were carried out to investigate this effect. The experimental results showed that the differential lubrication method effectively avoided cracking, which agreed with the simulation results. [ABSTRACT FROM AUTHOR]

To explore the enhancement mechanism of CFRP overwrap in the aluminum-CFRP square hybrid, hybrid tubes with different braided angles were investigated both experimentally and numerically. Hybrid tube of 30 degrees had severe CFRP layers splitting damage in the tube corner. As the braided angle up to 60 degrees, CFRP layers with high transverse resistance force compressed the aluminum tube and caused it to fold inward; This led to the hybrid tube failing in a distinct inward eccentric fold deformation pattern and had an obvious energy absorption improvement in its inner aluminum tube due to its increase in the corner deformation. [ABSTRACT FROM AUTHOR]

The hot metal gas forming process can significantly improve the formability of a tube and is suitable for the manufacturing of parts with complex shapes. In this paper, a double wave tube component is studied. The effects of different temperatures (400 °C, 425 °C, 450 °C and 475 °C) and different pressures (1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa and 3 MPa) on the formability of 6063 aluminum alloy tubes were studied. The influence of hot metal gas forming process parameters on the microstructure was analyzed. The optimal hot metal gas forming process parameters of 6063 aluminum alloy tubes were explored. The results show that the expansion rate increases with the increase in pressure. The pressure affects the deformation of the tube, which in turn has an effect on the dynamic softening of the material. The expansion rate of parts also increases with the increase in forming temperature. The increased deformation temperature is beneficial to the dynamic recrystallization of 6063, resulting in softening of the material and enhanced deformation uniformity between grains, so that the formability of the material is improved. The optimum hot metal gas forming process parameters of 6063 aluminum alloy tubes are the temperature of 475 °C and the pressure of 2.5 MPa; the maximum expansion ratio is 41.6%. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the computational fluid dynamics to find the effects of Reynolds number, different volume fractions of aluminum oxide nanofluid and different heat fluxes in heat transfer performance (Nusselt number) in a helical tube. This simulation was investigated at Reynolds number range 2000 and 10,000 and volumetric fraction range 1% and 4% of aluminum oxide nanofluid and constant heat fluxes of 4000–6000 W/m2. The single-phase model was used to model the nanofluid and the feasible k-ε model was used to simulate the turbulent flow. Then, perceptron artificial neural networks with the Levenberg–Marquardt algorithm were used to predict the Nusselt number such that input parameters include Reynolds number, nanoparticle volume fraction and output or target was considered Nusselt number for the network. The results show that with increasing the volume fraction of aluminum oxide nanofluid and Reynolds number, the Nusselt number increases by about 20.35%. Also, by increasing the constant heat flux from 4000–6000 W/m2, the Nusselt number increases by 18.75%. The results of the artificial neural network show that the topology 2-10-1 is very successful in predicting the Nusselt number so that the minimum mean squared error for the data allocated to the training and validation sections were 0.024449627 and 0.117025052, respectively, which are obtained under optimal epochs 19 and 9. The value of the correlation coefficient obtained in predicting the Nusselt number is 0.944416302. [ABSTRACT FROM AUTHOR]

To improve the load carrying capacity, structural stiffness, and impact resistance of honeycomb sandwich structure, a novel tube-reinforced double-layer honeycomb sandwich structure was proposed by filling metallic tubes on the honeycomb holes. The low-velocity impact test was carried out on the tube-reinforced structure experimentally and numerically to evaluate its low-velocity impact response. It indicated that the stiffness, first linear stage slopes, and impact resistance of the honeycomb sandwich structure were increased by tube filling. Besides, the stress and deformation distribution of front and back panels were changed into more scattered and uniform, resulting in the reduction of maximum deflection. The maximum deflection of the front panel could be effectively reduced by filling the upper honeycomb core with aluminum tubes. Filling the lower honeycomb core with aluminum tubes could greatly reduce the maximum deflection of the middle and rear panels. The tube-reinforced honeycomb sandwich structure was a promising structure for weight sensitive applications owing to its improved load carrying capacity and impact resistance. [ABSTRACT FROM AUTHOR]

This study investigates the effect of carbon fiber reinforced polymers (CFRP) sheets on the flexure behavior of structural square cross-sectioned aluminum tubes. The specimens were extruded from an aluminum alloy 6063-T6 and shaped into hollow square tubes. Four-point bending tests were performed on three samples with different CFRP wrapping that included; (1) virgin (not strengthened), (2) strengthened with two layers of CFRP, and (3) strengthened with four layers of CFRP. Experimental tests were conducted and compared with finite element analysis. The load was applied by bearing plates that acted across each specimen section's full flange width. The results showed that wrapping CFRP on the aluminum structures increases the flexural strength of the aluminum by approximately by three times. A finite element model (FEM) was developed to simulate the four-point bending experimental tests for the three specimens. FEM results depicted that the use of CFRP materials is a powerful technique for strengthening aluminum structural members, which results in an increase in the load-carrying capacity and an increase in stiffness. The finite element analysis depicted good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A decoupling method is proposed for micro-Newton thrust measurement with a torsion pendulum. The basic approach is to reduce the influences introduced by the propellant tube and wires of the thruster. A hollow aluminum tube is used to hang the torsion pendulum and is also chosen as the transport pipe for the propellant of the thruster. The electric control box of the thruster is mounted on the pendulum body, which is powered by an externally installed power supply through a liquid metal conductive unit. The control of the electric control box is performed through wireless transmission. With this design, the influences of the propellant tube and connection wires between the torsion pendulum and the outside device are reduced and the stability of the torsion spring constant of the system can be improved. The use of the liquid metal conductive unit reduces the coupling between the wires and the measurement system. The feasibility of the wireless transmission is analyzed. The error sources during the thrust measurement are analyzed, and the expected three σ uncertainty of the thrust is 0.0 3 2 + (0.10 % * F) 2 μ N for the measurement of the cold gas thruster. The scheme provides a thrust measurement with higher precision and stability. [ABSTRACT FROM AUTHOR]