Tube Corner Research Articles

Study on the crashworthiness of multi-cell thin-walled tubes filled with triply periodic minimal surface lattices

To improve energy absorption and efficiency and develop a structure with outstanding energy absorption capability, this study proposed designing multi-cell tubes filled with triply periodic minimal surface (TPMS) lattices. Based on experimental and simulation methods, the crashworthiness of multi-cell tubes filled with three types of TPMS lattices (Diamond, Gyroid, and Primitive) was investigated. Five multi-cell tube structures were fabricated by increasing the thin-walled tube corner units, improving the energy absorption efficiency by 67.98%. The results show that due to the coupling between TPMS lattices and thin-walled tubes, multi-cell tubes filled with TPMS lattices exhibited better crashworthiness performance. The energy absorption of multi-cell tubes filled with Diamond, Gyroid, and Primitive lattices increased sequentially. The energy absorption per unit mass and energy absorption capability were most notably enhanced for the multi-cell tubes filled with Diamond lattice, with energy absorption efficiency 17.24% higher and energy absorption 104.26% greater than empty multi-cell tubes. This inspires crash designs of rail vehicles and automotive fronts.

Analysis of spontaneous ignition of hydrogen-enriched methane in a rectangular tube

This study investigates the spontaneous ignition of high-pressure hydrogen-enriched methane in air within a rectangular tube. A computationally efficient approach has been adopted, utilizing a reduced reaction mechanism and ignition delay model within a 3D Large Eddy Simulation (LES) framework. This approach overcomes the limitations of traditional 1D and 2D simulations with detailed chemistry models, which are unable to accurately reproduce the complex 3D shock wave structures within the tube. The simulated shock wave behavior during 9 MPa hydrogen leakage (case 1) and 11 MPa 90 vol% hydrogen/10 vol% methane mixture leakage (case 2) are found to agree well with experimental observations. In case 2, the hot spots generated by reflected shock waves and Mach reflections ignite the hydrogen/methane-air mixture, resulting in three sequential spontaneous ignitions. The flame is observed to primarily propagate along the tube corners and wall centers, with the central ignition spreading across the entire cross-section. For the 25 MPa 24 vol% hydrogen/76 vol% methane mixture leakage (case 6), the shock intensity is significantly reduced due to the increased methane proportion, leading to spontaneous ignition only at the tube corners when the hemispherical shock wave reflects from the wall. The flame predominantly forms downstream along the tube corner, gradually spreading along the tube wall. It is indicated that while the probability of spontaneous ignition decreases with increasing methane content, the risk remains significant under sufficiently high pressures. To the best our knowledge, this study represents the first 3D large eddy simulation of spontaneous ignition for high-pressure hydrogen-enriched methane leakage into air, providing valuable insights into the underlying physical phenomena.

Influence of tube cross-section geometry on high-pressure hydrogen-flow-induced self-ignition

Self-ignition within a cylindrical tube that discharges high-pressure hydrogen results in flame formation. Because rectangular tubes are used to visualize fuel-flow dynamics, the influence of the tube cross-section on the self-ignition characteristics is investigated. As experimental investigation of the mechanisms underlying the self-ignition phenomenon in cylindrical tubes is difficult, three-dimensional numerical simulation is employed. Following the bursting of diaphragm by high-pressure hydrogen with a storage pressure of 9.0 MPa and a temperature of 300 K, initial self-ignition occurs at the center of the rectangular tube sidewall. This is because of the mixing of air and hydrogen induced by the bow-shock reflection-generated jet flow and resulting adiabatic shock compression-induced temperature increase. This temperature rise induces a secondary self-ignition at the tube corners. In the cylindrical tube, a solitary ring-shaped self-ignition occurs near the sidewall. The flame evolutions in rectangular and cylindrical tubes reveal similar flame-spreading trends, which indicates similar bow-shock reflection-induced self-ignition mechanisms.

Crashworthiness Analysis of Square Aluminum Tubes Subjected to Oblique Impact: Experimental and Numerical Study on the Initial Contact Effect

This study investigates the crashworthiness behavior of square aluminum thin-walled tubes subjected to both axial and oblique impact loading, emphasizing the effects of crushing angle and initial contact between impactor and tube on the plastic collapse initiation and energy absorption capacity. A parametric study in crushing angle is conducted until 15°, while the two examined types of initial contact between impactor and tube consist of a contact-in-edge case and a contact-in-corner one, aiming to capture the effect of initial contact on both plastic collapse and energy absorption. Both experimental quasi-static tests and numerical simulation via finite element modeling in LS-DYNA software are carried out for the evaluation of the crushing response of the tested tubes. The 5° oblique cornered crushing revealed the greatest energy absorption, reflecting the most efficient loading case as significant tearing failure occurred around the tube corners in axial crushing due to a higher peak crushing force, while the increase in crushing angle caused a drop in energy absorption and peak force regarding the oblique loading. Finally, an initial contact-in-corner case revealed higher energy absorption compared to both axial and edged oblique loading, while peak force showed a slight decrease with crushing angle in that case.

Numerical study on the shock evolution and the spontaneous ignition of high-pressure hydrogen during its sudden release into the tubes with different angles

High-pressure hydrogen storage is one of the best choices of hydrogen storage at present and in the future. However, the spontaneous ignition of high-pressure hydrogen release blocks its wide application. This paper further studies the shock evolution, temperature accumulation and spontaneous ignition inside the tubes with different angles by employing LES, RNG and EDC models, 10-step like opening process of burst disk and detailed hydrogen/air combustion mechanism. Four tubes with different angles (60, 90, 120 and 150°) are employed based on the previous experimental result. It is found that the smaller the angle of the tube, the greater the maximum pressure and temperature of the first shock reflection zone. And the maximum pressure and temperature of the second shock reflection zone is the highest inside the 90° angle tube. This is due to two shock reflection mechanisms inside the tubes: in acute angle tube, only the reflected hemispherical shock hits the inner wall of the tube corner, however, for non-acute tubes, both the reflected hemispherical shock and reflected normal shock hit the inner wall of the tube corner. In addition, it requires a longer time and a further distance to initiate the spontaneous ignition inside the tubes with larger angle. And the flame induced by the spontaneous ignition could move upstream steadily inside the 60° angle tube and the flame length increases with the release time to a maximum value of 21.44 mm.

Behavior of circular-steel-tube-confined square CFST short columns under axial compression

This paper proposes circular-steel-tube-confined square concrete-filled steel tube (CFST) to improve the mechanical property of the newly built and existing deficient square CFST. The external adding circular steel tube does not enter the beam-column connection area and mainly functions as lateral confinement to the inner square CFST. Twelve circular-steel-tube-confined square CFST short column specimens and twelve conventional square CFST short column specimens were designed and tested under axial compressive load. The main variables of the test include column type, steel ratio, outer circular steel tube size, and concrete strength. The overall failure modes, axial load-displacement curves, macroscopic deformation characteristics, and the inner and outer circular steel tube confinement were analyzed and compared systematically. The study revealed that the outer circular steel tube yielded horizontally in tensile strength and provided effective confinement to the inner square CFST. Therefore, the bearing capacity of the square stub column was improved significantly, and the brittle failure in the confined area was prevented. Due to the effective confinement by the outer circular steel tube, the stress state in the square steel tube was much more uniform. The column configuration led to an effective but uneven confinement in the outer circular steel tube, concentrating near the square steel tube corner. Based on the superposition method, a suitable design method is proposed to predict the compressive strength of circular-steel-tube-confined square CFST, and the theoretical predictions are in good agreement with the test results of this paper.

Eccentric compression behaviour of diagonal rib-stiffened thin-walled square concrete filled steel tubes

Thin-walled square concrete filled steel tubular (CFST) members have attracted more attention in practice because of less steel consumption, high construction efficiency, and convenient arrangement for furniture or curtain wall. Compared with circular members, the local buckling of thin-walled square CFST members is a big concern since tube buckling often results rapid strength and ductility degradation. So in this investigation, diagonal ribs were welded on the internal tube corners to improve the performance of square CFST members. Nine diagonal rib-stiffened square CFST specimens, with large width-to-thickness ratio B/t=100, were experimentally investigated under eccentric compression. The main test parameters included column slenderness ratios (λ=13.9, 34.6, 55.4) and loading eccentricities (2e/B=0, 0.25, 0.50, 1.00). Detailed finite element models were established and verified. The composite effect of the stiffened column was elaborated through combining test results and the finite element analysis, followed by feasibility of column–column connection details and parametric studies. Finally, design methods for calculating the member resistances subjected to axial and eccentric compression were proposed.

Inward eccentric fold failure in the progressive crushing of aluminum-CFRP square hybrid tubes

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.

Mechanism of Roadway Floor Heave Controlled by Floor Corner Pile in Deep Roadway under High Horizontal Stress

In order to overcome the support difficulty of serious floor heave caused by rock burst, with the floor heave of ventilation roadway in Hegang Xing An Coal Mine as the engineering background, the treatment scheme of the concrete-filled steel tube corner pile and floor grouting is put forward. Based on the solution of the slip line field under plane strain condition, the mechanical model of the slip-type floor heave is established, and the formula for calculating the critical failure depth of the roadway floor and the minimum support depth of the corner pile is derived. Through numerical analysis and similar model tests, the deformation and stress distribution of surrounding rock under the support of the corner piles are studied, and the force law of the pile under high horizontal stress is analyzed. The results show that, compared with the floor corner anchor, the floor corner pile + floor grouting support scheme can significantly improve the mechanical properties of the floor rock mass, and the plastic slip line of the floor plate part can be cut by corner piles, which effectively controls the deformation of the floor plate under high horizontal stress; the length and inclination angle of the corner pile have a great influence on the support effect. In the on-site treatment scheme, 1.1 times the calculated length of pile should be selected. The results of a similar model and field test show that the corner pile is effective in controlling the deformation of roadway floor and two sides.

Numerical study on the mechanism of spontaneous ignition of high-pressure hydrogen in the L-shaped tube

There have been reports of ignition of high-pressure hydrogen during its sudden release for unexplained reasons and ignition mechanism still need to be further investigated. In this paper, mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into the L-shaped tube is investigated. LES, EDC model, 10-step like opening process of burst disk and 18-step detailed hydrogen combustion mechanism are employed. Three cases with burst pressures of 2.16, 6.21, and 9.10 MPa are simulated. It is found that shock wave is strongly reflected after it hits the tube corner wall, forming a reflected-shock-affected region and an energy conversion region with higher temperature, greater pressure and lower velocity. Afterwards, the reflected shock wave moving forward is reflected several times by the tube wall until it disappears and oblique shock is generated. After the hydrogen/air mixture enters the corner, it extends downstream along inner wall and separated from the main hydrogen/air mixture. The reflected shock wave moving backward interacts with the expansion waves and increases the temperature and pressure again, but spontaneous ignition cannot be initiated. Three mechanisms of spontaneous ignition of high-pressure hydrogen in the L-shaped tube are proposed eventually. The results reproduce the experimental spontaneous ignition conditions and positions, indicating that the numerical models can be applied as a tool for hydrogen safety engineering.

Heat transfer and pressure drop characteristics of gas–liquid Taylor flow in mini ducts of square and rectangular cross-sections

The thermal and flow characteristics of gas–liquid Taylor flow in vertical mini square and rectangular ducts were studied numerically for water and ethylene glycol as the liquid phase and nitrogen as the gas phase. The effects of fluid properties, flow parameters, and aspect ratio on the bubble shape, recirculation time, friction factor, and Nusselt number are discussed. The results indicate that the gas phase is confined by the tube wall in square and rectangular tubes leading to an asymmetrical Taylor bubble at low Capillary numbers, while an axisymmetric bubble is formed at high Capillary numbers. The liquid film thicknesses in the square and rectangular ducts are not uniform with a thicker liquid film formed at the tube corner. The recirculation region decreases and the dimensionless recirculation time increases with increasing Capillary number, which means that the intensity of recirculation decreases with increasing Capillary number. The friction factor decreases with increasing two-phase mixing velocity and aspect ratio and increases in gas void fraction, while the reverse is true for the two-phase Nusselt number. Compared with the ethylene glycol/nitrogen cases, the addition of Taylor bubble plays a more significant role on the pressure drop increase and heat transfer enhancement for the water/nitrogen cases because of the larger recirculation volume and smaller dimensionless recirculation time. Two empirical correlations are developed to predict the apparent slug Nusselt number and the film-to-slug Nusselt number for gas–liquid Taylor flow in square and rectangular ducts.

Contact Angle Effects on Pore and Corner Arc Menisci in Polygonal Capillary Tubes Studied with the Pseudopotential Multiphase Lattice Boltzmann Model

In porous media, pore geometry and wettability are determinant factors for capillary flow in drainage or imbibition. Pores are often considered as cylindrical tubes in analytical or computational studies. Such simplification prevents the capture of phenomena occurring in pore corners. Considering the corners of pores is crucial to realistically study capillary flow and to accurately estimate liquid distribution, degree of saturation and dynamic liquid behavior in pores and in porous media. In this study, capillary flow in polygonal tubes is studied with the Shan-Chen pseudopotential multiphase lattice Boltzmann model (LBM). The LB model is first validated through a contact angle test and a capillary intrusion test. Then capillary rise in square and triangular tubes is simulated and the pore meniscus height is investigated as a function of contact angle θ. Also, the occurrence of fluid in the tube corners, referred to as corner arc menisci, is studied in terms of curvature versus degree of saturation. In polygonal capillary tubes, the number of sides leads to a critical contact angle θc which is known as a key parameter for the existence of the two configurations. LBM succeeds in simulating the formation of a pore meniscus at θ > θc or the occurrence of corner arc menisci at θ < θc. The curvature of corner arc menisci is known to decrease with increasing saturation and decreasing contact angle as described by the Mayer and Stoewe-Princen (MS-P) theory. We obtain simulation results that are in good qualitative and quantitative agreement with the analytical solutions in terms of height of pore meniscus versus contact angle and curvature of corner arc menisci versus saturation degree. LBM is a suitable and promising tool for a better understanding of the complicated phenomena of multiphase flow in porous media.

A novel approach in manufacturing two-stepped tubes using a multi-stage die in tube hydroforming process

Optimization of operating conditions is one of the most signicant issues concerning hydroforming the tubular components, including stepped tubes, conical tubes, box shape tubes, and etc. Obtaining a sharp corner without any defects such as thinning and rupturing is one of the main goals in the production of these components. In order to manufacture tubes with filled corners, it is common to increase the imposed pressure to the tubes. However, it may result in rupturing and thinning at the die corner radius, especially when it is too small. In this paper, a new multistage die has been proposed for producing two stepped tubes. Numerical modeling has been conducted using Abaqus/Explicit code. The results of simulation were afterwards checked against experiments in which it is shown that a better thickness distribution could be obtained employing the proposed die set. There is no thinning in the final workpiece, particularly at the copper tube corners. Moreover, it could be possible to produce two stepped tubes with complete filled corners. Finally, comparing to other well-established methods, a lower pressure profile is required and a better thickness distribution can be achieved.

Behavior of High-Strength Concrete-Filled FRP Tube Columns under Simulated Seismic Loading: An Experimental Study

This paper reports on part of an ongoing experimental program at The University of Adelaide on the seismic behavior of high-strength concrete (HSC)-filled fiber reinforced polymer (FRP) tubes (HSCFFTs). The results from three square concrete-filled FRP tube (CFFT) columns that were tested under combined constant axial compression and reversed-cyclic lateral loading are presented. The main parameters of the experimental study included the axial load level, concrete strength, and FRP tube corner radius. The results indicate that square HSCFFT columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that increasing the corner radius beyond a certain threshold value provides no increase in column lateral drift capacities. It was observed that column deformability decreased with an increase in axial load level (P/Po) and concrete compressive strength (fc). The results of the experimental program are presented together with a discussion on the influence of the main parameters on the seismic behavior of CFFT columns.

Seismic Behavior of High-Strength Concrete-Filled FRP Tube Columns

This paper reports on an experimental program that investigated the seismic behavior of high-strength concrete (HSC)-filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs), designed to perform as building columns. Five square and one circular concrete-filled FRP tube (CFFT) columns were tested under constant axial compression and reversed-cyclic lateral loading. The main parameters of the experimental study were the axial load level, column cross-sectional shape, concrete strength, amount and type of FRP confinement, and FRP tube corner radius. Examination of the test data resulted in a number of significant conclusions with regard to the influence of the investigated column parameters on the performance of CFFT columns. Of primary importance, the results indicate that square HSCFFT columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that increasing the FRP tube corner radius up to a certain threshold leads to a significant increase in column lateral drift capacities. By contrast, increasing the corner radius beyond that threshold value provides no additional improvement in the hysteretic behavior of square CFFT columns. The influence of the cross-sectional shape is found to be significant, with the circular CFFT exhibiting a larger lateral drift capacity compared with the companion square CFFTs. A set of comparable columns from previous studies has also been included in the discussion to clarify the influence of each parameter on the column behavior. The results of the experimental program are presented together with a discussion on the influence of the main parameters on the seismic behavior of CFFT columns.

Effects of buckling initiators on mechanical behavior of thin-walled square tubes subjected to oblique loading

Thin-walled structures usually collapse in Eulerian buckling mode under oblique loads. Energy absorption capacity and crush force efficiency of the structure in this type of collapse are low. Collapse initiators are used to improve these properties. In this research, effect of collapse initiators on energy absorption characteristics of square tubes under oblique quasi-static loads is investigated both experimentally and numerically. Initiators are in the form of cuttings on the tube corners. Results show that collapse initiators in most of the specimens change deformation mode from general buckling to progressive buckling and decrease considerably the peak load; therefore increase crush force efficiency. Furthermore, effect of location and number of initiators is studied. There is good agreement between the numerical results and data from experiments.

Manufacture and testing of a novel FRP tube confinement system

Fiber reinforced polymer (FRP) tubes are an attractive form of concrete confinement, where the tubes can fulfill multiple functions of: (i) formwork, (ii) confinement reinforcement, (iii) protective shell against corrosion, weathering, and chemical attacks. This paper reports on the development and testing of a new type of rectangular FRP tube that is designed to improve the inherently low confinement effectiveness of rectangular FRP tubes. Axial compression tests were conducted to investigate confinement effectiveness of rectangular tubes with various arrangements. The tubes were designed as column confinement reinforcement and were manufactured using unidirectional carbon fiber sheets. The effects of the tube corner radius and the presence of internal FRP reinforcement were investigated experimentally. The results of the experimental investigation indicate that confinement of rectangular columns with FRP tubes leads to substantial improvement in the ductility of the columns. Confinement provided by the FRP tube may also improve the axial load-carrying capacity of the rectangular columns if the confinement effectiveness of the FRP tube is sufficiently high. The results also indicate that the FRP tube developed by the authors and presented in this study provides significantly higher confinement effectiveness than that of conventional rectangular FRP tubes.

Effect of contact angle on drainage and imbibition in regular polygonal tubes

Wettability and pore structure are primary factors in determining the capillary behavior of porous media. A key characteristic of the pore structure of real porous media is the angular corners of the pores. As a model of pore structure, angular tubes are much more realistic than the commonly used cylindrical tube model. However, their behavior is quite complicated because contact angle, corner angle, and the meniscus in the corners are all variables. The Mayer and Stowe-Princen (MS-P) theory of drainage, together with a detailed model of meniscus behavior in a corner during imbibition, enables the relationships between capillary pressure and saturation to be investigated as a function of contact angle and pore geometry. In this study, a general relationship between contact angle, corner angle, liquid saturation, and the curvature of a meniscus in the corner of an n-sided tube is derived. For any corner angle, there is a critical contact angle at which the meniscus becomes flat and the capillary pressure falls to zero. Drainage of polygonal tubes (having cross-sections such as equilateral triangles and squares) is analyzed as a function of contact angle using the MS-P theory. For imbibition, there are two filling mechanisms: the tube can be filled by a meniscus advancing along the tube or it can be filled by expanding the menisci from the tube corners. For both mechanisms, the contact angle is treated as having either zero or finite contact angle hysteresis. Systematic changes in drainage and imbibition capillary pressure curves with contact angle are obtained. The results are qualitatively consistent with several features of the behavior of natural porous media, including the effect of wettability on the displacement efficiency of crude oil by water.

繰返し力を受ける鋼部材の局部座屈断面に生じるき裂の発生に関する研究

It is the purpose of this study to elucidate the mechanism how cracks arise at the local buckling portion of steel members. The authors conducted alternating bending tests with square-shaped steel tubes. The strain hysteresis at the steel tube's corner where cracks should arise was measured. Then, with test pieces cut from the same tube, we conducted alternating tensile-compression tests which were controled by the strain hysteresis measured at the tube's cracked portion, so as to know the stress hysteresis at the portion. After skeltonizing the stress-strain curves obtained by means of the way above mentioned, we found that cracks arose when the strain had reached the material's uniform elongation.

Integral sunshade for an optical reception antenna

Optical reception antennas (telescopes) must be capable of receiving communications even when the deep-space laser source is at a small solar elongation (appears from Earth to be located within a small angle of the Sun.) Direct sunlight must not be allowed to shine on the primary reflector of an optical reception antenna, because too much light would be scattered into the signal detectors. A conventional sunshade that does not obstruct the antenna aperture would have to be about five times longer than its diameter for reception at a solar elongation of 12 deg. Such a long sunshade is unwieldy, either on the ground or in space. Since a new large-aperture optical reception antenna will probably have a hexagonally segmented primary reflector, a sunshade consisting of closely packed hexagonal tubes is proposed. It will be mounted in alignment with the segmentation to avoid producing any additional geometric obstruction. The tubes will be extended downward toward the primary reflector, until they reach the envelope of the focused beam to the secondary reflector. When the optical reception antenna is ground based, the other ends of the tubes will be trimmed and the antenna will be mounted so that both the sunshade and the antenna will swing within a sphere whose diameter is only six-fifths the diameter of the primary reflector. If the segmentation involves four rings of hexagons around an absent central hexagon, then this sunshade will be useful when the solar elongation is as small as 12 deg. The usefulness can be extended to 10 deg by adding shutters to block the tube corners that admit off-axis sunlight. Vanes or slats may be inserted in the tubes to permit operation at 6 deg, or double vanes down to 3 deg. The structure of the sunshade is very strong and may be used to support the secondary reflector instead of an independent support.