Tubular Material Research Articles

Meso-structure and modeling of a new three-dimensional braided tubular material

A new three-dimensional braided tubular preform was introduced in this study. The new preform structure can be derived from the representative volume unit which was deduced by the symmetry operations of space group P4. The braiding process of the tubular preform has been discussed. A mathematical model was established to analyze the structural properties of the three-dimensional braided tubular preform. The interrelation of geometrical parameters is analyzed. The fiber volume fraction of the preform was predicted. The new tubular preform was obtained in laboratory to verify the feasibility of the braiding process.

An insight into neutral layer shifting in tube bending

Abstract Neutral layer shifting (NLS) is the most fundamental phenomenon during tube bending, which characterizes tension-compression (T-C) non-uniform bending deformation and directly affects multi-defect constrained formability and bending limits. However, the essentials of NLS in tube bending have not yet been clarified, viz., why does the neutral layer (NL) generally shift inward, can the NL shift outward possibly and even can be positively reconstructed? To address these issues, via analyzing the equilibrium conditions of moment and force during tube bending, an axial force equilibrium (AFE)-based hybrid analytical-numerical framework for NLS calculation is established and numerically implemented, in which the tubular materials properties such as the anisotropy/asymmetry behaviors, and the geometry parameters such as bending radius, tube diameters and wall thickness can be comprehensively considered. Taking rotary draw bending of Ti-3Al-2.5 V tube and press bending of AZ31 and A6063 tubes as the cases, the above NLS model is fully evaluated and validated. Using the above platform, the NLS rules related to the geometrical parameters and intrinsic material parameters are quantitatively identified, and within the above framework combined with the experiments, a thorough insight into the NLS upon tube bending is thus presented, viz., given geometrical parameters of bending, under combined action of the evolution of material properties and multi-tool induced additional forces, the inevitable transient T-C non-uniform deformation can be positively coordinated to satisfy the equilibrium of force, then the NLS can be reconstructed to propose innovative processes for improving bending formability.

Experimental investigation of the weldability of tubular dissimilar materials using the electromagnetic welding process

This paper describes the magnetic pulse welding process (MPW) for tubes. Material combinations of aluminium to steel and copper to aluminium were experimentally evaluated. The first major goal of this work is to experimentally obtain the optimal input parameters like the discharge energy, the stand-off distance and the tool overlap for MPW of the material combinations. Welding windows with all possible input parameters are created for both material combinations. Furthermore, a comparison is done between three coil systems; a single turn coil with field shaper, a single turn coil with a field shaper and transformer and a multi-turn coil and field shaper. Metallographic investigation of the samples, hardness tests and leak tests were executed to determine the most suitable machine set-up and the optimal input parameters for each set-up. A second major goal is to determine the influence of the target tube wall thickness on the deformation of tube-tube welds when no internal support is used.

Elastic properties of noncarbon nanotubes as compared to carbon nanotubes

A comparative study of stability, structural, and elastic properties of single-wall noncarbon nanotubes, including BN, AlN, GaN, AlP, GaP, and B nanotubes using ab initio simulation is presented. The proposed nanotubes can be found in nature, which is confirmed by calculation of their binding energy. The values of Young's modulus and Poisson's ratio for (0,$n$) and ($n,n$) proposed nanotubes with $n=3\ensuremath{\cdots}20$ are obtained. The conception of two-dimensional (2D) Young's modulus of planar and tubular materials was developed. The calculations show that stable forms of boron nitride nanotubes have the 2D Young's modulus almost similar to carbon nanotubes. At the same time, it is stated that boron nanotubes have a higher 2D Young's modulus than any other known carbon and noncarbon nanostructures.

Unified ring-compression model for determining tensile properties of tubular materials

The stress-strain relation is the key mechanical properties in safety design and evaluation for tubular structures. However, conventional uniaxial tension and compression tests have some drawbacks and limitations for these structures. In the current investigation, a unified ring-compression model to acquire the stress–strain relation of tubular material is introduced based on the equivalent energy principle. In the model, a unified relation among strain energy, load, deflection, geometric parameters and material property parameters is proposed to depict the elastoplastic response during ring compression test. The model has only four undetermined parameters which can be calibrated by a few FEA (finite element analysis) calculations. The accuracy of the model has been verified within a wide range of imaginary materials by using FEA. Results show that both the forward-predicted load-deflection relation and the reverse-predicted stress-strain relations from the model are in excellent accord with the results from FEA. In addition, the model is verified with three homogeneous ductile materials by conducting ring compression and standard tensile tests. And it is applied in obtaining the hoop stress-strain relation of tubular zirconium alloy in the nuclear power engineering.

Pincushion of Tubule Discovery and Tubular Morphology Landscape Establishment of Block Copolymer Self-Assemblies.

Block copolymer (BCP) self-assembly is a versatile technique in the preparation of polymeric aggregates with varieties of morphologies. However, its morphology library is limited. Here, the discovery of pincushion of tubules is reported for the first time, via BCP self-assembly of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) with very high molecular weight (500 kDa) and asymmetry (2 mol% P4VP). The investigation confirms the importance of core-forming block length on morphology control of BCP self-assemblies, especially with respect to tubular structures. The morphology landscape of tubular structures is successfully established, where dumbbell of tubule, tubule, loose clew of tubules, tight clew of tubules, and pincushion of tubules can be prepared by adjusting the core-forming block length. This work therefore expands the structure library of BCP self-assemblies and opens up a new avenue for the further applications of these tubular materials.

Design of conjugated microporous polymer nanotubes for efficient benzene molecular adsorptions

AbstractSingle‐walled conjugated microporous polymer (CMP) nanotubes containing alternative phenylene and ethynylene units were described computationally for the first time in this work. The electronic structures and adsorption properties were studied by the density‐functional tight‐binding method augmented with a van der Waals dispersion term. Our calculations show that the morphology of CMP influences the benzene‐adsorption performance significantly. The tubes show smaller binding energies to benzene molecule than the film counterparts, consistent with the observation of low adsorption capacities of tubular materials in our experiments. Enlarging the linker or adding substituents in the node can both reduce the tube's band gap. The introduction of OH or NH2 substituents in the tube node increases the binding strength between the adsorbent and the adsorbate, which is energetically favorable to enhance the adsorption capacity. Our results are expected to provide theoretical insights into the rational design of novel CMP nanotubes with improved adsorption capacities for organics.

An experimental method for characterizing unsaturated 1D flow in tubular braided preforms during bladder‐assisted resin transfer molding

The work presented in this paper addresses the development of an efficient approach to investigate the unsaturated in‐plane impregnation behavior of tubular braided reinforcement materials in a bladder‐assisted resin transfer molding process. The basic idea is to record the macroscopic flow front advancement during a pressure‐driven injection of a test fluid by using a transparent monolithic mold and optical measurement methods. The experimental setup further comprises sophisticated process control to accomplish a fully automated and highly repeatable test procedure. As the filling behavior of the braided fabrics predominantly shows unidirectional characteristics, the so‐called unsaturated apparent permeability of these textile reinforcements can be determined, which can be used as an input parameter in one‐dimensional flow simulations. A verification of the test setup is accomplished by means of saturation measurements on different braided preforms, which are compared with predicted flow front profiles. POLYM. COMPOS., 39:4666–4677, 2018. © 2017 Society of Plastics Engineers

Improving hydro-formability of stainless steel tubes by tube channel pressing

Tube channel pressing (TCP), which is one of the severe plastic deformation (SPD) technologies to refine grain size into submicron size for tubular materials, have been applied to ferritic stainless steel tubes for one pass, in order to alleviate ridging and enhance the hydro-formability. It was found that grain-scale shear bands were introduced by one-pass TCP, and texture and microstructure was successfully modified by promoting recrystallization of deformation microstructure, which is otherwise hard-to-recrystallize, in the post-TCP annealing. Elongation to failure, strain-hardening exponent (n-value) and Lankford values of both longitudinal and circumferential directions increased in comparison to with the tube fabricated by conventional process.

Porous hollow tubular carbon materials based on zeolitic imidazolate framework-8 derived from ZnO nanorods as new enzyme immobilizing matrix for high-performance bioanode of glucose/O2 biofuel cells

In this work, Au NPs decorated porous hollow tubular carbon materials (PHTCs@Au) by direct carbonization of zeolitic imidazolate framework-8 (ZIF-8) derived from ZnO nanorods were prepared and used as enzyme immobilizing matrix to construct a bioanode for glucose/O2 biofuel cells (BFCs). Due to high surface area, good electric conductivity and extraordinary porous-hollow tubular structure of PHTCs@Au, the resulted enzyme electrode (PHTCs@Au/GOD (glucose oxidase)-GA (glutaraldehyde)/glassy carbon (GC) electrode) exhibited excellent catalytic capacity towards glucose oxidation and good stability. For the assembled glucose/O2 BFC with the PHTCs@Au/GOD-GA/GC electrode as the bioanode and a commercial Pt plate electrode as the cathode, the maximum power density of 310μWcm−2 can be obtained at 0.23V, and the open circuit potential is 0.63V. The attractive features of PHTCs also provide potential applications in energy storage and conversion devices such as supercapacitor and fuel cells, etc.

Preliminary Mechanism of Tubular Nano-Mg(OH)2 Formation

Since the discovery of tubular nano-scale materials in 1990s, they have been considered as the ideal materials for a variety of applications due to their unique mechanical, ferromagnetic properties for spintronics, magnetic, chemical and biological properties. In our previous work, nano-tube structured magnesium hydroxide has been discovered in solution phase under the normal atmospheric pressure. The present work focus on discussing the effects of reaction concentration, temperature, reaction time, crystal shape control agent dosage on the tubular nano-Mg(OH)2 formation initially. The crystal shape control agent plays an important template role in inducing Mg(OH)2 crystal nuclei forming tubular nano-Mg(OH)2 during the synthesis process. The resulting tubular nano-Mg(OH)2 implies its potential expanded applications in many research areas like the papermaking industry, fertilizer additive, pharmacy, biomaterials and etc.

Describing tube formability during pulsating hydroforming using forming limit diagrams

Pulsating hydroforming is a novel forming technique that applies pulsating hydraulic pressure to deform tubular materials. Larger expansions and more uniform wall thicknesses in tubes have reportedly been achieved using this technique. However, periodic oscillations of hydraulic pressure acting on the tubes during pulsating hydroforming make the tube deformation behaviour and formability unpredictable. Forming limit diagrams, which consist of two forming limit curves in a major–minor strain coordinate system, are widely used to indicate the formability of sheet materials in plastic deformation. The comparable use of forming limit diagrams to indicate the formability of tubular materials under the pulsating action of hydroforming has not been previously established. In this study, pulsating and non-pulsating hydro-bulging experiments were performed on SS304 stainless steel tubes. Under distinct tension–compression and tension–tension strain states with and without active axial feeding, the forming limit curves for the deformed tubes were constructed based on the experimental data. The effects of various hydraulic pressure pulsating parameters, including pulsating amplitude and frequency, on the forming limit curves were analysed and compared. The experimental results showed that each of the forming limit curves under pulsating hydro-bulging was higher than the forming limit curves under non-pulsating hydro-bulging, thereby confirming the influence of the pulsating parameters. In general, the height of the forming limit curves increased as the pulsating amplitude and frequency increased, largely independent of the tension–compression and tension–tension states. Overall, the results showed that the proposed method for determining the forming limit curves (and the subsequent forming limit diagram) for tubes during pulsating hydro-bulging is feasible.

Effects of direction and shape of osteocyte lacunae on resisting impact and micro-damage of osteon.

Animal bones bear varied impact loadings during in the movements of animals. The impact resistance and micro-damage of bones are influenced by their various microstructures at different length scales. In this paper, according to the microstructure of osteon, three 2-D microstructure models (circumferential ellipse lacunae (Model A), radial elliptical lacunae (Model B) and circular lacunae (Model C) were constructed for investigating the influences of the arranged direction and shape of osteocyte lacunae on resisting impact and micro-damage. Impact analytical results show that the maximal stress of the Model A is the minimum and that of the Model B is the maximal under same boundary conditions, which indicates that the circumferentially elliptical lacunae, whose minor axis is along the radial direction of the osteon (Model A), can enhance impact resistance of osteons effectively. The investigated results of the progressive damage show that the circumferentially ellipse lacunae (Model A) are more benefit to resist micro-damage and that the micro-cracks in the model are mainly along the circumferential direction of the osteon. These investigated results for the novel microstructures found in osteon can serve engineers as guidance in the designs of biomimetic and bioinspired tubular structures or materials for engineering applications.

Anisotropic and asymmetrical yielding and its evolution in plastic deformation: Titanium tubular materials

The coupling effects of low asymmetry of HCP structure and transient non-uniform stress/strain states during multi-pass deformation processing cause a great variation in crystallographic orientation of titanium tubes, which may induce anisotropic/asymmetrical behaviors and affect the formability and service performance of the materials. The unique plastic deformation and mechanisms under 3D stress need to be accurately and fully understood for integrated design of fabrication and forming of titanium tubular products achieving shape forming and property tailoring simultaneously. How to address this eluded and tantalized issue, however, is still a bottleneck issue. In tandem with this, taking high strength titanium tube (HSTT) as a case, by using macro/meso scaled hybrid methodology, a correlation among loading condition, distorted plasticity and texture evolution of the material is established and articulated: 1) Via Knoop indentation, tension/compression and EBSD, the distorted plasticity of HSTT is identified, and the coupling of three slip and two twinning modes are found to dominate the inhomogeneous deformation, which must be introduced in viscoplastic self-consistent (VPSC) crystal plasticity; 2) A compression-based orthogonal inverse method is used to calibrate the crystal plasticity parameters and validated from various aspects, and the VPSC-based computation is conducted for tubular materials with six typical initial textures under six fundamental loadings; 3) The remarkable distorted plasticity and evolution in strain hardening, strain flow and yield loci are observed for most cases; The interactions among slipping/slipping, slipping/twinning and twinning/twinning coordinate the anisotropic/asymmetrical behaviors and hence induce the distorted evolution of plasticity; The relationship between deformation modes (strain vectors) and texture evolution is constructed, and the tubes with the desired textures and bespoke properties can be tailored in cold rolling by allocating spatial plastic flow.

Chromogenic Tubular Polydiacetylenes from Topochemical Polymerization of Self-Assembled Macrocyclic Diacetylenes

Tubular materials formed by self-assembly of small organic molecules find great utility in chemical and material science. Conventional tubular structures often lack stability because noncovalent molecular interactions are responsible for their conformational integrities. Herein we report the development of covalently linked chromogenic organic nanotubes which are prepared by using topochemical polymerization of self-assembled macrocyclic diacetylenes (MCDAs). Crystal structures of five MCDAs having different diameters were elucidated, and four of these substances were transformed to tubular polydiacetylenes (PDA) by UV-induced polymerization. Surprisingly, MCDA-1 was found to self-assemble in stacks with a tilt angle of 62.1°, which significantly deviates from the optimal value for polymerization of 45°. This observation suggests that geometric parameters derived using linear diacetylene (DA) models might not be strictly applicable to polymerization of MCDA systems. Blue-phase PDAs obtained by polymerizat...

Research on the internal pressure behavior of metal gas distribution pipelines with different types of tubing defects

The paper aims to approach an important subject related to natural gas distribution networks which, depending on the expansion of the localities, are composed of intercommunicating pipes, pressure reducing stations and branch connections fittings. The urban networks are the most complex ones and the rural areas networks are the simplest. However, irrespective of their installation, they must meet the safety operating requirements as much as possible. According to standards, all these components must be tight and pressure resistant. In this regard, we intend to approach a very important issue related to the behavior of the tubular steel material showing corrosion and/or material defects, and to the internal stress caused by the gas pressure on the walls of the tubing material.

Numerical and experimental study of bursting prediction in tube hydroforming of Al 7020-T6

In this study, forming limit diagram (FLD) of tubular material (Al 7020-T6) was determined numerically and experimentally. A set of experimental bulge tests were carried out to determine FLD under combined internal pressure and axial feeding. Also, a numerical approach which is based on the acceleration of plastic strain (i.e., the second derivation) was applied to compute the hydroforming strain limit diagram. Based on this method, the localized necking would be started when the acceleration of the max plastic strain got its maximum value. Finally, the numerical FLD was verified by experimental test results on the aluminum tube 7020-T6 and a good agreement between the proposed method and the experimental works was observed.

Carbon nanotubes kirigami mechanical metamaterials.

Imparting elasticity and functionality to materials is one of the key objects of materials science research. Here, inspired by the art of kirigami, mechanical metamaterials comprising carbon nanotubes (CNTs) are hypothetically constructed. Using classical molecular dynamics (MD) simulations, a systematic study of the elastic limit, extensibility and yield stress of as-generated CNTs kirigami (CNT-k) is performed. Three designated kirigami patterns are employed to achieve high stretchability of CNTs. It is shown that CNT-k typically exhibits three distinct deformation stages, of which the first stage, which is referred to as geometric deformation, contributes quite a high proportion of the ductility. Various geometric parameters of CNT-k that influence the key mechanical properties of interest are respectively discussed. Three types of CNT-k with specifically identical geometric parameters exhibit distinct mechanical characteristics. This study provides an interesting example of interplay between the geometry, ductility, and mechanical characteristics of tubular materials.

Determination of Material Constants in Ductile Fracture Criterion for Tubular Materials with Conical Flaring Test

How to determine the material constants with high accuracy in the fracture criterion play an important role for predicting the fracture of materials in the forming process using the fracture criterion. In the present work, a new method is proposed to obtain the tube material constants of ductile fracture criterion. This method is based on combining FEM simulation and experiment of tube flaring test. It is easy to realize and has high accuracy as its small measurement error. The method and its reliability evaluation are briefly summarized in four steps: (i) The flaring tests using conical tools with three different semi-angles are executed experimentally and numerically; (ii) The FEM simulation results of the flaring tests with any two conical tools are chosen to calculate the tubular material constants; (iii) The calculated material constants are used to predict the flaring limit with FEM simulation results of the test with the third conical tool; (iv) The flaring limits predicted with FEM simulation are compared with the ones obtained by the flaring tests. By analyzing the experimental and FEM simulation results, it is found that the flaring limits predicted by FEM simulation agreed very well to the ones obtained in the real experiment.

Deformation behaviours of SS304 tubes in pulsating hydroforming processes

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.