Large Compressive Deformation Research Articles

Density dependent constitutive model for Bi-2212 powder compression deformation

Bi-2212 HTS materials are fabricated into multi-filamentary wires via powder-in-tube (PIT) method followed by proper heat treatment to obtain superconductivity, but how to predict the large compression deformation behaviors of the Bi-2212 powder is critical to design the processing of the Bi-2212 HTS wire. Drucker Prager/Cap (DPC) model was the most commonly used model for powders including Bi-2212 with soil-like mechanical behavior to consider its shear failure as well as hydrostatic compression. However, the parameters for DPC Cap evolve with densities change and the original model is inadequate to precisely describe the densification process of Bi-2212 powder with large strain. In this study, the modified DPC model with density dependent parameters was introduced for Bi-2212 powder compressions by measuring the failure strength and hydrostatic compressive behavior under different density states. The DPC yield surface was plotted with an evolution trend of non-linear outward expansion with density increased. FEM model of uniaxial compression based on the as-introduced model was built with subroutine VUSDFLD applied. The distribution of Mises stress and relative density were analyzed. The axial stress-density curve for FEM and experimental results were normalized and quantitively evaluated by Mean Square Error (MSE). The introduced model shows good convergence and could match the experimental results well with normalized MSE of 0.000207 and Root Mean Square Error (RMSE) of 0.0144, indicating the mean error percentage of 1.44%. The model introduced in this article provides supports toward large strain deformation simulation of Bi-2212 powder.

Mesoscopic simulation of the mechanical behaviour of foam concrete subjected to large compressive deformation

As an energy-absorbing material, foam concrete has gained recent application in tunnel support systems. Despite its capacity for substantial compressive deformation, including stress plateau and densification, limited research has delved into this aspect. This study investigates the stress-strain characteristics, fracture behaviour and energy absorption capacity of foam concrete, with a focus on the contact behaviour between its pore structures during large compressive deformation. Through experimental and numerical research, it was found that foam concrete retains compressive strength after reaching the peak stress, with stress levels showing recovery and increase during compression. X-ray computed tomography (X-CT) was utilised to acquire the mesostructured and perform mesoscopic simulations of foam concrete. The experimentally obtained stress-strain curves were used to validate the numerical model. The study discusses and compares mechanical properties and energy absorption capacity of foam concrete with different porosity conditions subjected to large compressive deformation, highlighting the effects of the pore structure and contact property on the densification behaviour of foam concrete. Overall, this research contributes to a deeper understanding of the mechanical behaviour of foam concrete subjected to large compressive deformation.

Dynamic properties and plastic dissipative mechanisms of polymeric adhesive under dynamic compression at various strain rates

This work investigated the dynamic compression behavior of structural vinylester adhesive under dynamic compression tests using the Split Hopkinson Pressure Bars technique. The obtained results showed that the dynamic parameters were strain rate sensitive. No macroscopic damage was observed in the specimen at the different applied strain rates. However, the presence of a characteristic second peak mainly at high strain rates on the strain rate profiles was attributed to the plasticity occurrence in the polymer under impact. The non-linear response that appeared on the stress-strain curves of the adhesive had been attributed to the combined material softening and thermal softening. These results demonstrated that the studied adhesive could be considered a potential material for high-rate applications due to the combination of significant toughness with high strength and extensive plasticity. An energetic study determined the energy balance and quantified energy absorption. It was observed that used vinylester adhesive was suitable for dynamic applications because it could absorb a large amount of energy and undergo large compressive deformations without damage. This work provided a complete range of experimental data for structural adhesive, which could help the designer of an energy-absorbing adhesively bonded composite joint structure for high-strain rate applications.

Microstructure and Texture of Pure Copper under Large Compression Deformation and Different Annealing Times

In this study, the plastic deformation of pure copper under room-temperature compression and different annealing times was examined, and the microstructure and texture evolution were studied via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and microhardness tests. The results showed that when the deformation degree was 93.75%, the microhardness increased from 76 HV (Vickers hardness) before deformation to 110 HV. After annealing, the hardness decreased with increasing annealing time, and the pure copper grain size could be refined from 150 μm to 6.15 μm. An increase in annealing time did not continue to promote recrystallization, while the effect on grain refinement was weakened. The geometrically necessary dislocation (GND) density decreased from 6.0 × 1014/m2 to 4.83 × 1014/m2 after annealing, which implies that static recrystallization occurs at the cost of dislocation consumption during the annealing process. The compression deformation of pure copper produced a strong deformation weave (<001> orientation), and a portion of the deformation weave within the material was transformed into a recrystallization weave (<111> orientation) after the annealing process.

Auxetic mechanical metamaterials with symmetry-broken Re-entrant units

Three innovative auxetic metamaterials with symmetry-broken unit cells and possible applicability in the construction and automotive industries are presented by breaking the mirror symmetries of the conventional re-entrant unit cell. The single symmetry-broken re-entrant (SBR), double symmetry-broken re-entrant (DBR), and hybrid symmetry-broken re-entrant (HBR) structures are fabricated via 3D printing and examined by experimental compression tests and finite element analysis (FEA). The proposed metamaterials exhibit remarkable specific energy absorption (SEA) properties in comparison to the benchmark symmetric-unit honeycomb, with the SBR model showing 103.9 % higher SEA. The novel structures also show superior stability under large compressive deformation, exhibiting excellent auxeticity in comparison to the symmetric-unit model. Parametric investigations reveal that the level of asymmetricity of the unit cells plays a key role in the stability and superior mechanical properties of the proposed metamaterials under compression. One set of parametric studies discovers an HBR structure with a special combination of SBR and DBR units which outperforms the parent structures under compression. Finally, parametric investigation of transverse and inclined compression of the structures indicated superiority of the DBR metamaterial to other structures due to having a deformation mechanism with organized self-contact regions. The DBR metamaterial owns 314 % and 86 % higher SEA rather than the benchmark honeycomb under transverse and inclined compression, respectively.

Mechanical Properties of Highly Deformable Elastomeric Gyroids for Multifunctional Capacitors

Triply periodic minimal surface lattices have mechanical properties that derive from the unit cell geometry and the base material. Through computation software like nTopology and Abaqus, these geometries are used to tune nonlinear stress–strain curves not readily achievable with solid materials alone and to change the compliance by two orders of magnitude compared to the constituent material. In this study, four elastomeric TPMS gyroids undergo large deformation compression and tension testing to investigate the impact of the structure's geometry on the mechanical properties. Among all the samples, the modulus at strain ε varies by over one order of magnitude (7.7–293.4 kPa from FEA under compression). These lattices are promising candidates for designing multifunctional systems that can perform multiple tasks simultaneously by leveraging the geometry's large surface area to volume ratio. For example, the architectural functionality of the lattice to bear loads and store mechanical energy along with the larger surface area for energy storage is combined. A compliant double‐gyroid capacitor that can simultaneously achieve three functions is demonstrated: load bearing, energy storage, and sensing.

Numerical simulation of solid-fluid-thermal coupling in the heating stage of in-situ injection of supercritical water for hydrogen production from coal

ABSTRACT Hydrogen production via in-situ injection of supercritical water into underground coal seams is a new coal conversion technology. This study proposes a solid-fluid-heat coupling mathematical model for the heating stage of the injection of supercritical water into the coal seam and studies the evolution law of the temperature distribution, pore pressure, solid deformation, and other aspects of the coal seam, the roof strata, and the floor strata using numerical simulation. The results showed that after the injection of supercritical water, the temperature and flow rate near the injection well increased rapidly, gradually decreased, and expanded outwards. Subsequently, the temperature rose to about 1050°C and the flow rate decreased slightly near the injection well. The flow rate near the production well showed a negative exponential growth pattern six months prior; however, the temperature and flow rate remained constant after six months. The temperature around 700 m from the injection well changed little over one year. A large compression deformation zone may form above the injection well and the maximum uplift displacement of the deformation zone within one year can reach 8 mm. The extreme value of vertical stress was located in the surrounding rock layer closest to the coal seam and its maximum value can be 17 MPa.

Preparation and Properties of Self-Cross-Linking Hydrogels Based on Chitosan Derivatives and Oxidized Sodium Alginate.

A self-cross-linking and biocompatible hydrogel has wide application potential in the field of tissue engineering. In this work, an easily available, biodegradable, and resilient hydrogel was prepared using a self-cross-linking method. This hydrogel was composed of N-2-hydroxypropyl trimethyl ammonium chloride chitosan (HACC) and oxidized sodium alginate (OSA). A stable and reversible cross-linking network was formed by the Schiff base self-cross-linked and hydrogen bonding. The addition of a shielding agent (NaCl) may weaken the intense electrostatic effect between HACC and OSA and solve the problem of flocculation caused by the rapid formation of ionic bonds, which provided an extended time for the Schiff base self-cross-linked reaction for forming a homogeneous hydrogel. Interestingly, the shortest time for the formation of the HACC/OSA hydrogel was within 74 s and the hydrogel had a uniform porous structure and enhanced mechanical properties. The HACC/OSA hydrogel withstood large compression deformation due to improved elasticity. What's more, this hydrogel possessed favorable swelling property, biodegradation, and water retention. The HACC/OSA hydrogels have great antibacterial properties against Staphylococcus aureus and Escherichia coli and demonstrated good cytocompatibility as well. The HACC/OSA hydrogels have a good sustained release effect on rhodamine (model drug). Thus, the obtained self-cross-linked HACC/OSA hydrogels in this study have potential applications in the field of biomedical carriers.

Fractional viscoelastic models of porcine skin and its gelatin-based surrogates

Viscoelasticity of porcine skin and its material substitute, modelled by variously concentrated bovine gelatin, was determined in static (creep test) and dynamic (oscillatory test) mode by the means of rotational rheometry to obtain creep compliance and complex shear modulus. Mechanical properties characterization was also supplemented with large deformation compression test in order to determine and correlate shear and compression moduli of gelatin with its concentration dependence. Obtained data was fitted with fractional viscoelastic models (Poynting-Thomson, Maxwell) in order to quantify in detail gelatin's transition from viscous-like behavior towards solid-like state with increasing gelatin concentration and hence crosslinking density. Potential of gelatin as biomaterial for skin surrogate was identified as well as a concentration region in which gelatin exhibits closest viscoelastic behavior to native porcine skin used.

Load-carrying and energy-absorbing performance of honeycombs with different cross sections under cyclic loading

Honeycombs, characterized by advantages including large compressive deformation and controllable deformation, have been widely used in energy-absorbing components. The loading process of honeycombs is generally influenced by recovery after unloading in application environments. Expounding the load-carrying and energy-absorbing performance of honeycombs under cyclic loading is critical for the practical engineering application of honeycombs. Honeycombs with four different cross sections were selected to compare their deformation process and load-carrying performance under cyclic loading by conducting quasi-static compression tests and displacement-controlled cyclic loading and unloading tests. On this basis, influences of the cyclic loading on the energy-absorbing performance of honeycombs were revealed. It is shown that cyclic loading does not change the four-stage characteristics of the displacement-force curve of honeycombs while to some extent influences the load-carrying capacity of honeycombs. Under cyclic loading, the honeycombs have larger plateau force and plateau force efficiency and exhibit better stable load-carrying capacity and uniformity. Moreover, evaluation of the energy-absorbing performance of honeycombs based on the total energy absorption index has some limitations, which takes the energy absorption of structures in each stage into account. In view of this, the effective energy absorption was proposed to accurately evaluate the energy-absorbing performance of honeycombs. It is found that honeycombs exhibit better energy-absorbing performance under cyclic loading. The research achievements provide theoretical support for application of honeycombs in fields including mines and underground spaces.

Multifunctional ultralight, recoverable, piezoresistive, and super thermal insulating SiC nanowire sponges

AbstractUltralight three‐dimensional (3D) architectured silicon carbide (SiC) nanowire sponges with integrated properties of recoverable compressibility, outstanding high‐temperature thermal and chemical stability, and fire‐retardance have been actively pursued in recent years. However, efficient construction of SiC nanowire sponges with well‐controlled overall shapes and distribution of SiC nanowires remains challenging. Herein, by coupling the electrospinning technique and carbothermal reduction process, we have developed a new fabrication process for highly porous and free‐standing 3D SiC nanowire (SiCNW) sponges with closely attached nanowires through thermal treatment of stacked electrospun PAN/SiO2 nanofiber membranes. The resulting SiCNW sponges possess ultralow density (∼29 mg cm−3), excellent compressive recoverability from large compressive deformation (up to 40% strain), and fatigue resistance, which endow them with excellent piezoresistive sensing capability under a variety of complex conditions. Furthermore, the sponges display superb thermal insulation (thermal conductivity of 24 mW m−1K−1) and fire‐retardance. We believe that the present process provides technical clues for the development of other multifunctional ceramic sponges, and that further development of these ultralight multifunctional ceramic sponges offers potential for the design of advanced components for application in harsh engineering environments.

Numerical analysis for mining-induced stress and plastic evolution involving influencing factors: high in situ stress, excavation rate and multilayered heterogeneity

PurposeThis study aims to analyse the deep resource mining that causes high in situ stress, and the disturbance of tunnelling and mining which may induce large stress concentration, plastic deformation and rock strata compression deformation. The depth of deep resources, excavation rate and multilayered heterogeneity are critical factors of excavation disturbance in deep rock. However, at present, there are few engineering practices used in deep resource mining, and it is difficult to analyse the high in situ stress and dynamic three-dimensional (3D) excavation process in laboratory experiments. As a result, an understanding of the behaviours and mechanisms of the dynamic evolution of the stress field and plastic zone in deep tunnelling and mining surrounding rock is still lacking.Design/methodology/approachThis study introduced a 3D engineering-scale finite element model and analysed the scheme involved the elastoplastic constitutive and element deletion techniques, while considering the influence of the deep rock mass of the roadway excavation, coal seam mining-induced stress, plastic zone in the process of mining disturbance of the in situ stress state, excavation rate and layered rock mass properties at the depths of 500 m, 1,500 m and 2,500 m of several typical coal seams, and the tunnelling and excavation rates of 0.5 m/step, 1 m/step and 2 m/step. An engineering-scale numerical model of the layered rock and soil body in an actual mining area were also established.FindingsThe simulation results of the surrounding rock stress field, dynamic evolution and maximum value change of the plastic zone, large deformation and settlement of the layered rock mass are obtained. The numerical results indicate that the process of mining can be accelerated with the increase in the tunnelling and excavation rate, but the vertical concentrated stress induced by the surrounding rock intensifies with the increase in the excavation rate, which becomes a crucial factor affecting the instability of the surrounding rock. The deep rock mass is in the high in situ stress state, and the stress and plastic strain maxima of the surrounding rock induced by the tunnelling and mining processes increase sharply with the excavation depth. In ultra-deep conditions (depth of 2,500 m), the maximum vertical stress is quickly reached by the conventional tunnelling and mining process. Compared with the deep homogeneous rock mass model, the multilayered heterogeneous rock mass produces higher mining-induced stress and plastic strain in each layer during the entire process of tunnelling and mining, and each layer presents a squeeze and dislocation deformation.Originality/valueThe results of this study can provide a valuable reference for the dynamic evolution of stress and plastic deformation in roadway tunnelling and coal seam mining to investigate the mechanisms of in situ stress at typical depths, excavation rates, stress concentrations, plastic deformations and compression behaviours of multilayered heterogeneity.

Numerical Simulation of Large Compression Deformation Disaster and Supporting Behavior of Deep Buried Soft Rock Tunnel with High In Situ Stress Based on CDEM

Large compressive deformation of tunnels is a phenomenon involving plastic deformation and failure of surrounding rocks and often refers to the weak surrounding rock self-bearing capacity loss or partial loss. This research discusses the formation and evolution of large compressive deformation and effectiveness of the combined support of high in situ stress tunnel. From the new perspective of large deformation disaster caused by the structural failure of high in situ stress surrounding rock to clarify it, this paper illustrates the mechanism of progressive cracking and large deformation of high in situ stress soft rock tunnel from the aspects of the formation of self-bearing system, deformation evolution of the surrounding rock, mechanical properties of the surrounding rock, and failure characteristics. Accordingly, the continuous and discontinuous numerical simulation methods are used. The following conclusions are drawn by comparing the simulation results of surrounding rock under combined support with no support. (1) The supporting structure constitutes the self-supporting system with the surrounding rock and plays the roles of codeformation and load-bearing. (2) The support structure has evident reinforcing effect on the rock mass in the relaxation zone, thereby leading to the phenomenon of weakened rock mass failure. Moreover, the shear area develops to the compaction zone. (3) The supporting structure improves the bearing capacity of rock mass in the relaxation zone. It also increases the surrounding rock stress and reduces the range of the compaction zone. Simulation results verify that the combined support measures have a good suppression effect on the large compressive deformation, thereby providing a reference for similar projects and research on the large compressive deformation of soft rock.

A unified non-linear system model view of hyperelasticity, viscoelasticity and hysteresis exhibited by rubber

Rubber modeling is an old subject and so many models exist that it is difficult to have a clear vision of what exists and is more appropriate. Rather than attempting a standard review, this paper proposes classification using the traditional system modeling strategy, where raw measurements are either processed to obtain non-parametric models, or used to identify parametric models, whose accuracy can be controlled by order selection or by numerical implementation considerations. A full test campaign, including multi-step relaxation, low speed triangular and sine tests, on a large deformation compression sample is used to illustrate the need to model and combine the base behaviors known as hyperelasticity, viscoelasticity, and rate independent hysteresis. The equivalence between linear viscoelasticity and linear time invariant systems is used to clarify the link between order selection and accuracy of a generalized Maxwell model. Rate independent hysteresis is analyzed using a convolution product like the one used for viscoelastic transients by introducing a relaxation modulus. Measurements of the hysteretic relaxation modulus are used to propose strategies to measure the asymptotic hyperelastic modulus and discriminate between different hysteretic model forms. A parallel between Iwan and Maxwell models is detailed, and non-parametric models are used to show that the two overlap in the low frequency small deformation regime. Regularized rate independent hysteresis and non-linear viscoelasticity are finally shown to lead to a similar view allowing a transition between the rate independent and linear relaxation models. The instantaneous ratio analytic force and displacement signals, or instant complex modulus, is introduced as novel non-parametric estimation of sine measurements and shown to be a powerful tool to analyze and validate the fact that a force rate relaxation with non-linear relaxation frequencies is most appropriate to represent the non-linear coupling of all three effects.

Thermal and Conjugate Heat Transfer Analysis of Exhaust Manifold of Multi-cylinder IC Engine

The exhaust manifold of multi cylinder IC engine is kept in between the engine block and the catalytic converter. So the exhaust manifold is exposed to very high temperature and care should be taken at the critical zone during the design stage. At several critical zones of the exhaust manifold, large compressive deformations are generated at elevated temperatures and tensile stresses remain at cold conditions. The thermal analysis will help in estimating the deformations and stress concentrations due to thermal loads. Therefore, the main aim of this study is to perform thermal analysis and conjugate heat flow analysis of an exhaust manifold of a multi-cylinder engine. The 3D model is generated using SolidWorks and analysis is carried out using Ansys workbench. Materials like grey C.I., aluminium nitride, silicon nitride, and stainless steel are used in this analysis. The results of total heat flux, directional heat flux and temperature distribution were compared. Silicon nitride material is suggested to be the suitable material for engine exhaust manifolds based on the material mechanical properties and thermal distribution-related thermal stress developed on the exhaust manifold.

Elastically-isotropic open-cell minimal surface shell lattices with superior stiffness via variable thickness design

Triply periodic minimal surface (TPMS) shell lattices are attracting increasingly attention due to their unique combination of geometric and mechanical properties, and their open-cell topology. However, uniform thickness TPMS shell lattices are usually anisotropic in stiffness, namely having different Young's moduli along different lattice directions. To reduce the elastic anisotropy, we propose a family of variable thickness TPMS shell lattices with isotropic stiffness designed by a strain energy-based optimization algorithm. The optimization results show that all the six selected types of TPMS lattices can be made to achieve isotropic stiffness by varying the shell thickness, among which N14 can maintain over 90% of the Hashin-Shtrikman upper bound of bulk modulus. All the optimized shell lattices exhibit superior stiffness properties and significantly outperform elastically-isotropic truss lattices of equal relative densities. Both uniform and optimized types of N14 shell lattices along [100], [110] and [111] directions are fabricated by the micro laser powder bed fusion techniques with stainless steel 316L and tested under quasi-static compression loads. Experimental results show that the elastic anisotropy of the optimized N14 lattices is reduced compared to that of the uniform ones. Large deformation compression results reveal different failure deformation behaviors along different directions. The [100] direction shows a layer-by-layer plastic buckling failure mode, while the failures along [110] and [111] directions are related to the shear deformation. The optimized N14 lattices possess a reduced anisotropy of plateau stresses and can even attain nearly isotropic energy absorption capacity.

Self-Healing and Highly Stretchable Hydrogel for Interfacial Compatible Flexible Paper-Based Micro-Supercapacitor.

Most reported wearable electronic devices lack self-healing chemistry and flexible function to maintain stable energy output while irreversible damages and complex deformations. In this work, we report a dual-dynamic network electrolyte synthesized by micellar elastomers introduced into strong hydrogel matrix. The gel electrolyte is fabricated by physically cross-linking the borax-polyvinyl alcohol (B-PVA) network as tough matrix and poly (ethylene oxide) (PEO)-poly (propylene oxide) (PPO)-poly (ethylene oxide) (Pluronic) to frame elastic network, followed by immersion in potassium chloride solution. Under the action of dynamic borate ester bond and multi-network hydrogen bond, the as-prepared electrolyte exhibits high stretchability (1535%) and good self-healing efficiency. Based on the electrolyte, we assemble the interfacial compatible micro-supercapacitor (MSC) by multi-walled carbon nanotubes (MWCNT) interdigital electrode printed on cellulosic paper by direct ink writing (DIW) technique. Thanks to the large specific area and compressive deformation resistance of cellulosic paper, the MSC with tightly interfacial contact achieves high volumetric capacitance of 801.9 mF cm−3 at the current density of 20 μA cm−2. In the absence of stimulation of the external environment, the self-healing MSC demonstrates an ideal capacity retention (90.43%) after five physical damaged/healing cycles. Our research provides a clean and effective strategy to construct wearable MSC.

Settlement of Footings on Compacted and Natural Collapsible Soils upon Loading and Soaking

Collapsible unsaturated soils experience large volumetric compressive deformations upon wetting. Soil collapse is a geotechnical problem that occurs in different regions of the world and profoundly impacts buildings and civil infrastructure constructed on this type of soil, with the associated impact on safety and economy. Compaction is a simple, relatively cheap, and yet effective soil improvement technique that could significantly reduce soil collapsibility. This paper combines laboratory tests, in-situ investigations, and numerical modeling to gain a better understanding of the effect of soil compaction on collapsible-soil settlements upon wetting under field conditions. The finite elements program CODE_BRIGHT was adopted for the numerical simulations of the field tests using model parameters that were previously obtained from independent laboratory experiments. The laboratory campaign comprised suction-controlled oedometer and triaxial tests of the natural and compacted soils considered in this study, as well as permeability and water retention experiments. The numerical simulations show that the proposed approach can model the behavior observed in the in-situ tests involving footing prototypes on collapsible soils subjected to soaking. These analyses also demonstrate that soil compaction is a viable technique to reduce collapsibility in order to meet predefined maximum allowable settlements. Additional analyses were carried out to extend the main findings to other soils and loading conditions. Based on stress-bulb concepts, a method is proposed to reduce settlements in collapsible soils for typical footing operational conditions.

Highly Elastic Hydrated Cellulosic Materials with Durable Compressibility and Tunable Conductivity.

Anisotropic cellular materials with direction-dependent structure and durable mechanical properties enable various applications (e.g., nanofluidics, biomedical devices, tissue engineering, and water purification), but their widespread use is often hindered by complex and scale-limited fabrication and unsatisfactory mechanical performance. Here, inspired by the anisotropic and hierarchical material structure of tendons, we demonstrate a facile, scalable top-down approach for fabricating a highly elastic, ionically conductive, anisotropic cellulosic material (named elastic wood) directly from natural wood via chemical treatment. The resulting elastic wood demonstrates good elasticity and durable compressibility, showing no sign of fatigue after 10 000 compression cycles. The chemical treatment not only softens the wood cell walls by partially removing lignin and hemicellulose but introduces an interconnected cellulose fibril network into the wood channels. Atomistic and continuum modeling further reveals that the absorbed water can freely and reversibly move inside the elastic wood and therefore helps the elastic wood accommodate large compressive deformation and recover to its original shape upon compression release. In addition, the elastic wood showed a high ionic conductivity of up to 0.5 mS cm-1 at a low KCl concentration of 10-4 M, which can be tuned by changing the compression ratio of the material. The demonstrated elastic, mechanically robust, and ionically conductive cellulosic material combining inherited anisotropic cellular structure from natural wood and a self-formed internal gel may find a variety of potential applications in ionic nanofluidics, sensors, soft robots, artificial muscle, environmental remediation, and energy storage.

Effect of pre-annealing on microstructure, mechanical properties and current-carrying properties of Bi-2212 wires

Abstract In order to solve the problem of excessive porosity of Bi-2212 Cable in Conduit Conductor (CICC) after the overpressure heat treatment, which leads to a significant decrease of mechanical stability of the conductor, a pre-annealing of Bi-2212 wires with a total pressure of 50 bar has been carried out in this paper. After the pre-annealing, the density of oxide cores of Bi-2212 wires was close to the theoretical density, which avoided the problem of diameter reduction of the wires in Bi-2212 CICC during overpressure heat treatment. At the same time, the mechanical properties, microstructures and current carrying properties of pre-annealed wires have been also analyzed. It showed that after pre-annealing, the Bi-2212 wires had not only high yield strength σ0.2, which reached 167 Mpa, but also great tensile strainse, which reached 7.4 %. High yield strength of the wires could effectively avoid serious scratches on the surface of wires during the preparing process of Bi-2212 CICC. Large tensile strain of the wires could prevent the crack of the wires caused by large compressive deformation or twisting deformation of the wires during preparation of Bi-2212 CICC, so that the conductors with smaller pitch and low hysteresis loss could be prepared. In addition, the phase composition of oxide cores in Bi-2212 wires did not change obviously during the pre-annealing process, but the crystallinity of Bi-2212 powder of the cores increased significantly, which was beneficial to the simultaneous melting of Bi-2212 powder of the cores during the overpressure heat treatment and the improvement of the content of Bi-2212 phase of the final wires. As a result, the current carrying capacity of the wires was slightly improved, and its engineer critical current density (Je) reached 825 A/mm2 (4.2K, 12T), which could meet the requirements of future fusion systems. In summary, it is expected that Bi-2212 CICC with less surface defects of the wires, low hysteresis loss, high filling ratio and excellent current-carrying performance can be obtained by the pre-annealing method.