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Water existing in micro-pores has tremendous influences on the mechanical and damage characteristics of rocks. This study aims to investigate the micro-pore water effects on the mechanical and damage characteristics of sandstone subjected to different loading configurations, in which four groups of sandstone specimens with different water contents were applied in the conventional uniaxial compression, cyclic loading and unloading experiments. X-ray CT imaging and 3D reconstruction techniques are applied to capture the cracking behaviors under uniaxial compression and cyclic loading–unloading. The digital microstructural variables are defined to describe the characteristics of microstructures and evolution of micro-pore water in rocks. Numerical simulation is applied to study the micro-pore effects on the mechanical properties of rocks. Results show that the specimens are mainly failed by the mixture modes of primary shear cracks and secondary tensile cracks. With increasing mass water content, the uniaxial compressive strength (UCS) decreases and the pore size first decreases, then increases, and finally decreases due to the infiltration of water phase in microstructures. The water content has a negative effect on the mechanical properties, in which the digital porosity and volumetric water content and the micro-pore water saturation have a negative effect on the UCS. In addition, the damage becomes easier near the pores with larger sizes.

In this study, to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete, a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive experiments under confined and unconfined conditions. The confining pressure was achieved by applying a lateral metal sleeve on the testing specimen which was loaded in the axial direction. The experimental results prove that dynamic peak axial stress, dynamic peak lateral stress, and peak axial strain of concrete are strongly sensitive to the strain rate under confined conditions. Moreover, the failure patterns are significantly affected by the stress-loading rate and confining pressure. Concrete shows stronger strain rate effects under an unconfined condition than that under a confined condition. More cracks are created in concrete subjected to uniaxial dynamic compression at a higher strain rate, which can be explained by a thermal-activated mechanism. By contrast, crack generation is prevented by confinement. Fitting formulas of the dynamic peak stress and dynamic peak axial strain are established by considering strain rate effects (50–250 s−1) as well as the dynamic confining increase factor (DIFc).

In this paper, a field-enriched finite element method is proposed to simulate the crack propagation and coalescence of brittle rocks subjected to mixed mode loading. The basic theory is derived, and numerical implementation is achieved. The mixed fracture characteristics and fracture parameters of brittle rocks are studied, and the disc-type specimens are taken as sample configurations. Firstly, a centrally cracked circular disc (CCCD) is used to verify the correctness and accuracy of the numerical model in dealing with mixed fracture problems. The field distribution and crack propagation path are also analyzed. The final failure mode is compared with the experimental observation and previous numerical result. Then, three semi-circular bending (SCB) configurations are employed to investigate the effect of different factors on the fracture patterns under mixed mode loading. The numerical results are qualitatively displayed, and the influence of each controlling factor on the crack initiation angle is also quantitatively analyzed. Finally, Brazilian disk specimens with two and three parallel flaws are used to simulate the fracture process. The present numerical results are in good agreement with those obtained by the other numerical methods, which indicates that the proposed numerical method has ability to simulate cracks propagation and coalescence.

In this paper, the creep behavior of sandstone under the different confining pressures is investigated. The nuclear magnetic resonance (NMR) measurements are carried out to detect the micro-pore characteristics of sandstones before and after compression tests and creep tests. The variations of the parameters, including transverse relaxation time (T2) spectra distribution, percentage of the pore distribution and the changes of porosity are analyzed quantificationally. The experimental results show that creep behavior can be regarded as a process of gradual accumulation of damage to rocks. The confining pressure can limit the increase in porosity during the creep stage, and the effect of confining pressure on the incremental value of porosity is more obvious under high-stress conditions than under low-stress conditions. Moreover, the relationship between the creep stain and the incremental value of porosity is established to reveal the relationship between micro-crack expansion of rocks and macro-creep characteristics of sandstone. It is found that, as the loading ratio or confining pressure increases, the variation of the creep strain is similar to the variation of the incremental value of porosity. The larger the confining pressure, the smaller the effects of creep strain on the incremental value of porosity. However, the greater the loading ratio is, the faster the incremental value of porosity increases. The present study can provide a theoretical basis for the deep mining of mineral resources and the structural stability analysis of deep-buried underground engineering.

In this paper, a compressive-shear fracture model of the phase-field method is proposed to simulate the compressive-shear failure behaviours of pre-cracked rock materials and investigate their fracture mechanisms. In the proposed model, a modified Hoek–Brown criterion is incorporated into the driving term in the evolution equation of the phase field to control the crack phase field. Rock-like specimens containing single flaw and double flaws were used to validate the performance of the proposed numerical model in capturing compressive-shear fractures. The numerical results were in good agreement with the experimental observations. Subsequently the effects of flaw geometries, i.e. flaw inclination angle, spacing and continuity, on the cracking behaviours and mechanical properties of rock-like specimens containing double parallel flaws were investigated. Typical shear cracks, such as coplanar or quasi-coplanar secondary cracks and oblique secondary cracks as well as coalescence types of different shear cracks, were captured. The mechanical properties were also strongly related to the flaw geometry. These performances indicated that the proposed numerical model has ability to simulate compressive-shear cracks.

A 2D novel non-local lattice bond model (NLBM) is proposed to study the initiation, propagation and coalescence of cracks in rock materials. In the proposed NLBM, multiple neighboring lattices are utilized to solve the crack path preference problems. Furthermore, both the normal bonds and the tangent bonds are considered to overcome the limitation of the fixed Poisson's ratio in the classical lattice model. The stiffness parameters are determined by comparing the strain energy stored in a discrete unit lattice with the classical continuum strain energy. Both the elastic problems and the crack path preference problems are simulated by using the proposed method. Compared with the existing numerical methods and experimental results, the performance of the proposed NLBM is satisfactory for predicting the fracturing behaviors in rock materials and for overcoming the limitation of the fixed Poisson's ratio in the classical lattice model.

A novel coupled hydro-mechanical non-ordinary state-based peridynamics is proposed to investigate hydro-mechanical problems in fissured porous rocks. The hydraulic bond is introduced to the coupled numerical model to transfer the water flow stored in material points. The flow equations for fissured porous rocks are obtained in the framework of peridynamics. Then, the relationship between peridynamic hydraulic conductivity and classic hydraulic conductivity for one-dimensional and two-dimensional flow cases is established. Moreover, Biot's porous media theory is employed to determine the deformation caused by water pressure, which is introduced to the non-ordinary state-based peridynamic government equation. In addition, the effects of mechanical deformation and fracture on hydraulic conductivity are considered in the coupled hydro-mechanical non-ordinary state-based peridynamic model. Finally, three different numerical experiments are carried out to verify the correctness of the coupled hydro-mechanical peridynamic model proposed in this paper, and it is found that the present numerical results are in good agreement with the analytical solutions.

A 3D cross-network Co3O4–xNx nanostructure is obtained from the cobalt–alanine complex (Co(C3H5O2N)2) by amino acid self-assembly and subsequent pyrolysis. In this process, Co(C3H5O2N)2 forms a 2D ...

Ring Brazilian disc specimens are favored for determining the tensile strength and mixed mode fracture toughness. To further understand the fracture mechanism of ring Brazilian disc specimens, the phase field method is used to investigate the cracking process and peak load of ring Brazilian disc specimens. First, the numerical validity and accuracy of the phase field method is verified by a benchmark example. Then, the effect of aperture ratio and crack inclination angle on the failure process and peak load of ring Brazilian disc specimens is studied. Finally, by combining the phase field method and J-integral method, the influence of prefabricated crack inclination angle and aperture ratios on mode I and II fracture toughness of cracked ring Brazilian disc specimens is discussed.

Single-atom Ag-decorated MnO2 hollow microspheres (Ag-MnO2 HMSs) with oxygen vacancies are successfully fabricated via a self-template strategy and redox etching method. The transmission electron m...

Natural gas-hydrates are valuable energy resource with rich deposits, and their thermal transport and thermal dynamic mechanical behaviors significantly affect the long-term production process and phase change-based thermal energy storage characteristics of these energy resources. This paper aims to propose novel relations to predict the thermophysical properties, to investigate the hydrate phase evolution in microstructures, and to study the thermal transport and thermal dynamic mechanical properties. Hydrates formation experiments in sandpack samples and ultrasonic wave tests are conducted with the aid of X-ray CT imaging. Digitalization microstructures models and variables are defined to describe the hydrate phase evolution, and novel relations are proposed to accurately predict the thermophysical properties based on the microporosity and ultrasonic wave velocities. The thermal transport and thermal dynamic mechanical properties in microstructures with hydrate, water, residuary pore and grain phases are studied. Results show that the average errors of porosity, P-wave and S-wave velocities between the experimental data and computed results by the proposed relations are less than 5%, indicating the accuracy and reliability of the proposed method. The temperature fraction decreases with increasing underground temperature and decreasing hydrate saturation. The thermal stress and thermal displacement increase as temperature and hydrate saturation increase. There are strong anisotropy for the temperature fraction, thermal stress and thermal displacement during the thermal transport of hydrates.

A sodium polyacrylate-mediated strategy was employed to prepare well-defined MoS2 ball-flower-like nanomaterials. It was found that the polyacrylate acted as a morphology-directing agent to promote MoS2 nanosheets to self-assemble into ball-flowers with 3D hierarchical structures. Moreover, as an electrode applied in a supercapacitor, the ball-flower-like MoS2 exhibited a remarkable pseudocapacitive performance such as a high specific capacitance and superior cycling durability.

A binder-free electrode has been fabricated by directly growing MoSe2 nanosheets on the macroporous Ti mesh skeleton (MoSe2 NS-Ti) via a facile hydrothermal deposition method. The as-prepared MoSe2 NS-Ti electrode is characteristic of robust porous hierarchical nanostructures with large surface area, enriched exposed active edges and improved electroconductivity. As a result, in comparison to the bare MoSe2 electrode, the MoSe2 NS-Ti electrode shows dramatically enhanced electrocatalytic activity and pseudocapacitive performance due to its desirable structural features.

With the aim of developing lanthanide fluoride-based nanoparticles (NPs) with enhanced upconversion (UC) luminescence properties, Ca2+-doped water-soluble β-NaErF4:Yb nanocrystals are prepared by a facile solvothermal reaction using ethylene glycol and water as the solvents and comb-like superplasticizer (SP), polyacrylic-co-methyl allyl polyoxyethylene ether copolymer as the capping agent. The SP-capped upconversion nanoparticles (UCNPs) are characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The results show that the capping agent has great influence on the morphology and colloidal solubility of the nanocrystals. The morphological and phase evolution of the nanocrystals is studied. Furthermore, bright red UC luminescence is observed when the sol is irradiated by a 980 nm laser, and the red UC photoluminescence (UCPL) emission is enhanced by eight times upon doping with 50 mol% Ca2+. The decay time and stability of the UCPL are also discussed. With the efficient stable red UC, the Ca2+ doped water-soluble NaErF4:Yb nanocrystals may find use in various optical applications.

Pore scale variables (e.g., porosity, grain size) are important indexes to predict the hydraulic properties of porous geomaterials. X-ray images from ten types of intact sandstones and another type of sandstone samples subjected to triaxial compression are used to investigate the permeability and fracture characteristics. A novel double threshold segmentation algorithm is proposed to segment cracks, pores and grains, and pore scale variables are defined and extracted from these X-ray CT images to study the geometric characteristics of microstructures of porous geomaterials. Moreover, novel relations among these pore scale variables for permeability prediction are established, and the evolution process of cracks is investigated. The results indicate that the pore-scale permeability is prominently improved by cracks. In addition, excellent agreements are found between the measured and the estimated pore scale variables and permeability. The established correlations can be employed to effectively identify the hydraulic properties of porous geomaterials.

A field-enriched finite-element method for simulating crack propagation and coalescence in geomaterials is proposed in this work. In the novel numerical method, the physical position of the...

Three-dimensional N/S co-doped succulent-like hierarchical carbon (3D NS-SHC) is synthesized by carbonization of a supramolecular cluster. In this supramolecular process, potassium citrate can act as a reliable carbon source, while the thiourea as a N/S source and then, two molecules gradually tend to generate a giant “all-in-one” precursor via hydrogen bonding verified by Independent Gradient Model (IGM) calculation. TEM and SEM images show the N/S co-doped carbon holds a novel 3D succulent-like hierarchical structure. For NS-SHC-8:8 sample, element mapping images display the uniform N/S atoms distribution. These distinct features can be related to the supramolecular polymerization which promotes in-situ N/S co-doping homogenously and conduces to build 3D structure. Typically, NS-SHC-8:8 electrode exhibits prominent specific capacitance (258.5 F g−1 at 0.5 A g−1) and excellent cycle stability (94.4% after 20000 cycles) in three-electrode system. Furthermore, an assembled quasi-solid state symmetric supercapacitor delivers good energy density (10.2 Wh kg−1 at 250 W kg−1) and steady cycle endurance (85.1% after 10000 cycles). These eximious behaviors of NS-SHC-8:8 are mainly attributed to (1) the uniform N/S atoms distribution and their synergistic effect, which brings extra Faradaic reaction to higher specific capacitance, (2) the charming 3D succulent-like hierarchical structure, which serves as a multifunctional reservoir that can accommodate the ion/charge and facilitate their migration to further promote the electrochemical performance. Above mentions suggest that this uniformly heteroatom-modified carbon material produced by supramolecular technique is promising for high-performance energy storage devices.

Inspired by supermolecular self-assembly strategy, the N, P co-doped reduced graphene oxide (NP-rGO) material is fabricated by heat treatment from the supermolecular system of GO/MP (melamine and p...

In this paper, a weakly coupled thermo-mechanical model within the framework of ordinary state-based peridynamics is proposed to investigate thermal cracking behaviors of rocks subjected to heating from boreholes. The weakly coupled thermo-mechanical ordinary state-based peridynamic model is decomposed into two parts, i.e., thermal conduction and mechanical deformation. In the first part, temperature distributions in solids are analyzed based on the heat conduction equations. While, in the second part, thermally-induced deformation and fracture can be simulated by the mechanical computations. Moreover, a multi-rate explicit time integration scheme is proposed to model thermal cracking phenomena in rocks to overcome different time-scale problems in multi-physical systems. A benchmark example with analytical solutions is firstly modeled to validate the correctness and accuracy of the proposed numerical method, and numerical convergence studies of the weakly coupled thermo-mechanical ordinary state-based peridynamics are also conducted. The present numerical results are in good agreement with the analytical solutions and the previous experimental data. Then, three numerical examples are performed to investigate thermally-induced cracking behaviors, i.e. cracking patterns and temperature and stress evolutions. The proposed numerical method not only provides a new tool for coupled thermal-mechanical fracture problems in geothermal engineering, but also reveals the mechanism of thermal cracking phenomena in rocks.

Inspired by the supramolcular chemistry assembly theory, carbon-coated MnO2 nanospheres (C@MnO2) were successfully synthesized by a two-step method. First, the supramolecular solution was prepared by β-cyclodextrin inclusion of manganese acetate, which was then treated by a hydrothermal reaction and the calcination in the following. The scan electron microscopy (SEM) and transmission electron microscopy (TEM) images present that the C@MnO2 composites have the nanosphere morphology, in which the carbon layer originated from the carbonization of β-cyclodextrin was uniformly coated on the MnO2 nanoparticles. The electrochemical characteristics were examined by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results demonstrated that C@MnO2 exhibited high specific capacitance (396.4 F g−1 at 2 A g−1) and good rate capability. In addition, 84.1% of the initial capacitance was maintained after 10000 cycles, indicating the excellent electrochemical stability. The superior electrochemical performance of the C@MnO2 was attributed to the outstanding uniform nanospheres structure that facilitates ion mobility and the synergistic effect between conductive carbon and pseudocapacitive MnO2. Hence, C@MnO2 can be a potential candidate material for the applications in supercapacitors.

Inspired by steaming bread, a novel three dimensional N and S co-doped reduced graphene oxide (3D NS-rGO) foam is fabricated via a gas foaming method similar to steaming bread procedure, in which (NH4)2S2O3 is selected as the foaming agent as well as N and S source. Such cross-linked 3D structure not only has the high specific surface area also enable more transport channels for electrons/ions transport. Furthermore, introducing of N and S-containing functional groups creates lattice defects in graphene, which provides more active sites where the Faradaic pseudocapacitance occurs. Consequently, the electrochemical test of 3D NS-rGO sample in a three-electrode system demonstrates a high specific capacity of 306.3 F g−1 at 1 A g−1, two times higher than that of rGO prepared at the same temperature. Moreover, 3D NS-rGO sample reveals the superb cycling stability with less than 2% capacitance loss after 10,000 cycles and it exhibits potential application for high performance supercapacitors.

Supramolecular in-situ self-assembly is achieved to prepare carbon nanodots decorated graphene/polyaniline composites by adding β-cyclodextrin (β-CD) as the bonding agent in this work. With its unique structure, β-CD can form a supramolecular system with graphene oxide layers, generating the inclusion compound with aniline monomers, which makes the in-situ polymerization of polyaniline on the surface of graphene oxide. In the hydrothermal process, β-CD is carbonized to carbon nanodots anchored on the surface of reduced graphene oxide. The scanning electron microscopy (SEM) images show that the prepared reduced graphene oxide/carbon nanodots/polyaniline (RGO@CN/PANI) nanocomposites exhibit the micro morphology of a regular polyaniline particle array on the surface of graphene layers. The electrochemical tests demonstrate that the RGO@CN/PANI nanocomposites exhibit high specific capacitance (up to 871.8 F g−1 at 0.2A g−1), low charge transfer resistance (Rct), and presentable cycling performance (72% capacitance retention after 10000 cycles), indicating the satisfied performance for supercapacitors. The promising performance of RGO@CN/PANI can be attributed to the synergistic effect of RGO, carbon nanodots and PANI, as well as the regular microstructure in which the effective reaction area of polyaniline is increased and the rapid ion transport channel is provided.

In this work, carbon nanoparticle-anchored MoS2 nanosheets are synthesized by a supramolecular self-assembly method, through which β-cyclodextrins (β-CDs) are combined with l -cysteine by the hydrogen bond and the electrostatic interaction in the aqueous solution, which are then carbonized to carbon nanoparticles and anchored on the surface of MoS2 nanosheets during the hydrothermal process. The carbon nanoparticles anchored on MoS2 nanosheets effectively inhibit the aggregation and restacking of MoS2, and then enhance the electrical conductivity of the composite. The superior electrochemical performance is exhibited through cyclic voltammetry and galvanostatic charge-discharge, including a high specific capacitance of 394.2 F g−1 at the scan rate of 5 mV s−1 and a high rate retention ratio of 63.3% when the scan rate increases from 5 to 200 mV s−1. The remarkable performance is mainly attributed to the better electrical conductivity and the higher rates of electron migration and ion transport, making the carbon nanoparticle-anchored MoS2 nanosheets a potential candidate material for advanced energy storage systems.

To study the rock fracturing characteristics in cold-region engineering, uniaxial compression tests are conducted on double unparallel fissure-contained sandstone specimens subjected to freeze-thaw (FT) cycles. First, the effects of FT cycles on the water absorption, peak strength, initiation stress and deformation behavior of flawed sandstone specimens are investigated. The water absorption, uniaxial compressive strength, initiation stress, elastic modulus and deformation modulus of flawed sandstone specimens decrease with an increase in the number of FT cycles. However, the peak strain of flawed sandstone specimens increases with an increase in the number of FT cycles. Second, the cracking processes of flawed sandstone specimens are investigated in detail via images captured by a high-speed digital video camera system. The relationship between the real-time crack coalescence and the axial stress-strain curve of flawed specimens, which evaluates the macroscopic deformation characteristics of precracked rock subjected to FT cycles well, is considered. Third, the interaction mechanism of fissures in rock specimens is discussed. Fourth, the influence of water and temperature on the rock-weakening process is discussed. In this study, during the rock FT cycle weakening process, the effect of water, including the dissolution effect and the stress effect, is analyzed, whereas temperature damages the rock by means of different temperature gradients and the phase transition of water. Finally, the local strong fatigue-damaged zones around the fissure tips of sandstone specimens are also analyzed. These experimental results are helpful to improve the understanding of fracture mechanisms of a rock mass in cold-region engineering.

In natural rock masses, joints or flaws usually occur in sets that are more or less parallel and regularly spaced. Many problems occurred in tunnel engineering mainly result from the failure of joints or faults because they are weaker compared with the rock matrix. Therefore, it is important to study the interaction of joints with the tunnel, as well as the interactions between themselves. In this research, rock-like specimens of non-persistent jointed rock masses containing a circular hole are prepared and tested under uniaxial compression. The test results show that the peak strength and elastic modulus of the non-persistent jointed rock specimens display a “U” type variation with respect to the joint inclination. The multiple joints can be simplified and regarded as a combination of three types of two-joints relative location, and the crack coalescence types and failure modes are in accordance with the classic crack coalescence types of the two joints. The crack coalescence between the joints and a circular hole can be categorized into three modes with respect to the joint inclination. The Discrete Element Method (DEM) model of the jointed rock specimen that contains a circular hole is established in particle flow code 2D (PFC2D). The simulation results show a good agreement with the experiment results. Furthermore, the displacement fields at the crack zones reveal that the coalescence of joints is mainly caused by tensile cracks and that shear slipping cracks easily occur at the sidewalls of the circular hole. By comparing the parallel-bond force fields in jointed models containing a circular hole with no a circular hole, it is shown that the circular hole can change the stress state at the top and bottom. The joints at a joint inclination of 90° have the smallest effect on the mechanical behavior of the rock specimen.

An improved coupled thermo-mechanical bond-based peridynamics with multirate time integration scheme is developed to study the thermal shock cracking behaviors in brittle solids. In the proposed numerical method, effects of the relative distance between material points on thermoelastic stiffness of a bond are considered in the deformed configuration . The periodical and hierarchical characteristics of thermal crack patterns of ceramics in quenching tests are accurately predicted in 2-D and 3-D cases. The present numerical results are in good agreement with the previous experimental observations and data. It is shown that the proposed numerical model is simple and efficient to simulate the periodical and hierarchical initiation and propagation of cracks in brittle solids under thermal shocks. The present numerical simulations provide direction observations on the whole processes of crack initiation and propagation , which is a quite difficult problem in the laboratory experiments.

Anode material Li2TiO3–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance. Charge/discharge capacities of 266 mA h g−1 at 0.100 A g−1 and 200 mA h g−1 at 1.000 A g−1 are reached for Li2TiO3–coke. A cycling life-time test shows that Li2TiO3–coke gives a specific capacity of 264 mA h g−1 at 0.300 A g−1 and a capacity retention of 92% after 1000 cycles of charge/discharge.

This work discusses the results from tests conducted to investigate the uniaxial compression and creep behavior of red sandstone. The original untreated sample and the 800 ℃ treated sample have been selected to carry out the experiments. It has been found that high temperature has obvious influence on the mechanical properties of red sandstone. The relationship between creep strain and instantaneous strain, as well as instantaneous deformation modulus and creep viscosity coefficient have been analyzed. It has been found that high temperature reduces the ability of red sandstone to resist instantaneous deformation and creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests, providing a powerful means for damage evolution analysis of red sandstone.

Fe52Cr15Mo26C3B1Y3 amorphous particle-reinforced pure aluminum (Al) matrix composite was prepared by powder metallurgy. The ferrum (Fe)-based amorphous particles prepared by atomization method have good amorphous structure, and the circular reinforcement particles are evenly distributed in the Al matrix. The composite has high strength, hardness, and excellent corrosion resistance. The hardness of the composite increases gradually with the increase in the content of the reinforcement, from 46 Vickers hardness (HV) of pure Al to 220.5 HV, with remarkable effect. The tensile strength of the composite increases first and then decreases with the increase in the content of the reinforcement. When the content of reinforcement is 15%, the maximum tensile strength is 234 MPa, which is 154% higher than that of pure Al. The fracture mode of the composite is the mixture of plastic fracture and brittle fracture. The corrosion resistance of pure Al is significantly improved by the addition of reinforcements, which shows that the composite has a smaller corrosion current density and a more positive corrosion potential than that of pure Al.

We report a supramolecular strategy to fabricate high-doping-leveled (10.5 at.%) porous nitrogen-doped reduced graphene oxide (P-NrGO) with outstanding electrochemical properties as electrode material for supercapacitors. The introduced supramolecular polymers melamine cyanurate (MC) acts a barrier to prevent the graphene sheets from restacking, and meanwhile functions as a soft template to create porous structure as well as nitrogen source for in-situ N-doping. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images show that the P-NrGO exhibits wrinkled and loose-packed thin layer structure with a large number of pores. X-ray photoelectron spectrometer (XPS) spectra demonstrate that pyridine and pyrrole-N was the main nitrogen bonding states, which were favorable for the improvements of supercapacitive performance. Attributed to the synergistic effects of the porous structure and the N-doping, the P-NrGO1 exhibits an increase of 56.5% in the specific capacitance (335 F g−1) when compared with the rGO (214 F g−1). In addition, the capacitance retention ratio reaches 94.3% after 10000 cycles, indicating the excellent electrochemical stability. The present work benefits the large-scale production of N-doped graphene oxide for high-performance supercapacitors.

The new weakly coupled thermal mechanical bond-based peridynamic model enriched with shear deformation is developed to study crack propagation and branching instability in brittle solids subjected to thermal shocks. First, the proposed numerical model is validated via comparisons with the classical finite element method (FEM) results. Next, thermal shock crack branching instability in brittle ceramic disks under infrared radiation heating is investigated using the proposed numerical model. Three different types of thermal shock cracking patterns, including no crack branching, crack branching inside heating region and crack branching outside heating region, can be captured by using the proposed numerical model, which are consistent with the previous experimental and numerical results. Effects of heat flux density, heating size, pre-existing notch length, horizon size and nonlocal ratio on thermal shock cracking patterns, crack propagation speed, strain energy distributions around crack tips and crack branching angle are also systematically investigated. The mechanism of thermal shock crack branching instability is revealed. Finally, some characteristics of thermal shock crack branching instability in brittle solids are discussed and summarized.

Li4Ti5O12 (LTO)-carbon (C)-reduced graphene oxide (rGO) microspheres are synthesized via in situ supramolecular self-assembly, combined with spray drying and high-temperature calcination. Dopamine can polymerize on the surface of Ti(OH)4 and form polydopamine, through which graphene oxide(GO) connects with Ti(OH)4 uniformly and tightly to form a homogeneous supramolecular sol system. During the high-temperature calcination, polydopamine is carbonized to carbon to connect LTO with rGO, so that the aggregation of rGO is inhibited, and small-sized LTO particles are obtained. The scanning electron microscopy (SEM) image shows that in the as-prepared LTO-C-rGO microspheres, LTO particles with diameters of ∼50 nm remained homogeneous and wrapped in a three-dimensional network built by the rGO nanosheets. Electrochemical measurements show that the LTO-C-rGO anode exhibits a high reversible capacity of 184 mAh g–1 at 1 C and a high capacity retention of 94.5% after 500 cycles at 20 C. The above excellent electroc...

A simple hydrothermal plus annealing method has been developed to fabricate SnS/NC nanocomposites and their electrochemcial Li-storage performance has also been investigated. The as-prepared composites are characterized by XRD, SEM, EDS, Raman, BET and XPS. In this composite, ultrathin SnS nanosheets are well hybridized with glucosamine-derived nitrogen-doped carbon to form hierarchical porous architectures with large surface areas. Benefiting from the desirable structural merits as well as the generated synergism between components, the SnS/NC composite electrode delivers an enormously enhanced electrochemical lithium-storage performance including large reversible capacity of 832 mA h g−1 after 100 cycles, enhanced cyclability and superior high-rate capability.

A 3-D conjugated bond-pair-based peridynamic model is developed to comprehensively investigate failure characteristics of rock-like materials with intermittent fissures in the compressive-shear loading tests. Rock-like specimens containing one single central fissure are first simulated. Numerical results indicate that the 3-D conjugated bond-pair-based peridynamic model can faithfully reproduce failure characteristics of rock-like materials under compressive-shear loads. Then, the failure characteristics of rock-like specimens containing two parallel central intermittent fissures are numerically investigated. Effects of fissure inclination angle, fissure ligament length and rock bridge angle on fracturing behaviors, such as crack coalescence patterns, are also studied as well as crack initiation stress and coalescence stress.

Rock-like materials are driven not only by applied stresses, but also by time that exhibits creep characteristics. It is significant to establish three-dimensional long-term strength criterion of rocks. In this paper, it is assumed that there exist three-dimensional penny-shaped microcracks in viscoelastic rock matrix. The mode II and mode III stress intensity factors at tips of three-dimensional penny-shaped microcracks in viscoelastic rock matrix are determined. The orientation angle of micro-failure in rock materials is obtained to describe the creep failure of rocks. The relationship between the micro-failure orientation angle and stress components is derived from the creep fracture criterion. Failure characteristic parameters of penny-shaped microcracks under triaxial creep compressive condition are defined, which are an invariant. A three-dimensional long-term strength criterion of rocks is established using micromechanical method, in which the effects of the intermediate principal stress are taken into account. The proposed three-dimensional long-term strength criterion is novel, and never published before. By comparison with the previous experimental data, it is found that the presented three-dimensional long-term strength criterion is in good agreement with the experimental data.

The key failure mechanism of rock mass subjected to compressive loads is due to the damage localization. Conventional methods can not be applied to study the dynamic damage localization physical behavior of crack-weakened rock mass. The strain energy method has the capability to investigate the dynamic damage localization feature in crack-weakened rock mass. Therefore, in order to analyze the dynamic damage localization behavior, strain energy density factor approach is adopted in this paper. A two-dimensional model with periodic rectangular noncollinear array of cracks is established. Then, the onset condition of periodic distribution cracks in rock mass is obtained using strain energy density factor approach. By analyzing the bifurcation of crack growth pattern, the critical length and stress of damage localization of crack-weakened rock mass is determined as well as the location of damage localization. In addition, parameters sensitivity analysis is carried out, the effects of the length of crack, friction coefficient, fracture toughness, confining stress, velocity of crack growth, inclination and spacing between lines and rows on the onset condition for damage localization and bifurcation pattern of rocks are discussed. It can be concluded that onset condition of damage localization is mainly affected by its distribution of initial cracks.

Brittleness has significant effects on the fracturing behaviors of preflawed rock-like materials. In this study, uniaxial compressive experiments are conducted on rock-like specimens containing three flaws, and a three-dimensional digital image correlation technique is applied to capture the real-time displacement and strain fields on the rock-like specimens’ surface. The present experimental study focuses on the effects of the brittleness of rock-like materials on crack initiation, propagation, and coalescence behaviors in three flaw-contained specimens. The experimental results show that the crack initiation mode transforms from the tensile mode to the shear mode with a decrease in the brittleness index of rock-like materials. Meanwhile, crack coalescence modes transform from the tensile crack coalescence mode to the mixed tension–shear coalescence mode, then to the shear coalescence mode as the brittleness index of rock-like materials decreases. Moreover, the ratio of the crack initiation stress to the peak stress increases, while the ratio of the crack coalescence stress to the peak stress decreases as the brittleness index decreases. This paper also addresses the influences of the rock bridge angle on the mechanical and cracking behaviors of three flaw-contained specimens. For specimens with the lower brittleness index, the ratio of the crack initiation stress to the peak stress decreases, while the ratio of the crack coalescence stress to the peak stress increases as the rock bridge angle increases. However, for specimens with the higher brittleness index, the ratio of the crack initiation stress to the peak stress and the ratio of the crack coalescence stress to the peak stress decrease with increasing the rock bridge angle. The experimental results provide a better understanding of the sensitivity of mechanical and cracking behaviors of three flaw-contained specimens to the brittleness of rock-like materials under uniaxial compression.

SbPO4 hierarchical microspindles are successfully prepared through a facile solvothermal route. The X-ray powder diffraction, scanning electronic microscopy and nitrogen adsorption-desorption techniques are utilized to characterize the obtained SbPO4 materials. It is found out that the as-prepared SbPO4 microspindles are composed of nanoplates with mesoporous features. A self-assembly process is proposed for the formation of the SbPO4 microspindles. Besides, the SbPO4 microspindles is also tested as an electrode for supercapacitor, which demonstrates an enhanced electrochemical property due to their novel nanostructures.

A manganese dioxide (MnO2) film is electrodeposited onto a gold-coated quartz crystal electrode by a galvanostatic method. The scanning electron microscopy (SEM) image shows that the electrodeposited MnO2 film consists of nanorods with diameters of 15–20 nm. The cyclic voltammetric (CV) and electrochemical quartz crystal microbalance (EQCM) results demonstrate that the MnO2 electrodes exhibit similar specific capacitance (SC) and mass-to-charge ratios (MCR) in those electrolytes that contain the same cation but different anions. However, the SC and MCR are different in those electrolytes that contain the same anion but different cations. The SC of MnO2 electrodes increases with a decrease of the cationic radius and an increase of the cationic charge. The smaller the cationic radius, the smaller the deviation of the MCR from the equivalent weight (EW) of the cation. The results illustrate that the pseudocapacitive charge storage mechanism of MnO2 involves the cation in the electrolyte and its intercalation/deintercalation, which are affected by the charge number and the cationic radius. This work offers a theoretical basis for selecting suitable electrolytes to couple MnO2-based electrodes in supercapacitors.