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Explosive shock wave protection is an important issue that urgently needs to be solved in the current military and public security safety fields. Non-metallic protective structures have the characteristics of being lightweight and having low secondary damage, making them an important research object in the field of equivalent protection. In this paper, the numerical simulation was performed to investigate the dynamic mechanical response of non-metallic annular protective structures under the internal blast, which were made by the continuous winding of PE fibers. The impact of various charges, the number of fiber layers, and polyurethane foam on the damage to protective structures was analyzed. The numerical results showed that 120 PE fiber layers could protect 50 g TNT equivalent explosives. However, solely increasing the thickness of fiber layers cannot effectively enhance the protection efficiency. By adding polyurethane foam in the inner layer, the stress acting on the fiber could be effectively reduced. A 30 mm thick polyurethane layer can reduce the equivalent stress of the fiber layer by 41.6%. This paper can provide some reference for the numerical simulations of non-metallic explosion protection structures. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing stimulation technology is an effective method for increasing coalbed methane production, especially for coal seam with low permeability, low reservoir pressure and low gas saturation. Normally, fracture is simulated according to the law of equivalent percolation resistance, leading to the limit that fracture is several hundred times enlarged meanwhile the permeability is decreased, with wellbore located in the enlarged fracture, more fluids will produce through high conductive fracture path into wellbore. Based on theories and methods from oil–gas geology and mechanics of flow through porous media, this paper presents a two-phase, 3D flow and hydraulic fracturing model of dual-porosity media. A finite difference numerical model with independent fracture grid has been developed and applied successfully to a coalbed methane reservoir. Comparison results show that independent fracture grid is more effective than equivalent percolation resistance method in production fitting. Actual gas production data is consistent with results calculated by the new model, while prediction from equivalent percolation resistance is higher. [ABSTRACT FROM AUTHOR]

Highlights: [•] Comprehensive evaluation of long term sand control and conductivity maintain. [•] Compatibility with commonly used fracturing fluid of fracture stabilizer was evaluated. [•] Dosage of fracture stabilizer was optimized. [Copyright &y& Elsevier]

The unconventional reservoirs such as carbonate formation develops complex and diverse storage space structures, and it is composed of large-scale cavity, dissolved vug, and fractures. The carbonate reservoir is highly heterogeneous. Acid fracturing of carbonate reservoir is completed through the complex mechanical mechanism of interaction between vug and hydraulic fracture (HF). We use the equivalent method of reducing the rock strength by acid etching and serious fluid leakoff during interaction of HF and vug to establish a finite element (FE) model of HF propagation during acid fracturing in the fractured-vuggy carbonate reservoir. The model considers the effect of serious fluid leakoff during interaction between HF and vug, mechanism of interaction between HFs and the fracture-vug system, and change in acid etching intensity. Then, we carry out numerical simulation on impacts of injection rate, fluid viscosity, leakoff behavior in fractures and vugs, and natural fracture (NF) approaching angle on HF propagation in acid fracturing and compare the characteristics of injection pressure, fracture pressure, and HF size. It is suggested that the acid fracturing treatment should be operated by increasing the acid solution viscosity to reduce fluid leakoff, injecting fracturing fluid and acid fluid alternatively, increasing injection rate, and injecting fibers and ceramics when small pressure drop occurs during the HF interacts with the fracture-vug. When a large pressure drop occurs, it is suggested that the middle-low viscosity acid be injected at a low rate to etch the carbonate rock and enhance the fracture conductivity. HF propagates under higher pressure when the NF approaching angle is smaller. [ABSTRACT FROM AUTHOR]

• Comparative impact tests of novel FHCB were performed. • Foam filling enhances impact resistance. • Gradient design can optimize foam energy absorption. Auxetic structures have attracted a lot of attention as they can meet the requirements of impact resistance and lightweight performance of protective structures in aerospace and defense industries. To enhance the impact resistance and improve the capacity of energy absorption of auxetic structures, foam-filled hybrid-chiral honeycomb beams (FHCB) were designed and fabricated through SLM (Selective laser melting) printing method and foaming method. The localized impulse loading was generated through the impact from foam projectile, accelerated by light gas gun. The dynamic responses of EHCB (empty hybrid-chiral honeycomb beam) and FHCB were compared. In the experimental results, FHCB showed enhanced impact resistance and higher SEA (specific energy absorption) value than EHCB. A validate finite element model was used to study the influence of cell-wall thickness on the impact resistance of EHCB and FHCB. Results indicated that by changing the cell-wall thickness, the potential energy absorption capacity of the filled foam can be fully utilized. Furthermore, the impact resistance of FHCB can be effectively improved by using a gradient cell-wall thickness arrangement. This study can provide reference for the optimal design of blast mitigation and impact resistant structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Frontal coating on steel plates enhances ballistic performance. • The frontal coating has a cushioning effect to attenuate and disperse contact force. • The frontal polyurea-coating promotes energy dissipation of the steel substrate. This study investigates the effect of polyurea coating on the ballistic resistance of polyurea-steel laminate plates. Ballistic tests are carried out to compare the residual velocities and failure modes of the monolithic steel plate and polyurea-steel laminate plates on an equal mass basis. Experimental results show that polyurea coating could lead to an enhanced ballistic resistance of the laminate plate (with 5.2% greater ballistic limit velocity), but only when applied at the impact-receiving face. Finite element simulations are performed to provide insights into the penetration process and the energy partitioning to reveal the enhancing mechanisms of the frontal polyurea coating. Excellent agreement was obtained between the numerical simulations and the experimental results. Simulation results suggest that the frontal polyurea-coating has a cushioning effect to alleviate and redistribute the total contact force acting on the substrate steel layer, which helps to spread the local impact to a far-field response. The polyurea-coating on the impact-receiving face provides additional ballistic resistance by promoting greater energy dissipation of the steel layer through global deformation. [ABSTRACT FROM AUTHOR]

Abstract: (1− x)Bi0.5Na0.5TiO3–x(Ba0.7Ca0.3)TiO3 (BNT–xBCT, 0≤ x ≤0.15) solid solutions have been synthesized by a conventional solid state sintering method for obtaining a morphotropic phase boundary (MPB) with good piezoelectric properties. X-ray diffraction patterns reveal that a MPB of rhombohedral and tetragonal phases is formed at compositions 0.09≤ x ≤0.12. Addition of BCT into BNT greatly lowered coercive field E c without degrading remanent polarization P r. The specimen with x =0.09 has the good piezoelectric properties: d 33 =125pC/N and k p =0.33. A modified Curie–Weiss law was used to fit the dielectric constant of BNT–xBCT ceramics, and a frequency dispersion was observed during the phase transitions from antiferroelectric to paraelectric in specimens with x exceeding 0.06. [Copyright &y& Elsevier]

• The weight function method takes pre-existing fracture into consideration for the prediction of breakdown pressure of borehole. • The breakdown pressure calculated by weight function method is compared with both the 3rd party and in-house lab results, and its accuracy was proved; • The proven weight function method simplifies the prediction of breakdown pressure, and shows a great potential in improving the accuracy of breakdown pressure prediction because it captures more physical factors during rock fracturing process. Accurate estimation of fracture gradient is critical for both drilling and hydraulic fracturing. Fracture gradient by traditional methods is greatly overestimated due to the ignorance of preexisting fractures, nonlinear near wellbore stress concentration acting on fracture surfaces, or non-uniform fluid pressure distribution inside fractures. To overcome the limitations of current methodologies, a weight function method is firstly introduced to calculate breakdown pressure where there are a pair of symmetrical radial fractures collinear with borehole axis emanating from the borehole. The results are compared against both measured breakdown pressure in both field and laboratory and results of classical fracture models. Parametric studies are conducted to investigate the influence of pre-existing crack length, orientation, in-situ stress contrast, fracture toughness, and internal pressure distribution on breakdown pressure. It indicates that breakdown pressure (1) does not always decrease with increasing dimensionless crack length at different stress contrast, (2) for the fracture with non-uniform pressure is higher than the one with constant internal pressure, and (3) increases with increasing absolute value of inclination angle 1 It means an angle between the local maximum horizontal principal stress and the axis of the fracture. 1 and fracture toughness. Comparison of breakdown pressure by traditional and weight function methods demonstrates that breakdown pressure by traditional methods is overestimated. The proven weight function method simplifies the prediction of breakdown pressure, and shows a great potential in improving the accuracy of breakdown pressure prediction because it captures more physical factors during rock fracturing process. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF)-derived CuO microstructures suffer from low specific surface area and poor surface reactivity due to the severe agglomeration during calcination, which restricts their sensing response and reaction kinetics as gas sensors, especially at room-temperature (RT) manipulation. In this study, one-dimensional (1D) porous CuO tube-like nanofibers (TNFs) were constructed using a MOF approach combined with an electrospinning technique. The CuO TNFs displayed 1D hollow tubular structure with numerous cavities on the tube walls. In particular, these MOF-derived CuO TNFs interlaced with each other, forming a 3D netlike nanofiber structure with good anti-aggregation property. Compared with the MOF-derived CuO nanoparticles (NPs), the CuO TNFs had much better NO 2 sensing characteristics in terms of great response (27.9-fold improvement @ 500 ppb), fast response/recovery rate, and high selectivity at RT (25 °C). The CuO TNFs also displayed reliable repeatability and good antihumidity. Sensing measurements under various oxygen partial pressures identified that O ads resulted in a decreased R a , and had a negative effect on the improvement of NO 2 response of CuO TNFs. The enhanced NO 2 gas sensing properties of CuO TNFs were ascribed to their unique tube-like nanofiber network structure, high specific surface area, abundant porosities, and low activation energy. [Display omitted] • CuO tube - like nanofibers (TNFs) were prepared by a MOF and electrospinning method. • CuO TNFs showed evidently enhanced surface area and good anti-aggregation property. • The CuO TNFs exhibited sensitive and selective detection of ppb-level NO 2 at RT. • The O ads showed a negative effect on the improvement of NO 2 response of CuO TNFs. • The gas-sensing enhancement mechanism of CuO TNFs was proposed. [ABSTRACT FROM AUTHOR]

Mode-I stress intensity factor ( SIF ) for single radial crack emanating from hollow cylinder in an infinite plane under complex nonlinear loadings is firstly solved with the weight function method. A weight function providing wide-spectrum expressions for such cracks is developed. The weight function based SIFs are validated against different boundary collocation based SIF s. Three correlations of weight function parameters are derived for simplifying engineering applications and numerical simulations. Finally, the parameters are applied to calculate SIF of inclined crack subjected to complex nonlinear loadings in hydraulic fracturing, and show great potential in addressing cracks initiation from hollow cylinder. [ABSTRACT FROM AUTHOR]

A carbon nanocage material (CKT) was first successfully sulfonated by introducing sulfophenyl groups on the surface of pore channels through benzenesulfonic acid-containing aryl radical in situ generated from the reaction of 4-aminobenzenesulfonic acid and isoamyl nitrite in water. The sulfonated carbon nanocage material (S-CKT) was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, powder small-angle X-ray diffraction and nitrogen sorption measurements. The results showed that the S-CKT still possess the high specific surface area (787 m/g) and uniform mesoporous (pore diameter 4.7 nm) structures, although the structure of S-CKT is slightly disorder, compared with its unsulfonated precursor. S-CKT, as a carbon-based solid acid catalyst, showed good catalytic performance and reusability in the cross-Aldol condensation of ketones with aromatic aldehydes under solvent-free condition. Graphical Abstract: [Dispersibility of S-CKT in HO, DMF, EtOH (from left to right) after 6 month][Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (NBTB) and 0.05BiFeO3–0.95NBTB (BF-doped NBTB) lead-free ceramics were prepared by solid state reaction method. The ceramics were sintered at 1180°C for 2h in O2 and N2. All ceramics exhibited a single phase of perovskite structure. Relative amount of tetragonal phase was related to the sintering atmospheres. Both grain size and shape were influenced by the sintering atmospheres. Sintering the ceramics in N2 weakened their dielectric anomalies corresponding to the transition from ferroelectric phase to the so-called “intermediate phase”. When the NBTB and BF-doped NBTB ceramics were sintered in N2, their maximum dielectric constant and the degree of diffuseness of the transition from the “intermediate phase” to paraelectric phase increased, but their Curie temperatures decreased. The difference in dielectric properties of the ceramics sintered in different atmospheres was closely related to the difference in oxygen vacancy concentration. The correlation between ferroelectric properties and sintering atmospheres is associated with a competing effect among oxygen vacancy concentration, A-site vacancy concentration and percentage of tetragonal phase. [ABSTRACT FROM AUTHOR]

Abstract: Different morphologies of nanostructured bismuth sulfide (Bi2S3) including nanotubes and nanorods have been prepared by solvothermal synthesis at a low temperature of 120 °C for 12 h using various mixed solvents as the reaction medium and urea as the mineralizer. X-ray diffraction analysis showed that all the as-prepared Bi2S3 samples are orthorhombic phase. Transmission electron microscopy analysis showed that the morphologies of the nanostructures are mainly related to the viscosity and surface tension of the mixed solvent used in the solvothermal synthesis. [Copyright &y& Elsevier]