Experimental study on the influences of cutter geometry and material on scraper wear during shield TBM tunnelling in abrasive sandy ground

When shield TBM tunnelling in abrasive sandy ground,the rational design of cutter parameters is critical to reduce tool wear and improve tunnelling efficiency.However,the influence mechanism of cutter parameters on scraper wear remains unclear due to the lack of a reliable test method.Geometry and material optimisation are often based on subjective experience,which is unfavourable for improving scraper geological adaptability.In the present study,the newly developed WHU-SAT soil abrasion test was used to evaluate the variation in scraper wear with cutter geometry,material and hardness.The influence mechanism of cutter parameters on scraper wear has been revealed according to the scratch characteristics of the scraper surface.Cutter geometry and material parameters have been optimised to reduce scraper wear.The results indicate that the variation in scraper wear with cutter geometry is related to the cutting resistance,frictional resistance and stress distribution.An appropriate increase in the front angle(or back angle)reduces the cutting resistance(or frictional resistance),while an excessive increase in the front angle(or back angle)reduces the edge angle and causes stress concentration.The optimal front angle,back angle and edge angle for quartz sand samples areα=25°,β=10°andγ=55°,respectively.The wear resistance of the modelled scrapers made of different metal materials is related to the chemical elements and microstructure.The wear resistances of the modelled scrapers made of 45#,06Cr19Ni10,42CrMo4 and 40CrNiMoA are 0.569,0.661,0.691 and 0.728 times those made of WC-Co,respectively.When the alloy hardness is less than 47 HRC(or greater than 58 HRC),scraper wear decreases slowly with increasing alloy hardness as the scratch depth of the particle asperity on the metal surface stabilizes at a high(or low)level.However,when the alloy hardness is between 47 HRC and 58 HRC,scraper wear decreases rapidly with increasing alloy hardness as the scratch depth transitions from high to low levels.The sensitive hardness interval and recommended hardness interval for quartz sand are[47,58]and[58,62],respectively.The present study provides a reference for optimising scraper parameters and improving cutterhead adaptability in abrasive sandy ground tunnelling.

Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.

Recent Advances in Design Strategies and Multifunctionality of Flexible Electromagnetic Interference Shielding Materials

With rapid development of 5G communication technologies,electromagnetic interference(EMI)shielding for electronic devices has become an urgent demand in recent years,where the development of corresponding EMI shielding materials against detrimental electromagnetic radiation plays an essential role.Meanwhile,the EMI shielding materials with high flexibility and functional integrity are highly demanded for emerging shielding applications.Hitherto,a variety of flexible EMI shielding materials with lightweight and multifunctionalities have been developed.In this review,we not only introduce the recent development of flexible EMI shielding materials,but also elaborate the EMI shielding mechanisms and the index for"green EMI shielding"performance.In addition,the construction strategies for sophisticated multifunctionalities of flexible shielding materials are summarized.Finally,we propose several possible research directions for flexible EMI shielding materials in near future,which could be inspirational to the fast-growing next-generation flexible electronic devices with reliable and multipurpose protections as offered by EMI shielding materials.

Calculation of photon shielding properties for some neutron shielding materials

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number(Z_(eff)), the effective electron density(N_(eff)) for photon interaction and photon energy absorption,and gamma-ray kerma coefficient(kc). The calculations of Z_(eff)are presented as a single-valued and are energy dependent. While Z_(eff)values were calculated via simplistic powerlaw method, the energy-dependent Z_(eff)for photon interaction(Z_(PI-eff)) and photon energy absorption(Z_(PEA-eff)) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 Me V, respectively. The kccoefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and crays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies and then converges with pure polyethylene at energies greater than 100 keV.

Progress on Space Materials Science in China:Debris Shielding Fibrous Materials and High Specific Energy Lithium Sulfur Batteries

The development of China’s space industry puts forward urgent requirements for high-performance debris shielding materials and high energy density rechargeable battery.In this review,the recent progress on debris shielding fibrous materials and high energy density Li-S battery are particularly summarized.According to the experimental results,basalt fibers and silicon carbide fibers were chosen as the effective filling shielding materials.The geometric structure of fabrics was also investigated.For the novel shielding materials,high-strength and flexible silicon carbide micro-nano fibrous membranes were designed and fabricated.The obtained membranes with excellent mechanical properties portend the potential applications in debris protection structure.Furthermore,the high specific energy lithium sulfur batteries have made remarkable progress in fundamental research and application research in recent years.In order to solve the key problems of polysulfides shuttle and slow redox kinetics in lithium sulfur battery,a series of transition metal compound@hollow carbon-based material as sulfur host with dual functions of catalysis and adsorption towards polysulfides were designed and constructed.The obtained Li-S pouch cells with high areal sulfur loading of 6.9 mg·cm^(-2)yield exceptional high practical energy density of 382 W·h·kg^(-1)under lean electrolyte of 3.5μL·mg^(-1),demonstrating the great potential of realistic high-energy Li-S batteries.

Green,Sustainable Architectural Bamboo with High Light Transmission and Excellent Electromagnetic Shielding as a Candidate for Energy-Saving Buildings

Currently,light-transmitting,energy-saving,and electromagnetic shielding materials are essential for reducing indoor energy consumption and improving the electromagnetic environment.Here,we developed a cellulose composite with excellent optical transmittance that retained the natural shape and fiber structure of bamboo.The modified whole bamboo possessed an impressive optical transmittance of approximately 60%at 6.23 mm,illuminance of 1000 luminance(lux),water absorption stability(mass change rate less than 4%),longitudinal tensile strength(46.40 MPa),and surface properties(80.2 HD).These were attributed to not only the retention of the natural circular hollow structure of the bamboo rod on the macro,but also the complete bamboo fiber skeleton template impregnated with UV resin on the micro.Moreover,a multilayered device consisting of translucent whole bamboo,transparent bamboo sheets,and electromagnetic shielding film exhibited remarkable heat insulation and heat preservation performance as well as an electromagnetic shielding performance of 46.3 dB.The impressive optical transmittance,mechanical properties,thermal performance,and electromagnetic shielding abilities combined with the renewable and sustainable nature,as well as the fast and efficient manufacturing process,make this bamboo composite material suitable for effective application in transparent,energy-saving,and electromagnetic shielding buildings.

Flexible Nanocomposite Conductors for Electromagnetic Interference Shielding

With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference(EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible(particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges.

First principles investigation on Li or Sn codoped hexagonal tungsten bronzes as the near-infrared shielding material

The 52%energy of the solar radiation is contributed by near-infrared radiation(NIR,780-2500 nm).Therefore,the material design for the energy-saving smart window,which can effectively shield NIR and has acceptable visible transmittance,is vital to save the energy consumed on the temperature control system.It is important to find a non-toxic stable material with excellent NIR-shielding ability and acceptable visible transmittance.The systematic first-principles study on Li_(x)Sn_(y)WO_(3)(x=0,0.33,0.66,and y=0,0.33)exhibits that the chemical stability is a positive correlation with the doping concentration.After doping,the Fermi-energy upshifts into the conduction band,and the material shows metal-like characteristics.Therefore,these structures Li_(x)Sn_(y)WO_(3)(except the structure with x=0.33 and y=0)show pronounced improvement of NIR shielding ability.Our results indicate that when x=0 and y=0.33,the material exhibits the strongest NIR-shielding ability,satisfying chemical stability,wide NIR-shielding range(780-2500 nm),and acceptable visible transmittance.This work provides a good choice for experimental study on NIR shielding material for the energy-saving window.

An origami shield with supporting frame structures optimized by a feature-driven topology optimization method

In this paper,the design,manufacture and testing of an origami protective shield with a supporting frame structure are presented.It consists of an origami shield surface and a deployable supporting frame structure that needs to be portable and sufficiently stiff.First,for the design of the shield surface,a threestage origami crease pattern is developed to reduce the shield size in the folded state.The shield surface consists of several stiff modular panels and layered with flexible fabric.The modular panels are made of a multi-layer composite where a ceramic layer is made of small pieces to improve durability as those small pieces enable restriction of crack propagation.Then,the supporting frame structure is designed as a chain-of-bars structure in order to fold into a highly compact state as a bundle of bars and deploy in sequence.Thus,a feature-driven topology structural optimization method preserving component sequence is developed where the inter-dependence of sub-structures is taken into account.A bar with semi-circular ends is used as a basic design feature.The positions of the bar’s end points are treated as design variables and the width of the bars is kept constant.Then,a constraint on the total length of the chain of bars is introduced.Finally,the modular panels made of multi-layer composite and the full-scale prototype of the origami shield are fabricated and tested to verify the bullet-proof performance.

Measurements of Natural Radioactivity of Industrial Raw Materials from the West of Saudi Arabia (Arabian Shield)

Rock samples of industrial raw materials that are used in the building, from the West of Saudi Arabia (Arabian Shield), have been investigated using X-ray diffraction to identify the mineral chemical composition. The concentrations of Al%, Bi, Pb, Th, U, and K in ppm were measured by atomic absorption analysis. The activity concentrations in Bq/kg dry weight of 226Ra, 232Th and 40K were measured using gamma-ray spectrometry where the range and average were found to be (03.04 - 10.91) 07.90, (03.19 - 13.31) 09.14 and (95.59 - 361.52) 234.81 in Basalt, for Granite (33.81 - 89.13) 80.85, (28.42 - 112.77) 68.50 and (1260.13 - 1629.21) 1376.69, for Gold (00.78 - 11.84) 04.73, (01.48 - 4.69) 02.69 and (13.76 - 445.09) 197.58, for Andesite 05.72, 03.73 and 471.93, and for Marble 01.56, 01.38 and 10.15 respectively. Most results existing within the given values in building materials by UNSCEAR 1993 included Raeq (Bq/kg), D (nGy/h), Deff (mSv/y), Hex and Hin, which meant that it was safe for humans.

Flexible and Waterproof 2D/1D/0D Construction of MXene-Based Nanocomposites for Electromagnetic Wave Absorption,EMI Shielding,and Photothermal Conversion

High-performance electromagnetic wave absorption and electromagnetic interference(EMI)shielding materials with multifunctional characters have attracted extensive scientific and technological interest,but they remain a huge challenge.Here,we reported an electrostatic assembly approach for fabricating 2D/1D/0D construction of Ti_(3)C_(2)Tx/carbon nanotubes/Co nanoparticles(Ti_(3)C_(2)Tx/CNTs/Co)nanocomposites with an excellent electromagnetic wave absorption,EMI shielding efficiency,flexibility,hydrophobicity,and photother-mal conversion performance.As expected,a strong reflection loss of-85.8 dB and an ultrathin thickness of 1.4 mm were achieved.Mean-while,the high EMI shielding efficiency reached 110.1 dB.The excel-lent electromagnetic wave absorption and shielding performances were originated from the charge carriers,electric/magnetic dipole polariza-tion,interfacial polarization,natural resonance,and multiple internal reflections.Moreover,a thin layer of polydimethylsiloxane rendered the hydrophilic hierarchical Ti_(3)C_(2)Tx/CNTs/Co hydrophobic,which can prevent the degradation/oxidation of the MXene in high humidity condition.Interestingly,the Ti_(3)C_(2)Tx/CNTs/Co film exhibited a remark-able photothermal conversion performance with high thermal cycle stability and tenability.Thus,the multifunctional Ti_(3)C_(2)Tx/CNTs/Co nanocomposites possessing a unique blend of outstanding electromagnetic wave absorption and EMI shielding,light-driven heating perfor-mance,and flexible water-resistant features were highly promising for the next-generation intelligent electromagnetic attenuation system.

Preparation and characterization of iron-ore-imbedded silicone rubber materials for radiation protection

Iron-ore-imbedded silicone rubber materials were produced for radiation shielding. Samples were tested against a Co-60 gamma source, which is widely used in nuclear technology and medicine. Decreasing the particle size of iron ore resulted in better gamma radiation protection owing to more homogenous distribution. In addition, the materials had flexible properties up to the addition of 60 wt% iron ore content. Further, 0.5 mm Pb E gamma protection was provided by using 2.06-mm-thick SDT-60 as the Co-60 source. Iron ore–silicone rubber composites are candidate materials for lead-free flexible radiation protection systems owing to their relatively inexpensive and easy production.

Reciprocity principle-based model for shielding effectiveness prediction of a rectangular cavity with a covered aperture

According to the reciprocity principle, we propose an efficient model to compute the shielding effectiveness of a rectangular cavity with apertures covered by conductive sheet against an external incident electromagnetic wave. This problem is converted into another problem of solving the electromagnetic field leakage from the cavity when the cavity is excited by an electric dipole placed within it. By the combination of the unperturbed cavity field and the transfer impedance of the sheet, the tangential electric field distribution on the outer surface of the sheet is obtained. Then, the field distribution is regarded as an equivalent surface magnetic current source responsible for the leakage field. The validation of this model is verified by a comparison with the circuital model and the full-wave simulations. This time-saving model can deal with arbitrary aperture shape, various wave propagation and polarization directions, and the near-field effect.

M-C simulation of shielding effects of PE,LiH and graphite fibers under 1 MeV electrons and 20 MeV protons

Shielding effects of different materials under 1 MeV electron and 20 MeV proton beams were simulated with Geant4 code. It was found that shielding effects of polyethylene and graphite fibers are much better than aluminum. Energy depositions in the phantom shielded by the materials are calculated, with the least energy deposition by graphite fiber shielding. The results show that graphite fibers are good radiation shielding material in space programs.

Development of high performance and high strength heavy concrete for radiation shielding structures

Heavy concrete currently used for construction contains special materials that are expensive and difficult to work with.This study replaced natural aggregate（stones） in concrete with round steel balls,which are inexpensive and easily obtainable.The diameters of the steel balls were 0.5 and 1 cm,and their density was 7.8 kg/m3.Dense packing mixture methods were used to produce heavy concrete with densities of 3500 and 5000 kg/m3.The various properties of this concrete were tested according to the standards of the American Society for Testing and Materials（ASTM）.The results indicated that the construction slump of the concrete could reach 260-280 mm and its slump flow could reach 610-710 mm.More important,its compressive strength could reach 8848 MPa.These results will significantly alter traditional construction methods that use heavy concrete and enhance innovative ideas for structural design.

Gamma ray absorption of cylindrical fissile material with dual shields

This work analyzed the gamma ray attenuation effect from the self-absorption and shield attenuation per-spectively. An exact mathematical equation was given for the geometric factor of the cylindrical fissile material with dual shields. In addition, several approximation approaches suitable for real situation were discussed, especially in the radial and axial directions of the cylinders, since the G-factors have simple forms. Then the space distribution patterns of the G-factor were analyzed based on numerical result and effective ways to solve the geometric informa-tion of the cylindrical fissile material, the radii and the heights, were deduced. This method was checked and verified by numerical calculation. Because of the efficiency of the method, it is ideal for application in real situations, such as nuclear safeguards, which demands speed of detection and accuracy of geometric analysis.

Hierarchical Ni-plated melamine sponge and MXene film synergistically supported phase change materials towards integrated shape stability,thermal management and electromagnetic interference shielding

Along with the integrated and miniaturized development of advanced electronic devices,phase change materials(PCMs)simultaneously with efficient thermal management and high electromag-netic interference(EMI)shielding effectiveness(SE)are ungently demanded.Herein,the shape-stabilized MXene/Ni-platted melamine sponge/Regenerated cellulose/Graphene nanoplate/Polyethylene glycol(MX/Ni@MS/RCG/PEG)composite PCMs comprising hierarchical Ni@MS/RCG and MXene film were fabricated via a facile encapsulation approach.Hierarchical Ni@MS/RCG hybrid aerogel was prepared by electroless plating and sol-gel methods,and MXene film was obtained using vacuum-assisted filtra-tion procedure.The synergistic effect of conductive Ni@MS/RCG networks and tight MXene film endows MX/Ni@MS/RCG/PEG composite PCMs with good shape stability,high cyclic reliability,large latent heat of phase change(154.3 J g^(–1)),excellent thermal conductivity(TC,0.47 W m^(–1)K^(–1))and favorable EMI shield-ing performance(32.7 dB).The TC of acceptable 0.47 W m^(–1)K^(–1)is observed for MX/Ni@MS/RCG-5/PEG at a rather low GNP content of merely 0.39 wt%.In addition,the temperature variation of MX/Ni@MS/RCG-5/PEG is a lot faster than that of pure PEG in the heating/cooling process,revealing the remarkable energy storage and release efficiency for the composite PCMs.This investigation has taken an important step to-wards shape-stabilized composite PCMs with both effective thermal management and high EMI SE for promising applications in electronic packaging and advanced energy.

The Effective Surface Metallization of Hollow Glass Microspheres for Flexible Electromagnetic Shielding Film

The surface of hollow glass microspheres (HGMs) was roughened by a HCl+NH_(4)F strategy,which achieved a broken ratio as 16.10%,and then metallized by electroless plating by Co nanoparticles up to 90 wt% (abbreviated as Co-HGMs).The average grain size of Co was measured to range from 0.4 to 0.5 μm.Then Co-HGMs were mixed with liquid silicone rubber and xylene,and cured on a perspex plate applicable for flexible electromagnetic shielding.By attentive parameter optimization,a film about 0.836 mm in thickness was obtained with a density of 0.729 g/cm^(3),showing a shielding effectiveness of 15.2 dB in the X-band (8.2-12.4 GHz) at room temperature,which was ascribed to the formation of a conductive network of Co-HGMs inside the film.Simultaneously,the tensile strength of 0.89 MPa at an elongation ratio of 194.5% was also obtained,showing good mechanical properties and tensile strength.

Correlation between Electrical Conductivity and Microwave Shielding Effectiveness of Natural Rubber Based Composites, Containing Different Hybrid Fillers Obtained by Impregnation Technology

The paper presents the synthesis and characterization of carbon black/silicone dioxide hybrid fillers obtained by an impregnation technology. The electromagnetic interference shielding effectiveness of the composites filled with carbon black/silicone dioxide hybrid fillers was measured in wide frequency range of 1 - 12 GHz. The dc and ac electrical conductivity of composites also have been investigated. The relationship between electrical (dc and ac) conductivity and shielding effectiveness was analyzed. A positive correlation was found between the absorptive shielding effectiveness and ac conductivity for composites comprising conductive carbon black/silica filler, when the filler loading is above the percolation threshold.