Numerical modelling of particle distribution effects on fatigue in Al–SiCp composites

Various reports in the literature have highlighted the effects of particle distribution on the fatigue behaviour of particulate reinforced metal matrix composites (PMMCs), although few attempts have been made at modelling such effects. A micromechanical understanding of the effects of clustering on short crack growth behaviour in Al–SiC_p composites has been achieved via finite element modelling. Comparison of preliminary models with the literature has shown that shielding/anti-shielding effects were significantly affected by the relative sizes of the particle and the overall model such that, when edge effects were removed, a crack was predicted to be accelerated rather than decelerated as it propagated through closely spaced pairs of particles. Consistent differences were identified between models with homogeneous versus clustered particle arrangements in terms of crack path morphologies and local crack–tip stress intensity fluctuations. Furthermore, predicted influences of clustering on growth rates in the numerical models were found to be consistent with previous experimental results (i.e. growth rates rose with increased clustering), demonstrating that load transfer effects associated with changes in particle distribution may play a direct role in controlling the growth of short cracks in these materials.     

The interaction between screw dislocations and an interfacial blunt crack and a sharp crack

The interaction between screw dislocations and an interfacial blunt crack and a sharp crack under loads at infinity is dealt with. Utilizing the Muskhelishvili complex variable method, the closed form solutions are derived. The stress intensity factor and critical stress intensity factor for dislocation emission are also calculated. The results show that the shielding effect increases with the increase of the shear modulus and the distance between the two cracks, but decreases with the increase of dislocation azimuth. The critical loads at infinity for dislocation emission increase with the increment of the emission angle and the distance.     

探伤室屏蔽设计

X射线探伤室屏蔽设计对保障人员辐射安全意义重大。介绍了探伤室的墙体、屋顶、铅门和通风等的结构设计,计算了设计材料的理论厚度。测试了一般工况下探伤室内不同监测点的辐射剂量。实际测试表明,采用砖混结构与铅门相结合的设计方案,可有效屏蔽辐射及散射的X射线,满足理论计算及安全防护标准的要求。     

A Computational Approach to Investigate Electromagnetic Shielding Effectiveness of Steel Fiber-Reinforced Mortar

The electromagnetic shielding effectiveness of steel fiber-reinforced mortar was numerically examined in this study. A series of numerical analysis on twenty-seven types of specimens of different diameters, lengths, and volume fractions of fibers were conducted using the FE program HFSS to investigate the effect of the dimensions of steel fibers and the amount of fibers added to the mortar on the shielding effectiveness. S-parameters of some specimens were experimentally measured by the free space method and the experimentally measured S-parameters were compared with those computed in order to verify the present numerical analysis method. It was found that smaller diameters and larger volume fractions provided better shielding effectiveness. Fiber length did not strongly influence the shielding effectiveness. The number of fibers was found to strongly influence the shielding of electromagnetic waves, and the optimal number of fibers in the mortar was found.     

MIG Brazing of Galvanized Thin Sheet Joints for Automotive Industry

MIG welding of zinc-coated thin plates in the automotive industry leads to major issues, mainly zinc evaporation followed by a decrease of corrosion resistance, as well as residual strains and stresses difficult to minimize. The use of a lower heat input technique for joining galvanized steels would bring significant benefit, if the final overall mechanical properties of the joints are adequate for the application. The use of MIG brazing (MIGB) with the recently commercialized alloyed copper-based filler metal is an alternative worth considering. The present paper addresses the MIGB processes, describing the influence of the different shielding gases and the process parameters on the mechanical, corrosion, and metallurgical properties of the joint, when lower heat input procedures are targeted. The paper describes the influence of the gases on the mechanical properties of the brazed joint, both in normal conditions after joining and after corrosion in a salt water environment. Microstructural features of the different zones are discussed. Results of corrosion and tensile tests are presented and interpreted.     

Gamma radiation attenuation characteristics for lithium-zinc-tellurite glasses using Geant4 code and PDS computer software

Six glass samples with the composition of TeO₂-Li₂O-ZnO were analyzed for their radiation shielding properties. The radiation shielding factors for the lithium-zinc-tellurite glasses were reported using the Geant4 code and Phy-X/PSD program. The transmission factor (TF) was determined for different thicknesses and the results revealed that the TF decreases with increasing the thickness of the glass. For TeLiZ1, increasing the thickness of the sample from 0.4 cm to 1.6 cm led to decrease the transmission of the photon from 0.84 to 0.48 at 0.5 MeV and from 0.94 to 0.76 at 4 MeV. The radiation protection efficiency (RPE) results showed that a thicker glass sample absorbs a higher number of photons, implying that lower radiation pass among the glass, increasing RPE. Also, the glass coded as TeLiZ6 has higher RPE than that of TeLiZ1 glass which suggests that at higher content of TeO₂ (85 mol%), the more efficient the glass is at shielding the incoming photons. The linear attenuation coefficient (LAC) obtained by both methods (Geant4 and Phy-X/PSD showed a good agreement for all the glasses and at all investigated energies. The LAC indicates a strong energy dependence, especially at low energies. The LAC also increases as more TeO₂ is added to the glasses. TeLiZ6 (85TeO₂-15Li₂O, ρ = 5.164 g/cm₃) has the highest RPE and lowest TF, while TeLiZ1 (60TeO₂-15Li₂O-25ZnO, ρ = 4.976 g/cm³) has the lowest RPE and highest TF. The tenth value layer (TVL) was also determined and it was observed that TVL increases with increasing energy, reaching a maximum value at 10 MeV and varying between 12.919 and 13.808 cm. By contrast, the minimum TVL is reported at 15 keV and varies between 0.0106 and 0.0112 cm. The addition of TeO₂ decreases the TVL, with TeLiZ6 having the least TVL.     

Effect of Bi2O3 on mechanical features and radiation shielding properties of boro-tellurite glass system

This paper focuses on the effect of Bi₂O₃ content (up to 80 mol%) on mechanical features and radiation shielding characteristics of boro-tellurite glasses within TeO₂–B₂O₃–Bi₂O₃ system. The basic mechanical parameters such as oxygen molar volume, packing density, hardness, and elastic moduli were studied based on Makishima–Mackenzie's theory. The shielding studies of the TeO₂–B₂O₃–Bi₂O₃ glasses included gamma, electron and neutron radiations. The newly developed Phy-X/PSD program and Geant4 simulation were used to calculate the shielding parameters such as mass attenuation coefficient (μ/ρ), tenth value layer (TVL), mean free path (MFP), stopping power (ψ_e)), removal cross section (RCS), CSDA range, effective atomic number (Z_eff), and half value layer (HVL). The concentration of Bi₂O₃ content had a significant effect on the gamma shielding competence of the investigated glasses. Form the results of gamma shielding studies, the highest μ/ρ (99.845 cm²/g) occurred at 0.015 MeV for TBB80 and the lowest μ/ρ (0.039 m²/g) occurred at 4 MeV for TBB40. The maximum values of Z_eff for gamma interaction occurred at 0.02 MeV and they were 77.26, 78.81, 79.94, 80.80, and 81.48 for TBB40, TBB50, TBB50, TBB60, TBB70, and TBB80, respectively. The gamma shielding features of the investigated glasses were compared with those of various ordinary concretes, and Pb-free, Pb-based, and commercial glasses. The Bi₂O₃ content had also a considerable influence on the electron shielding competence of the tested glasses. The maximum values of Z_eff for electron interaction occurred at 14 MeV and they were 44.58, 47.72, 50.41, 52.75, and 53.73 for TBB40, TBB50, TBB50, TBB60, TBB70, and TBB80, respectively. The results revealed that the bismuth boro-tellurite glasses could be useful for the shielding against gamma, electron, and neutron radiations, wherein the Bi₂O₃ content can be balanced according to the type and energy of radiation.     

Waste cotton Fabric/MXene composite aerogel with heat generation and insulation for efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials have become more and more indispensable due to serious electromagnetic-radiation pollution. Herein, waste cotton cellulose aerogels were prepared by dissolving waste cotton fabrics (WCF) in NaOH/urea aqueous solution, and MXene nanosheets were subsequently deposited on the cellulose aerogels by a facile dip coating method to obtain WCF/MXene composite aerogels. The WCF/MXene composite aerogels with highly porous network structure show remarkable electrical conductivity (8.2 Ω/sq of surface resistance), high EMI shielding effectiveness (EMI SE) in the range of 2–18 GHz (39.3–48.1 dB). The WCF/MXene aerogel possesses high SSE and SSE/t of 677.94–829.74 dB cm³ g^?1 and 3512.62–4299.17 dB cm² g^?1, respectively (2–18 GHz). In addition, the heating temperature of WCF/MXene composite aerogels reaches 199 °C when 3 V positive voltage is applied on them. The WCF/MXene composite aerogels possess excellent electromagnetic shielding effectiveness, heat generation property and insulation, which can be potentially used as multifunctional materials for EMI shielding, electrical-heating and high temperature protection.     

医用诊断X线机防护改装效果浅析

本文介绍了对医用诊断 X 线机进行防护改装的方法及其防护性能的测试结果。从渡口市不同容量和类型的20台医用诊断 X 线机改装前后的测试结果可以看出,防护改装的方法是可行的,改装的效果比较好。     

有机无机精细复合紫外屏蔽包装材料的研制

将无机Ｃｒ２Ｏ３超微粒子进行表面处理，使其与单体相溶，用本体聚合方法制成透明均一的紫外屏蔽包装材料。