Modelling of the thermomechanical coupling during hot forming of viscoplastic materials

In the present paper, a strategy for solving transient thermoviscoplastic problems is described. The general thermal and mechanical coupling phenomena are discussed by assuming material properties to be temperature-dependent and accounting for the mechanical terms in the non-stationary heat conduction equation. Time integration is carried out with an implicit scheme. An interesting version of the three-field approach is presented to obtain an accurate solution for the stress field. Finally, a global product coupling algorithm, in which the unknown nodal velocities and temperatures are solved with a two-step solution procedure is suggested. The proposed fractional step method partitions the initial coupled problem into an isothermal viscoplastic problem followed by a purely heat conduction problem at fixed configuration. Applications in metal forming analyses involving full thermomechanical coupling conclude the paper.     

环保高性能防腐涂料驱动未来市场

介绍了防腐涂料的新品种和防腐体系的选择,指出了我国防腐涂料的发展趋势。     

Preparation of a sensor substrate using functionalized mesoporous silica on a gold film for surface plasmon resonance (SPR) spectroscopy

The use of surface plasmon resonance (SPR) spectroscopy has been applied to a wide variety of fields such as biosensors and surface analysis instruments. In general, a SPR substrate is prepared using self-assembled monolayer (SAM) method of organic molecules as receptor for the target on a layer of gold or silver. However, mesoporous inorganic materials such as SBA-15 have benefits as sensor substrate for SPR. Mesoporous silica has a large surface area which receptor molecule can be attached and has a rigid body which has an excellent stability in the extreme condition compared to organic sensing layer. We prepared an organic modified mesoporous silica and successfully immobilized it on a gold surface, in an attempt to use as a substrate for SPR spectroscopy. For the comparison of sensitivity of prepared substrate, Pt²⁺ detection was selected as a model system. Substrate prepared in this study exhibited the capability of selective sensing for Pt²⁺ ions.     

Direct current bias applied to hot flame diamond deposition produces smooth low friction coatings

As-deposited diamond coatings generally have a high surface roughness which results in a high friction coefficient and extensive wear of the counter material in sliding contact. Therefore several methods for smoothening diamond coatings have been proposed, such as laser polishing, molten metal etching, thermochemical polishing and mechanical polishing. All these methods have some disadvantage e.g. long processing time or high processing temperature. Furthermore, they are all post-deposition treatments i.e. the manufacture of these coatings requires at least two processing steps, deposition and smoothening. With the present method which combines d.c. bias with hot flame diamond deposition, a smooth diamond surface is produced during the actual growth of the film. No post-deposition treatment is necessary. The surface roughness is not dependent on the coating thickness which means that thick coatings with smooth surface can be produced. In fact, the method has a smoothening effect, i.e. rough surfaces can be made smooth. The method is comparable to conventional hot flame deposition of diamond as to growth rate and cost of producing the coatings. The coatings have a nano-crystalline structure and a surface roughness of Ra = 25 nm, and result in a friction coefficient of 0.1 or less in dry sliding and about 0.05 in water-lubricated sliding against cemented carbide. Their wear resistance is virtually the same as that of conventional diamond films.     

紫外光固化聚合物涂层的原位光稳定化研究

选用实验室制备的四种新型反应型受阻胺类光稳定剂(r-HALS):4-甲基丙烯酰氧基-2,2,6,6-四甲基哌啶醇酯(MTMP)、4-丙烯酰氧基-2,2,6,6-四甲基哌啶醇酯(ATMP)、4-甲基丙烯酰氧基-1,2,2,6,6-五甲基哌啶醇酯(MPMP)和4-丙烯酰氧基-1,2,2,6,6-五甲基哌啶醇酯(APMP),实现了紫外光固化聚合物涂层(膜)的原位(in situ)光稳定化。通过室内人工光老化实验和在光氧化过程中黄度指数(Yellowness Index,YI)的监测,再与典型的商用HALS(Tinuvin770和Tinuvin292)进行平行实验对比,考察了r-HALS对紫外光固化聚合物涂层的光防护效果,探索一条紫外光固化聚合物涂层原位(in situ)光稳定化的新途径。     

贮氢合金组成对电极性能的影响

本文研究了混合稀土MmBx贮氢合金B组分的钴含量和Mm(Ni_(0.70)Co_(0.16)Mn_(0.08)Al_(0.06))_x的配比数x对P-C-T曲线平衡氢压、放电容量和电池的循环使用寿命的影响。     

热重法确定MMH微晶中各种水分的相对含量

借助热分析仪对MMH微晶进行了TG和DTG分析,研究了MMH微晶中各种水分的相对含量。提出MMH微晶中存在4种水分,即自由水、松散吸附水和紧密吸附水、结晶水和羟基水,给出了MMH微晶的完整表达式,即 MgAl_(0.965)(OH)_(4.75)Cl_(0.145·1.70)H_2O。     

Performance of a cutting tool made of steel matrix surface nano-composite produced by in situ laser melt injection technology

Steel-matrix (105WCr6 steel) surface nano-composites with (Ti,W)C micron-sized and (Fe,W)₆C nano-sized carbide precipitates were produced by in situ laser melt injection technology with subsequent heat treatment. The microhardness of a 1 mm thick nano-composite layer was found to be higher than that of the initial matrix. The machinability of the surface nano-composite by a cubic boron nitride (CBN) wheel was found lower, but still reasonable compared to the initial matrix. Cutting tools produced from our new nano-composite by the CBN wheel were found to have higher wear resistance, longer tool life and provided lower cutting forces against a C45 steel workpiece compared to the initial matrix of the nano-composite.     

Synthesis and spectral properties of new tetrakis-2,3-{5,7-bis[(E)-2-(4-methylphenyl)vinyl]pyrazino}porphyrazine metal complexes

The new styryl substituted pyrazinoporphyrazine complex has been synthesised for the first time. The spectral properties of the ytterbium complex have been studied. The introduction of the styryl fragments in the cycle leads to bathochromatic shift of the Q-band. It can be explained by the stabilisation of LUMO.     

Structure and water-barrier properties of vanadate-based corrosion inhibitor films

Uniform, crack-free vanadium-based corrosion inhibitor films were grown on aluminum alloy 2024. Neutron and X-ray reflectivity were utilized to investigate the structure, water-barrier properties and speciation of the inhibitor film. The top part of the alloy participates in the formation of vanadate film. The similarity of films prepared from H₂O and D₂O implies the vanadate film is not hydrated. The film has a layered structure with vanadium enriched at the alloy interface. The film behaves as an effective water barrier when the thickness is greater than 800 Å. Films grown without K₃Fe[CN]₆ accelerator are found to be extremely thin.