First results with the upgraded TLK tritium calorimeter IGC-V0.5

At Tritium Laboratory Karlsruhe (TLK) calorimetry has been used for almost 20 years as the main accountancy method for tritium inventory. An extensive work has been carried out in order to improve the existing calorimeters. This paper covers the efforts made for the upgrade of the IGC-V0.5 calorimeter. We replaced the hardware interface – including the obsolete PC – and developed a new control and data acquisition software. The new software applies a smart automatic process control during measurements, significantly reducing measurement time and possible user errors. The three PID control loops have been re-tuned using the standard closed loop Ziegler–Nichols procedure to find the optimal PID parameters. Five calibration runs have been performed between 0.5 μW and 1 W, and their results are being presented and discussed.     

Improving post irradiation stability of high density polyethylene by multi walled carbon nanotubes

Sterilization of implants and other clinical accessories is an integral part of any medical application. Although many materials are used as implants, polyethylene stands unique owing to its versatility. Carbon nanotubes are being used as a filler material to enhance the properties of polyethylene. However, the role of multi walled carbon nanotubes (MWCNTs) as an effective antioxidant and radical scavenger in resisting the deteriorating effects of sterilization is yet to be studied in detail. The present work is aimed to investigate the mechanical properties and oxidation stability of irradiated high density polyethylene (HDPE) reinforced by MWCNTs with various concentrations such as 0.25%, 0.50%, 0.75% and 1.00 wt.%. The composites were exposed to ⁶⁰Co source in air and irradiated at different dosage level starting from 25 to 100 kGy and then shelf aged for a period of 120 days prior to investigation. The loss in toughness, Young’s modulus and ultimate strength at 100 kGy for 1 wt.% MWCNTs composite were found to be 21.5%, 20.3% and 19.2%, respectively compared to that of unirradiated composite. FTIR and ESR studies confirmed the antioxidant and radical scavenging potentialities of MWCNTs with increased concentration and irradiation dosage. It was found that by the addition of 1 wt.% MWCNTs into virgin HDPE, the oxidation index of the composite at 100 kGy was decreased by 56.2%. It is concluded that the addition of MWCNTs into polyethylene not only limits the loss of mechanical properties but also improves its post irradiation oxidative stability.     

基于信捷PLC对细石混凝土泵电气系统的设计

为了推进细石混凝土泵的国产化,在保证产品性能的前提下,降低其电气系统的生产成本,采用以国产信捷PLC(Programmable Logic Controller)为主的控制元件对细石混凝土泵电气系统进行了设计。在保证细石混凝土泵使用稳定性的同时,降低了其电气系统的制造成本,提高了适用性。所设计电气系统经菏泽永安机械制造有限公司检验使用,实际应用情况良好。     

火箭蒙皮和壁板柔性装配定位技术及其应用

针对新一代运载火箭蒙皮和壁板在试制阶段高精度、低成本、短周期的制造需求,采用多点阵真空吸盘式柔性装配工装对蒙皮或壁板进行定位、固持.生成与装配件外形精确吻合的吸附点阵,精确、牢靠地固持蒙皮或壁板类装配件,同时通过基准孔的精确定位,保证整个装配件的定位精度,改善了生产灵活性,提高生产效率,对于多品种小批量蒙皮、壁板类零件的生产具有独特优势.     

Microstructural evolution and mechanical properties of niobium processed by equal channel angular extrusion up to 24 passes

We have systematically investigated the microstructural evolution of niobium (Nb) subjected to severe plastic deformation via equal channel angular extrusion (ECAE) up to 24 passes. The starting Nb billet material consists of a centimeter-scale grain size with a columnar structure. We have found that the grain size reduction of the Nb is almost saturated at ∼300 nm after eight passes of ECAE. However, the population of high-angle grain boundaries continues to increase with further ECAE, and no saturation appears to have been reached at 24 passes. We have evaluated the mechanical properties of the samples with different number of ECAE passes over a wide range of strain rates, from quasi-static to high strain rates. We have used strain-rate jump tests to examine the strain-rate sensitivity (SRS) of the processed samples and found that the SRS of the ECAE-processed Nb is ∼0.012, which is a factor of three smaller than that of the coarse-grained counterpart. The activation volume derived for plastic deformation indicates that the double-kink formation of screw dislocations is still the predominant deformation mechanism in the ECAE-processed Nb. Quasi-static true stress-strain curves exhibit elastic-nearly perfectly plastic behavior. The quasi-static yield strength is also nearly saturated after eight passes of ECAE. High-strain-rate compressive true stress-strain curves show uniform flow softening. However, the dynamic peak stress keeps rising with an increased number of ECAE passes, suggesting a strong grain boundary contribution to dynamic strengthening. Scanning electron microscopy of post-loaded surfaces displays a morphology of diffuse shear bands accompanying highly compressed grains. In our report, we demonstrate that grain boundaries of severely deformed metals play different roles at low, quasi-static vs. high-strain rates of mechanical loading. The difference is primarily determined by the strength of grain boundaries acting as dislocation barriers at different loading rates. This discovery is significant for the understanding of the effect of the microstructure as a function of the applied loading rate.     

浅议离心式水泵的一个重要参数

分析了离心式水泵的一个重要参数——允许吸上真空度Hs的含义,阐述了水泵的安装高度Hx与允许吸上真空度Hs的关系。     

森兰变频器在循环水供水系统中的应用

介绍森兰变频器在循环水供水系统中的应用,实现了能耗的节约以及故障的自动切换。     

Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endo-polygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG → 10% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04.     

Reactive extrusion: A useful process to manufacture structurally modified PLA/o-MMT composites

In the present work, poly(lactic acid) (PLA) sheets reinforced with organically modified montmorillonite (o-MMT) were manufactured through reactive extrusion-calendering using a masterbatch approach in a pilot plant. Reaction monitoring analysis suggests the occurrence of premature reactions between o-MMT and the reactive agent; lowering further structural changes in the polymeric matrix. While calendered sheets exhibited a homogenous and preferential distribution of clay particles in MD, the coexistence of mixed structures, involving tactoids of various sizes as well as intercalated clay layers was observed. However, a higher and finer dispersion of o-MMT particles was achieved through clay–polymer tethering via chain extender molecules. Under tensile loading, the aforementioned clay dispersion enhanced multiple cavitation processes, notably improving PLA shear flow.     

Effect of TiO2 addition on the sintering densification and mechanical properties of MgAl2O4–CaAl4O7–CaAl12O19 composite

Materials designed in the high-alumina region of Al₂O₃–MgO–CaO system have been widely used in many technological fields. However, their further applications are limited by the high sintering temperatures necessary to achieve densification due to the poor sintering ability of calcium hexaluminate (CaAl₁₂O₁₉) and spinel (MgAl₂O₄). Considering this aspect, the present work investigated the effect of TiO₂ addition on the sintering densification and mechanical properties of MgAl₂O₄–CaAl₄O₇–CaAl₁₂O₁₉ composite by solid state reaction sintering. The results showed that the CA₆ grains presented a more equiaxed morphology instead of platelet structure by incorporating Ti⁴⁺ into its structure, which greatly improved the densification after heating at 1600 °C. The flexural strength was greatly enhanced with increasing addition of TiO₂ due to the significant decrease in porosity and improvement in uniformity of grain size as well as the absence of microcracks in the presence of Al₂TiO₅. The increased content of TiO₂ also played an active role in toughening this composite attributed to the increase in resistance to crack initiation and propagation.