Effect of temperature on mechanical properties of Ti-based metallic glass matrix composite

Systematic mechanical behaviors were investigated in a Ti-based metallic glass matrix (MGM) composite containing the in-situ β-dendrite phase at 100 K–298 K. We found that the yielding strength increased but the plastic strain decreased with a decrease temperature. The sharp ductile to brittle transition occurred at 100 K. The MGM composite exhibits the large work-hardening behavior at 298 K, but all sample display the work-softening behavior below 298 K. The nominal work-hardening parameter was employed to express the dependence of mechanical properties on temperatures including the brittle failure, the work-hardening and work softening behaviors. It may provide a useful way to evaluate the dependence of mechanical properties on temperatures of MGM composite.     

Deformation mechanism in NiAl single crystals at low temperatures

Available data on the temperature dependence of yield stress and of associated activation volume of high-purity NiAl single crystals between 76 and 205 K have been analyzed within the framework of a solid-solution hardening model, which is based on the concept of depinning of an edge-dislocation segment from several randomly dispersed, isolated, point defects simultaneously. The vacancies in NiAl single crystals act as point-defect obstacles to the stress-assisted thermally-activated glide of edge dislocations, and their concentration is estimated as about 10 at.%. The product of yield stress and associated activation volume (≈0.146 eV) is found to be independent of temperature and yield stress, as envisaged in the model.     

Assessment of hydrogen embrittlement on advanced high strength steels revealed by in-situ electrochemical micro-cantilever bending test

In the current study, the hydrogen-induced embrittlement on advanced high strength steels (AHSSs) is evaluated by in-situ electrochemical microcantilever bending (IECB) tests. Microcantilevers of 1200 M and 1400 M steels were bent while hydrogen charged inside a miniaturized electrochemical cell and then compared to bent-cantilevers in the air. The results of bending experiments and post-mortem evaluation of the bent-cantilevers showed that the plastic deformation occurred for the bent-cantilevers in the air. At the same time, the reduction of yield stress and the formation of hydrogen-enhanced cracking happened for the hydrogen-charged cantilevers. The results indicated that the microcracks are initiated and propagated adjacent to the clamped boundaries of the cantilevers, where the stress intensity is topmost. This finding is demonstrated by created step-wise cracks in 1400 M representative bent cantilever. The results show that the hydrogen-enhanced dislocation nucleation and hydrogen-reduced dislocation mobility are responsible for plastic deformation and hydrogen-enhanced cracking behavior.     

浅谈综合机械化采煤设备的配套

综合机械化采煤将工作面的落煤、装煤、运煤、支护等各个环节有机地联系在一起，而运输设备是实现采煤机械化必不可少的重要设备之一，运输设备匹配的合理，单产将显著提高，将改善劳动条件。     

基于组合模型的矿山设备产量预测研究

鉴于矿山设备产量具有灰色和不确定性的特征，本文利用矿山设备产量的历史数据，建立了基于灰色和BP神经网络的组合预测模型。组合预测模型中各单一模型的权系数通过熵值法确定，克服了传统权系数确定方法的主观性，使得组合预测方法更具客观性最后，实例验证了所构建的组合模型较传统的单一预测模型有良好的预测效果。     

Kinetic characterisation of an enriched Nitrospira culture with comparison to Nitrobacter

Nitrospira and Nitrobacter are nitrite-oxidising bacteria commonly identified in nitrogen removal wastewater treatment plants. Little is known about the growth parameters of Nitrospira or the effects of environmental conditions or inhibitory compounds on Nitrospira activity. These bacterial properties were investigated using an enriched Nitrospira culture and an enriched Nitrobacter culture or Nitrobacter literature values. Compared to Nitrobacter, Nitrospira was found to have a comparable optimal pH range (8.0-8.3); similar normalised activity-temperature relationship (0.44e(0.055(T-15))) for temperatures between 15 and 30 degrees C and a similar oxygen half-saturation constant, K(O) (0.54+/-0.14 mgL(-1)). The major differences identified were that Nitrospira had a lower nitrite half-saturation constant, K(S) (0.9+/-0.07 mgNO(2)-NL(-1)); lower inhibition threshold concentrations for free ammonia (between 0.04 and 0.08 mg NH(3)-NL(-1)) and free nitrous acid (less than 0.03 mg HNO(2)-NL(-1)) and a higher yield (0.15+/-0.04 g VSS g N(-1)). Therefore, Nitrospira is more likely to dominate nitrite oxidation under conditions with low ammonium and nitrite concentrations, which would provide an advantage to them due to their lower K(S) value while avoiding any free ammonia or free nitrous acid inhibition.     

Compression and extension yield of an anisotropically consolidated soil

A series of undrained and drained triaxial tests were conducted to investigate the yielding behavior of anisotropically consolidated reconstituted Shanghai clay under triaxial compression and extension loading conditions. The soil was consolidated with K of 0.5, where K is the ratio of cell pressure to axial pressure. The tests included drained constant η (=q/p′) loading tests and undrained and drained triaxial compression and extension shear tests on anisotropically consolidated specimens. It was found that the anisotropically consolidated Shanghai clay obeys Rendulic’s principle under compression loading, but not under extension loading, and that the yield surface inclined inside the state boundary surface under extension loading. Moreover, the pre-yield behavior and the post-yield behavior were found to be very different under these two loading conditions (compression and extension loading). The test results confirm the validity of the sloping elastic wall theory, and the influence of anisotropic parameter β on the shape of the yield curve in the p′?v plane was also studied in the paper. Constitutive modeling methods for anisotropic consolidated soils were also discussed based on the test results.     

Effects of water content,water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

The pumping ability and placement performance of fresh cemented paste backfill(CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement(PC), a newly released commercially manufactured cement called Minecem(MC) and fly ash(FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature(25 °C), with regards to the unconfined compressive strength(UCS) performance, the replacement of 4% PC mixed CPB(28 days UCS 425 k Pa) to 3% MC mixed CPB(28 days UCS 519 k Pa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water(MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.     

Tailoring the Texture and Mechanical Anisotropy of Multi-cross Rolled Mg-Zn-Gd Alloy by Annealing

The unidirectional rolled Mg-Zn-Gd sheet usually exhibited non-basal texture with two peaks whose tilting angle were about 42° from normal direction to transverse direction (TD), which would cause the mechanical anisotropy. In this study, multi-cross rolling followed by annealing was used to tailor the texture and mechanical anisotropy for Mg-Zn-Gd alloy. With increasing annealing temperature, the rolled basal texture with two peaks gradually transformed into the circle texture with multi-peaks. In order to figure out different texture components evolution during annealing, the basal texture, R-texture and T-texture component were defined and studied. The results showed that the change of R-texture and T-texture component was asynchronous with increasing annealing temperature from 250 to 400 °C. The tilting angle of R-texture component increased slightly, while the tilting angle of T-texture component increased obviously, and this phenomenon was attributed to the preferential nucleation at grain nucleation stage rather than preferential grain growth. The yield strength along TD was more sensitive to annealing temperature compared with that along rolling direction (RD), resulting in different descending slopes and yield strength anisotropy with increasing annealing temperature. Annealing at 300 °C was the best annealing temperature due to low yield strength anisotropy, moderate strength and good elongation among these annealing temperatures. The Schmid factor for basal slip indicated that the activity of basal slip along RD increased slightly, while that along TD increased obviously with increasing annealing temperature from 250 to 400 °C, which should be caused by the asynchronous change of R-texture component and T-texture component, consequently resulting in the transformation from isotropic yield strength to anisotropic yield strength.     

碱酸联合处理法ZSM-22沸石介孔改性研究

通过水热合成及铵交换制备不同硅铝比的氢型沸石H-ZSM-22;用碱、酸介质对H-ZSM-22样品进行介孔改性。研究起始沸石硅铝比对改性沸石相对结晶度、介孔结构、晶貌和产率的影响。N2吸附-脱附和XRD分析表明,改性沸石兼有结晶性的微孔-介孔结构;随着起始沸石n(Si)∶n(Al)由31.7增至43.2,改性沸石介孔体积出现极大值而结晶度保留率和产率呈相反的变化趋势;典型样品[n(Si)∶n(Al)=37.0]的介孔体积高达0.44cm3/g,结晶度保留率和相对产率分别为56.0%、44.4%。SEM观察显示,改性沸石的附加介孔结构主要源于H-ZSM-22骨架脱硅、脱铝产生的结构缺陷。