锻造液压机振动特性机液联合仿真

以YA32-315锻造液压机为研究对象，基于ADAMS、AMESim和ABAQUS平台，建立了锻造液压机弹性动力学联合仿真模型，研究了卸载冲击作用下锻造液压机均载和偏载工况的振动特性，分析了锻造力、系统压力、偏载量对振动特性的影响规律，结果表明：锻造力和偏载量越大，冲击越大；偏载量相同时，Y向振动大于X向振动；系统压力对振动影响不大。振动测试实验验证了联合仿真模型的正确性。     

Improved properties of low-carbon MgO-C refractories with the addition of multilayer graphene/MgAl2O4 composite powders

The paper investigated the effects of different amounts (0%, 3%, 6%, 9%) of in situ multilayer graphene/MgAl₂O₄ composite powders on the slag resistance, thermal shock resistance, and oxidation resistance of low-carbon MgO-C refractories. Comparing with commercial MgAl₂O₄, the MgAl₂O₄ in in situ multilayer graphene/MgAl₂O₄ composite powders has higher lattice strain of crystal, which can trap more Mn and Fe ions, resulting in the better slag resistance. The oxidation decarbonation layer of MgO-C specimen with 3% composite powders is 9.71 mm, which is lower than not only the specimen with other contents but also specimen containing carbon black/MgAl₂O₄ powders. Moreover, the residual strength ratio of the specimen C/MA-3 was 47.47%, which is 28.5% and 8.08% higher than specimens with no additive and with carbon black/MgAl₂O₄ powders, respectively. Both improving thermal shock and oxidation resistance properties are related with the unique nano structure, multilayer graphene in situ formed between MgAl₂O₄ grains, of added composite powders. The former is due to higher strain energy consumed by multi-deflection of cracks inside the multilayer graphene/MgAl₂O₄ composite powders. And the latter is due to the higher energy of oxidation activation of multilayer graphene/MgAl₂O₄ composite powders due to effective protection of multilayer graphene by MgAl₂O₄.     

Ti6Al4V钛合金表面Al2O3颗粒改性微弧氧化涂层制备及性能

微弧氧化技术是一门新的表面处理技术,在很多领域有着广泛的应用前景,但其结构受限于电解液成分。本文通过在磷酸盐电解液中加入Al2O3陶瓷颗粒,使得在Ti6Al4V钛合金表面的微弧氧化涂层结构和性能得到改性。涂层的结构和性能通过扫描电镜和XRD衍射仪进行表征和测试,涂层的抗高温氧化性能和热震性能通过高温热循环氧化试验和热震试验进行测试。结果表明,通过在电解液中添加Al2O3陶瓷颗粒,涂层由Al2TiO5 and TiO2组成,涂层更为致密,表现出更为优异的抗高温氧化和热震性能。电解液中游动的Al2O3陶瓷颗粒在微弧氧化过程中被吸入到样品表面并进入涂层,涂层的结构和性能得到改性。     

Effect of particle grading on fracture behavior and thermal shock resistance of MgO-C refractories

Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl₂O₄) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.     

Thermal shock effects on the impact resistance,tolerance and flexural strength of alumina based oxide/oxide ceramic matrix composites

In this study the effects of thermal shock on the impact damage resistance, damage tolerance and flexural strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates with balanced and symmetric layup were gradually heated to 1200°C in an air-based furnace and held for at least 30 min before being removed and immersed in water at room temperature. The laminates were then subjected to low velocity impacts via a hemispherical steel impactor. The resultant damage was characterized non-destructively, following which the laminates were subjected to compression tests. Three-point bend tests were also performed to evaluate the effect of thermal shock on the flexural strength and related failure modes of the laminates. Thermally shocked laminates showed smaller internal damage and larger external damage areas in comparison to their pristine counterparts. For the impact energy and resultant damage size considered, the residual compressive strengths for the thermally shocked and pristine laminates were similar.     

Virtual fencing technology to intensively graze lactating dairy cattle. II: Effects on cow welfare and behavior

Virtual fencing technology uses a neckband-mounted device to deliver an audio cue when an animal nears a virtual boundary that is set via a global positioning system, followed by an electrical stimulus if it crosses the boundary. The flexibility offered by this technology could revolutionize grazing management on dairy farms, but its application and effects on lactating dairy cattle have not been assessed. This experiment reports on the effects of an electric or a virtual front-fence on dairy cow behavior and welfare. Two temporally separated treatments were applied to a herd of 30 multiparous cows. Cows were provided an estimated 14 to 15 kg of dry matter/cow of fresh pasture in a new paddock every 24 h. From d 1 to 10 cows were grazed using a conventional electric front-fence (control treatment) and from d 14 to 23 they were grazed using a virtual front-fence (eShepherd, Agersens Pty Ltd.). Cows were trained to the technology from d 11 to 13. The milk production and live weight of individual cows were recorded daily. Cortisol concentrations were obtained from milk samples collected from individual cows on 3 d during each of the control and the virtual fence grazing periods, plus the first day of training. From d 6 of the experiment, 6 focal cows were fitted with a RumiWatch (Itin + Hoch GmbH) noseband sensor to monitor grazing and ruminating time, and 8 focal cows were fitted with an IceTag (IceRobotics Ltd.) sensors to monitor activity. Milk production, live weight, and the time cows spent standing and lying did not differ between the electric and virtual fence periods. Milk cortisol concentrations, activity, and the times spent ruminating and grazing were comparable between the electric and early virtual fence periods (i.e., d 1–3 with a virtual fence). However, at d 4 to 6 with a virtual fence, activity (steps taken and motion index) and time spent grazing were lower, and time spent ruminating was greater, compared with an electric fence. Further, least significant difference tests suggest milk cortisol concentrations were higher at d 5 with a virtual fence than at d 8 with an electric fence and d 1 with a virtual fence. We conclude there is no evidence of behavioral and welfare effects of virtual fencing on dairy cows in the days immediately following implementation of the technology in a simple intensive grazing regimen, but a longer study is required to fully elucidate effects beyond this period.     

Deionization shocks in crossflow

Shock electrodialysis is a recently developed electrochemical water treatment method that shows promise for water deionization and ionic separations. Although simple models and scaling laws have been proposed, a predictive theory has not yet emerged to fit experimental data and enable system design. Here, we extend and analyze existing “leaky membrane” models for the canonical case of a steady shock in crossflow, as in recent experimental prototypes. Two-dimensional numerical solutions are compared with analytical boundary-layer approximations and experimental data. The boundary-layer theory accurately reproduces the simulation results for desalination, and both models predict the data collapse of the desalination factor with dimensionless current, scaled to the incoming convective flux of cations. The numerical simulation also predicts the water recovery increase with current. Nevertheless, neither approach can quantitatively fit the transition from normal to over-limiting current, which suggests gaps in our understanding of extreme electrokinetic phenomena in porous media.     

岩石爆破损伤模型实验研究

岩石中含有以孔隙、气泡、微观裂隙、节理面等形态表现出来的岩石损伤。损伤的存在无疑要对岩石的爆破破碎效果产生影响。本文在相似性分析的基础上,提出了在实验室进行岩石爆破损伤模型实验的新方法,进而对损伤以及介质强度对爆破破碎效果的影响进行了分析研究。