Laboratory evaluation of interfacial mechanical properties in geogrid-reinforced bituminous layers

In this study, the mechanical properties of composite bituminous structures with geogrid products, used as an interlayer between different types of bituminous mixtures, at a constant temperature, were examined. A twofold experimental program based on new approaches was selected. A new configuration of the 3-Point Bending Test (3-PBT) was adopted to capture the J-integral and crack resistance property defined by crack resistance index (CRI) at the interface against bottom-up crack propagation. The bonding quality at the interface was also defined through a new index named coefficient of interface bonding (CIB), which was measured via a modified version of the slant shear device. The results derived from this research revealed that reinforcement of the interface, with varying degree of surface texture, by geogrid products significantly enhances the fracture toughness of the whole system in terms of the J-integral, which could be properly connected to the combined functions of bonding quality and crack resistance indices defined at the interface.     

Oxygen vacancies as a link between the grain growth and grain boundary conductivity anomalies in titanium-rich strontium titanate

Titanium-rich (Sr/Ti?=?0.995) strontium titanate (ST) ceramics, air-sintered in a temperature range of 1400–1625?°C, were reported to possess anomalies in the grain growth and analogous anomalies in the grain boundary (GB) conductivity activation energy. However, these two interface-related phenomena, occurring at GBs, could not be associated with each other using a simple “brick-layer” model. In this work we revise the topic and advocate that the deviation from the model comes from the oxygen vacancies localized at GBs of the rapidly-cooled ST ceramics. To verify this, we annealed the ceramics in oxygen and performed their systematic and comparative analysis using impedance spectroscopy. A levelling-off in the GB conductivity activation energy, which increases for ≤1.24?eV, and a four-fold decrease in the GB permittivity are observed after annealing. Thus, we confirm a key role of oxygen vacancies in relation between the grain growth and GB conductivity anomalies of as-sintered Ti-rich ST ceramics.     

Mullite-bonded SiC-whisker-reinforced SiC matrix composites: Preparation,characterization, and toughening mechanisms

A novel mullite-bonded SiC-whisker-reinforced SiC matrix composite (SiCw/SiC, SiC whisker-to-SiC powder mass ratio of 1:9) was designed and successfully prepared. Before preparing the composite, the inexpensive lab-made SiCw was first modified by an oxidation/leaching process and then coated with Al₂O₃. The kinetics results indicate that the oxidation process can be described by improved shrinking-cylinder models. The aspect ratio of SiCw improved after modification. Subsequently, raw materials with a SiC–SiO₂–Al₂O₃ triple-layered structure were obtained after the Al₂O₃-coating process and used as feedstocks during the subsequent hot-pressing sintering. Finally, the characterization of the composites indicates that the mullite-bonded sample performs better (relative density of 93.8?±?1.4%, flexural strength of 533.3?±?18.2?MPa, fracture toughness of 13.6?±?2.1?MPa?m^1/2, and Vickers hardness of 20.6?±?2.5?GPa) than the reference sample without the mullite interface. The improved toughness could essentially be attributed to the moderately strong interface bonding and effective load transfer effects of the mullite interface.     

四川盆地高石梯-磨溪地区下二叠统气源示踪

以天然气、烃源岩及储层沥青的地球化学特征为主要依据,通过天然气-天然气、储层沥青-烃源岩、天然气-烃源岩3个方面对比,深入探讨四川盆地高石梯-磨溪地区下二叠统天然气来源。研究表明,四川盆地高石梯-磨溪地区下二叠统天然气主要来源于筇竹寺组泥岩。其5项证据分别为:下二叠统天然气乙烷碳同位素小于-30.5‰,甲、乙烷碳同位素倒转是由高演化程度烃源岩所致;多数下二叠统天然气与龙王庙组天然气特征最为相似;GS18,NC1井下二叠统天然气特征与寒武系相似,说明上下层气源一致;高石梯-磨溪地区下二叠统储层沥青地球化学特征与筇竹寺组泥岩最为相似;筇竹寺组泥岩主要为下二叠统供气,这一认识符合干酪根油气生成理论和同位素分馏规律。     

矿井顶板水探测方法及富水区成因分析

某矿1303工作面为三采区首采工作面，顶板含水层主要为第四系含水层、K₁₀和K₈砂岩裂隙含水层。为了解顶板K₁₀和K₈砂岩裂隙含水层的富水性，在1303工作面运输巷布置了覆盖全工作面的10个钻场（46个顶板探放水钻孔）进行探测，结合地表钻孔的顶板覆岩规律以及抽水试验结果可知，K₁₀和K₈砂岩裂隙含水层属于弱富水含水层，在2号钻场和8号钻场周边局部存在局部富水区；局部富水区均与构造有关，2号钻场位于背斜翼部，8号钻场位于向斜轴部，而背斜翼部和向斜轴部易出现砂岩裂隙带，成为地下水的富集区。     

扩散退火和热轧温度对钛铜界面结合强度的影响

对热挤压的钛铜复合棒进行扩散处理,研究扩散退火温度及保温时间对界面结合强度的影响,并通过测试Ti和Cu在高温下的拉伸性能来选择较为合适的热轧温度。结果表明:扩散退火可有效促进界面处金属原子的扩散和增强结合强度,当扩散退火在780～800 ℃/30 min时复合界面的结合强度最高;钛铜复合棒热轧温度应选择780 ℃较为合适,此时Ti、Cu的强度和塑性指标相近,利于热轧时的均匀变形;钛铜复合棒的热轧结合机理可用N.Bay理论、热作用机制及位错学说进行解释。     

翅片结构对单向开缝翅片管换热器传热与阻力性能的影响

通过对不同开缝数量、不同相对开缝高度的单向开缝翅片管换热器进行模拟,分析开缝数量、相对开缝高度对单向开缝翅片管换热器传热与阻力性能的影响规律。结果表明:在开缝数量为3～7片时,翅片侧Nu和f因子随着开缝数量的增加而增大,但Nu增幅逐渐减小;将开缝的数量取为5片能得到最好的综合性能;在相对开缝高度为0.3～0.7时,翅片侧Nu和f因子随着相对开缝高度的增加而增大,但当相对开缝高度在0.5～0.7范围内,翅片侧Nu的增幅减小;将相对开缝高度取为0.5能得到最好的综合性能。     

Effect of Ni-coated MoS2 on microstructure and tribological properties of (Cu−10Sn)-based composites

The (Cu−10Sn)−Ni−MoS₂ composites, prepared by powder metallurgy, were studied for the effects of Ni-coated MoS₂ on the microstructure, mechanical properties and lubricating properties. The mechanism of effects of Ni and MoS₂ on the properties of composites was analyzed through a comparative experiment by adding Ni and MoS₂ separately. The results show that the nickel wrapping around the MoS₂ particles decreases the reaction rate of MoS₂ with the copper matrix, and greatly improves the bonding of the matrix. The composites with 12 wt.% Ni-coated MoS₂ (C12) show the optimum performance including the mechanical properties and tribological behaviors. Under oil lubrication conditions, the friction coefficient is 0.0075 with a pressure of 8 MPa and a linear velocity of 0.25 m/s. The average dry friction coefficient, sliding against 40Cr steel disc, is measured to be 0.1769 when the linear velocity and pressure are 0.25 m/s and 4 MPa, respectively.     

Bonding strength and thermal shock resistance of a novel bilayer (c-AlPO4-SiCw-mullite)/SiC coated carbon fiber reinforced CMCs

Mullite coating, SiC whiskers toughened mullite coating (SiC_w-mullite), and cristobalite aluminum phosphate (c-AlPO₄) particle modified SiC_w-mullite coating (c-AlPO₄-SiC_w-mullite) were prepared on SiC coated C/SiC composites using a novel sol-gel method combined with air spraying. Results show that molten SiO₂ formed by the oxidation of SiC whiskers and molten c-AlPO₄ improved the bonding strength between mullite outer coating and SiC–C/SiC composites due to their high-temperature bonding properties. The bonding strength between mullite, SiC_w-mullite, c-AlPO₄-SiC_w-mullite outer coatings and SiC–C/SiC composites were 2.41, 4.31, and 7.38 MPa, respectively. After 48 thermal cycles between 1773 K and room temperature, the weight loss of mullite/SiC coating coated C/SiC composites was up to 11.61%, while the weight losses of SiC_w-mullite/SiC and c-AlPO₄-SiC_w-mullite/SiC coatings coated C/SiC composites were reduced to 7.40% and 5.12%, respectively. The addition of appropriate SiC whiskers can considerably improve the thermal shock resistance of mullite coating owing to their excellent mechanical properties at high temperature. In addition, c-AlPO₄ particles can further improve the thermal shock resistance of SiC_w-mullite coating due to their high-temperature bonding and sealing properties. No obvious micro-pores and cracks were observed on the surface of c-AlPO₄-SiC_w-mullite coating after 48 thermal cycles due to timely healing effect by formation of secondary mullite.     

近地表采空区处理及残矿开采技术研究与应用

某铅锌矿采用分段空场嗣后法开采,由于充填系统建设滞后导致近地表开采区域遗留大面积采空区及矿柱。针对采空区及残矿赋存现状,运用中深孔顶板及矿柱联合崩落的方式,崩落近地表采空区顶板隔离层及矿柱。采空区顶板及矿柱崩落后利用井下现有出矿系统集中出矿,出矿结束后对采空区进行充填。该技术方案有效消除采空区垮塌的安全隐患同时回采矿柱残矿,为同类矿山采空区处理及残矿回采提供技术参考。