水平井分段体积压裂复杂裂缝形成机制研究现状与发展趋势

水平井分段体积压裂是油气储层中复杂裂缝网络形成的重要技术之一，准确了解复杂裂缝网络形成机制、预测复杂裂缝网络形态对非常规油气资源高效开发具有重要意义，同时也是水力压裂设计优化的理论基础。围绕非常规储层复杂裂缝形成机制，国内外学者根据"应力阴影"效应对水力裂缝同步扩展、水力压裂顺序对多裂缝动态延伸影响、层理面对水力裂缝纵向扩展遮挡效应和天然裂缝与水力裂缝交互动态等方面，分别建立了相应的水力压裂模型，并从数值模拟角度对其进行了定性分析。通过总结国内外研究现状，并从模型建立假设条件、数值模拟模型思想和模型局限性3方面对现有模型进行了剖析，并对未来研究方向提出了建议，研究结果可对未来水力压裂复杂裂缝形成机制研究提供借鉴。     

汽车悬架球头拉杆冷成形技术

为提高生产效率、改变原来通过车削加工汽车悬架球头拉杆的方式,提出了一种球头拉杆的多工位冷镦成形工艺。基于DEFORM-3D软件建立了有限元模型,对球头拉杆的塑性成形过程进行了仿真,研究了预成形凸模入模角α、预成形凹模圆角R1、终成形凹模圆角R2以及终成形凹模入模角β等工艺参数对球头拉杆成形的影响,并进行了正交试验,以模具在球头拉杆成形过程中所受载荷及工件损伤值为优化目标,获得了合理的工艺参数组合。结果表明:在保证工件成形质量及模具寿命的前提下,当预成形凸模入模角α为30°、预成形凹模圆角R1为12 mm、终成形凹模圆角R2为3 mm、终成形凹模入模角β为60°时,模具载荷及工件损伤有显著的降低。采用优化后的参数进行试模生产,工件成形质量较好,验证了模拟结果的可信性,能够有效地指导工艺设计人员的设计工作。     

Thermally driven failure of Nd:YVO4 amplifier crystals

We report on an unusual failure pattern resulting from thermally driven fracture of laser amplifier single crystals. The pattern led to some confusion with regard to the point of initiation due to the coalescence of hackle lines to a region within the fracture surface, rather than the more common divergence of hackle away from the origin. The pattern leads to new fracture terms: Hackle node - the coalescence of hackle marks to a point of prior compression. The feature is produced as a thermally-generated, centrally-located compressive region transforms to tension thereby drawing crack propagation and hackle to the compressive region, forming an internal terminus. Hackle terminus – a hackle node formed by final crack propagation within the component. As part of the analysis, the fracture toughness and slow crack growth constants of neodymium doped, yttrium ortho-vanadate (Nd:YVO₄) were measured. Nd:YVO₄ exhibits slow crack growth and is very brittle with a fracture toughness of only 0.48 MPa√m.     

Damage formation and suppression in rotary ultrasonic machining of hard and brittle materials: A critical review

Rotary ultrasonic machining (RUM) combines diamond grinding with small-amplitude tool vibration, to improve machining processes of hard and brittle materials. It has been successfully applied to the machining of a number of brittle materials from optical glasses to advanced ceramics as well as ceramic matrix composites. The emphasis of this literature review was on formation mechanism and suppression methods of machining induced damages that truly limit RUM machining efficiency improvement of brittle materials. In this review paper, material removal mechanism and cutting force modeling of RUM of brittle materials were presented, as well as all corresponding roles in the damage formation process. The critical processing capacity of RUM machine tools was described, which guarantees the RUM effectiveness and consequently constitutes the boundary condition of processing parameters determination. Formation mechanisms of edge chipping, tearing defects, subsurface damages, and their interactive effects were summarized. Advances in damage suppression methods were also described, including optimization of processing parameters, tool design of low damage, and other methods such as rotary ultrasonic elliptical machining.     

Numerical simulation of the effects of elastic anisotropy and grain size upon the machining of AA2024

Turning modeling and simulation of different metallic materials using the commercially available Finite Element (FE) softwares is getting prime importance because of saving of time and money in comparison to the costly experiments. Mostly, the numerical analysis of machining process considers a purely isotropic behavior of metallic materials; however, the literature shows that the elastic crystal anisotropy is present in most of the ‘so-called’ isotropic materials. In the present work, the elastic anisotropy is incorporated in the FE simulations along with the effect of grain size. A modified Johnson-Cook ductile material model based on coupled plasticity and damage evolution has been proposed to model the cutting process. The simulation results were compared with experimental data on the turning process of Aluminum alloy (AA2024). It was found that the elastic anisotropy influences the average cutting force up to 5% as compared to the isotropic models while the effect of grain size was more pronounced up to 20%.     

Influence of initial ovality on creep life of P92 pipe bends subjected to in-plane bending

Initial ovality is an inevitable problem in the process of pipe bends manufacturing which results in the stress redistribution of the pipe bends working at high temperature. In order to study the influence of ovality on creep life of pipe bends, full-size creep experiment of P92 pipe bend subjected to in-plane bending has been conducted. The creep strains and outside diameters of dangerous positions have been measured. The microstructures of three different positions of the pipe bend were compared through SEM and the results showed the number and size of the carbide precipitation were the largest at the flank of the pipe bend, which indicated that the creep damage developed fastest at the flank. The modified Kachanov–Robatnov constitutive equations were used to stimulate the creep of P92 pipe bends with FEA software. The representative stress, damage and multiaxiality distributions of the pipe bends have been discussed. The FEA results were consistent with the experimental results and the influence of initial ovality on creep life of P92 pipe bends were analyzed. The results showed that creep life of pipe bends reduced by the increase of ovality and their relationship coincided with the parabolic law.     

The impact of flood risk on the price of residential properties: the case of England

This paper examines the impact of flood risk on the value of English residential properties. We find that a location within a flood zone significantly lowers property values even if we control for the proximity to a watercourse, the history of flooding and neighbourhoods effects. Although the flood risk discount is more compelling for waterfront properties, it is still highly significant for dwellings further from the water. The markdown arises around 2004–2005, which coincides with the publication of detailed flood maps by the UK Environment Agency and with a more risk-based pricing of flood insurance policies. As expected, the effect of flood risk on house prices is stronger in the months following major flood events but, interestingly, it almost disappears in a hot market when buyers have arguably less negotiating power.     

Healable,Recyclable, and Mechanically Tough Polyurethane Elastomers with Exceptional Damage Tolerance

There is a huge requirement of elastomers for use in tires, seals, and shock absorbers every year worldwide. In view of a sustainable society, the next generation of elastomers is expected to combine outstanding healing, recycling, and damage-tolerant capacities with high strength, elasticity, and toughness. However, it remains challenging to fabricate such elastomers because the mechanisms for the properties mentioned above are mutually exclusive. Herein, the fabrication of healable, recyclable, and mechanically tough polyurethane (PU) elastomers with outstanding damage tolerance by coordination of multiblock polymers of poly(dimethylsiloxane) (PDMS)/polycaprolactone (PCL) containing hydrogen and coordination bonding motifs with Zn²⁺ ions is reported. The organization of bipyridine groups coordinated with Zn²⁺ ions, carbamate groups cross-linked with hydrogen bonds, and crystallized PCL segments generates phase-separated dynamic hierarchical domains. Serving as rigid nanofillers capable of deformation and disintegration under an external force, the dynamic hierarchical domains can strengthen the elastomers and significantly enhance their toughness and fracture energy. As a result, the elastomers exhibit a tensile strength of ≈52.4 MPa, a toughness of ≈363.8 MJ m⁻³, and an exceptional fracture energy of ≈192.9 kJ m⁻². Furthermore, the elastomers can be conveniently healed and recycled to regain their original mechanical properties and integrity under heating.     

Aromatic Linkers Unleash the Antiproliferative Potential of 3-Chloropiperidines Against Pancreatic Cancer Cells

In this study, we describe the synthesis and biological evaluation of a set of bis-3-chloropiperidines (B−CePs) containing rigid aromatic linker structures. A modification of the synthetic strategy also enabled the synthesis of a pilot tris-3-chloropiperidine (Tri-CeP) bearing three reactive meta-chloropiperidine moieties on the aromatic scaffold. A structure–reactivity relationship analysis of B−CePs suggests that the arrangement of the reactive units affects the DNA alkylating activity, while also revealing correlations between the electron density of the aromatic system and the reactivity with biologically relevant nucleophiles, both on isolated DNA and in cancer cells. Interestingly, all aromatic 3-chloropiperidines exhibited a marked cytotoxicity and tropism for 2D and 3D cultures of pancreatic cancer cells. Therefore, the new aromatic 3-chloropiperidines appear to be promising contenders for further development of mustard-based anticancer agents aimed at pancreatic cancers.     

过硫酸盐活化方式与氧化降解有机物效能及其在污染场地修复中的应用

过氧单硫酸盐（PMS）及过二硫酸盐（PDS）在工业污染场地修复中应用广泛，通过活化作用能够产生氧化性更强的·\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\text{-}}自由基，从而更好地氧化降解有机污染物。本文比较了几种典型活化方式，包括紫外（UV）、碱、过渡金属、热以及含碳物质，并分析了它们的优缺点及适用条件；讨论了过硫酸盐活化机理及动力学过程；分析了无机阴离子（Cl^-、\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\text{-}}\text{/}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{2}\text{-}}、\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{\text{-}}、\mathrm{N}{\mathrm{O}}_{\mathrm{2}}^{\text{-}}、\mathrm{H}\mathrm{P}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}\text{-}}、{\mathrm{H}}_{\mathrm{2}}\mathrm{P}{\mathrm{O}}_{\mathrm{4}}^{\text{-}}）与·\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\text{-}}自由基相互作用及其对有机污染物氧化降解的影响；针对活化过硫酸盐在工业污染场地修复领域的应用，对过硫酸盐活化方法的发展趋势进行了展望。理论研究和实践表明，过硫酸盐不同活化方式为工业污染场地修复提供了多样选择，多种活化方式协同作用将是过硫酸盐高效活化氧化降解有机污染物的发展方向。由于Cl^-、\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\text{-}}\text{/}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{2}\text{-}}抢夺·\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\text{-}}的能力较强，认为这些无机盐与有机物复合的污染场地或土壤采用PDS修复需格外谨慎选择活化方法。