基于非线性强度准则的土工结构安全系数有限元计算

将幂律型广义非线性强度准则应用到土工结构安全系数计算中,令土体强度逐渐降低,直至结构破坏,得到最终的安全系数,并开发了基于幂律型广义非线性强度准则的有限元强度折减法程序。该方法不需事先假设滑裂面,计算方便可靠,能适用于各种复杂地质条件。作为算例,该文分别采用线性和非线性两套指标计算了一常见高土石坝和一机场高填方边坡的安全系数。在线性指标下该文方法与PLAXIS内置有限元强度折减法计算结果一致,相对非线性指标,线性指标计算的滑裂面偏浅,计算的安全系数大小随线性参数的确定方法不同而不同。建议使用非线性强度指标计算高围压下土工结构的安全系数。     

基于坡面卸荷的土质边坡应力状态及稳定性分析

边坡稳定性分析中极限平衡法难以考虑土体应力状态,坡体滑面应力计算又长期停留在数值方法上。为解决这一问题,提出坡面卸荷应力等效思路,将坡面按半无限边界考虑后利用弹性理论求解坡体应力,并根据滑面应力进行稳定性安全系数计算,最后结合多个算例将潜在滑动面位置、滑面应力分布、安全系数与已有理论进行比较。研究结果表明:坡面卸荷应力等效思路概念清晰,符合边坡受力特征,且通过该思路求得的滑面应力与有限元分计算结果基本一致,搜索得到的潜在滑动面位置,以及对应的稳定性安全系数与有限元强度折减法、极限平衡法计算结果十分接近。此外,该计算方法还能有效与支护结构预应力结合,体现预应力的加固作用。     

埋入式抗滑桩承担的滑坡推力分析

采用有限元强度折减法对埋入式抗滑桩加固的滑坡模型进行了数值分析。模拟结果表明,在设计工况下埋入式桩承担的滑坡推力与全长桩承担的滑坡推力相当,推力大小与设计安全系数有关。在极限破坏工况下,桩悬臂段越长,滑体越顶滑动破坏时对应的稳定安全系数也越大,桩承担的滑坡推力越大。由此提出埋入式抗滑桩加固滑坡设计时,埋入式桩的合理桩长可采用强度折减数值方法根据设计安全系数确定,埋入式桩应承担的滑坡推力可用传统极限平衡法按全长桩计算,也可用有限元强度折减法进行校核。     

西南山区机场高填方边坡反压护道优化设计

针对西南山区机场高填方地基存在有限深度相对软弱土层的工程地质情况,提出单级反压护道的优化设计方法及优化设计中所涉及到的各类典型滑移面稳定安全系数的简化计算方法,并对其进行了证明及验证,分析了所提方法计算结果与强度折减有限元法的差别大小及方法的适用性。验证结果表明:所提方法计算的安全系数与有限元计算结果的相对误差均不超过12%;计算的反压护道断面尺寸相对误差不超过20%;应用于有硬壳层的工程地质条件或有反压护道的典型滑移面时,误差更小。     

复理石顺层边坡最危险岩层倾角及简化的单一层面模型

最危险岩层倾角为0°～90°范围内使边坡安全系数最小的岩层倾角,该倾角是对顺层边坡稳定性最不利的岩层产状。以由岩块和岩层面组成的层状边坡为分析对象,采用有限元极限分析法的隐式节理模型分析了不同坡角对应的最危险岩层倾角。结果表明:最危险岩层倾角随坡角的增大而增大,对应安全系数的变化规律相反,最危险岩层倾角下的破坏均为整体顺层滑移破坏;通过极限平衡法得到最危险岩层倾角的理论公式,计算结果与有限元极限分析法偏离不超过2%;在众多岩层面中,对缓倾顺层边坡稳定性起决定性作用的为过坡脚的层面,采用单一层面简化模型得到的边坡破坏模式与常规模型相近,安全系数偏离不超过3%,缓倾顺层边坡可利用此模型进行简化的边坡稳定分析。     

边坡渐进破坏多参量评价指标

传统的强度折减法就是以强度折减表征岩土体破坏后区的软化力学行为,该折减系数实质为描述边坡的整体稳定系数,但物理意义不明显。边坡稳定性是一个与众多因素相关的复杂科学课题,当边坡局部处于破坏后区应力状态时,其整体并不一定发生破坏,这种由破坏区和非破坏区组成的整体实质为非稳定力学系统,难以用连续介质力学的方法获得真实解。该研究提出了描述边坡点、面(滑面)和体(滑体)的多参量稳定性评价指标;定义了点破坏、面破坏(破坏面积比、破坏应力率、破坏应变率、摩擦力变化系数、正压力变化系数、下滑力变化系数、滑面位移变化系数等)和体破坏(富余摩阻力稳定系数、主推力稳定系数、富余摩阻力稳定系数、综合位移稳定系数、富余位移稳定系数等)边坡多参量稳定性评价指标,用来对边坡点破坏、滑面扩展、连通等实施全方位演化过程描述。并充分利用部分强度折减法、理想弹塑性模型、全过程本构模型等揭示滑坡点、面和体多参量随位移和力的变化规律;以传统和推广的不平衡推力条分法为例,利用多参量描述边坡的渐进破坏过程,揭示了在边坡临界状态一步一步移动过程中点、面及体的全过程多参量稳定性演化特征。大冶市桃花山边坡计算结果表明:多参量稳定性评价指标可以较好地描述桃花山边坡各特征量的演化规律,且基于理想弹塑性模型的部分强度折减条分法点、面描述参量(破坏率、破坏比等)的值小于全过程剪应力-应变本构模型的值,边坡整体稳定系数(主推力法、综合位移法和富余位移法)描述指标大于全过程剪应力-应变本构模型,但富余摩阻力法稳定系数则相反等。该研究重点是建立了边坡多参量稳定性评价指标,并使传统的稳定系数可以和该文建议的方法加以比较,为边坡监测预警提供了理论支撑。     

爆破荷载作用下露天边坡稳定性分析

露天边坡的稳定性受爆破振动作用影响较大,为进一步分析研究爆破振动作用下露天边坡的稳定性特征,对露天边坡的静力稳定性进行分析,得到边坡在静力条件下的位移、应力和静力安全系数,并在静力计算的基础上,计算边坡在爆破振动下的动态响应特征,进而求得爆破荷载下边坡的位移、应力及动力安全系数等响应特征,可以来分析边坡在爆破振动作用下的稳定状态.利用ANSYS有限元软件,采用强度折减法对别矿露天边坡在静力和动力荷载条件下的稳定状态进行分析,得出爆破荷载下边坡的安全振速和临界振速.仅考虑边坡自重下时的安全系数为1.66,处于稳定状态;在不同强度爆破荷载作用下边坡的安全系数分别为1.46、1.5、1.56、1.62,相对静力条件下安全系数衰减了2.4％ ～12％.通过安全系数与水平径向振动速度关系,推导出了南帮边坡的安全振动速度为10.64 cm/s,临界振动速度为13.16 cm/s.     

基于有限单元法的岩土边坡动力稳定分析及评价方法研究进展

该文给出了基于有限元法的岩土边坡动力稳定分析的主要方法,对这些分析方法进行了较为详细的表述和分析,在此基础上提出了平均地震系数计算的新方法,即对潜在滑动区域分块按有限元法计算地震系数,进而再按拟静力法计算安全系数。为了考虑滑动体变形对地震稳定系数和永久变形的影响,应建立地震响应与地震永久变形相耦合的计算方法。指出边坡在地震荷载作用下产生的永久位移或累积变形作为边坡稳定性评价指标是科学合理的。最后提出了基于性态的边坡抗震设计方法,包括边坡抗震性态水准的划分、性能指标的建立和抗震设计方法。     

基于强度折减法的边坡动力稳定性研究

基于强度折减法,利用有限元软件ANSYS建立二维边坡模型,采用Plane82单元进行网格划分,并对可能出现的滑坡体细化网格,研究爆破荷载作用下的边坡动力稳定性。以计算不收敛作为边坡失稳的判定准则,求得边坡静力安全系数为2.36;以边坡坡底节点位移突变作为边坡动力失稳的判定准则,求得爆破动荷载作用下的边坡动力安全系数为2.24。模拟结果表明:给定边坡在当前爆破动荷载作用下,其动力安全系数相对于静力安全系数降低了5.08%。通过对坡底节点位移时程曲线的变化规律进行研究发现,随着边坡抗剪强度参数的折减,边坡坡底节点的水平最大位移也在缓慢增加,主要是由于边坡强度折减造成的塑性位移增加。     

地震作用下土钉支护边坡稳定性计算方法

考虑土钉对土质边坡稳定性影响的情况下,根据土体边坡滑动面的破坏模式,拟静力法,建立了地震作用下土钉支护边坡稳定性模型,推导了边坡滑移面圆心位置与稳定系数之间的函数关系.在水平地震作用下,竖向条分在计算地震惯性力和抗滑力矩时存在计算上的不合理,从而使地震惯性力与实际值有误差,抗滑力矩偏小,因此采用竖向条分和水平条分结合的方法对土钉支护边坡地震稳定性分析方法进行了改进.利用遗传算法对最危险滑移面的圆心进行动态搜索,并且避免了在圆弧搜索中陷入局部最小值的缺点.采用面向对象程序设计语言VC++编制了程序,实现了上钉支护边坡稳定最小安全系数的自动寻优.最后结合具体工程实例进行了验算,结果表明这种计算方法对土质较均匀的黄土地区是适用的.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Effect of Permeable Crystalline Material on Steel Reinforcement Corrosion of Concrete

Permeable crystalline materialcan permeate into pores and cracks of concrete and catalyze the reaction between Ca(OH) 2and unhydrated cement to generate a great quantity needle non-soluble crystals, which can stop up the pores and cracks of concrete, and increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate steel reinforcement corrosion of concrete specimens uncoated and coated with permeable crystalline material as well as mixed with the permeable crystalline material. The properties evaluated for corrosion test were water impermeability, water absorption, compressive strength and potential. The results of water impermeability, water absorption, compressive strength clearly showed that the permeable crystalline material could prohibit water, any soluble salts and moisture from penetrating the concrete to cause corrosion, leaking, and other problems, and it did increase the compressive strength, which was favorable for protection of corrosion of reinforcing steel. Moreover, it was concluded from the potential-time curve that the steel reinforcement of uncoated specimen was in the state of activation whereas that of other specimens coated and mixed with the permeable crystalline material was in the state of inactivation. Above all, it was indicated that the permeable crystalline materialis very effective to protect the steel reinforcement of concrete from corrosion.     

The Research and Application About "Dry Peeling Off" Technology for Airplane Surface Paint Layer

In this paper, the principle of spurting take off lacquer were introduced; and with orthogonal method the unsaturate polyester was prepared ;it was easy to peel airplane paint layer off with this material and equipment.     

Quality Study of Honeycomb Core Shaping Without Wax Stabilization

Sandwich panels utilizing honeycomb cores result in lightweight, high-strength units that are very rigid. Indeed, they give honeycomb panels the best strength-to-weight ratio of any construction type available. Conventionally, the wax is poured into the cell of the core to strengthen the structure and prevent the core from being crushed during milling. Much time and labor is required to wax, mill, and clean the cores. In this study, the process of pouring wax into the core was skipped. In other words, the cutter directly milled the core. Experiments showed that the compressive strength of the core produced without wax stabilization was only 3% lower than that of cores produced using the traditional method. In addition, the drum peel strengths of cores produced without wax stabilization were 38.4% higher than cores produced using the traditional method, in which residual wax seriously polluted the adhesive. It was also found that eliminating the wax process can reduce costs.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.