Shear behavior of intact granite under thermo-mechanical coupling and three-dimensional morphology of shear-formed fractures

The shear failure of intact rock under thermo-mechanical(TM)coupling conditions is common,such as in enhanced geothermal mining and deep mine construction.Under the effect of a continuous engineering disturbance,shear-formed fractures are prone to secondary instability,posing a severe threat to deep engineering.Although numerous studies regarding three-dimensional(3D)morphologies of fracture surfaces have been conducted,the understanding of shear-formed fractures under TM coupling conditions is limited.In this study,direct shear tests of intact granite under various TM coupling conditions were conducted,followed by 3D laser scanning tests of shear-formed fractures.Test results demonstrated that the peak shear strength of intact granite is positively correlated with the normal stress,whereas it is negatively correlated with the temperature.The internal friction angle and cohesion of intact granite significantly decrease with an increase in the temperature.The anisotropy,roughness value,and height of the asperities on the fracture surfaces are reduced as the normal stress increases,whereas their variation trends are the opposite as the temperature increases.The macroscopic failure mode of intact granite under TM coupling conditions is dominated by mixed tensileeshear and shear failures.As the normal stress increases,intragranular fractures are developed ranging from a local to a global distribution,and the macroscopic failure mode of intact granite changes from mixed tensileeshear to shear failure.Finally,3D morphological characteristics of the asperities on the shear-formed fracture surfaces were analyzed,and a quadrangular pyramid conceptual model representing these asperities was proposed and sufficiently verified.

Research on Fe-based impregnated diamond drill bits strengthened by Nano-NbC and Nano-WC

In order to improve the matrix performance of impregnated diamond drill bit to better meet the drilling needs,the effects of the addition of nano-WC and nano-NbC particles on the matrix material together with the mechanical properties and microstructure of the diamond-matrix composite material of the Fe-based diamond drill bit were studied by using the method of uniform formula design,regression analysis and solution finding.An indoor drilling test was also carried out using the fabricated impregnated diamond drill bit.The results showed that after the addition of nano-NbC and nano-WC,the hardness and flexural strength of the matrix material got improved,as the flexural strength of the diamond composite material increased to 4.29%,the wear-resistance ratio increased to 8.75%,and the tighter the chemical bonding between the diamond and the matrix.This,indicates that the addition of nanoparticles has a positive significance in improving the performance of the diamond composite.The results of the drilling test showed that the mechanical drilling speed of the impregnated diamond drill bit after nanoparticle strengthening is 25.85%higher than that of the conventional drill bit,and the matrix wear was increased by 17.5%.It proves that nanoparticles can improve the drilling performance and efficiency of drill bit.

Topology Optimization of Stiffener Layout Design for Box Type Load-Bearing Component under Thermo-Mechanical Coupling

The structure optimization design under thermo-mechanical coupling is a difficult problem in the topology optimization field.An adaptive growth algorithm has become a more effective approach for structural topology optimization.This paper proposed a topology optimization method by an adaptive growth algorithm for the stiffener layout design of box type load-bearing components under thermo-mechanical coupling.Based on the stiffness diffusion theory,both the load stiffness matrix and the heat conduction stiffness matrix of the stiffener are spread at the same time to make sure the stiffener grows freely and obtain an optimal stiffener layout design.Meanwhile,the objectives of optimization are the minimization of strain energy and thermal compliance of the whole structure,and thermo-mechanical coupling is considered.Numerical studies for square shells clearly show the effectiveness of the proposed method for stiffener layout optimization under thermo-mechanical coupling.Finally,the method is applied to optimize the stiffener layout of box type load-bearing component of themachining center.The optimization results show that both the structural deformation and temperature of the load-bearing component with the growth stiffener layout,which are optimized by the adaptive growth algorithm,are less than the stiffener layout of shape‘#’stiffener layout.It provides a new solution approach for stiffener layout optimization design of box type load-bearing components under thermo-mechanical coupling.

一种11bit流水线高速模数转换器

为解决流水线模数转换器(ADC)在连续工作时功耗高、电容器匹配度有限以及运算放大器大摆幅输出信号下线性度下降的问题,基于0.5μm BCD工艺,设计了一款11 bit流水线高速ADC。提出了无采样保持放大器、幅度减半和多位量化相结合的设计方法,使ADC在大摆幅信号下有足够的线性度来处理信号,同时使电容数模转换器(DAC)的匹配精度满足ADC分辨率的要求,极大地降低了对电容阵列几何参数的匹配精度要求,具有较低的功耗。采用Cadence Virtuoso设计版图,测试结果表明,芯片的微分非线性(DNL)在-0.5~+0.5 LSB范围内,有效位数(ENOB)为10.61 bit,功耗为97 mW,获得了较好的性能。

一种具有纹波消除技术的10 bit SAR ADC

逐次逼近寄存器模数转换器(SAR ADC)在逐次逼近的过程中,电容的切换会使参考电压上出现参考纹波噪声,该噪声会影响比较器的判定,进而输出错误的比较结果。针对该问题,基于CMOS 0.5μm工艺,设计了一种具有纹波消除技术的10 bit SAR ADC。通过增加纹波至比较器输入端的额外路径,将参考纹波满摆幅输入至比较器中;同时设计了消除数模转换器(DAC)模块,对参考纹波进行采样和输入,通过反转纹波噪声的极性,消除参考纹波对ADC输出的影响。该设计将信噪比(SNR)提高到56.75 dB,将有效位数(ENOB)提升到9.14 bit,将积分非线性(INL)从-1~5 LSB降低到-0.2~0.3 LSB,将微分非线性(DNL)从-3~4 LSB降低到-0.5~0.5 LSB。

ADC-ADS1255实现23 Bits有效位的应用

文中介绍了24 BitsΣ-△型模数转换器ADS1255主要特性。利用ADS1255典型单极性输入电路和AD8138单极-差分变换器构成的差分输入电路,采用AD580M高性能芯片的参考电压电路、优化了供电电源纹波处理方法、注意了印刷电路板的设计,最后在恒温下对ADS1255采集板进行有效位数测试。结果表明,单极性输入采样率为2.5SPS时,有效位数(ENOB)达到22.6Bits。

3bits相位量化数字储频信号加权分析

本文从理论上对DRFM技术中信号加权进行了分析 ,推导出抑制低次谐波的最佳权系数。仿真结果表明 :采用最佳权系数加权后 ,低次谐波得到有效抑制 。

中外双边投资协定争端解决机制模式选择——以中国与上合组织成员国间BITs为视角

中国在加入《华盛顿公约》时声明将中国提交至ICSID仲裁管辖案件范围"限于征收补偿额争议",近年来的中外双边促进与保护投资协定却允许将"投资者与东道国争议"提交ICSID解决。鉴于中国在SCO成员国中的投资状况,中国与SCO其他成员国的BITs应推行此类做法。

图书表示模型BITS及其对中文科技图书的适用性分析

出版物的结构化处理是语义出版发展的基础。图书交换标签集(Book Interchange Tag Suite,BITS)是一套面向科技类图书的结构化表示模型。本文通过分析BITS模型的元素和结构,比较BITS与期刊标签集JATS以及电子书标准Docbook和DITA的异同,并结合中文科技类图书的特点,以探讨BITS对中文图书的适用性和改进方向。

双边投资条约是否确实促进了外资增长——BITs引资效果的经验研究

定量分析双边投资条约(BITs)对FDI区位选择的影响,是近年来新兴的一个研究课题。本文详细介绍了研究的进展情况,区分出两种不同的研究途径———研究BITs数量与FDI整体流入水平之间的关系,探讨BITs对缔约者之间双边FDI活动的影响,评论了它们各自得到的结果,并探讨了其中蕴含的政策涵义———为吸引更多的外资,完善内部制度要比缔结BITs更为重要。

论中外BITs在港澳特区的适用——以“谢业深案”和“世能案”为视角

在2007年的香港居民谢业深诉秘鲁政府投资仲裁案中,ICSID仲裁庭裁定1994年《中国-秘鲁BIT》适用于该案,曾引发各界对中外BITs能否适用于香港地区的热烈讨论。2015年,新加坡高等法院在另一起涉及中国澳门地区投资者的仲裁案件中,裁定1993年《中国-老挝BIT》不适用于澳门特别行政区。上述两案仲裁庭的裁决虽然有不同理由作为基础,但其最终结论的迥异表明,中外BITs能否适用于港澳地区问题仍悬而未决。究其原因,主要在于:(1)港澳地区的国内、国际法律地位本身具有复杂性;(2)《基本法》作为国内法层面的单边规定无法对抗BIT中的双方合意;(3)中外BITs措辞用语存在不足;(4)谢业深案仲裁庭有扩大解释之嫌;(5)澳门世能案中的双边解决模式存在不足。在中外BITs是否适用于港澳特区的问题上,不宜采取一刀切的方式,应通过双边协商途径实现与《基本法》规定的对接。

双边投资条约真吸引了外资吗?——BITs引资效果的经验研究

定量分析双边投资条约(BITs)对FDI区位选择的影响,是近年来新兴的一个研究课题。本文详细介绍了研究的进展情况,区分出两种不同的研究途径——研究BITs数量与FDI整体流入水平之间的关系,探讨BITs对缔约者之间双边FDI活动的影响,评论了它们各自得到的结果,并探讨了其中蕴含的政策涵义——为吸引更多的外资,完善内部制度要比缔结BITs更为重要。

论BITs例外条款可仲裁性的扩张

近年来双边投资保护协定中例外条款出现了可仲裁性扩张的趋势。笔者从案例分析的视角揭示出双边投资保护协定例外条款可仲裁性扩张的启示,并从理念、制度和实践方面阐述了中国的应对措施。

中国在BITs实践中如何坚持经济主权

双边投资条约 ( BITs)是资本输出国与资本输入国之间签订的保护私人投资关系的协定。BITs的签订有助于改善东道国的投资环境 ,吸引外资大量流入。但盈利是资本的天性 ,实务中外资免不了与东道国的经济主权发生磨擦和冲突。中国的 BITs实践成绩明显 ,坚持原则 。

多协议可变位宽40bits高速串口发射机

本文提出一种多协议,可变位宽发射机系统,最高数据位宽40 bits,最高数据速率10.312 5 Gbps.整个系统由归一化数据位宽(Normalization of Data Width,NMDW)变换电路,40:1合路器(MUX),时钟分布电路及3抽头前馈均衡器(Feed-Forward-Equalizer,FFE)组成,文章中提出了改进的40:1 MUX电路结构.本文采用SMIC 40 nm CMOS工艺,电源电压1.1 V.发射机(Transmitter,TX)整体功耗34mW@10.3125 Gbps,信道前差分输出眼图最大幅度大于800 mV.同时,本发射机支持4种不同协议,7种不同数据速率,9种工作状态,工作温度范围-45℃~125℃.

一种可支持多种类型电路进行BIT的检测方法

机内测试(Built-in-Test, BIT)技术是机载计算机实现故障检测、故障处理及提高系统可靠性的重要技术。提出了一种可同时支持过压保护电路、频率检测电路、模拟量采集电路、离散量输出电路进行BIT的检测方法。实际应用证明使用该方法后,产品的故障覆盖率与检测正确率明显增长,可有效提高产品的可靠性和可维护性,进而降低产品维护成本。

通信楼综合定时系统(BITS)的开发及应用

从通信楼定时系统 BITS设备在同步网中的应用方式出发 ,介绍了 BITS设备 Clock-Star的设计原理和功能结构 ,并且重点分析了其中的直接频率合成 DDS技术的原理和特点 。

Theoretical and experimental study of the pulling force of jet bits in radial drilling technology

Radial drilling technology, of which the jet bit is the key device, is a research focus in the field of oil drilling and production. This paper establishes mechanical equations for jet bits and analyzes the hydroseal of backward jets in bottom holes. Meanwhile this paper establishes a mechanical equation for a high pressure hose and analyzes the axial force distribution. Laboratory experiments indicate that the flow rate, the angle between the backward nozzle axis and the jet bit axis, and the hole diameter are the major influencing factors; the generation of the pulling force is mainly due to the inlet pressure of the jet bit; the backward jets can significantly increase not only the pulling force but also the stability of jet bits. The pulling force would reach 8,376 N under experimental conditions, which can steadily pull the high-pressure hose forward.

NUMERICAL SIMULATION OF THE THERMO-MECHANICAL PROCESS FOR BEAM BLANK CONTINUOUS CASTING

The aim of this study was to simulate the solidification process of beam blank continuous casting, and then find the reasons for the typical defects of the beam blank. A two-dimensional transient coupled finite element model has been developed to compute the temperature and stress profile in beam blank continuous casting. The enthalpy method was used in the heat conduction equation. The thermo-mechanical property in the mushy zone was taken into consideration in this calculation. It is shown that at the mold exit the thickness of the shell had its maximum value at the flange tip and its minimum value at the fillet. The temperature had a great fluctuation on the surface of the beam blank in the secondary cooling zone. At the unbending point, the surface temperature of the web was in the brittleness temperature range under the present condition. To ensure the quality, it is necessary to weaken the intensity of secondary cooling. At the mold exit the equivalent stress and strain have higher values at the flange tip and at the web. From the spray 1 to the unbending point, the maximum values of stress and strain gradually moved to the internal section of the flange tip and the web. However, whenever, there were bigger stress and strain values near the flange tip and the web than in the other parts, it must be very easy to generate cracks at those positions. Now, online verification of this simulation has been developed, which has proved to be very useful and efficient to instruct the practical production of beam blank continuous casting.

Multi-objective Topology Optimization of Thermo-mechanical Compliant Mechanisms

The material characteristics of a structure will change with temperature variation,and will induce stress within the structure.Currently,the optimal design for the topology of compliant mechanisms is mainly performed in single physical field.However,when compliant mechanisms work in high temperature environments,their displacement outputs are generated not only by mechanical load,but also by the temperature variation which may become the prominent factor.Therefore,the influence of temperature must be considered in the design.In this paper,a novel optimization method for multi-objective topology of thermo-mechanical compliant mechanisms is presented.First,the thermal field is analyzed with finite-element method,where the thermal strain is taken into account in the constitutive relation,and the equivalent nodal thermal load is derived with the principle of virtual work.Then the thermal load is converted into physical loads in elastic field,and the control equation of the thermo-mechanical compliant mechanism is obtained.Second,the mathematical model of the multi-objective topology optimization is built by incorporating both the flexibility and stiffness.Meanwhile,the coupling sensitivity function and the sensitivity analysis equations of thermal steady-state response are derived.Finally,optimality criteria algorithm is employed to obtain numerical solution of the multi-objective topology optimization.Numerical examples show that the compliant mechanisms have better performance and are more applicable if the temperature effect is taken into account in the design process.The presented modeling and analysis methods provide a new idea and an effective approach to topology optimization of compliant mechanisms in electrothermic coupling field and multiphysics fields.