A thermo-mechanical damage constitutive model for deep rock considering brittleness-ductility transition characteristics

This paper developed a statistical damage constitutive model for deep rock by considering the effects of external load and thermal treatment temperature based on the distortion energy.The model parameters were determined through the extremum features of stress−strain curve.Subsequently,the model predictions were compared with experimental results of marble samples.It is found that when the treatment temperature rises,the coupling damage evolution curve shows an S-shape and the slope of ascending branch gradually decreases during the coupling damage evolution process.At a constant temperature,confining pressure can suppress the expansion of micro-fractures.As the confining pressure increases the rock exhibits ductility characteristics,and the shape of coupling damage curve changes from an S-shape into a quasi-parabolic shape.This model can well characterize the influence of high temperature on the mechanical properties of deep rock and its brittleness-ductility transition characteristics under confining pressure.Also,it is suitable for sandstone and granite,especially in predicting the pre-peak stage and peak stress of stress−strain curve under the coupling action of confining pressure and high temperature.The relevant results can provide a reference for further research on the constitutive relationship of rock-like materials and their engineering applications.

Physical and Thermo-Mechanical Properties of Composite Materials Based on Raw Earth and Crushed Palm Leaf Fibers (Borassus aethiopum)

The objective of this study is to seek solutions to reduce the impact of buildings on climate change and to promote the use of local bio-sourced or geo-sourced materials for sustainable construction. Different samples of raw earth from 3 sites were taken in the commune of Mlomp. Geotechnical tests showed that the raw earth samples from sites 2 and 3 have more clay fraction while site 1 contains more sand. The fact of integrating fibers from crushed palm leaves (Borassus aethiopum) (2%, 4% and 6%) into the 3 raw earth samples reduced the mechanical resistance to compression and traction of the 3 raw earths. The experimental results of thermal tests on samples of earth mixtures with crushed Palma leaf fibers show a decrease in thermal conductivity as well as thermal effusivity as the percentages increase (2%, 4% and 6%) of fibers in raw earth for the 3 sites. This shows that this renewable composite material can help improve the thermal insulation of building envelopes.

一种基于冗余位结构CDAC的12 bit SAR ADC

提出一种基于非二进制冗余位结构CDAC的12 bit全差分逐次逼近型模拟数字转换器(SAR ADC)。传统SAR ADC中CDAC的单位电容数量随位数指数增长,且采用全差分结构的电容数量是单端结构的两倍,导致CDAC建立时间过长。为此,设计一种加入冗余位的分段式电容阵列,减少单位电容数量,提高CDAC建立速度。动态比较器的比较速度快,会导致数字码误判,通过加入冗余位弥补比较器对数字码误判的缺陷;采用底板采样技术,避免沟道电荷注入和时钟馈通,提高采样精度;采用SMIC 130 nm CMOS工艺。在电源电压1.2 V、20 MS/s采样率下,对1024点FFT仿真。结果显示:当输入频率(9.824 MHz)接近奈奎斯特频率时,该ADC的整体信噪失真比(SNDR)达到72.42 dB,有效位数(ENOB)达到11.73 bit;无杂散动态范围(SFDR)达到88.4 dBc,功耗为1.29 mW。

一种基于2 bit阶梯波时间调制的高精度幅度调控方法

本文介绍了一种基于2 bit阶梯波时间调制(step-wave time-modulation,SWTM)的高精度幅度调控方法。首先建立了2 bit SWTM理论模型,分析了阶梯波形对射频信号时间调制的幅度调控精度影响;然后设计了2 bit SWTM电路,进行了高精度幅度调控实验。测试结果表明,在40 MHz信号带宽下,该2 bit SWTM电路实现了0~31.75 dB衰减动态范围的7 bit幅度调控,误差范围小于±(0.1+0.8%AS)dB,均方根误差为0.07 dB。

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.

Ti/SnO_(2)-Sb-Ni电极电化学氧化去除水中BIT

1,2-苯并异噻唑啉-3-酮(BIT)是一种新型广谱工业杀菌剂,因其强杀菌能力而难以直接通过传统生化法处理,电化学氧化是一种有效的预处理方法。通过实验对比不同典型阳极对BIT去除率的影响;以锑镍共掺杂钛基二氧化锡电极(Ti/SnO_(2)-Sb-Ni)为阳极电化学氧化BIT,考察BIT电化学氧化过程中不同初始BIT浓度、初始pH、电流密度和硫酸钠浓度等操作参数对BIT去除率的影响,结合紫外-可见吸收光谱和荧光光谱分析,探究BIT降解过程中的结构变化。结果表明:相较于商业电极,Ti/SnO_(2)-Sb-Ni电极可高效电化学氧化BIT及其产物,消除其生物毒性;Ti/SnO_(2)-Sb-Ni电极电化学氧化BIT过程中,最佳电流密度为15 mA/cm^(2),pH和初始硫酸钠浓度对BIT降解影响较小,最佳BIT初始浓度15 mg/L,BIT降解过程中杂环先被破坏,苯环再被破坏。

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。

基于micro:bit的中小学劳动教育跨学科主题学习

在中小学开展基于micro:bit的劳动教育跨学科主题学习,是新时代劳动教育的新尝试,旨在将新技术充分融入劳动教育,整合多学科知识,通过项目式学习方式,立足跨学科主题学习活动设计,引领学生面对生活中的真实问题,创造性地提出解决方案,并用新技术尝试解决问题,最终提升劳动素养和综合能力。通过小学四年级和八年级的实践检验,该主题学习取得较好效果,具有现实可行性。同时,教师在实施过程中,还需在主题学习设计、教学实施策略以及评价反馈等方面予以重视。

基于micro:bit的初中信息科技项目式教学设计与实践

基于Micro:bit的初中信息科技项目式教学设计与实践,引入项目式学习模式,旨在提高学生的信息技术能力、创新思维与团队协作能力。分析了当前初中信息科技教学的现状及存在问题,设计并实施了一套基于Micro:bit的课程。通过实践操作与实验探索、分层次挑战与个性化学习、团队合作与角色分工以及问题导向学习等策略,提升学生的信息技术能力、创新思维和团队合作能力。

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。

采用1-bit压缩感知的信号识别网络黑盒对抗攻击方法

在无线信号识别的神经网络对抗样本研究中,针对目标网络结构参数与数据集均未知,且查询无法获取识别置信度或识别结果的黑盒攻击场景,提出一种采用1-bit压缩感知的对抗样本生成方法。假设攻击者能够通过查询获取某一批信号样本在待攻击模型下的识别准确率。首先,将模型准确率的梯度视为待感知的稀疏变量,并利用一批样本准确率高于或低于另一批的信息(用1或-1表示)构建1-bit压缩感知模型。其次,通过多次查询并估计梯度,结合0范数约束,使用梯度下降法迭代优化信号扰动,从而生成有效的对抗样本。最后,使用对抗样本攻击目标网络以降低识别准确率。实验结果表明,该方法在公开信号调制识别数据集上能够将识别准确率从79.02%降低至65.39%。相比于现有其他方法,该方法进一步拓展了黑盒攻击的限制条件。

Effect of thermo-mechanical treatment process on microstructure and mechanical properties of 2A97 Al-Li alloy

2A97 Al-Li alloy was processed by thermo-mechanical treatment at different pre-stretch deformations of 0, 3% and 6%. The microstrucatre observation results reveal that some δ＇ and T1 precipitates are found in a（Al） matrix of 2A97 alloy processed by the heat treatment with no pre-stretch deformation. When the pre-stretch deformation is 3% and 6%, respectively, amounts of tiny T1 and a few of S＇ precipitates precipitates are observed in the microstructures of 2A97 alloy. The tensile test results show that the tensile properties of 2A97 alloys are improved via thermo-mechanical treatment. When the pre-stretch deformation is from 0, 3% to 6%, the ultimate tensile strength values of the 2A97 alloys increase gradually from 447.7, 516.5 to 534.3 MPa, and the elongations decrease from 17.6%, 12.8% to 10.2%, respectively. Moreover, with increasing pre-stretch deformation amount from 0 to 6%, the in-plane anisotropy value of 2A97 alloys becomes more obvious.

Effects of T9I6 thermo-mechanical process on microstructure, mechanical properties and ballistic resistance of 2519A aluminum alloy

The effects of T916 thermo-mechanical process on microstructures, mechanical properties and ballistic resistance of 2519A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, tensile tests and ballistic resistance test. After T916 treatment, the yield strength, tensile strength and elongation rate of 2519A aluminum alloy reach 501 MPa, 540 MPa and 14%, respectively. And the ballistic limit velocity of 2519A-T916 alloy （30 mm in thickness） is 715 rn/s. The microstructure varies near the sidewalls of crater. The interrupted ageing contributes to these excellent properties of the alloy. During T916 process, the precipitation of Guinier Preston （GP） zone is finer and denser during the interrupted ageing, thus resulting in well precipitated strengthening phase.

Mechanical properties of Mg-6Gd-1Y-0.5Zr alloy processed by low temperature thermo-mechanical treatment

An as-solution treated Mg-6Gd-1Y-0.4Zr alloy was processed by low temperature thermo-mechanical treatments （LT-TMT）, including cold tension with various strains followed by aging at 200 °C to peak hardness. The results show that the precipitation kinetics of the alloy experienced LT-TMT is greatly accelerated and the aging time to peak hardness is greatly decreased with increasing tensile strain. The tensile yield strength, ultimate tensile strength and elongation at room temperature of the alloy after cold tension with strain of 10% and peak aging at 200 °C are 251 MPa, 296 MPa and 8%, respectively, which are superior to the commercial heat-resistant WE54 alloy, although the latter has a higher rare earth element content.

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。