贺兰山岩画典型病害损伤的声发射演化特征研究

裂(隙)纹是宁夏贺兰山岩画表面完整性严重破坏的典型病害问题.本研究基于声发射原理,利用单轴压缩试验模拟岩画载体材料岩石所受荷载,分析岩画载体材料强度破坏模式,获取声发射信号特征,探究AE时空演变规律,建立基于声发射累计振铃计数的损伤演化模型.研究结果表明：岩石破坏呈现“圆锥形”,其损伤发展主要经历原生裂纹闭合、次生裂纹发育以及裂纹贯穿破坏3个演化历程;损伤演化模型的力学和物理意义明确.声发射特征与变形特征紧密相关,能够表征岩石内部损伤过程,可以用来判断岩样岩石内部(微)裂纹状态,为石质文物载体材料裂纹扩展至破裂失稳这一热点和难点问题提供解决思路.     

基于声发射的层状复合岩石损伤演化规律实验研究

为了研究层状复合岩石内部微观裂隙的损伤情况,采用单轴压缩试验,结合声发射分析仪对试件内部破坏过程进行实时监测,分析岩石的破坏过程、声发射的参数等力学特性。研究结果表明:层状复合岩石的破坏特征不是单一岩石破坏特征的直接相加,而是在荷载作用下耦合破坏的结果。强度高的硬岩可以约束强度低的软岩发生横向变形,而强度低的软岩对强度高的硬岩的横向变形具有推动作用;声发射的能量计数与复合岩石内部裂纹的压密、扩展、贯通过程有紧密联系,可以评估岩石内部的损伤程度;根据累计能量建立的损伤演化方程,其拟合数据与试验数据吻合较好,实现了用声发射能量计数反应层状复合岩石的损伤演化规律,为层状复合岩石的损伤研究提供了参考。     

连续级配胶结充填体力学特性及声发射特征

基于程潮铁矿尾砂胶结充填背景,配制7组不同Talbol指数n的连续级配胶结充填体试样,开展了单轴压缩胶结充填体声发射(AE)监测试验,获取了胶结充填体强度及声发射特征参数.研究结果表明:连续级配胶结充填体的强度随n的增大呈震荡上升,达到最大值后骤然下降,当n=0.5时,连续级配胶结充填体强度最优,连续级配胶结充填体试样破坏后表壁以主裂纹为主,主裂纹发育完整,属于单一裂纹贯穿破坏,当n≠0.5时,主裂纹沿扩展方向发生偏转,属于裂纹绕行扩展破坏;当n=0.5时,声发射能率与累积能量均呈现出明显与全应力应变曲线对应的阶段性变化特征,当n≠0.5时,声发射能率呈现周期性间断峰值变化规律,累积能量表现为明显的阶梯性变化特征.     

基于声发射技术的单轴受压混凝土损伤细观研究

为了从细观角度了解不同强度等级,以及不同碳化龄期的混凝土的损伤演化特征,对强度等级分别为C20、C30、C40以及碳化龄期分别为0、28、56、77、90 d的混凝土棱柱体试件进行了单轴受压试验;并利用声发射(AE)技术对试验全过程进行了动态监测,获得了表征混凝土损伤演化过程的典型声发射事件累积计数(burst line cumulate,BLC)曲线;以及声发射事件数-相对应力水平关联曲线.结果显示:①BLC曲线的三个部分分别反映出材料损伤演化过程的三个阶段,曲线的两个转折点分别对应混凝土材料内部的起裂点和失稳点;②在低应力时,不同强度等级以及不同碳化龄期的混凝土试件的声发射特征没有明显区别;随着应力的增加,高强度等级和碳化龄期长的混凝土试件的声发射事件数增长较快,并且声发射活性急剧增加点明显前移.     

电脉冲循环冲击作用对花岗岩抗剪性能弱化研究

为探究坚硬岩体在高压电脉冲循环冲击作用下的致裂效果,开展花岗岩高压电脉冲循环冲击后的直剪试验,研究冲击次数对抗剪强度和裂纹扩展的影响规律。研究结果表明：花岗岩试样内部损伤程度随冲击次数增加而逐步累积,5 kV电压条件下,前3次冲击作用在试样内部几乎无新裂纹产生,冲击4次后试样内部开始萌生微小裂纹,并最终扩展形成贯穿裂缝;冲击4,5和6次后,试样内部损伤面积占比依次增加至6.65%,66.72%和70.80%;抗剪强度随冲击次数增加不断弱化,与未受冲击试样相比,冲击6次后试样抗剪强度弱化71.59%,剪切过程中声发射振铃计数降低58.41%,累积能量降低82.85%;声发射(AE)累积能量呈现出明显的“平静期—缓慢增加期—急速增加期”阶段变化特征;当冲击无明显裂纹产生时,试样剪切载荷加载过程中平静期延长,缓慢增加期缩短;当产生明显裂纹后,平静期缩短,缓慢增加期延长;冲击后,试样均在急速增加期呈现出更活跃的声发射信号,可以将声发射信号的突变作为试样剪切破坏的前兆,声发射事件点空间演化分布呈现出“抗剪破坏所需外部能量更低且声发射信号提前”的特征。     

基于声发射技术的混凝土压缩损伤研究

结合力学特性参数及声发射特征参数对混凝土压缩破坏过程进行分析,结果表明声发射特征参数能有效表征混凝土材料内部裂纹扩展数量及损伤程度.基于小波变换对采集的声发射信号进行瞬态分析,获得了裂纹萌生、裂纹生长和微孔洞压缩、裂纹汇合所对应的声发射信号的时频特征.实验中裂纹萌生、裂纹生长和微孔洞压缩、裂纹汇合所对应的声发射信号的上升时间依次增长,频率依次降低与应变能释放理论相符合.     

单轴压缩作用下CFST柱的声发射特征

通过对不同配筋率和不同壁厚钢管混凝土(CFST)柱进行单轴压缩声发射试验,对比分析了各试件破坏全过程的声发射信号特征.试验结果表明:试件的整个破坏过程可分为弹性段、弹塑性段、强化段和失效段四个阶段,声发射特征参数变化与试件破坏过程表现出较好的对应关系.声发射累积能量和累积撞击数均随荷载的增加而稳步增加;b值经历了缓慢上升、平稳波动、迅速下降的变化,反映了试件内部裂纹的逐步扩展情况;通过对声发射RA值、AF值分析可知,钢管混凝土柱的破坏过程既产生拉伸型裂纹又产生剪切型裂纹,随着荷载的增大,破坏中剪切型裂纹所占比例逐渐增多.研究表明声发射技术可以有效监测轴压下钢管混凝土柱的损伤状态.     

单轴压缩下粉砂岩声发射事件与撞击对比试验研究

为更深入地研究岩石受载失稳过程中声发射(AE)撞击和事件参数对岩石内部损伤的响应关系,试验采用PCI-2全数字化声发射信号采集分析系统及TAW-2000型微机伺服岩石力学实验系统,对粉砂岩进行单轴加载声发射监测,观察粉砂岩在单轴加载过程中声发射事件参数与撞击参数的变化特征。通过参数对比分析,发现事件参数与撞击参数对粉砂岩破坏表征的优劣性,得出如下结论:AE撞击参数较AE事件参数变化趋势明显,更能体现岩石内部损伤过程;在岩石受载中期声发射活动相对前后期较为平稳且各参数值也相对偏低;在粉砂岩未处于失稳破坏阶段时,撞击数与事件数的变化趋向相同;但受载末期撞击数迅速增加而事件数很少,两者变化呈不同趋向,其直观地反映出岩石内部裂隙发展过程。     

木基复合材料破坏过程中声发射特性的研究

利用声发射监测系统获取了胶合板和贴面刨花板两种木基复合材料三点弯曲加载状态下断裂损伤的声发射信号。利用累计能量和振铃总计数两项声发射信号特征参量分析了胶合板和贴面刨花板损伤破坏过程及其特点;利用幅值和有效电压（RMS）研究了随挠度增大胶合板和贴面刨花板内部裂纹产生、扩展、宏观裂纹形成至断裂的过程。结果表明:声发射信号的幅值、有效电压、累计能量、振铃总计数等参量可以有效表征木基复合材料内部损伤演化过程;贴面刨花板的断裂损伤发生早于胶合板,且贴面刨花板的损伤演化过程分为线弹性阶段和断裂韧性阶段,胶合板分为线弹性阶段、非线性变形阶段和断裂韧性阶段。     

英安岩三轴压缩试验力学特征及声发射特征研究

为研究英安岩的岩石力学特性及破裂损伤全过程中的声发射特征,通过MTS815伺服试验与PAC型声发射系统结合,对英安岩进行单轴压缩和常规三轴压缩声发射试验。试验表明:(1)英安岩单轴压缩和低围压下稳定破裂发展阶段具有"折线型"特点,临近破坏前,荷载值稍有停顿,然后继续上升,随即迅速大幅度下降,应力-时间曲线此刻的折线点(主破裂)对应监测的声发射(acoustic emission,AE)事件突出;高围压下曲线光滑,AE事件在累进性破坏阶段监测较集中。(2)随围压增大,英安岩物理力学参数也增大,监测的声发射AE事件也相应滞后出现,由张性破坏(竖向破裂)转变为剪切破坏。(3)英安岩有残余强度的在峰值后声发射活动持续,AE事件变化幅度小。无残余强度的声发射活动主要在峰值强度前,峰后无或微弱。(4)AE事件-时间、AE累计事件-时间曲线,以及岩石的应力-时间曲线三者结合,更好地反映出英安岩破坏全过程特点。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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