混凝土不同骨料粒径对声发射检测的影响

利用声发射技术对不同骨料粒径的混凝土试件进行断铅试验。探究不同骨料粒径对声发射检测混凝土材料定位精度、声速标定、时间参数设定的影响和最优传感器布置方式的选取。结果表明: 骨料是影响声发射检测精度的主要因素之一, 骨料粒径每增大5 mm, 声速下降7.5%;骨料粒径每增大5 mm, 上升时间下降3.5%左右, 且最大上升时间不超过200 μs; 进行“多次多点”测试能合理的确定最优传感器布置方式并有效减小定位误差, 但不能消除误差。     

钢筋拔出试验中粘结破坏过程缺陷源定位分析

为确定声发射源定位技术在混凝土检测中的精度,同时验证所采用的声发射检测参数值的合理性.通过3D定位法分析了混凝土中心拔出试件在粘结破坏过程中试件内部缺陷源发展情况.分析结果与实际情况相吻合,所采用的声发射参数设置值使源定位获得了较高的精度.     

钢筋混凝土梁声发射检测参数设置和受力特征试验研究

为了建立声发射参数与钢筋混凝土梁受力特征之间的关系,进行了钢筋混凝土梁的四点弯曲试验和声发射测试试验.通过预加载和断铅试验,给出了适用于钢筋混凝土梁的门槛值确定方法、时间参数(峰值定义时间、撞击定义时间和撞击闭锁时间)确定方法、声发射波速的测定方法,以及相应的测试结果.通过四点弯曲试验和声发射测试试验,得到了振幅、振铃计数、能量和上升时间等声发射参数随荷载的变化关系,揭示了利用上述声发射参数表征钢筋混凝土梁受力特征的规律和方法.基于声发射参数,通过计算得到了试件在初始开裂和屈服时的裂缝分布情况,与试验结果相比,在裂缝数量和裂缝位置上,均吻合较好.     

基于声发射和分形的钢筋混凝土受剪梁损伤

通过5根不同剪跨比和不同配箍率的钢筋混凝土梁受剪破坏试验,运用声发射检测技术和分形理论对混凝土梁细观和宏观损伤演化过程进行研究.根据梁受剪破坏过程中产生的声发射信号的能量和振铃计数等参数以及裂纹分形特征,定量分析了混凝土梁受剪损伤演化过程.试验结果表明:声发射振铃计数和能量随损伤程度呈三阶段变化,累计振铃计数和累计能量...     

含不同缺陷的金属材料声发射特性

根据声发射测试原理,利用信号峰值电压与材料形变过程中释放能量的关系建立了裂纹开裂的声发射参数与应力关系的数学模型,提出了声发射总计数和声发射计数率的一般表达式,研制了声发射装置,并在拉伸试验条件下对具有不同缺陷的ZG25试件进行了声发射检测。实验结果表明:无缺陷的ZG25材料与有气孔、疏松、夹渣和微裂纹缺陷的该材料具有不同的声发射AE事件特征,这对金属材料声发射无损检测具有实际意义。     

受载岩石与混凝土声发射特性对比实验研究

通过室内加载岩石和混凝土的实验方法,测试了两类不同性质的岩石以及混凝土的破裂全过程的力学特征及其声发射特性,得到了岩石和混凝土破坏全过程力学特性曲线、声发射事件累积数、声发射事件率等相关曲线及参数,研究了声发射事件数、事件率、应力水平与时间参数之间的关系.通过对比岩石和混凝土声发射特性,指出了岩石声发射特性与混凝土声发射特性的相似与不同之处,以及两类不同性质岩石本身声发射特性的区别.研究着重讨论了一次性加载过程中混凝土与塑性阶段明显的岩石在加载接近峰值强度时都出现明显的"耗时"现象,指出存在这种现象的试样在此阶段声发射事件率出现明显下降,出现声发射相对平静,而对于塑性阶段不明显岩石来说,这一阶段则基本不存在明显的"耗时"现象,声发射的监测中也没有相对平静现象.此外,还对时间参数在声发射监测研究中的重要性进行了总结和分析,指出常规室内岩石力学研究中可以忽略的时间参数在声发射研究中应该被足够地重视.     

混凝土声发射规律的协同学研究及可视化模拟

混凝土破裂过程中声发射现象能够很好地揭示混凝土破裂机理。首次利用协同学的基本原理，对混凝土破裂过程中声发射现象进行了探索性研究，并通过混凝土破裂过程中内部结构状态变化（损伤演化）和声发射特征的对应关系，从更深层次上认识混凝土的破裂机理。首先分析了混凝土声发射参数与损伤演化的关系，并以声发射事件计数率作为混凝土破坏过程的序参量，建立了混凝土声发射序参量的演化方程，求出了其定态和非定态解，并分析了其科学意义，对混凝土声发射的协同特征进行了全面描述。最后，应用RFPA软件对混凝土声发射进行模拟，首次应用数值模拟的方法验证了混凝土声发射的协同效应，从而进一步证实了研究结果的准确性和利用协同学研究混凝土声发射的可行性，为混凝土声发射技术的工程应用提供理论依据；同时，所做的数值模拟工作，也为混凝土破裂机理研究提供了新的手段，即数值试验手段。     

钢纤维灰砂混凝土中裂纹位置的确定

运用声发射检测技术，探讨了确定钢纤维灰砂混凝土中裂纹位置的机理、测试精度问题，提出了确定裂纹位置的主要声参数和影响因素等，所研究问题同样存在于混凝土类人造石材，因而具有普遍意义。     

超声波检测灌芯玻璃纤维石膏墙板质量的研究

内部混凝土的密实性决定了灌芯玻璃纤维石膏墙板的质量。通过对不同浇筑质量墙板试件的超声试验,研究了利用超声波法检测灌芯石膏墙板混凝土浇筑质量的检查方法,分析了超声波在墙板内的传递路径。试验证明,超声波能够在墙板内传递。当空腔内混凝土浇筑质量较好时,波形比较规整,首波频率为50～69Hz,当存在缺陷时,超声波声时加长,首波频率明显减小,波形出现畸变。说明超声波检测方法用于灌芯墙板的无损检测是可行的和适用的。     

基于ARAMIS的铝合金拉伸过程声发射特性分析

对5052铝合金板材进行了单向拉伸试验,利用ARAMIS应变测量系统获得了铝合金材料在拉伸过程中的应变场,并同时用声发射检测仪检测了铝合金拉伸过程中的声发射信号。通过分析试件拉伸过程中各个阶段声发射特征信号,对比同时刻ARAMIS所得的应变云图,结合金属学原理,分析了5052铝合金在拉伸过程中各个阶段声发射信号产生的机制。结果表明:ARAMIS应变测量系统和声发射检测仪均能较好地测得5052铝合金在拉伸过程的变形破坏特征,利用ARAMIS应变测量系统测得试件表面吕德斯带的变化规律可以进一步解释试件在拉伸过程中声发射信号产生原因。     

钢筋混凝土板裂缝对声发射波传播特征影响

目前利用声发射技术对混凝土结构进行裂缝定位或损伤检测时,并没有考虑已存在裂缝对声发射波传播特征的影响,这往往会使检测结果产生较大的偏差.为了探究裂缝参数对声发射波传播特征的影响,对3个不同保护层厚度的钢筋混凝土板试件进行了四点静力加载破坏试验和声发射测试,研究了裂缝深度、宽度、数量对钢筋混凝土板声发射波速和振幅衰减等传播特征的影响规律.试验和分析结果表明:裂缝深度对声发射传播特征的影响显著,声发射振幅衰减随裂缝深度增大而增大,声发射波速随裂缝深度增大而减小;声发射波速和振幅衰减几乎不随裂缝数量、宽度两参数变化而变化.在此基础上,提出考虑裂缝影响的修正波速时差定位法,进一步探讨了与采用传统时差定位法相比对钢筋混凝土损伤定位的影响,结果显示,基于修正波速的时差定位法对钢筋混凝土板进行损伤定位精度更高.     

Experimental Study on AE Characteristics of Granite under Uniaxial Tension at Different Strain Rates

To investigate the acoustic emission (AE) characteristics of quasi-brittle materials like rock and concrete,and to further analyze their damage and failure mechanism under seismic and other dynamic loads,the uniaxial tension test of granite cylinder specimens within the strain rate range of 10~(-7)-10~(-4) s~(-1) was monitored by AE technology,and the typical AE characteristic parameters were analyzed using statistical and correlation analysis.The experimental results show that,with the increase of strain rate,the peak of AE hit rate appears earlier and increases;the proportion of AE hits with higher duration or amplitude increases significantly,the b-value shows a decreasing trend,and the distribution of AE frequency-amplitude is increasingly discrete.In addition,the obvious characteristic of double dominant frequency bands was observed in AE waveforms by using spectrum analysis,with the increase of strain rate,the percentage of A-type waveforms corresponding to low dominant frequency band increases,while that of D-type waveforms corresponding to high ones decreases accordingly,which is significance for the further study of the damage and failure mechanism of quasi-brittle materials.     

Sensitivity Analysis, Determination and Optimization of Granite RHT Parameters

The RHT model has 34 parameters, among which 19 parameters can be obtained by experiments or theoretical calculations and the remaining 15 parameters are difficult to acquire. In this study, firstly, 10 Hopkinson impact tests were conducted to acquire the typical stress-strain curves of granite under dynamic loads. Through the sensitivity analysis, it is found that 13 of the 15 difficult-acquired parameters are effective to affect the shape of the stress-strain curve, and the other two parameters have no effect. Following the initial determination of model parameters with reference to the concrete RHT model, a new approach is proposed to optimize the 13 influential parameters through the LS-DYNA numerical simulation and orthogonal experiments. Finally, the determined granite RHT model parameters are verified by the results of Hopkinson impact tests conducted in this study and the bullet penetration test by Wang et al. Both results of the numerical simulations are in a good agreement with the tested results, which validates the suitability of the proposed method to acquire RHT model parameters for granite and the other rocks.     

花岗岩-喷射混凝土梁损伤的声发射可视化表征

为研究输水隧洞围岩-喷射混凝土衬砌结构的协同抗弯损伤特性,制备两种花岗岩-喷射混凝土组合梁进行不同加载速率的四点弯曲试验,并采用数字图像相关(DIC)和声发射(AE)两种无损监测技术对花岗岩-喷射混凝土组合梁的四点弯曲试验进行监测。结果表明：在裂缝从喷射混凝土中扩展至花岗岩表面时,荷载-应变曲线在峰后下降段出现明显的拐点,该拐点可以作为花岗岩起裂的标志;通过声发射技术对喷射混凝土中的损伤类型识别发现,剪切损伤所占的比例随着应变率的提高而增加。为实现对组合梁内部损伤的可视化分析,利用声发射损伤定位数据计算了空间b值。结合损伤定位在空间中的密度分布规律,给空间b值附加系数后构建新的Rb值。与空间b值相比,Rb值的云图对不同损伤程度的区分度更高,改善了损伤可视化分析的效果。最后,将Rb值定位的损伤云图与DIC监测到的裂缝云图进行对比,验证了这种利用声发射技术对损伤进行可视化分析方法的有效性。     

Macro and meso characteristics evolution on shear behavior of rock joints

Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.     

再生混凝土轴心受拉性能试验与格构数值模拟

通过轴心受拉试验获取再生混凝土各相材料(老硬化砂浆、新硬化砂浆、界面过渡区)的力学参数,并研究再生混凝土在轴心受拉状态下的破坏机理.基于固体力学相关知识,结合再生混凝土各相材料的力学性能,建立一种再生混凝土细观格构模型.根据试验获得的再生混凝土各相材料力学参数,通过格构模型对再生混凝土进行轴心受拉模拟分析,获取再生混凝土轴心受拉应力-应变曲线,并探讨再生混凝土的内部破坏过程和轴心受拉破坏机理.结果表明,再生混凝土的受拉断裂部位主要集中在新或老硬化砂浆处,针对再生混凝土受拉力学性能,格构模型的模拟分析与轴心受拉试验结果基本吻合.     

Damage Processes of Polypropylene Fiber Reinforced Mortar in Different Fiber Content Revealed by Acoustic Emission Behavior

The performances of the cement-based materials can be improved by the incorporation of polypropylene fiber, but the damage processes become more complex with different fiber contents at the same time. The acoustic emission(AE) technology can achieve the global monitoring of internal damage in materials. The evolution process of failure mode and damage degree of polypropylene fiber reinforced mortar and concrete were analyzed by measuring the AE energy, RA value, AF value and b value. It was found that the cement matrix cracked on the initial stage, the cracks further developed on the medium stage and the fibers were pulled out on the last stage. The matrix cracked with minor injury cracks, but the fiber broke with serious damage cracks. The cumulative AE energy was proportional to the polypropylene fiber reinforced concrete and mortar's ductility. The damage mode and damage degree can be judged by identifying the damage stage obtained by the analysis of the AF value.     

预制混凝土结构插入式预留孔灌浆钢筋搭接试验

为研究具有自主知识产权的预制混凝土结构钢筋连接方法,在钢筋锚固试验结论的基础上,设计制作了108个预制混凝土结构插入式预留孔灌浆钢筋搭接试件。依据搭接接头率为100%的要求确定了钢筋搭接长度,考虑了钢筋直径、混凝土强度、搭接长度等不同影响因素,完成了试件的单向拉伸试验,得到了插入式预留孔灌浆钢筋搭接连接的破坏模式及各因素的影响规律,计算分析并给出了合理的搭接长度。通过实验证明,插入式预留孔灌浆钢筋搭接的方法,其连接性能可靠且施工简便,适合于住宅产业化下的预制混凝土结构的钢筋连接。     

Analysis of Dynamic Tensile Process of Fiber Reinforced Concrete by Acoustic Emission Technique

The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber (fiber of low elastic modulus) and steel fiber (fiber of high elastic modulus) reinforced concrete under medium strain rate (10^-6 s^-1-10^-4 s^-1). In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission (AE) technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor (DIF) of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.