混凝土-钢筋粘结破坏过程的凯塞效应研究

通过直流电腐蚀得到7种不同腐蚀程度的混凝土中心拔出试件,并对这些试件进行粘结破坏试验,同时采用声发射仪监测试验过程。声发射仪监测前先通过模拟加载和断芯试验以确定适合拔出试件的检测参数值。通过对试件粘结破坏过程的事件数进行分析,验证了混凝土粘结破坏初期的声发射过程具有不可逆性。     

混凝土无损检测中常用声发射检测参数的设置

为了采集到具有高信噪比的声发射信号,实现声发射检测技术在大型混凝土结构在役监测工程实际中的推广应用,通过分析噪音信号、利用铅笔芯折断模拟声发射源试验,确定符合试验材料的检测参数:门槛、时间参数、波速、衰减等,为混凝土声发射检测参数选取提供了可靠的依据.     

声发射技术的裂纹失稳预测分析

当前在定量分析、对原料的估计和损耗的估计以及工程应用方面都未产生实际的进步。文中基于声发射技术的混凝土损伤检测,分析了声发射技术的基本原理和小波分析声发射源信号处理,在混凝土材料声发射的分析中探讨了混凝土材料声发射的特点和应用的试验方法,结果表明声发射技术能够较早的预测裂纹失稳的发生,在分析材料损伤发展中具有明显优势,这一研究对于进一步促进声发射技术在混凝土损失检测中应用具有一定的意义。     

基于CT图像的混凝土材料声发射损伤检测优化

为了使声发射仪器自身定位系统的损伤定位更加准确。基于CT图像信息,利用Amira三维可视化重建软件完成三维混凝土裂纹模型,以损伤定位点在CT图像裂纹区域作为合格准则,讨论声发射仪器检测参数的设置。结论表明:重建的三维裂纹模型能够比较真实的反映出混凝土的实际裂纹结构。声发射仪器参数设置中,利用断芯试验标定声速,门限值取值稍高于检测环境的噪声幅值,时间参数设置PDT∶150μs,HDT∶300μs,HLT∶500μs,声发射损伤定位图与CT实验的结果一致,为声发射的损伤检测的参数设置提供可靠依据。     

混凝土材料声发射过程分形特征及其在断裂分析中的应用

为了寻求混凝土材料声发射过程与断裂演化之间的关系,从实验入手,首先给出了声发射过程关联分维函数的概念,并通过实验,证明了声发射过程分形特征的存在。然后,通过混凝土试块的三点弯曲实验,分析了材料断裂过程中声发射关联数的变化规律。进而确定了混凝土试块在临界断裂时的分形特征识别模式。研究结果表明,混凝土材料的声发射过程不仅具有明显的分形特征,而且在临界状态下,知声发射分形特征参数都表现出一定的异常“模式”,这种识别模式可以作为材料出现临界断裂的识别特征。     

混凝土材料断裂的声发射自相似性识别特征

将对材料声发射的研究,力学过程的研究,同对材料断裂损伤等破坏过程的研究相似结合,提出了声发射过程的概念。给出定量考察声发射过程的自相似性特征函数。并在此基础上,根据混凝土试块的三点弯曲试验,确定出了混凝土试块断裂的声发射自相似性识别特征。     

混凝土材料声发射与应力-应变参量耦合关系及应用

在混凝土结构的可靠性检测中，声发射是一种重要的可测信息，声发射同应力，应变一样，也是表明材料力学特性的本构参量，声发射参量与应力，应变参量之间存在着密切的相关关系。这种相关性可以通过耦合的本构方程来表达，由于声发射对于材料的受力历史具有独特的“记忆”特性，可以通过声发射检测来确定材料所受过的最高荷载，进而可以对材料或结构的可靠性进行评价。     

混凝土轴压受载声发射特征及失稳演化过程研究

桥梁桩基混凝土承受轴向压载过大,其内部破坏开裂过程会释放弹性波,为量化压载失稳演化过程特征,通过现场原位钻取桥梁桩基结构芯样,采用轴向压载与声发射同步监测试验,研究混凝土试件加载全过程声发射时空演化特征,分析混凝土材料压载失稳破坏全过程与声发射振铃计数、能量释放、震源定位等表征参数的演化关系,获得加载过程与声发射特征关联性的定量描述,分析其失稳演化过程。研究结果表明：轴向压载条件下混凝土试件的应力与声发射振铃计数、能量释放随时间的变化规律具有一致性,声发射定位点主要在剪应力集中区形成宏观“定位带”与混凝土裂缝发展及破坏表现一致,可根据声发射事件活跃度量化判断混凝土受载阶段,反映混凝土失稳临界特征,对桩基混凝土服役监测具有重要意义。     

混凝土材料断裂过程中声发射空间自组织演化特征及其在结构失稳预报中的应用

利用声发射定位检测技术,对混凝土材料在三点弯曲断裂过程中,声发射事件的空间分布规律进行了观测.通过给出的声发射事件的位置熵函数,可以对这种空间演化规律进行定量描述.结合三点弯曲实验,对声发射空间演化规律同临界断裂的关系进行了分析.试验结果表明,混凝土试块在三点弯曲过程中,相应的声发射过程的空间自组织程度,随着应力状态的变化而变化.声发射空间位置熵的急剧下降,预示着宏观断裂的来临.     

全波形声发射技术用于混凝土材料损伤监测研究

在研究了混凝土材料三点弯曲试验下声发射累积能量随载荷变化关系曲线的基础上,提取了混凝土材料不同破坏阶段的全波形声发射信号并分析了其频谱特性,并且通过与参数分析结果的比较,发现全波形声发射信号能够实时反映混凝土材料在载荷作用下破坏过程的特征信息。     

高温后混凝土损伤评估的声发射试验研究

为研究高温后混凝土的损伤特征,对25~900℃范围10种温度水平的混凝土立方体试块进行单轴压缩和变幅循环加卸载试验,同步进行声发射采集。试验结果表明高温后试块表观特征、受压破坏形态、力学性能、加载过程中的Kaiser效应和声发射速率过程参数均能有效表征高温对混凝土的损伤作用;以声发射速率过程理论和损伤力学建立的高温后混凝土损伤模型,实现了利用初始损伤因子D0对高温后混凝土损伤程度进行定量评估。     

橡胶自密实混凝土断裂性能及声发射特征

为研究橡胶对自密实混凝土断裂性能的影响,针对4种橡胶掺量(0％、10％、20％和30％)的自密实混凝土,采用声发射(AE)技术,开展三点弯曲梁断裂试验,获得其荷载-裂缝口张开位移(P-CMOD)曲线、断裂能及声发射特征参数.通过荷载、累计振铃计数和累计撞击次数随时间的变化关系曲线,分析了橡胶掺量对自密实混凝土边界效应的...     

An experimental study on acoustic emission energy as a quantitative measure of size independent specific fracture energy of concrete beams

Notched three point bend specimens (TPB) were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and during the fracture process acoustic emissions (AE) were simultaneously monitored. It was observed that AE energy could be related to fracture energy. An experimental study was done to understand the behavior of AE energy with parameters of concrete like its strength and size. In this study, AE energy was used as a quantitative measure of size independent specific fracture energy of concrete beams and the concepts of boundary effect and local fracture energy were used to obtain size independent AE energy from which size independent fracture energy was obtained.     

Crack classification in concrete based on acoustic emission

The fracture mode of cracking in concrete is normally changing from tensile mode to shear mode at impending failure. As for crack classification in concrete by acoustic emission (AE) techniques, two crack classification methods have been carried out. One of them is parameter-based method (parameter analysis) which has been carried out by employing two parameters of the average frequency and the RA value. The proportion of these two parameters, however, has not been determined yet. The other crack classification is simplified Green’s functions for moment tensor analysis (SiGMA) procedure which is known as signal-based method. The SiGMA analysis is based on the generalized theory of AE, while the parameter analysis results from an empirical relation. Therefore, an optimal proportion of the parameter analysis is in great demand. In this study, these crack classification methods are compared and discussed from results of three types of concrete failure tests. As a result, ratios of the shear crack which are identified by SiGMA analysis are good agreement with those by parameter analysis in the case that the proportion of the RA value and the average frequency is set to 1–200.     

Acoustic emission parameters correlated with fracture and deformation processes of concrete members

Acoustic emission (AE) techniques is extensively applied to a variety fields in civil engineering. Currently a new generation of AE technique, which is able to register and process AE data in real-time, has appeared. Still, there exist some problems to correctly interpret these data and to completely understand the meaning of AE parameters. In order to solve these, several AE waveform and spectral parameters are investigated, based on an experimental study of concrete and reinforced concrete structures.     

Acoustic emission moment tensor analysis: development for crack identification in concrete materials

The moment tensor analysis of acoustic emission (AE) provides quantitative information on kinematics of cracks. Simple AE moment tensor analysis has been developed and named SiGMA-AE analysis. In-plane unconfined compression tests of mortar and concrete plates with a slit are carried out. The inclination of slits are varied as 0, 30 and 45° to the loading axis. The sources are located from detected AE signals. Then, orientations of cracks, crack types and crack volumes are determined by the SiGMA-AE analysis. Furthermore, it is clarified that the damage parameters can be estimated from the moment tensor components. The results show close correlation between the calculated crack volumes and the damage parameters.     

The damage evolution behavior of polypropylene fiber reinforced concrete subjected to sulfate attack based on acoustic emission

To study the damage evolution behavior of polypropylene fiber reinforced concrete (PFRC) subjected to sulfate attack, a uniaxial compression test was carried out based on acoustic emission (AE). The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model. The changes to AE ringing counts during the compression could be divided into compaction, elastic, and AE signal hyperactivity stages. In the initial stage of sulfate attack, the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect, and this corresponded with detection of few AE signals and with concrete compression strength enhancement. With increasing sulfate attack time, AE activity decreased. The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete. PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber. After 150 d of sulfate attack, the cumulative AE ringing counts of plain concrete went down by about an order of magnitude, while that for PFRC remained at a high level. The initial damage factor of hybrid PFRC was −0.042 and −0.056 respectively after 150 d of corrosion, indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC. Based on a deterioration equation, the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying−wetting sulfate attack cycles, which was 40% longer than that of plain concrete.     

受酸腐蚀混凝土的剪切性能及声发射特征研究

用pH值为1.5的硫酸和硝酸混合溶液对Z型混凝土试件进行侵蚀,对腐蚀后试件进行加载并全程进行声发射信号采集.结合应力-应变曲线与声发射参数对腐蚀前后混凝土剪切性能进行分析.结果表明:随着腐蚀周期增加,试件剪切强度和声发射参数均有明显降低,且声发射参数衰减率远大于剪切强度衰减率;未腐蚀试件加载过程声发射参数呈3阶段特征,...