煤体剪切破坏过程电磁辐射与声发射研究

用剪切实验台和电磁辐射、声发射接收系统对煤体剪切破坏的电磁辐射、声发射特征进行了研究 .结果表明 ,煤体剪切破坏过程中电磁辐射和声发射有两种类型 :一种是在加载初期出现较高的强度 ,加载中间阶段有较为平静的区域 ,主破坏发生前又逐渐增强 ,破坏时出现较高的强度 ,破坏后逐渐减弱 ;另一种是随应力增大电磁辐射和声发射持续增强直至破坏 ,破坏后减小 .试验结果与预测冲击矿压、煤与瓦斯突出等动力灾害的现场测试结果吻合 .     

钢轨胶结剪切强度的声发射监测

研究了胶结剪切强度的声发射特性，发现用声发射可以观察断裂的详细过程：从加载开始就出现声发射，说明较弱的连结点已开始断裂；极大的声发射振铃增长，表明胶结产生了破坏；断裂的声发射信号幅值大；从声发射图上所得的最大载荷低于从Ｘ－Ｙ函数记录仪所得的；声发射可以用于评价胶结质量     

Acoustic emission characteristics and stress release rate of coal samples in different dynamic destruction time

Considering the importance of the prediction of rock burst disasters, and in order to grasp the law of acoustic emission(AE) of coal samples in different dynamic destruction time, the SH-II AE monitoring system was adopted to monitor the failure process of coal samples. The study of the change rule of the AE numbers, energy, ‘b' value and spectrum in the micro crack propagation process of the coal samples shows that as dynamic damage time went by, AE presented high-energy counts and the accumulated counts increased during the compression phase. The AE energy and cumulative counts increased during the elastic stage. The AE blank area increased gradually and the blank lines were more and more obvious in the molding stage. The AE counts and energy showed a trend of decrease in the residual damage phase.AE ‘b' values gradually became sparse, and the large scale cracks percentage compared with micro cracks decreased and the degree of damage decreased. The AE frequency spectrum peak went from the residual damage phase to the molding phase, and finally it was nearly stable, besides the bandwidth of the main frequency is gradually narrowed. Also, the frequency peak changed from single peak frequency to bi-peak frequency and to the single peak frequency. Uniaxial compressive strength is more sensitive than the elastic modulus to dynamic damage time.     

Couple analyzing the acoustic emission characters from hard composite rock fracture

Rock mass is fractured media. Its fracture is a nonlinear process. The accumulation of acoustic emission (AE) is closely related to the degree of damage. The dynamics problem is simply described based on the non-equilibrium statistical theory of crack evolvement, trying to use the hybrid analysis of the statistical theory and scan electron microscopy (SEM), the characters of AE sig-nals from rock damage in a mined-out area is synthetically analyzed and evaluated. These provide an evidence to reverse deduce and accurately infer the position of rock fracture for dynamical hazard control.     

Space–time evolution rules of acoustic emission location of unloaded coal sample at different loading rates

By using MTS815 rock mechanics test system, a series of acoustic emission (AE) location experiments were performed under unloading confining pressure, increasing the axial stress. The AE space–time evolution regularities and energy releasing characteristics during deformation and failure process of coal of different loading rates are compared, the influence mechanism of loading rates on the microscopic crack evolution were studied, combining the AE characteristics and the macroscopic failure modes of the specimens, and the precursory characteristics of coal failure were also analyzed quantitatively. The results indicate that as the loading rate is higher, the AE activity and the main fracture will begin earlier. The destruction of coal body is mainly the function of shear strain at lower loading rate and tension strain at higher rate, and will transform from brittleness to ductility at critical velocities. When the deformation of the coal is mainly plasticity, the amplitude of the AE ringing counting rate increases largely and the AE energy curves appear an obvious “step”, which can be defined as the first failure precursor point. Statics of AE information shows that the strongest AE activity begins when the axial stress level was 92–98%, which can be defined as the other failure precursor point. As the loading rate is smaller, the coal more easily reaches the latter precursor point after the first one, so attention should be aroused to prevent dynamic disaster in coal mining when the AE activity reaches the first precursor point.     

岩石爆破逾渗断裂行为与块度分布研究

岩石是一种内部空间结构具有强烈随机性的高度无序介质，其爆破损伤断裂和破碎过程极为复杂．运用逾渗理论和重整化群方法分析了岩石损伤断裂的临界性质，阐明了岩石断裂破坏的物理机制，建立了临界参数与岩石宏观物理性质之间的联系，揭示了临界参数的物理意义．根据破裂面分维与碎块分维的关系结合损伤演化方程，提出了块度分维计算式，研究了爆破块度分布规律．     

Creep properties and resistivity-ultrasonic-AE responses of cemented gangue backfill column under high-stress area

To investigate the creep and instability properties of a cemented gangue backfill column under a highstress area, the uniaxial compression creep tests were conducted by single-step and multi-step loading of prismatic samples made of cemented gangue backfill material(CGBM) under the high stressstrength ratio. The creep damage was monitored using an electrical resistivity device, ultrasonic testing device, and acoustic emission(AE) instrument. The results showed that the CGBM sample has a creep hardening property. The creep failure strength(CFS) is slightly larger than the uniaxial compressive strength(UCS), ranging in ratio from 108.9% to 116.5%. The instantaneous strain, creep strain, and creep rate increase with increasing stress-strength ratio in the single-step loading creep tests. The instantaneous strain and creep strain decrease first and then increase during the multi-step loading creep process. The axial creep strain of the CGBM column can be expressed by the viscoelastic-plastic creep model. Creep instability is caused by the accumulation of strain energy under multi-step loading and the continuous lateral expansion at the unconstrained middle position during the creep process. The creep stability of a CGBM column in a high-stress area can be monitored based on the variation of electrical resistivity, ultrasonic pulse velocity(UPV), and AE signals.     

Comprehensive assessment on dynamic roof instability under fractured rock mass conditions in the excavation disturbed zone

The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine,China.The rock mass was particularly weak and fractured.There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone (EDZ) with the collapsing volume of 216 m3.First,the field detailed geological environment,regional seismic dy-namics,and dynamic instability of roadways were generally investigated.Second,the field multiple-index monitoring measurements for detecting the deep delamination of the roof,convergence deformation,bolt-cable load,acoustic emission (AE) characteristic pa-rameters,total AE events,AE energy-releasing rate,rock mass fracture,and damage were arranged.Finally,according to the time-space-strength relations,a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.     

声发射技术在拱桥吊杆损伤监测中的应用

目的为了克服常规无损检测方法不能动态监测吊杆损伤程度和类型，提出利用声发射技术监测吊杆损伤的活性.方法使用上升时间和持续时间关系图确定有效信号，设置浮动门槛值和增设警卫传感器去掉环境噪声；运用声发射参数法分析吊杆内水泥砂浆和钢绞线的损伤程度，并且还使用波形分析技术判断吊杆的损伤类型；在此基础上，对四川峨边大渡河拱桥的所有吊杆进行了全面的声发射在线监测.结果结果表明声发射信号幅值、能量、计数随时间实时变化图能直观显示吊杆的损伤程度关系；波形和频率范围上的差异能有效判断各种损伤类型，其监测结果与实际情况非常吻合.结论采用合理的降噪手段和识别方法，能够从强噪声环境中提取有效声发射信号，声发射特征参数相关图和波形分析技术能够动态监测拱桥吊杆的损伤程度和类型.     

Simulation experiment of AE-based localization damage and deformation characteristic on covering rock in mined-out area

The localization damage and deformation characteristics of multiple rock in mined-out area under thick soil layer were investigated by acoustic emission (AE)-based physical similar simulation experiment and damage test combined with the AE theory on rock damage. During different mining courses, the degree of wall rock suffered from mining disturbed process in mined-out area was different, so did the AE density of initial damage and fracture. Some characteristic parameters, including large events, total events, and energy rate, presented fluctuations with temporal and spatial change and take on a certain extent statistic relation. Subse-quently, the percent of damage degree was defined and divided into 4 stages, and the localization damage and deformation character-istics of surrounding rock in mined-out area and coal pillars were analyzed quantitatively.     

An experimental investigation on acoustic emission characteristics of sandstone rockburst with different moisture contents

Rockburst occurred frequently during deep mining in China. The mechanism of rockburst is very complicated and related to many factors. In order to investigate the influence of moisture contents of rockmass on rockburst, we conducted a series of laboratory rockburst experiments of sandstone under three different moisture contents by the Modified True-Triaxial Apparatus (MTTA), in which the acoustic emission (AE) system was employed to monitor the internal damage of rock mass. A high-speed video camera was utilized to record the detail of rockburst. Based on the experimental results, the AE characteristics, such as AE count, AE energy, and AE frequency, were analyzed. The rockburst process, type, and indensity under different moisture contents were discussed. The research results show that with the increase of moisture contents, rock strength was soften, the elastic and the cumulative damage of the rock were reduced, resulting in a gradual decrease in AE cumulative counts and cumulative energy over the course of rockburst. This study provides an experimental basis and reference for better understanding to the rockburst mechanism and control.     

Theoretical and experimental analysis on the mechanism of the Kaiser effect of acoustic emission in brittle rocks

The Kaiser effect is formally described as the absence of detectable acoustic emission （AE） events until the load imposed on the material exceeds the previous applied level and is usually used to estimate geostress. By focusing on the heterogeneity of rock material, the mechanism of the Kaiser effect under cyclic loading is analyzed based on statistic damage mechanics. Two groups of granite specimens have been cyclically loaded with two different loading paths to verify the theoretical results. The heterogeneity of rock is the real reason that causes irrecoverable damage on the Kaiser effect of acoustic emission in cyclic loading. The Kaiser effect reflects the damaged state in rocks rather than the previous stress imposed on it. Applications for using the Kaiser effect to estimate geostress were discussed here. It is shown that the commonly used uniaxial loading method for estimating geostress is not in accor- dance with the theoretical and experimental results. The analysis is of importance to use the Kaiser effect correctly for estimating geostress or in other fields. 2008 University of Science and Technology Beijing. All rights reserved.     

弯曲加卸载下杂质盐岩断裂力学行为特征研究

为研究弯曲荷载下杂质盐岩断裂力学行为及损伤演化规律,利用四川大学MTS815岩石力学测试设备及三维声发射监测系统,展开了纯盐岩、含杂卤石盐岩及杂质盐岩三点弯曲加卸载试验。试验结果表明：(1)杂卤石及泥质胶结提升了盐岩的韧性,纯盐岩的断裂韧度均值KIC=6.36MPa.mm^-0.5,杂卤石盐岩的断裂韧度较纯盐岩高43.08%,杂质盐岩的断裂韧度为纯盐岩的3.18倍;(2)杂质导致盐岩脆性提高,纯盐岩声发射事件覆盖区域大于杂卤石盐岩及杂质盐岩;三点弯曲加卸载下岩石内部声发射事件由切槽尖端逐渐向荷载点扩散,直至岩石完全断裂;(3)盐岩损伤程度随循环次数增长逐渐提高,但增长速度逐渐降低,损伤变量与切槽张开度符合指数函数关系,损伤变量-张开度曲线拐点对于研究岩石失稳倾向性具有一定的预测效果;(4)声发射参数rc值能够反映盐岩弯曲加卸载破坏全过程中主裂纹与微裂纹的发展趋势,峰后残余阶段纯盐岩及杂卤石盐岩rc曲线持续上升,微裂隙稳定发展;杂质盐岩表现出更强的脆性,其在峰后残余阶段rc曲线表现出与纯盐岩及杂卤石盐岩相反的变化趋势。     

大理岩特征应力的加载速率效应研究

为研究加载速率对脆性岩石特征应力的影响规律,利用MTS815型试验机和声发射测试系统进行大理岩的单轴压缩试验.采用体积应变法、声发射法和基于微裂纹发育特性的黏结颗粒离散元法确定试样的特征应力,探究特征应力的加载速率效应.结果表明,3种方法确定的特征应力值较为接近,基于微裂纹数的黏结颗粒离散元法是一种较可靠有效的方法.在中低加载速率范围内,随加载速率增加,归一化特征应力值呈现减小规律.数值模拟结果显示,加载速率在中低和较高范围内增加时,归一化起裂应力和损伤应力均减小.当处于中低加载速率范围时,其归一化特征应力降幅较大.当处于较高加载速率范围时,归一化特征应力趋于平稳,尤其是归一化损伤应力.相比较而言,归一化损伤应力的加载速率效应整体上比归一化起裂应力明显.     

NMR-based damage characterisation of backfill material in host rock under dynamic loading

It is not uncommon that backfill material used in underground mining being exposed to repetitive dynamic stresses induced by blasting operations or rockburst events. Understanding the strength and fracture evolution of backfilled stopes is critical to maintain the long-term stope stability and ensure safe mining activities. This paper aims to study the damage evolution of the backfill material and its host rock behaviour under three-dimensional(3D) dynamic loading. Using a true-triaxial testing machine, multiple samples of backfill material enclosed by country rock were fabricated and tested under various dynamic loadings with different true-triaxial confining stress conditions. In addition, the nuclear magnetic resonance(NMR) measurement was conducted on the samples before and after exerting static and dynamic loading to obtain their porosity distribution changes. The experiment results suggested that with the increase of the dynamic loading, the porosity of the backfill sample goes through a two-stage process,which shows a slightly linear decrease and then followed by an exponential increase. The research findings can help understand the damage mechanism and fracture development of backfilled stopes and its host rock in deep underground mines, which are constantly subject to the combination of 3D static confining stress and dynamic loading.     

点荷载下岩石记忆效应的声发射数值模拟试验研究

利用岩石破裂过程数值模拟软件RFPA对点荷载下岩石的声发射特征进行数值模拟,通过对试验循环声发射事件数强度百分比、声发射累积数的应变百分比及声发射空间分布进行对比,发现点荷载下岩石不仅对先期应力具有很好的记忆效应,对先期最大线应变也有明显的记忆能力.     

Compressional Punch Loading Test of a Polymer Bonded Explosive Simulant Using Digital Image Correlation Method

Punch loading is a loading scenario to study the fracture mechanism of materials at low strain rates.In this paper,three punch loading experimental patterns were chosen for the study of compressional punch loading.A polymer bonded explosive(PBX) simulant was experimentally studied using the digital image correlation(DIC) method.The displacement and strain fields were obtained and the fracture behavior and failure mechanisms of samples were investigated under different punch loading conditions.Moreover,scanning electron microscope(SEM) was used to examine the region of the plastic flow and the damage in the material.The formation of slip bands,shear displacement and fracture of the hard phase particle,were observed on the boundary of the dead zone due to the large shear strains.     

不同取样方向钢板试件的声发射特性分析

从ST13冷轧钢板中分别沿0°方向、45°方向和90°方向截取标准拉伸试样进行拉伸试验。结合金属材料的力学性能,分析试件在拉伸过程中声发射参数的表征和特性,以及在拉伸过程中声发射特征参数的异同性。结果表明：声发射计数、幅值和能量能较好地表征试件的整个拉伸过程,并得出0°方向钢板试件强度高,伸长率大,断裂能量大,90°方向次之,45°方向强度低,伸长率小,断裂能量小。     

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。