Fracture behavior and acoustic emission characteristics of sandstone samples with inclined precracks

Sandstone samples with precracks of different dip angles were collected from a coal mine roof and subjected to uniaxial compression tests,and acoustic emission(...     

Experimental analysis of thermally stimulated acoustic emission in various-genotype rock specimens under uniaxial compression

The consistent patterns of low temperature-stimulated acoustic emission (TAE) in rocks of various genotypes and porosity under uniaxial compression are experimentally examined and theoretically based. It is shown that these consistent patterns obtained in magmatic, metamorphic and sedimentary rocks qualitatively coincide. The authors compare limits of deformation stages in the tested rocks, found by a conventional method based on strain measurements in specimens under compression and by the TAE method. It is explained that the thermal acoustic emission phenomena are associated with the transfer of the studied objects between deformation stages depending on the initial faulted-porous structure of a geomaterial. The applicability of the TAE method to controlling stresses and their time and space dynamics in rocks is illustrated.     

反复浸水对煤样力学性质损伤的声发射实验研究

针对地下水对隔水煤柱和矿井地下水库边界的反复浸水损伤过程,研究反复浸水对煤样的力学性质损伤作用,对矿井地下储水和含水层保护等问题有借鉴意义.文中选择15个不同浸水次数的典型煤样进行单轴压缩声发射实验.研究发现,煤样的峰值应力、弹性模量、应变软化模量、后峰值模量均随着煤样浸水次数的增加而呈现不同程度的减小,而峰值应变随着浸水次数的增加而上升.综上反映了水对煤样的明显弱化作用.声发射累计计数、能率均能很好地表示出裂隙发育的各个阶段,对求取弹性模量研究煤样力学性质有重要作用.实验结果对反复浸水作用下煤样的力学性质和裂隙损伤的研究具有借鉴作用.     

Fracture toughness and hydraulic fracturing

A study of the influence of fracture toughness on the shape of a hydraulically induced fracture is presented. Three-dimensional numerical simulations of fracture propagation show that fracture toughness is not the main controlling parameter if one chooses fracture toughness values determined at ambient conditions. However, we performed some fracture toughness determinations at simulated down-hole conditions which gave sufficiently high values to indicate a significant effect of this parameter on fracture geometry. This effect will become very important if one considers that the presence of large-scale heterogeneities in the rock in the rock mass will increase the apparent value of in situ fracture toughness.     

Regularities of acoustic emission and thermoemission memory effect in coal specimens under varying thermal conditions

The experimental data on acoustic emission regularities are presented for specimens of different genetic coal types exposed to a wide range of cyclic heating modes. Peculiarities of formation and manifestation of thermal-emission memory effect depending on amplitude and duration of the thermal-field action are revealed. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 61–70, July–August, 2007.     

用声发射监测岩石与混凝土界面的破坏过程

利用声发射技术监测岩石与混凝土界面的破坏过程,提取了岩石与混凝土界面不同阶段的声发射信号,研究了应力-应变关系及其与声发射信号的耦合关系.研究表明,声发射信号能有效反映两者界面损伤破坏的演变过程.     

石膏和砂岩试样损伤破裂及声发射时空演化规律研究

通过对石膏和砂岩试样进行单轴压缩声发射试验,获取两种试样破裂全过程中的载荷-轴向变形曲线及声发射参数,观察试样破裂失稳情况,分析破裂过程中的声发射时空演化规律和波形的多重分形特征。研究结果表明:砂岩试样的单轴抗压强度是石膏试样的7倍多;由于岩性的变化,石膏和砂岩试样的破裂宏观形态由"X"型变化到倒"Y"型;两种试样声发射脉冲计数与应力变化规律比较一致,但是砂岩试样脉冲计数的最大值远远大于石膏试样;两种试样三维空间定位点分布与各自破裂宏观形态是一致的,但出现的时间以及分布位置是不同的;二者破裂过程中的波形都具有多重分形特征,破裂时的多重分形谱宽Δf(α)小于破裂前的Δf(α),破裂前的Δf(α)小于破裂后的Δf(α),砂岩试样各阶段的Δf(α)都小于石膏试样对应各阶段的Δf(α)。表明两种试样在破裂时的能量大于破裂前,破裂前的能量大于破裂后,而且石膏在各个阶段的能量小于砂岩对应各阶段的能量。通过对比分析,更加深入了解石膏冲击破裂的规律。石膏和砂岩一样会发生冲击破裂,只是冲击破裂形式不同,而且在同等条件下,石膏破裂产生的能量小于砂岩,为石膏矿冲击地压的防治打下了理论基础。     

2050铝锂合金厚板的断裂韧性及微观组织

通过力学性能测试及扫描电子显微镜(SEM)、透射电子显微镜(TEM),对2050铝锂合金厚板150℃T8态时效时不同方向的拉伸性能、断裂韧性及微观组织进行了研究.结果表明:随着时效的进行,2050铝锂合金厚板强度逐渐升高,伸长率和断裂韧性逐渐降低;时效至30h时,合金达到时效峰值,其抗拉强度、屈服强度和伸长率分别为598MPa,568 MPa,9.6%;继续延长时效时间,合金的拉伸性能和断裂韧性均趋于稳定.T1相和θ′相的析出有利于合金强度的提高,但T1相的长大易导致应力集中和微孔形成,从而降低合金的断裂韧性.该合金在L-T方向(轧向)的拉伸性能明显优于T-L(横向)和S-L(厚向)两个方向,且断裂韧性存在明显的方向依赖性.在时效各阶段,合金的断裂韧性值在L-T,T-L,S-L三个方向上依次降低;合金晶界在L-T方向的数量较少且裂纹扩展无方向性,断裂韧性和拉伸性能较优.     

岩石压裂过程中的声发射信号研究

当岩石受力变形和断裂时,会产生声发射现象（弹性波）,对其声发射事件的分析,可用来研究岩石裂纹形成机制和断裂过程。本文利用MEMS传感器对花岗岩单轴压裂过程的声发射事件进行研究,发现岩石试样破裂失稳可划分为四个过程。在整个应力加载过程中,声发射事件次数随岩石应变先呈增长趋势,后在岩石发生宏观断裂前呈减少趋势;声发射能量一直呈增长趋势,在岩石宏观断裂时达到最大;其声发射信号的频率一般为200～700Hz,随断裂的发生有降低的趋势。研究同时也表明,可通过对事件本身的定位（微震源定位）来研究岩石断裂位置。因此,MEMS传感器可应用于煤矿、水库和油田压裂等微地震的监测。     

Fracture toughness and surface energies of covalent minerals: theoretical estimates

Theoretical estimates of the ideal brittle fracture toughness and surface energies of 16 covalent minerals and materials have been obtained, based on a Morse-type bonding model. The materials range from ice to diamond, and include polymorphs of C, SiC, Si₃N₄, and SiO₂, together with B₄C, BN (borazone) and MoS₂ (molybdenite). The toughness model utilised enthalpy data, plus elastic compliance and stiffness constants. The resulting stress intensity, K_IC, for propagation of randomly planar transgranular cracks ranged from ∼0.11 (ice) to ∼3.3 MPa m^1/2 (diamond). The corresponding critical energy release rates, G_IC, ranged from ∼1.27 to ∼9.95 J m⁻². Estimates of the critical stress intensity for cleavage (K_IC)_hkl, of monocrystals on commonly observed (hkl) cleavage planes indicated (K_IC)_hkl<K_IC, consistent with expectations. Our analysis shows that the critical stress intensity (K_IC)_Gb and energy release rate (G_IC)_Gb for fracture along high angle grain boundaries are lower than K_IC and G_IC. The results are discussed with relevance to energy of comminution, and the influence of K_IC on particle size during ultra fine grinding. Based on comparisons between the Bond work index and energy required to form new surface area via particle fracture, the energy efficiency of comminution is confirmed to be very low (∼1%).     

Studying the mechanism of acoustic emission in failure of rock salt by dissolving

The laboratory-scale plant, procedure and test results are presented for the experimental failure of rock salt specimens by dissolving. It is established that dissolving proceeds irregularly in time and has three stages. This fact is confirmed by different standard deviates of the dissolving rates, acoustic emission activity behavior and its signal spectra recorded at each stage. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 39–48, January–February, 2006.     

岩石的声发射对比试验研究

通过单轴压缩条件下四种岩石的声发射的对比研究,分析了不同岩石破坏的声发射机理和规律。研究表明,岩石的声发射特性主要取决于岩石本身,且岩石的声发射事件率与其能量率规律并不完全一致。     

岩石脆性断裂试验的声发射分析

对不同岩石进行单轴受压试验,并采集岩石受压全过程的力学特征和声发射特征.通过对不同岩石声发射信号和力学参数的对比分析证实,不同岩石的声发射特征是有区别的,岩石变形损伤的声发射特征曲线与应力-应变曲线存在关联特征,岩石声发射的kaiser效应是存在的.     

Crack development and acoustic emission in potash rock

Acoustic emission (AE) techniques under laboratory testing conditions are used to understand the mechanical behavior and deformational processes of uniaxially compressed potash rock. Results obtained from the AE measurements are compared to deformational features identified using optical and electron microscopy. Although the potash rock from Saskatoon can be divided into four types based on the compositional ratio between sylvite, halite, clay, textural homogeneity and structural interlocking, it is shown that the analysis of the AE data collected during a complete load cycle can provide a general picture of the AE behavior. Detailed analysis of AE parameters such as b-value, amplitude and event-duration distribution can be used to monitor progressive changes in crack development.     

隧道围岩的损伤与声电监测

采用EAE-04声电测试系统，利用声发射(AE)和电磁辐射(EME)信号上升沿时间和持续时间的关系，排除噪音等影响，从而确定有效信号；采用AE频度和能量率的变化规律，以及EME脉冲数的变化规律，分析隧道围岩的活动性并进行实时监测．实践表明，连续动态监测隧道围岩的活动性就能够确保隧道及其上方建筑物的安全。