共查询到18条相似文献，搜索用时 156 毫秒
1.
依据对具有较高微裂纹密度的筑波花岗岩和极低微裂纹密度的花岗斑岩 2种极端的岩石标本、在等应力速率的快速加载 (约 6MPa/min)和蠕变加载 (轴向应力保持在约 95 %破坏强度 ) 2个极端的加载条件下的实验结果 ,讨论了预存微裂纹密度与加载速度对多晶质结晶岩变形破坏过程的影响。实验中利用高速多通道声发射波形数字记录系统 (每秒可记录多达 5 0 0 0个声发射事件的 32通道波形 ) ,获得了岩石标本破坏前微破裂活动的详细时空分布数据。声发射的发生率、震级 -频度关系中的b值及震源的空间分布揭示出岩石变形破坏过程中微破裂活动具有 3个典型阶段 :初期阶段、第 2阶段和成核阶段。尤其是在成核阶段 ,还观测到发生率和b值有大幅度前兆性起伏。一般而言 ,在相同加载条件下预存微破裂密度越高 ,或对同一岩石加载速度越慢 ,对应的断层成核过程就越长 ,因此最终破坏的可预报性也越高。为了进一步探讨微破裂活动的阶段性特征及其物理本质 ,还利用亚临界破裂扩展模型对声发射数据进行了理论分析 相似文献
2.
岩石试验声发射及天然地震的 b 值到底反映了什么样的物理实质,是一个长期以来引起争论的问题.本文运用断裂力学的观点和方法,研究岩石试验试件内微裂纹系中各裂纹的扩展顺序及声发射能量,由此确定整个声发射序列,并进而确定 b 值.如果假设裂纹长度的分布密度函数为 p()=B-.经过力学分析和数学推导,可得到关系式 b=3/2.由此看出:b 值的物理实质是,它反映了介质的断裂构造状态————包括介质中裂纹系的空间分布及其它影响材料中裂纹扩展的物理量(如断裂韧度、摩擦系数等)的空间分布.这一结论与大多数实验及观测结果相符.我们的研究结果与茂木清夫观点有共同之处.茂木清夫认为:介质的不均匀性是决定 b 值的重要因素.介质的不均匀性一词固然也包括了介质的断裂构造状态在内,但是本文之观点比茂木更进一步说明了问题的实质. 相似文献
3.
对几种不同结构的岩石标本在变形过程中声发射b值和频谱随时间的变化特征进行了对比研究 ,其中包括完整花岗岩标本、含有天然愈合节理的花岗岩标本、含有拉张型和挤压型雁列式断层以及平直断层的标本等。研究表明 ,声发射b值和频谱的特征不仅会受标本结构的影响 ,而且在同一标本的不同变形阶段也可能表现出不同的特征 ,其机制与变形方式以破裂为主或以摩擦为主有关。当变形以破裂为主时 ,声发射b值和频谱在失稳前会出现明显的下降 ;当变形以摩擦为主时 ,声发射b值和频谱在失稳前变化相对较小 ,且上升或下降均可能出现。实验结果意味着b值和频谱特征作为失稳前兆 ,在不同的构造环境下可能会有不同的特征 ,而强震孕震区内不同断裂构造的存在会造成前兆时空分布的非均匀性 相似文献
4.
1 研究背景
声发射是指岩石在受力过程中发生变形和破裂,其应变能释放所监测到的一种物理现象,而b值是表征地震震级—频度关系的参数,研究人员发现,b值具有非线性特征,且与岩石破裂过程密切相关.因此,利用岩石试件变形破坏过程中产生的声发射事件模拟地震,进而研究不同加载条件下岩石变形破坏过程中的声发射b值变化特征,可用于监测岩石受力破坏过程中内部预存微裂隙的活动状态,有助于揭示岩石损伤机理及岩石的破坏程度,也可作为岩石失稳预警参数,捕捉地震发生的前兆信息. 相似文献
5.
6.
本文从实验上研究了“人”字式断层声发射b值并从理论上对频度—震级关系及b值变化的物理机理进行了探讨。“人”字式断层的引入使b值呈现低值,b值随载荷呈现单调下降以及下降又上升或波状上升两类变化,反映了不同的破裂过程。根据微破裂的产生、发展和聚合过程的物理图象,建立了微破裂的分布方程。在裂纹无相互作用时,分布方程的解即是Gutenberg-Richter公式。在裂纹相互作用时,分布方程的解不是简单的幂函数,在对数坐标中频度—震级关系偏离线性 相似文献
7.
着重研究拉张或挤压型雁列式断层标本变形过程中声发射(简称AE，下同)的时空演化特征. 结果表明，预置构造对AE空间分布格局具有较强的控制作用，随着差应力的增加，AE首先在两个端点附近丛集，之后向两端点连线附近集中，出现明显的破裂局部化现象，较大事件还通常集中于某一端点附近反复发生. 前期微破裂丛集图象指示后期宏观破裂的扩展方向及扩展范围. 拉张和挤压型雁列区宏观破裂方向分别与轴向应力方向垂直和平行. 雁列式断层标本变形过程中，破裂前的弱化阶段相对较长、弱化过程明显. 微破裂事件累积频次指数增长可能是系统失稳前的典型征兆之一，而雁列区宏观破裂之后，AE数量逐渐减少、应变释放相对减弱. 摩擦滑动过程中，大的粘滑失稳前未见有AE活动前兆性的增强过程.雁列区的b值变化在失稳前显示趋势性降低——快速回升这一典型的变化过程，b值降低一般发生在差应力增强过程之中，并有可能延续至弱化阶段，而快速回升则一般发生在破裂失稳前的短时期内. 对比研究表明，构造差异所导致的b值差异远大于b值随差应力的增加而产生的变化量，而对同一构造标本，力学状态的改变会导致AE序列时序特征的急剧变化，较高的加载速率对应较高的应变能释放及明显的低b值. 先期破碎带由于较低的破坏强度，其对差应力的微小变化具有特殊敏感性，从而成为源、兆分离、窗口或敏感点效应等地震活动性前兆现象的一种可能的原因. 相似文献
8.
在单轴应力条件下对不同应力变化过程岩石的声发射b值或m值进行了研究。所用的岩石为济南辉长岩和房山大理岩。实验的方式有三种:(1)重复加载实验;(2)递增加载实验;(3)应力增减实验。实验表明,应力减小过程的声发射b值比应力增加过程的声发射b值低。重复加载时声发射率显著下降但声发射b值变比不大,声发射b值对岩石的应力历史的记忆效应也不及声发射率的记忆效应明显。 相似文献
9.
方亚如 《地震地磁观测与研究》1991,12(1):17-22
对混凝土样品在单轴应力条件下破裂前不同应力状态下的声发射m值进行了实验研究。混凝土样品为10×10×10cm~3的正方体。实验表明,干燥混凝土样品破裂前声发射m值随应力的增加而降低;含水混凝土样品的m值先随应力的增加而增加,当应力达强度的60％以后,m值随应力的增加而降低。混凝土样品破裂前声发射率先随应力的增加而缓慢增加,当应力达强度的70％以后,声发射率开始明显增加以至破裂前急剧增加。含水混凝土破裂前声发射率比同种干燥样品低两倍左右。 相似文献
10.
在双向压缩条件下,研究了一种非均匀断层模型标本在变形过程中的声发射(AE)时空特征.结果表明,随侧向应力sigma;2的增大,断层破裂强度提高,自加载至破坏的时间延长,破坏形式由突发失稳逐渐转变为渐进式破坏.预制断层及其非均匀性对标本变形过程中AE空间分布图象起明显的控制作用.预制断层,特别是预制断层上的强度不均匀部位及高强度段落,控制着微破裂空间分布的总体格局.破裂局部化均起始于断层上强度不均匀部位,随侧向应力sigma;2的增大,微破裂密集区域从预制断层强度不均匀部位逐渐扩展到整个高强度区段.侧向应力sigma;2的大小对AE时序特征具有显著影响.较低sigma;2条件下,断层表现为突发失稳,失稳发生在微破裂活动ldquo;增强-平静rdquo;的背景之上;而较高sigma;2条件下,断层表现为渐进式破坏,破坏前后AE频次持续增加,AER呈指数增长.sigma;2对b值变化也具有一定影响.当断层破坏表现为突发失稳时,b值在弹性阶段后期至弱化阶段显示出ldquo;前兆rdquo;性降低;而当断层表现为渐进式破坏时,b值变化平稳. 相似文献
11.
本文全面系统地研究了1960——1987年广州地磁台转换函数的变化.结果表明:(1)季节变化的特点是夏季幅度大,冬季幅度小,具有12和6个月的主要周期成份;长期变化则表现以每年0.0025的速率下降.转换函数 B 的长期变化和季节变化不明显;(2)由转换函数 A,B 求出的帕金森矢量的方向明显地受海洋的影响,反映了海洋效应;(3)转换函数 A,B 的逐月值与地磁活动相关,而年均值与地磁活动无关.A 的年均值无明显的11年或22年周期.长期变化可能主要受地球内部电性结构的影响. 相似文献
12.
Introduction By the experimental techniques of acoustic emission (AE) and surface strain observation, a lot of achievements on the study of deformation and fracture process of samples with en-echelon faults has been obtained (Bomblakis, 1973; LIU, et al, 1986; DU, et al, 1989; LI, et al, 1989; ZHANG, FANG, 1989; ZHANG, LI, 1989; MA, et al, 1995a, b; LI, et al, 2000). However, there still exist many problems. For example, most of discussion on the spatio-temporal evolution of microf… 相似文献
13.
We have made a data collection and analysis system for recording microcracks in rock to study the three dimensional pattern
of fracture and the dynamic properties of rock during pressurization. This system, with 8 channel data detection, records
in real-time, from the initial microcracks to the final vibration waveform excited by the master fracture. The detected data
are recorded digitally at the hard disk of an IBM computer (or 286, 386 personal computer) as well as transmitted to disk.
The sampling rate for each channel is 10 MHz.
Collecting every acoustic emission events in the loaded rock sample with 8 channels by this system, mathematically modelling
the AE event travel time, and taking the coordinates of the AE event hypocenter and the three components of P wave velocity
as unknown parameters, we set up a set of residual equations for joint inversion, so that the three dimensional localization
of AE event hypocenters can be completed under variable velocities, which will lay foundations for the research on rock fracture
clearly.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismological Sinica,13, 489–495, 1991.
The design and development of the system, and the experiments are sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
14.
本文利用THEMIS卫星的磁场数据和等离子体观测数据,统计分析地球磁尾等离子体片区域线性磁洞的发生率、时空尺度、分布特征、和发生率与地磁AE指数的相关性.分析结果表明磁尾等离子体片区域的磁洞的时间尺度为几秒到几十秒,空间尺度小于当地的质子回旋半径.通过磁洞在空间的位置分布和卫星数据在空间的数据采样分布的对比,我们发现线性磁洞在等离子体片内经常发生,然而在磁尾等离子体片中的发生率要小于太阳风中磁洞的发生率.本文最后统计分析了磁洞发生和AE指数的相关性,结果表明磁洞可能与地磁活动有关系. 相似文献
15.
New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly
granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture
process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded
at a `slow' constant strain rate of 2.5 × 10−6 /s) and an unstable fracture that develops near instantaneously (loaded at a `fast' constant strain rate of 5 × 10−5 /s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be
captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial
nucleation or stable growth phase at a rate of ~ 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation
speed of ~ 18 mm/s, and (3) unstable, accelerating propagation. In the ~ 100 ms before rupture, the high level of AE activity
(as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation
velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain
acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate
similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments.
It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding
the controls on fracture nucleation. 相似文献
16.
Experimental study of ultralong wave band for electro－magnetic signals and acoustic emission during rock fracture 总被引：1，自引：0，他引：1
Ｅｘｐｅｒｉｍｅｎｔａｌ ｓｔｕｄｙ ｏｆ ｕｌｔｒａｌｏｎｇ ｗａｖｅ ｂａｎｄ ｆｏｒ ｅｌｅｃｔｒｏ－ｍａｇｎｅｔｉｃ ｓｉｇｎａｌｓ ａｎｄ ａｃｏｕｓｔｉｃ ｅｍｉｓｓｉｏｎ ｄｕｒｉｎｇ ｒｏｃｋ ｆｒａｃｔｕｒｅ（曹惠馨）（钱书清）（吕... 相似文献
17.
Quantifying the spatial and temporal distribution of recharge is usually a prerequisite for effective ground water flow modeling. In this study, an analytic element (AE) code (GFLOW) was used with a nonlinear parameter estimation code (UCODE) to quantify the spatial and temporal distribution of recharge using measured base flows as calibration targets. The ease and flexibility of AE model construction and evaluation make this approach well suited for recharge estimation. An AE flow model of an undeveloped watershed in northern Wisconsin was optimized to match median annual base flows at four stream gages for 1996 to 2000 to demonstrate the approach. Initial optimizations that assumed a constant distributed recharge rate provided good matches (within 5%) to most of the annual base flow estimates, but discrepancies of >12% at certain gages suggested that a single value of recharge for the entire watershed is inappropriate. Subsequent optimizations that allowed for spatially distributed recharge zones based on the distribution of vegetation types improved the fit and confirmed that vegetation can influence spatial recharge variability in this watershed. Temporally, the annual recharge values varied >2.5-fold between 1996 and 2000 during which there was an observed 1.7-fold difference in annual precipitation, underscoring the influence of nonclimatic factors on interannual recharge variability for regional flow modeling. The final recharge values compared favorably with more labor-intensive field measurements of recharge and results from studies, supporting the utility of using linked AE-parameter estimation codes for recharge estimation. 相似文献
18.
Fracture toughness measurements under static loading conditions have been carried out in Barre and Lac du Bonnet granites.
An advanced AE technique has been adopted to monitor real-time crack initiation and propagation around the principal crack
in these tests to understand the processes of brittle failure under tension and related characteristics of the resulting fracture
process zone. The anisotropy of Mode I fracture toughness has been investigated along specific directions. Microcrack density
and orientation analysis from thin section studies have shown these characteristics to be the primary cause of the observed
variation in fracture toughness, which is seen to vary between 1.14 MPa.(m)1/2 and 1.89 MPa.(m)1/2 in Barre granite. The latter value represents the case in which the crack is propagated at right angles to the main set of
microcracks. The creation of a significant fracture process zone surrounding the propagating main crack has been confirmed.
Real-time imaging of the fracture process and formation of fracture process zone by AE techniques yielded results in very
good agreement with those obtained by direct optical analysis. 相似文献