共查询到19条相似文献，搜索用时 171 毫秒
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按照压剪应力场中袭纹具有的特点,简化成三种力学模型——狭长缺口、顺序闭合裂纹及初始闭合裂纹。利用文中建议的局部分析法,对其端部应力场做的一般分析,导出了他们的普遍表达式。用光弹性实验及有限元计算对所得结果做的分析表明,它们是成立的。这些结果有助于了解构造地震震源的破裂机制及其应力场分布的某些特点。 相似文献
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岩石中普遍存在的微裂纹对其物理性质有十分显著的影响.为了得到不同围压条件下岩样内部微裂纹形态的变化,选取几种具有明显层理的岩石圈岩石样品,在不同围压下沿相互正交的三个方向对纵横波速度和线应变等进行了测量,根据O’Connell模型通过计算得出有效泊松比、裂纹密度、裂纹孔隙度和裂纹的c/a比值（a为硬币形裂纹半长轴的长度,c为其半宽度）.结果表明,随着围压的增加,在垂直于层理面的方向上裂纹闭合最快但c/a比值不减反增.结合显微组构分析可知,岩石中的裂纹表面实际上是凸凹不平的,在围压增加引起裂纹闭合过程中一条裂纹可以变成几个,长度成倍减小但宽度变化不大,所以在垂直于层理面的方向上c/a比值随围压增加而增大.但另两个方向上的变化明显不同,应该与模型本身的适用范围有关.通过同时测量纵、横波速度,计算c/a比值,可以对样品中微裂纹的几何形态及空间分布方式有定性或半定量的了解. 相似文献
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在以往试验研究的基础上,建立了框架异型节点等效核心区在剪、压复合作用下的计算模型,应用简化拉压杆模型方法对等效核心区进行了受力分析.研究表明:基于简化拉压杆模型方法计算得到异型节点的抗剪承载力与现行规范建议方法计算结果相当,但简化拉压杆模型方法有明确的力学计算模型,基于该模型计算得到的抗剪承载力与试验结果吻合较好.在此... 相似文献
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腾冲火山区地震构造应力场研究 总被引：5，自引：2，他引：3
通过对腾冲火山区强震和中小地震震源机制制解分析,对火山区构造应力场方向空间分布,以及震源类型和破裂特征作了研究。利用腾冲火山区中小地震地震波资料,计算得到的地震震源处剪应力强度值,对火山区应力场强度或初始应力状态进行了研究。腾冲火山区构造庆力场主要为北北东－北东－北东东向,接近水平的压应力场。腾冲火山区凛环境剪应力场高值区所包围的低剪应力值分布区。腾冲火山区地震震源具有多种类型,震源破裂具有多种形 相似文献
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裂纹系微破裂集结和动态扩展的实验研究 总被引：3，自引：0，他引：3
研究了裂纹系的动态破裂,重点考察了裂纹系相互作用.选用大理石、玻璃为实验材料,将其加工成薄板状,并在板内预制各种不同形态的裂纹系,在单轴压下用可见光透视观察裂纹系动态相互作用的破裂过程.实验中发现,岩石的动态破裂过程和玻璃有很大差别,岩石的裂纹系动态相互作用后期是通过微破裂演化来实现的,而在玻璃中观察不到.裂纹系的不均匀应力场分布是破裂演化的初始原因.通过实验,给出大理石材料中各种不同形态裂纹系的动态破裂演化的全场过程图像,直观地揭示了含裂纹系岩石变形破坏的实质.实验显示了不同几何形态的裂纹系的破裂发育过程有明显区别.在微破裂集结时,周围的破裂部分闭合.因此,用二维模型描述的微破裂图像和实际有很大出入.为了消除这个差距,必须研究三维破裂.本文的实验结果表明,裂纹(断层)不能起到阻碍破裂扩展的作月;裂纹(断层)作为障碍体,和预存裂纹之间存在强烈的相互作用,使得样品的强度降低几乎一个量级.讨论了上述结论对于认识地震(包括矿震)断层行为的意义. 相似文献
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本研究搜集了GCMT中自1976年1月1日至2017年4月30日喜马拉雅东构造结及其周边区域的102个震源机制解数据,应用MSATSI软件反演了该区域的构造应力场.反演结果给出了该区域应力场的总体特征:最大主压应力轴自西向东呈现NNE-NE偏转,最小主压应力轴自西向东呈现NWW-NW-NNW扇形偏转;整个研究区域σ_3轴倾角较小接近水平,σ_1轴倾角情况复杂,大体上自西向东由水平转向直立;R值自西北至东南出现规律性递增现象.根据反演结果,部分网格点中应力轴倾角的置信区间过大,且不同应力轴的置信区间存在重叠现象,同时该部分网格内震源机制解类型多样.针对上述现象,本文利用两种反演方法对单个网格基于不同类型震源机制解数据进行单独反演、利用人工合成震源机制数据进行验证以及各震源机制解相对于参考应力张量的残差分析等方法对其进行了深入的验证和分析,分析结果表明导致这一现象的原因可能是单个网格内应力场不均匀所致,此时应力场反演结果为多个应力场的综合.本研究结果可为后续应力场研究中网格的合理划分以及应力场结果评价提供参考. 相似文献
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本文在实验室对所获取的东营地区层理发育的低孔隙度页岩和泥岩的各向异性裂纹演化特性进行了研究,获得了各向同性条件下泥页岩的力学与超声波响应特性,分析了应力幅度对于页岩声波速度和各向异性的影响.主要结论包括:(1)泥页岩在循环载荷下存在滞后效应,表明其经历了去压实或油气产生导致的超压;(2)泥岩和页岩具有不同程度的各向异性,随着各向同性压力的增高微裂隙逐渐闭合,样品的各向异性程度减弱;(3)分析了岩石韧度和裂纹损伤参数随压力的变化特征,相比泥岩,页岩各向异性程度更高,随压力变化更明显,其裂纹导致的附加各向异性更强;(4)分析了各向异性岩石的动态弹性模量特征,由于软裂隙空间的闭合,动态弹性模量在低压条件下都随着围压的增加有硬化趋势. 相似文献
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工程结构三维疲劳裂纹最大应力强度因子计算 总被引：3，自引：2，他引：1
介绍了裂纹的类型、裂纹尖端应力场的奇异性。以一维问题为例,推导论证了奇异单元能够很好的反映裂纹尖端应力场的奇异性。应力强度因子一般表达式表明应力强度因子与载荷呈线性关系,并依赖于物体和裂纹的几何形状和尺寸。本文借助大型通用有限元软件ANSYS,采用位移外插法计算了三维表面裂纹前沿不同位置处的应力强度因子,并与《应力强度因子手册》基于实验的理论公式计算结果相比较。结果表明:有限元结果与理论解误差较小,裂纹最深处应力强度因子最大。 相似文献
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本文介绍了以激光全息干涉法观测单轴压缩下,大理岩岩样表面的变形位移场。全息干涉图可以反映出由于岩石内部微裂隙丛集激增所导致的变形局部化,实验采用板状大理岩试件,在中心处预制了不同角度的裂缝,实验在MTS伺服压机中加载直至宏观破坏,观测了裂隙的发展过程。实验表明:当裂缝角小于45时,先在裂缝尖端处的张应力集中部位出现新裂纹,它的起裂角(与原裂缝的交角)90,裂纹弯向压力方向并趋于稳定。当>45时,在上述张裂纹稳定后,在裂缝尖端附近再次发生张裂,其起裂角60,同样弯向压力方向后稳定。在这些前期张破裂稳定后,在张裂的相反方向,也即裂缝的共轭方向上,出现内部微裂隙的丛集,并随后发生宏观的剪破坏,我们认为此逆向剪切破坏与大理岩的多晶组构有关,与应变弱化过程中变形和应力的调整有关。 相似文献
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Crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the Daisetsu Mountains, Hokkaido, northern Japan. Sequential data recorded the gradual widening of a crack to the point of critical crack extension, which resulted in catastrophic rock breakage. The data indicate that a combination of liquid water in?ltration into crack tip and subsequent freezing is the most signi?cant factor contributing to critical crack extension. The recorded sub‐critical crack movements involved a number of minor crack extensions and contractions, the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate‐shaped rock fragment. Larger crack extensions occurred when stress at the crack tip exceeded a threshold value, possibly re?ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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A numerical study on the influence that cracks and discontinuities (closed cracks) can have on the seismic response of a hypothetical soil–structure system is presented and discussed. A 2-D finite-difference model of the soil was developed, considering a bilinear failure surface using a Mohr–Coulomb model. The cracks are simulated with interface elements. The soil stiffness is used to characterize the contact force that is generated when the crack closes. For the cases studied herein, it was considered that the crack does not propagate during the dynamic event. Both cases, open and closed cracks, are considered. The nonlinear behavior was accounted for approximately using equivalent linear properties calibrated against several 1-D wave propagation analyses of selected soil columns with variable depth to account for changes in depth to bed rock. Free field boundaries were used at the edges of the 2-D finite-difference model to allow for energy dissipation of the reflected waves. The effect of cracking on the seismic response was evaluated by comparing the results of site response analysis with and without crack, for several lengths and orientations. The changes in the response obtained for a single crack and a family of cracks were also evaluated. Finally, the impact that a crack may have on the structural response of nearby structures was investigated by solving the seismic-soil–structure interaction of two structures, one flexible and one rigid to bracket the response. From the results of this investigation, insight was gained regarding the effect that discontinuities may have both on the seismic response of soil deposits and on nearby soil–structure systems. 相似文献
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In this work, a hybrid boundary integral equation method (BIEM) is developed, based on both displacement and hypersingular traction formulations, for the analysis of time-harmonic seismic waves propagating through cracked, multi-layered geological regions with surface topography and under plane strain conditions. Specifically, the displacement-based BIEM is used for a multi-layered deposit with interface cracks, while the regularized, traction-based BIEM is used when internal cracks are present within the layers. The standard uni-dimensional boundary element with parabolic shape functions is employed for discretizing the free surface and the layer interfaces, while special discontinuous boundary elements are placed near the crack tips to model the asymptotic behaviour of both displacements and tractions. This formulation yields displacement amplitudes and phase angles on the free surface of a geological deposit, as well as stress intensity factors near the tips of the cracks. Finally, in the companion paper, numerical results are presented which show that both scattered wave and stress concentration fields are sensitive to the incidence seismic wave parameters and to specific site conditions such as surface topography, layering, the presence of cracks and crack interaction. 相似文献
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We present a study of the motion of the ground in the near field of a preexisting vertical crack driven by excess tensile stress. Using the discrete wave number method, we make a complete representation of the three components of ground displacement resulting from a small incremental extension of the bottom tip of the crack and analyze the effects of the medium structure on the ground response. The results show the strong impulsive character of the dynamic motion near the source and demonstrate that the first motion is directed everywhere outward. Marked oscillations are observed in the ground response associated with the ringing of the crack faces triggered by the rupture. The displacement is dominantly vertical near the epicenter but becomes predominantly horizontal beyond the immediate source region. The presence of layers has a strong effect on the complexity and duration of the ground response. The static vertical and longitudinal displacements are respectively downward and inward in the epicentral area. 相似文献
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Vertical stresses in the earth's upper crust may be evaluated by the depth times the average unit weight of the overlying rock mass; however, the horizontal stress is difficult to obtain. Rock usually contains joints or cracks, and its fracture toughness is limited. If the horizontal stress acting on a cracked rock body exceeds a certain range, the crack will propagate and lead to rock fracture; and if a cracked rock is stable, the horizontal stress must be within a certain range. Therefore, from the stability condition of cracks, the range of horizontal stress can be evaluated. In this paper, a collinear crack model is employed to establish the cracked rock stability condition, and our theoretical results generally agree with the in-situ measurement results. The theoretical results can well explain the phenomenon that the ratio of horizontal stress to vertical stress near crust surface is scattered in a wide range, but in deep zone, it is scattered in a narrow range. 相似文献