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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：1，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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为了探明裂纹扩展时所受阻力的机制,寻求材料的动态断裂特性值(动态应力强度因子K_l~d(t)、起裂韧性K_c、止裂韧性K_d)之间的相互联系及这些值的物理解释,进而得到合适的断裂判据,本文用动态焦散线方法分析了脆性材料的三点弯曲试件、双悬臂梁试件在冲击载荷作用下的动态响应。 相似文献
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本文采用两自由度的裂纹扩展模型,以桅杆结构纤绳拉耳孔边裂纹前缘最深点和表面点的裂纹扩展增长量来追踪裂纹扩展。基于最小二乘法原理对通过有限元法所获得的各种裂纹形状所对应的裂纹前缘最深点和表面点的无因次形状因子进行多项式曲线拟合,用拟合曲线上的值代替离散的无因次形状因子扩充插值数据库,采用拉格朗日插值法计算任意形状裂纹前缘最深点和表面点无因次形状因子,并计算得到确定裂纹扩展速率所需要的应力强度因子幅度。最后根据裂纹前缘最深点和表面点的裂纹扩展速率确定桅杆结构纤绳连接拉耳孔边裂纹的扩展特性。 相似文献
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本文利用数值模拟方法对 2种典型地震断层系进行了研究。首次引入利用所有裂纹面上裂纹张开位移 ( COD)数据计算应力强度因子和应力场的方法 ,提高了计算精度。本文对此方法进行了验证 ,利用边界元算法获得 COD数据 ,将全裂纹面上的 COD数据代入公式 ,拟合出应力强度因子和应力场。此方法后处理少、可靠性好、计算时间也相应较短 ,且易于操作实现 ,适用范围较广。在上述工作的基础上 ,本文利用此算法讨论了 2种典型的平面双等长裂纹系问题。第一种是平面共线剪切双裂纹 ,主要讨论了这种非单一裂纹在外力作用下的相互作用 ,定量给出了裂… 相似文献
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在济南辉长岩的三轴压缩实验(3=1.3kb)中, 通过显微镜观测了岩石内部微裂纹的发展.实验结果说明, 在低应力状态下, 微裂纹主要出现在岩石矿物结晶颗粒内部, 其方向主要取决于矿物颗粒的结晶学形态.当应力达到岩石强度80%左右时, 在样品中部某一对角线附近, 微裂纹密度较高, 出现一些穿过几个矿物颗粒的微断层.微断层的取向与外力应力场有明显的关系, 一般与1成40左右的夹角.本实验还同时测量了样品弹性波的速度(Vp, Vs)和体积变化.实验表明, 岩石内部微裂纹的发展以及微裂纹对岩石物理性质所产生的影响, 是与晶体颗粒的尺度有关. 相似文献
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本文用 Split-Hopkinson 压力杆装置研究了应力波通过破裂岩石试件的衰减现象。给出了灰砂岩、石灰岩两种岩石动态的破裂强度与应力应变关系.结合受应力作用的岩样切片的微观观察,对应力裂纹、裂纹的动态分叉现象进行了分析讨论. 相似文献
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本文采用边界元法研究了半空间中一近表面裂纹对SH波的散射问题,导出了以裂纹张开位移为未知函数的边界积分方程,针对边界积分方程高阶奇异性的特点,运用降低奇异性的方法,计算了裂纹边界面的裂纹张开位移、半空间表面的散射位移、裂纹尖端的动态应力强度因子。给出的算例表明,本文的方法不仅计算量小,而且有较好的精度。 相似文献
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Application of caustic method to determining stress intensity factor of compressive shear crack 总被引：1，自引：0，他引：1
Introduction The caustics method has been introduced into seismology in recent years and preliminary in- vestigation indicates that it is effective to study the compressive stress (strain) of transparent sam- ples such as plexiglass (XU et al, 2001, 2002; Xu et al, 2000, 2002; XIONG et al, 2000, 2002). Especially, as a seismological concept, earthquake nuclei, becomes clearer according to the caustic shadow, which combines plastic area, nucleation area and crack concentration area together … 相似文献
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采用大理岩圆柱试样,与轴线约成30角预制不连续裂缝,再用环氧树脂胶接,以实验观测裂缝尺度及其填充物对剪切破裂能的影响.结果表明:当裂缝相对面积从0增加到90%时,破裂能从(6.92.1)103焦耳/米2逐步降到(0.60.5)1O3焦耳/米2;而使用 Knopoff方法和引入滑动弱化模式后的方法,求得的理论应力降几乎不变.它们与实测应力降的比却逐步增大并达到10.同时,分析了地震时和岩石破裂时的应力降差别很大,以及不同方法所得破裂能差别很大的原因,认为断层的蜂窝状接触对上述问题可能有重要影响. 相似文献
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１９９２年１月海南省东方县发生小震群活动，本文利用在震中附近设立的５台ＤＣＳ－３０２数字磁带加速度地震仪记录的近场资料，进行了剪切波分裂的研究采用相关函数方法，通过对１８个做了精确定位的地震事件共４２条有效记录的分析，计算出了快剪切波的偏振方向为１１３°±１８Ｏ°，慢剪切波的时间延迟为（３．１±１．１）ｍｓ／ｋｍ，裂隙密度的平均值为０．００９７±０．００３３．结合该地区的地震活动性，分析了区域应力变化对时间延迟的影响，并根据ＥＤＡ理论讨论了分裂剪切波的时间延迟的变化特征，发现快、慢剪切波的到时差（时间延迟）随地震活动性及应力积累而变化，并推断出该区的主压应力场为北西西方向． 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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— The mechanical behaviour of Bentheim sandstone, a homogeneous quartz-rich sandstone with porosity of 22.8%, was investigated by triaxial compression tests conducted on dry samples. At confining pressures up to 35 MPa, the failure mode was characterized by a typical brittle deformation regime, as the samples showed dilatancy and failed by strain softening and brittle faulting. Previous studies have shown that the mechanical behaviour and failure mode of brittle porous granular rocks are governed by the time-dependent growth of microcracks. We analyse this process using the “Pore Crack Model” based on fracture mechanics analysis. It is consistent with the microstructure of porous granular rocks since it considers the growth of axial cracks from cylindrical holes in two dimensions. These cracks grow when their stress intensity factors reach the subcritical crack growth limit. Interaction between neighbouring cracks is introduced by calculating the stress intensity factor as the sum of two terms: a component for an isolated crack and an interaction term computed using the method of successive approximations. It depends on crack length, pore radius, pore density, and applied stresses. The simulation of crack growth from cylindrical holes, associated with a failure criterion based on the coalescence of interacting cracks, is used to compare the theoretical stress at the onset of dilatancy and at macroscopic rupture to the experimental determined values. Our approach gives theoretical results in good agreement with experimental data when microstructural parameters consistent with observations are introduced. 相似文献
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Kacper R. Rybicki 《Pure and Applied Geophysics》1990,134(2):283-301
Faulting in a medium with an inhomogeneity is analysed applying two-dimensional models consisting of a shear crack in a presence of a circular inclusion. The stress drop and the stress intensity factor are calculated for mode II and III cracks of various positions in relation to the inclusion. The results demonstrate that the effect of an inhomogeneity on a shear zone strongly depends on the location of a zone for either mode II or mode III shear zone. This effect is mostly due to the spatial distribution of external effective shear stress around an inhomogeneity. Depending on the position, an inhomogeneity may have either a destabilizing effect (the stress intensity factor becomes greater) or a stabilizing influence (the stress intensity factor is decreased or faulting is prohibited so the inhomogeneity acts as an asperity or a barrier). There is a substantial difference, however, between mode II and mode III shear zones approaching an inhomogeneity centrally. Namely, the effect of inhomogeneity on the mode III shear zone located in the immediate vicinity of the inhomogeneity is in this case considerably more pronounced than that for mode II shear zone and depends to a far greater extent on the rigidity contrast between the inhomogeneity and the surrounding medium. Another important conclusion is that the quantitative effect of an inhomogeneity on faulting depends essentially on the initial value of the stress drop of a shear zone approaching an inhomogeneity, being decidedly higher for a shear zone of small stress drop. It means that in specified areas in the proximity of medium inhomogeneities one should expect substantially greater faulting activity in which weak events prevail than in other regions surrounding inhomogeneities where such activity should be distinctly reduced. Such conclusions apply to both high rigidity inhomogeneities, which, in particular, may be associated with intrusions from the upper mantle, and to low rigidity inhomogeneities such as volcanos. The present model sets forth the plausible explanation regarding why earthquakes from the same region are occasionally characterized by various values of the stress drop. The model also presents the quantitative insight concerning how heterogeneity of the medium, in the sense of spatial variation of elastic constants, affects faulting. 相似文献
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—In order to investigate the effects of injected water in hydraulic fracturing, experiments were conducted on cubic granite
specimens, comparing fracturings induced by conventional water injection with those induced by pressurization of a urethane
sleeve, thereby realizing "hydraulic fracturing" without the use of fracturing fluid. In both experiments, a shear type mechanism
was found to be dominant in fault plane solutions of AE events. However, in the case of water injection, cracks extended rapidly
with large drops in hole water pressure and bursts of AE, whereas in pressurization by the urethane sleeve, cracks extended
stepwise with no such large drops in hole pressure and no bursts of AE. The difference in crack extension in the two experiments
can be analyzed by comparing relations between crack length and stress intensity factor of mode I at a crack tip. The observation
and analysis indicate that existence of fracturing fluid like water helps initiated cracks to extend rapidly and widely in
hydraulic fracturing in actual HDR fields.
Received September 12, 1996, accepted January 24, 1997 相似文献