共查询到20条相似文献,搜索用时 156 毫秒
1.
本文研究了双轴压缩载荷下裂纹的起裂和非共面传播问题,用动态光弹性方法成功地记录下裂纹的动态扩展过程。获得了双轴压缩载荷下扩展裂纹的传播速度,临界开裂载荷以及开裂角第一系重要断裂参数。研究表明,在双轴压缩载荷下不闭合裂纹前缘应力场是一个混合型的奇异场,裂纹的扩展过程为稳态过程并且表现出显著的阶段性特点。 相似文献
2.
采用压缩单裂纹圆孔板确定岩石动态起裂、扩展和止裂韧度 总被引:2,自引:0,他引:2
爆炸、冲击、地震等人为或自然灾害不可避免,经常造成大量土木工程设施的破坏,因此岩石在动态载荷作用下的行为受到特别关注.岩石动态断裂韧度是评价岩石抵抗裂纹动态起裂、扩展和止裂性能的材料参数,开展岩石动态断裂韧度测试方法的研究对相关理论基础和实验技术的要求较高.岩石动态断裂韧度分为动态起裂、动态扩展、动态止裂三种,虽然关于动态起裂和动态扩展的研究已有一些成果,对岩石动态止裂的研究仍是一个难题,至今几乎无人问津.研究表明,在分离式霍普金森压杆撞击压缩单裂纹圆孔板岩石试样的I型动态断裂试验中,动态起裂、扩展、止裂的全过程可以由黏贴在压缩单裂纹圆孔板试样上的裂纹扩展计监测,岩石的动态起裂、扩展、止裂韧度可以用实验-数值-解析法确定.特别值得一提的是首次测出了岩石的动态止裂韧度.裂纹扩展计信号还显示,压缩单裂纹圆孔板在止裂后,停止的裂纹还会再次动态起裂、扩展并超出裂纹扩展计的检测范围.从能量的角度分析了动态止裂的过程,指出测试动态止裂韧度时要注意的一些问题.结果显示,岩石动态起裂韧度和动态扩展韧度分别随动态加载率和裂纹扩展速度的增大而增大,岩石动态起裂韧度略大于动态止裂韧度. 相似文献
3.
双交叉裂隙是工程岩体中构成断续交叉裂隙的基本单元。裂隙几何参数的变化,会带来裂隙之间岩桥组合形态的改变,并形成岩桥相互作用,对双交叉裂隙的起裂、扩展、贯通及断裂产生直接影响。本文以光敏树脂3D打印技术制备不同次裂隙长度的双交叉裂隙试样,并低温处置使其脆化;开展单轴压缩试验以获得试样的力学性能,利用DIC (Digital Image Correlation,数字图像相关技术)分析试样的变形行为,采用高速摄像机捕捉裂纹萌生和裂隙扩展过程。结果表明,随次裂隙长度的增加,双交叉裂隙试样的峰值强度呈先增大后减小的趋势;试样压缩破坏过程中,最短岩桥(主导岩桥)的两端最先形成应力集中,主导着初始裂纹的形成;尖端裂纹的扩展路径主要受到剪切路径的影响,而剪切路径随加载进程动态变化,由外侧向主导岩桥位置逐步靠拢,控制着次生裂纹的扩展角度。 相似文献
4.
5.
为了开展在不同冲击载荷作用下巷道围岩内裂纹的起裂、扩展及止裂等问题,以可调速冲击试验机进行动态加载试验,采用致密青砂岩制作裂纹巷道模型试件,并利用裂纹扩展计分别记录了动态起裂、扩展、止裂等时刻,对裂纹扩展速度的变化规律进行分析;随后采用AUTODYN有限差分法软件进行相应的数值模拟,数值模拟得到的裂纹扩展路径与试验结果基本一致。经过两者对比分析可知:随着冲击载荷作用的增加,裂纹平均扩展速度逐渐增大,随后趋于稳定值;预制裂纹的起裂时间随着冲击速度载荷的增加而逐渐降低,并在稳定值上下波动;随着冲击速度载荷的增加,裂纹扩展路径过程中的止裂时段逐渐变短。 相似文献
6.
7.
为研究岩石在压剪荷载作用下的断裂特性,在岩石试样侧边切斜裂缝,预制角度分别为30°、45°、60°的初始裂纹,利用TAW-2000微机控制电液伺服岩石三轴试验机进行单轴压缩断裂试验。试验结果表明:边切斜裂缝岩石单轴压缩试样表现为明显脆性,其峰值荷载随初始裂纹角度的增大而增大,大角度初始裂纹具有更高的安全性;试样从预制裂纹尖端开始起裂,并产生向荷载作用方向扩展的翼型裂纹或反翼裂纹,缝尖裂纹扩展初期先受到压剪应力作用,随着裂纹逐渐扩展过程转变为拉应力作用,试样的最终破坏由张拉裂纹主导破坏,初始裂纹角度为45°、60°时伴随部分剪切破坏;裂纹起裂角度随初始裂纹角度的增大而呈现增大趋势,且在初始裂纹角度为60°时,同时出现了反翼裂纹与翼裂纹,起裂模式及角度的控制因素为沿扩展路径方向上法向应力值的相对大小。 相似文献
8.
9.
为了开展含预制裂纹的巷道模型试样在冲击载荷下的动态断裂响应实验,选用青砂岩作为模型材料制作巷道模型试样,以可调速落锤冲击实验机作为冲击加载装置进行试样的动态断裂实验,分析冲击载荷作用下的巷道内裂纹的扩展规律。采用裂纹扩展计及应变片测试系统监测裂纹的起裂时间、扩展速度及止裂时间,并借助于AUTODYN、ABAQUS有限元数值分析软件对实验模型进行数值模拟,计算裂纹的动态起裂韧度、动态扩展韧度、动态止裂韧度等断裂参数。结果表明:巷道内裂纹在扩展路径过程中存在着明显的止裂现象;采用实验-数值方法能够较好地得出裂纹的起裂韧度、扩展韧度和止裂韧度等参数。另外,对止裂现象进行了初步的分析,讨论了试样内应力反射波与透射波对止裂问题的影响。 相似文献
10.
11.
Jiangyu Wu Meimei Feng Guansheng Han Benyu Yao Xiaoyan Ni 《Comptes Rendus Mecanique》2019,347(1):62-89
Investigating the dilatancy, acoustic emission and failure characteristics of fissured rock are significant to ensure their geotechnical stability. In this paper, the uniaxial and triaxial compression experiments with AE monitoring under different loading rates were carried out on fissured rock specimens with the same geometrical distribution of two pre-existing flaws. The dilatancy and AE activity of these specimens were discussed, and the effects of the confining pressure and loading rate on the mechanical parameters and failure characteristics were analyzed. The results show that the exponential strength criterion is more suitable than the Mohr–Coulomb strength criterion to characterize the strength characteristics of fissured rock. The crack evolution and failure characteristics of fissured rock specimens are more complicated than those of intact rock specimens. The failure characteristics of the fissured rock follow the tensile shear coalescence model, crack branching occurs with increasing the loading rate, and the multi-section coalescence model is verified with increasing the confining pressure. The phenomena of stress drop and yield platform usually occur after the dilatancy onset, the specimen does not fail instantaneously, and the propagation and coalescence of cracks cause a sharp increase in the AE signals, circumferential strain, and volumetric strain. 相似文献
12.
《International Journal of Solids and Structures》2005,42(9-10):2505-2516
An experimental approach on propagation and coalescence of pre-existing cracks (fractures) in marble samples under compression is carried out. Two types of newborn cracks are observed: wing (tensile) cracks and secondary (shear) cracks. Both types of cracks initiate from the tips of the fractures and propagate in a stable manner. Wing cracks initiate at an angle with the fractures and tend to propagate towards the direction of the most compressive stress. Secondary cracks, however, initiate in a direction quasi-coplanar to the fractures and also parallel to the wing cracks but in the opposite direction. The orientations and geometries of fractures can decide which kind of wing cracks and secondary cracks will be produced. The interactions between fractures strongly affect the initiation and propagation of wing cracks and secondary cracks, and make examples’ failure patterns thoroughly different. The initial fracture angles of wing cracks range among 52°–68°, which are lower than the results (about 77°) of previous experiments on molding materials. In addition, the characters of acoustic emission (AE) of pre-cracked marble samples are also studied. For some rock samples, a secondary peak value phenomenon of AE counts is observed. For the samples with zigzag fractures, the accumulated AE counts at the moment of failure occupy almost half of the summation of whole load processes. This reveals that the failure of materials with zigzag fractures is more unexpected. 相似文献
13.
C. Tekog̃lu J.-B. Leblond T. Pardoen 《Journal of the mechanics and physics of solids》2012,60(7):1363-1381
Depending on the relative positions of voids and on the loading conditions, shear loading components can play an important role in the void coalescence process leading to ductile fracture. Yet, most void coalescence criteria including the original criterion of Thomason, and its various extensions/improvements, take only normal loads into account and neglect the contribution from shear loads to coalescence. Shear can affect both the stress/strain at the onset of coalescence and the direction of deformation localization. In this paper, first, the predictive capabilities of different coalescence criteria without shear effect are critically assessed and the expressions involved in the original Thomason criterion are fine-tuned by comparing with 3D finite element calculations performed on a unit cell containing a spheroidal void. Then, the improved Thomason criterion is theoretically extended—by using limit load analysis—to incorporate the effect of shear. The predictions of this new coalescence criterion are in good agreement with the results produced by 3D finite element calculations, for both loadings involving or not a shear component. 相似文献
14.
岩体的破坏主要是岩体中裂纹的扩展与贯通的结果.受压岩体的裂纹尖端,可能处于压剪状态,也可能处于拉剪状态.从断裂力学的角度,研究了地下工程围岩中的裂纹在各种受力条件下(包括拉剪、压剪两种情况)的起裂、扩展及贯通以至最终形成劈裂裂缝的特征及各个阶段的判据.针对压剪断裂,裂纹之间存在有粘结力与摩擦强度的特征,提出了岩石压剪断裂性判据.最后以受压岩体中的斜裂纹扩展过程分析为例,模拟了岩体中裂纹逐渐发展成劈裂破坏的过程,并说明了各个阶段的计算方法. 相似文献
15.
Louis Ngai Yuen Wong Huan-Qiang Li 《International Journal of Solids and Structures》2013,50(22-23):3685-3706
Crack propagation and coalescence processes are the fundamental mechanisms leading to progressive failure processes in rock masses, in which parallel non-persistent rock joints are commonly involved. The coalescence behavior of the latter, which are represented as pre-existing coplanar flaws (cracks), is numerically investigated in the present study. By using AUTODYN as the numerical tool, the present study systematically simulates the coalescence of two pre-existing coplanar flaws in rock under compression. The cumulative damage failure criterion is adopted in the numerical models to simulate the cumulative damage process in the crack initiation and propagation. The crack types (shear or tensile) are identified by analyzing the mechanics information associated with the crack initiation and propagation processes. The simulation results, which are generally in a good accordance with physical experimental results, indicate that the ligament length and the flaw inclination angle have a great influence on the coalescence pattern. The coalescence pattern is relatively simple for the flaw arrangements with a short ligament length, which becomes more complicated for those with a long ligament length. The coalescence trajectory is composed of shear cracks only when the flaw inclination angle is small (such as β ? 30°). When the pre-existing flaws are steep (such as β ? 75°), the coalescence trajectory is composed of tensile cracks as well as shear cracks. When the inclination angle is close to the failure angle of the corresponding intact rock material, and the ligament length is not long (such as L ? 2a), the direct shear coalescence is the more favorable coalescence pattern. In the special case that the two pre-existing flaws are vertical, the model will have a direct tensile coalescence pattern when the ligament length is short (L ? a), while the coalescence between the two inner flaw tips is not easy to achieve if the ligament length is long (L ? 2a). 相似文献
16.
17.
18.
Relations between a micro-mechanical model and a damage model for ductile failure in shear 总被引:1,自引:0,他引:1
Viggo Tvergaard Kim Lau Nielsen 《Journal of the mechanics and physics of solids》2010,58(9):1243-1252
Gurson type constitutive models that account for void growth to coalescence are not able to describe ductile fracture in simple shear, where there is no hydrostatic tension in the material. But recent micro-mechanical studies have shown that in shear the voids are flattened out to micro-cracks, which rotate and elongate until interaction with neighbouring micro-cracks gives coalescence. Thus, the failure mechanism is very different from that under tensile loading. Also, the Gurson model has recently been extended to describe failure in shear, by adding a damage term to the expression for the growth of the void volume fraction, and it has been shown that this extended model can represent experimental observations. Here, numerical studies are carried out to compare predictions of the shear-extended Gurson model with the shear failures predicted by the micro-mechanical cell model. Both models show a strong dependence on the level of hydrostatic tension. Even though the reason for this pressure dependence is different in the two models, as the shear-extended Gurson model does not describe voids flattening out and the associated failure mechanism by micro-cracks interacting with neighbouring micro-cracks, it is shown that the trends of the predictions are in good agreement. 相似文献
19.
《Comptes Rendus Mecanique》2019,347(6):490-503
The present article investigates the influences of the rock bridge ligament angle, β, and the confinement on crack coalescence patterns by conducting laboratory and numerical tests on rock-like specimens. Laboratory tests show that no coalescence in the rock bridge occurred for low β. With an increase of β, tensile-shear coalescence and tensile coalescences subsequently occurred. In addition, the increase in the confinement first promoted shear coalescence and then restrained crack coalescence for low β, whereas the tensile coalescence was restrained by the increase in confinement for high β. The numerical results corroborate the laboratory tests in the coalescence patterns. In addition, the numerical study shows that tensile and shear cracks subsequently initiated near crack tips because of the concentrated tensile and shear stresses, respectively. Regarding the influence of β on crack coalescence, tensile or shear stress failed to concentrate in rock bridges for low β. Therefore, the cracks failed to coalesce, whereas with the increase in β, tensile and shear stress concentrations occurred in the bridge and led to either tensile shear or tensile coalescence. Regarding the influence of confinement on crack coalescence, the increase in confinement restrained the tensile stress concentrations and further hindered tensile crack coalescence in rock bridges for high values of β. 相似文献
20.
C. Soyarslan M. Malekipour Gharbi A.E. Tekkaya 《International Journal of Solids and Structures》2012,49(13):1608-1626
We present a combined experimental–numerical study on fracture initiation at the convex surface and its propagation during bending of a class of ferritic–martensitic steel. On the experimental side, so-called free bending experiments are conducted on DP1000 steel sheets until fracture, realizing optical and scanning electron microscopy analyses on the post mortem specimens for fracture characterization. A blended Mode I – Mode II fracture pattern, which is driven by cavitation at non-metallic inclusions as well as martensitic islands and resultant softening-based intense strain localization, is observed. Phenomena like crack zig-zagging and crack alternation at the bend apex along the bending axis are introduced and discussed. On the numerical side, based on this physical motivation, the process is simulated in 2D plane strain and 3D, using Gurson’s dilatant plasticity model with a recent shear modification, strain-based void nucleation, and coalescence effects. The effect of certain material parameters (initial porosity, damage at coalescence and failure, shear modification term, etc.), plane strain constraint and mesh size on the localization and the fracture behavior are investigated in detail. 相似文献