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基于对混凝土细观力学的认识,假定混凝土是由砂浆基质,骨料及它们之间的界面组成的三相复合材料,各组分的材料性质按照某个给定的Weibull分布来赋值,细观单元满足弹性损伤的本构关系,应用细观力学损伤模型研究了混凝土的宏观力学性质,并且通过有限元程序对中心裂缝混凝土试件在单向拉伸情况下的破坏过程进行了数值模拟.模拟结果表明,该模型可以用来研究单向载荷作用下混凝土结构的破坏机理. 相似文献
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多尺度嵌入式离散裂缝模型模拟方法 总被引:1,自引:0,他引:1
天然裂缝性油藏和人工压裂油藏内裂缝形态多样,分布复杂,传统的离散裂缝模型将裂缝作为基岩网格的边界,采用非结构化网格进行网格划分,其划分过程复杂,计算量大。嵌入式离散裂缝模型划分网格时不需要考虑油藏内的裂缝形态,只需对基岩系统进行简单的网格剖分,可以大大降低网格划分的复杂度,从而提高计算效率。然而,在油藏级别的数值模拟和人工压裂裂缝下的产能分析中,仍然存在计算量巨大、模拟时间过长的问题。本文提出嵌入式离散裂缝模型的多尺度数值计算格式,使用多尺度模拟有限差分法研究嵌入式离散裂缝模型渗流问题。通过在粗网格上求解局部流动问题计算多尺度基函数,多尺度基函数可以捕捉裂缝与基岩间的相互关系,反映单元内的非均质性,因此该方法既有传统尺度升级法的计算效率,又可以保证计算精度,数值结果表明这是一种有效的裂缝性油藏数值模拟方法。 相似文献
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刚体-弹簧元模型是一种离散化分析模型,可以反映连续体从开裂到破坏不连续过程的真实裂缝形态。本文在总结既有相关研究的基础上,引入并程序化刚体-弹簧元模型用于混凝土构件开裂破坏行为研究,特别是有关混凝土构件开裂后直至破坏的裂缝真实形态研究。首先确定了三维刚体-弹簧元模型中刚体单元的划分、弹簧元的特性(混凝土材料本构关系施加于弹簧元)、刚体单元与弹簧元装配方式、钢筋本构关系及其与混凝土相互作用,然后实现了刚体-弹簧元模型用于混凝土构件开裂破坏行为研究的程序化,并以剪切破坏的钢筋混凝土构件进行实例验证。结果表明,基于刚体-弹簧元模型的程序可以较为准确地反映该钢筋混凝土构件从开裂到破坏真实裂缝形态。 相似文献
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天然裂缝性油藏和人工压裂油藏内裂缝形态多样,分布复杂,传统的离散裂缝模型将裂缝作为基岩网格的边界,采用非结构化网格进行网格划分,其划分过程复杂,计算量大。嵌入式离散裂缝模型划分网格时不需要考虑油藏内的裂缝形态,只需对基岩系统进行简单的网格剖分,可以大大降低网格划分的复杂度,从而提高计算效率。然而,在油藏级别的数值模拟和人工压裂裂缝下的产能分析中,仍然存在计算量巨大、模拟时间过长的问题。本文提出嵌入式离散裂缝模型的多尺度数值计算格式,使用多尺度模拟有限差分法研究嵌入式离散裂缝模型渗流问题。通过在粗网格上求解局部流动问题计算多尺度基函数,多尺度基函数可以捕捉裂缝与基岩间的相互关系,反映单元内的非均质性,因此该方法既有传统尺度升级法的计算效率,又可以保证计算精度,数值结果表明这是一种有效的裂缝性油藏数值模拟方法。 相似文献
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再生大骨料自密实混凝土梁的裂缝开展机理作为梁结构可靠性设计的理论基础,具有重要的工程意义。本文对不同再生大骨料取代率的再生大骨料自密实混凝土梁进行了数值仿真模拟,分析了再生大骨料自密实混凝土梁的裂缝开展情况和荷载-挠度曲线。结果表明,采用随机骨料模型对再生大骨料自密实混凝土梁进行裂缝开展模拟的方法可行;裂缝主要沿着再生大骨料和自密实混凝土交界面扩展,少部分经过再生大骨料;不同再生大骨料取代率的再生大骨料自密实混凝土梁的裂缝开展机理相同;相比自密实混凝土,再生大骨料自密实混凝土梁的承载力降低,脆性增强。 相似文献
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Simulation of crack spacing using a reinforced concrete model with an internal length parameter 总被引:3,自引:0,他引:3
Summary A gradient-enhanced smeared crack model and bond-slip interface elements are utilized in finite element simulations of reinforced
concrete. The crack model is rooted in an enhanced plasticity theory. It uses the Rankine failure surface dependent on an
equivalent inelastic strain measure as well as on its Laplacian. As a result, finitely sized fracture process zones and realistic
crack spacings are obtained. A reinforced concrete bar in uniaxial tension is analyzed to demonstrate the regularizing influence
of the internal length parameter in the model and to evaluate the influence of the model parameters on the energy dissipation
in multiple cracks. A comparison of numerical simulations with experimental results for a beam without shear reinforcement
in four-point bending concludes the analysis.
Received 4 November 1997; accepted for publication 23 April 1998 相似文献
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综述了模拟准脆性材料开裂过程的数值计算方法的研究进展和工程应用,比较了表征强不连续问题的显式非连续模型和隐式非连续模型的优缺点.结合混凝土粘结裂纹, 重点讨论了嵌入非连续模型,扩展有限元方法和富集有限元技术等非连续方法的构造特征和本质区别.从各种富集方法的理论完备性考察,以假定发展应变为基础的嵌入非连续方法虽然可以解决混凝土开裂过程中的应力锁死,满足内部边界的静力平衡条件以及反映开裂后的位移不连续问题,但嵌入非连续所采用的富集函数在开裂单元中并不能满足协调条件,使非连续两侧的应变不独立. 其局限性是由于富集自由度在单元的水平上引入,而以单位分解为基础的扩展有限元和富集有限元的富集函数以节点自由度的方式引入,除具有嵌入非连续的优点, 还可以有效消除嵌入非连续引起裂纹两侧应变的相互影响.文中同时指出了网格重构技术,弥散裂纹模型的局限性以及扩展有限元和富集有限元技术在构造方式上的细微差别.对于节点自由度方式引入的富集函数, 其操作困难性在文中也作了说明. 相似文献
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Different fracture methods in meshfree methods are studied and compared. Our studies focuses on the elementfree Galerkin (EFG)
method though similar results were obtained with SPH and MPM. Three major fracture approaches are tested: Natural fracture,
smeared crack method and discrete crack method. In the latter method, the crack is represented as continuous line and as set of discrete crack segment. Natural fracture is a key feature of meshfree methods. In some numerical examples, we will
show that natural fracture criterion cannot handle even simple fracture adequately. Moreover, we will show in our numerical
examples that smeared crack models can capture global behavior appropriately for simple examples but not for complex examples
involving branching cracks. The most accurate methods are discrete fracture methods. 相似文献
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The authors have developed a new line-spring boundary element method in thepresent paper,which combines the advantage of the line-spring model with that of theboundary element method.This method reduces the three-dimension problem of thesurface cracks into a quasi-one-dimension problem and can be used to analyze thesurface cracked plate under various loading conditions.In this paper theoreticalanalyses and numerical verifications are carried out.The calculated results arereported,which indicate that the present method is efficient and can be used to analyzethe surface crack problem on a personal computer. 相似文献
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混凝土结构在服役期间受外界载荷的影响容易产生裂缝, 导致结构刚度降低、构件承载性能衰退, 而采用准确的计算方法预测混凝土裂缝的发展是治理裂缝的基本前提, 也是保障结构安全的重要手段. 连续损伤力学方法(continuou damage method, CDM)能够描述微裂缝的扩展过程, 但不能表示离散的开裂面, 且存在网格诱导偏差及虚假应力传递的弊端, 扩展有限单元法(mechanics-extended finite element method, XFEM)能够描述宏观裂纹的扩展过程, 但不能反映微裂缝的动态扩展, 两者计算出的裂纹分布与实际差异均较大. 现有的CDM-XFEM方法已经能够模拟混凝土微裂缝及宏观裂缝发展的整个过程, 但忽略了宏观裂缝出现时混凝土产生的塑性应变, CDM与XFEM的能量转化过程欠缺平衡性. 因此, 本文重点考虑能量转化时的塑性耗散, 选取指数型函数为粘结裂缝的牵引-分离模式, 基于能量及应力等效的条件重新构建了CDM与XFEM之间的能量转化方程. 采用广义逆最小二乘法求解能量转化系数, 确定能量转化时的临界位移, 并给出了裂缝面水平集的更新算法及整体计算方法的程序流程. 以双切口混凝土受剪拉开裂试验为例, 采用多种裂缝计算方法与试验进行了对比. 结果表明, 采用考虑混凝土塑性耗散的CDM-XFEM方法算出的裂缝分布及拉力-张开位移曲线与试验结果差异最小, 说明采用考虑混凝土塑性耗散的CDM-XFEM计算方法能够更好地计算混凝土裂缝. 相似文献
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C. Wessel A. Cisilino O. Santi J. Otegui M. Chapetti 《Theoretical and Applied Fracture Mechanics》2001,35(1)
This work is concerned with the assessment of propagation of multiple fatigue cracks in three-dimensions. Computational modelling of fatigue crack propagation is made together with detection and monitoring of the crack shape development. The boundary element method (BEM) is used for automating the modelling of crack propagation in linear elastic as well as elastic–plastic regimes. Strain at several positions on the specimen surface near the crack mouth is measured to monitor crack initiation, shape development and closure levels. Examples are provided to validate the model by comparing the experimental results with those obtained by numerical predictions. 相似文献
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梯度材料中矩形裂纹的对偶边界元方法分析 总被引:2,自引:0,他引:2
采用对偶边界元方法分析了梯度材料中的矩形裂纹. 该方法基于层状材料基本解,以非裂纹边界的位移和面力以及裂纹面的间断位移作为未知量. 位移边界积分方程的源点配置在非裂纹边界上,面力边界积分方程的源点配置在裂纹面上. 发展了边界积分方程中不同类型奇异积分的数值方法. 借助层状材料基本解,采用分层方法逼近梯度材料夹层沿厚度方向力学参数的变化. 与均匀介质中矩形裂纹的数值解对比,建议方法可以获得高精度的计算结果. 最后,分析了梯度材料中均匀张应力作用下矩形裂纹的应力强度因子,讨论了梯度材料非均匀参数、夹层厚度和裂纹与夹层之间相对位置对应力强度因子的影响. 相似文献
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In this paper the problem of a finite plate containing collinear surface cracks is considered. The problem is solved by using the line spring model with plane elasticity and Reissner's plate theory. The main purpose of the study is to investigate the effect of interaction between two cracks or between cracks and stress-free plate boundaries on the stress intensity factors and to provide extensive numerical results which may be useful in applications. First, some sample results are obtained and are compared with the existing finite element results. Then the problem is solved for a single (internal) crack, two collinear cracks and two corner cracks for wide range of relative dimensions. Particularly in corner cracks the agreement with the finite element solution is surprisingly very good. The results are obtained for semielliptic and rectangular crack profiles which may, in practice, correspond to two limiting cases of the actual profile of a subcritically growing surface crack. 相似文献
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《International Journal of Solids and Structures》2003,40(18):4925-4940
Transient dynamic responses of an elastic cracked solid subjected to in-plane surface loadings are investigated in this study. Two vertical cracks, a surface-breaking crack and a sub-surface crack, are considered. The frequency responses of the plane strain problem are calculated by the computational mechanics combining the finite element method with the boundary integral equation. The finite element method is used for the near-field enclosing the crack, while the boundary integral equation is applied for the far-field to satisfy the Sommerfeld radiation condition. The transient responses are then obtained using fast Fourier transform. Surface displacements, crack opening displacements, and dynamic stress intensity factors are presented to show the significant effects of the cracks. The interaction between the elastic waves and the cracks as well as the mode conversion phenomena can be observed and understood through the numerical simulations. 相似文献
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An effective boundary element method for analysis of crack problems in a plane elastic plate 总被引:3,自引:0,他引:3
闫相桥 《应用数学和力学(英文版)》2005,26(6):814-822
A simple and effective boundary element method for stress intensity factor calculation for crack problems in a plane elastic plate is presented. The boundary element method consists of the constant displacement discontinuity element presented by Crouch and Starfield and the crack-tip displacement discontinuity elements proposed by YAN Xiangqiao. In the boundary element implementation the left or the right crack-tip displacement discontinuity element was placed locally at the corresponding left or right each crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. Test examples (i. e. , a center crack in an infinite plate under tension, a circular hole and a crack in an infinite plate under tension) are included to illustrate that the numerical approach is very simple and accurate for stress intensity factor calculation of plane elasticity crack problems. In addition, specifically, the stress intensity factors of branching cracks emanating from a square hole in a rectangular plate under biaxial loads were analysed. These numerical results indicate the present numerical approach is very effective for calculating stress intensity factors of complex cracks in a 2-D finite body, and are used to reveal the effect of the biaxial loads and the cracked body geometry on stress intensity factors. 相似文献