共查询到18条相似文献，搜索用时 62 毫秒
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压电材料中的微裂纹屏蔽问题分析 总被引：2，自引：0，他引：2
分析当主裂纹与一个微裂纹在远场I型力（KI）和远场电位移（Ke)作用下的相互干涉问题,得出了在微裂纹的位置角和方向角周时独立变化时,微裂纹对主裂纹的屏蔽作用的全局使命主裂纹扩展,通过电算还发现Ortiz在各向同性材料和各向异性材料中得出的“微裂纹群对主裂纹最大屏蔽效应产生在微裂纹方向与最大主应力垂直的方向”在压电材料中不再成立,进而提出除Hutchinson指出微裂纹屏蔽效应两个来源（即：材料有效刚度的降低和残余应力的释放）外的另一个来源,微裂纹对主裂砂电场的扰动,在对主微裂纹J积分分析时发现J2积分与J1积分具有同等重要的地位。 相似文献
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基于无限大体深埋平片状椭圆形裂纹的变形场及其扩展条件,分别推导了脆性岩石材料内部具有任意空间取向的单个张开型或闭合型椭圆形微裂纹及其扩展引起的附加柔度张量;考虑微裂纹系统对材料变形的影响,引入了概率密度函数,得到了任意应力状态下脆性岩石材料的宏细观损伤模型;分析了椭圆形微裂纹的短长轴比率对材料损伤的影响.计算结果显示:材料损伤随着短长轴比率的增大而增大,短长轴比率对材料损伤的影响会随着载荷的增大而提高.将本文模型应用于混凝土的单轴拉伸和花岗岩的单轴压缩,结果表明本文模型能够对实验现象给予很好地解释. 相似文献
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含微裂纹材料的损伤理论 总被引：5，自引：1，他引：5
本文从含微裂纹材料的变形能出发引出了裂纹的方位张量。在考虑裂纹受压闭合与滑动摩擦的基础上,给出了损伤张量、损伤应变及有效弹性常数。文中给出了损伤机构离散化的方法,并对方位密度给出了演化方程。最后给出一个单向拉压的应力应变关系例子,并揭示了裂纹扩展时的应力突跌现象。 相似文献
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讨论了界面下裂纹对界面裂干涉的合理屏蔽参数问题。对于一条在远场载荷作用下、受到附近界面下裂纹干涉的界面裂纹,采用伪力法计算不同长度单位时界面裂纹的G／G0、k1/k10和k11/k110以及K1／K10和K11／K110（G是能量释放率、k1 ik110是通常定义的应力强度因子、K10＋iK110是含标定长度的应力强度因子;G0、k10 ik110、K10＋iK110对应单一界面裂纹情况）。结果表明,G／G0、K1／K10和K11／K110是较为合理的描述界面下裂纹对界面裂纹屏蔽的参数。 相似文献
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岩石裂纹演化及其力学特性的研究进展 总被引：25，自引：0，他引：25
综述评介了岩石裂纹（缺陷）演化及其力学特性研究的近期进展．其内容包括：微细观裂纹演化及其力学特性,时间相关性,裂纹扩展与岩石破坏,并结合某些工程问题进行了讨论． 相似文献
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D. Tikhomirov R. Niekamp E. Stein 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2001,81(1):3-16
This paper considers tensorial representations of several microcrack distribution functions due to tensile and compressive principal stresses in brittle materials in the framework of continuum mechanics. The common framework for deriving the damage tensors of different order from any density function is suggested. Second and fourth order damage tensors are derived for Dirac‐, truncated Gauss‐, and trigonometrical (cos2‐) microcrack distributions using harmonic Fourier‐like series. Each distribution is investigated under different combinations of tensile and compressive principal stresses for three‐dimensional load cases. It is emphasized that only the trigonometrical distribution yields a spherical crack density surface for the fourth order tensor approximation under three equal principal stresses. 相似文献
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针对复合材料层合板低速冲击损伤问题,提出了一种各向异性材料连续介质损伤力学模型,模型涵盖损伤表征、损伤起始判定和损伤演化法则3 个方面. 通过材料断裂面坐标下的损伤状态变量矩阵完成损伤表征,并考虑断裂面角度的影响,建立了主轴坐标系下的材料损伤本构关系. 损伤起始由卜克(Puck) 失效准则预测,损伤演化由断裂面上的等效应变控制,服从基于材料应变能释放的线性软化行为. 模型区分了纤维损伤和基体损伤,并根据冲击载荷下层内产生多条基体裂纹继而扩展至界面形成层间裂纹(分层) 的试验观察,引入基体裂纹饱和密度参数表征层间分层. 以[03/45/-45]S 和[45/0/-45/90]4S 两种铺层的复合材料层合板为例,预测了不同冲击能量下复合材料层合板的低速冲击损伤响应参数,试验结果证明了连续介质损伤力学模型的有效性.模型在不同网格密度下的计算结果表明单元特征长度的引入可以在一定程度上降低损伤演化阶段对网格密度的依赖性. 相似文献
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The fatigue life prediction for components is a difficult task since many factors can affect the final fatigue life. Based on the damage evolution equation of Lemaitre and Desmorat, a revised two-scale damage evolution equation for high cycle fatigue is presented according to the experimental data, in which factors such as the stress amplitude and mean stress are taken into account. Then, a method is proposed to obtain the material parameters of the revised equation from the present fatigue experimental data. Finally, with the utilization of the ANSYS parametric design language (APDL) on the ANSYS platform, the coupling effect between the fatigue damage of materials and the stress distribution in structures is taken into account, and the fatigue life of specimens is predicted. The outcome shows that the numerical prediction is in accord with the experimental results, indicating that the revised two-scale damage evolution model can be well applied for the high cycle fatigue life prediction under uniaxial loading. 相似文献
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The nonequilibrium steady gas flows under the external forces are essentially associated with some extremely complicated nonlinear dynamics, due to the acceleration or deceleration effects of the external forces on the gas molecules by the velocity distribution function. In this article, the gas-kinetic unified algorithm (GKUA) for rarefied transition to continuum flows under external forces is developed by solving the unified Boltzmann model equation. The computable modeling of the Boltzmann equation with the external force terms is presented at the first time by introducing the gas molecular collision relaxing parameter and the local equilibrium distribution function integrated in the unified expression with the flow state controlling parameter, including the macroscopic flow variables, the gas viscosity transport coefficient, the thermodynamic effect, the molecular power law, and molecular models, covering a full spectrum of flow regimes. The conservative discrete velocity ordinate (DVO) method is utilized to transform the governing equation into the hyperbolic conservation forms at each of the DVO points. The corresponding numerical schemes are constructed, especially the forward-backward MacCormack predictor-corrector method for the convection term in the molecular velocity space, which is unlike the original type. Some typical numerical examples are conducted to test the present new algorithm. The results obtained by the relevant direct simulation Monte Carlo method, Euler/Navier-Stokes solver, unified gas-kinetic scheme, and moment methods are compared with the numerical analysis solutions of the present GKUA, which are in good agreement, demonstrating the high accuracy of the present algorithm. Besides, some anomalous features in these flows are observed and analyzed in detail. The numerical experience indicates that the present GKUA can provide potential applications for the simulations of the nonequilibrium external-force driven flows, such as the gravity, the electric force, and the Lorentz force fields covering all flow regimes. 相似文献
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综合考虑宏细观缺陷的岩体动态损伤本构模型 总被引：1，自引：0，他引：1
针对节理岩体同时含有节理、裂隙等宏观缺陷及微裂隙、微孔洞等细观缺陷的客观事实, 提出了在节理岩体动态损伤本构模型中应同时考虑宏细观缺陷的观点。为此, 首先对基于细观动态断裂机理的经典岩石动态损伤本构模型—TCK(Taylor-Chen-Kuszmaul)模型进行了阐述, 其次基于Lemaitre等效应变假设推导了综合考虑宏细观缺陷的复合损伤变量(张量), 进而在此基础上建立了相应的节理岩体动态损伤本构模型, 并利用该模型讨论了载荷应变率及节理条数对岩体动态力学特性的影响规律。结果表明, 在不同载荷应变率下试件在变形初始阶段是重合的, 而后随着应变的增加, 试件峰值强度、峰值应变及总应变均随载荷应变率的增加而增加; 随着节理条数的增加, 试件峰值强度逐渐降低, 但降低趋势逐渐变缓并趋于某一定值。上述研究结论与目前的理论及实验研究结果的基本规律是一致的, 说明了本模型的合理性。 相似文献
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A. Rinaldi L. Placidi 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2014,94(10):862-877
Lattice models are powerful tools to investigate damage processes in quasi‐brittle material by a microscale perspective. Starting from prior work on a novel rational damage theory for a 2D heterogenous lattice, this paper explores the connection between the series of critical strains at which the microcracks form (i.e. lattice links fail) and the second gradient of the microscale displacement field. Taking a simple tensile test as a representative case study for this endeavour, the analysis of accurate numerical results provides evidence that the second gradient of the microscale displacement field (notably the quantity | ∇ (∂ ux/∂ x)| for the specific example elaborated here) conveys indeed crucial information about the microcracks formation process and can be conveniently used to introduce simplifications of the rational theory that are of relevance by practical purposes as full field strain measurements become routinely possible with digital imaging correlation techniques. Note worthy, the results support the new view that the damage evolution is a three regimes process (I dilute damage, II homogeneous interaction, III localization.) The featured connection with the second gradient of the microscale displacement field is applicable in regions II–III, where microcracks interactions grow stronger and the lattice transitions to the softening regime. The potential impact of these findings towards the formulation of new and physically based CDM models, which are consistent with the reference discrete microscale theory, cannot be overlooked and is pointed out. 相似文献
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采用14.5mm 滑膛枪发射直径6mm 的钢质球形弹丸对双层钢/铝、3层钢/铝/钢爆炸复合靶进行侵彻实验,借助LS-DYNA3D非线性有限元程序进行数值模拟,应用固连-失效模型反映层间结合,分析了不同组合形式对靶板抗侵彻性能的影响,并对毁伤机理进行初步分析。结果表明:靶板总厚度一定时,3层靶的抗侵彻性能优于双层靶;双层靶的钢面板与铝背板厚度比为约2∶1时抗侵彻性能最好。面板的毁伤机理为剪切冲塞耗能,铝背板的毁伤机理为延性扩孔,钢背板为开瓣扩孔;数值模拟同实验结果吻合良好,表明固连-失效模型可以较好地反映出层间结合对抗侵彻性能的影响。 相似文献