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该文致力于混凝土疲劳损伤发展机理的微细观解释.以速率过程理论为基础,通过考虑裂纹断裂过程区中的水分子动力作用,在细观尺度上建立了具有物理机理的疲劳损伤能量耗散表达式.结合细观随机断裂模型,以宏观损伤力学为框架,建立了疲劳损伤演化方程.通过数值模拟,计算了单轴受拉时的疲劳损伤演化以及不同加载幅度下的疲劳寿命.与相关试验结果的对比显示出该文模型能够很好地表现混凝土材料的疲劳损伤演化过程. 相似文献
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该文致力于混凝土疲劳损伤发展机理的微细观解释. 以速率过程理论为基础,通过考虑裂纹断裂过程区中的水分子动力作用,在细观尺度上建立了具有物理机理的疲劳损伤能量耗散表达式. 结合细观随机断裂模型,以宏观损伤力学为框架,建立了疲劳损伤演化方程. 通过数值模拟,计算了单轴受拉时的疲劳损伤演化以及不同加载幅度下的疲劳寿命. 与相关试验结果的对比显示出该文模型能够很好地表现混凝土材料的疲劳损伤演化过程. 相似文献
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页岩储层的力学行为和工程性质,是影响页岩油气安全、高效、经济开采的关键因素。目前,页岩的物理力学特征研究以宏观测试为主,存在制样、实验耗时长,对目的层精细研究效果不理想等问题。为此,从页岩多尺度组成、微/纳米力学测试、影响因素和跨尺度均匀化4个层面,综述了国内外页岩多尺度力学研究现状:基于多尺度方法建立的页岩微观-细观-宏观组分模型,为页岩多尺度组成-力学耦合提供理论基础;通过微/纳米力学测试技术,明确适合页岩的力学测量标准,完善影响页岩多尺度测量因素评价;基于开展多尺度力学耦合模型研究,评价多尺度间的组成-力学关系。该研究对深入认知页岩岩石力学特征及破坏机理、丰富岩石力学特性测试与表征方法具有重要作用。 相似文献
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固体破坏理论的若干问题 总被引:7,自引:1,他引:6
本文列举和初步探讨了位于当代固体破坏理论的前沿上的十五个问题。它们包括:固体破坏理论的封闭、宏微观非线性力学、尺度效应、多层次计算、细微观实验力学技术、断裂过程区的描述、异质体的强度与韧性、材料的多层次抗破坏设计、高速破坏过程、非均匀介质的动态断裂与前兆、疲劳的起源、破坏元技术、内损伤破坏与微结构形貌演化失稳的识别、材料的微结构演化、电致失效力学。 相似文献
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挠曲电效应是一种跨尺度的多场耦合现象。当前的宏观挠曲电理论均是基于应变梯度局部破坏晶体反演对称这一微观机理对该现象进行唯象描述。该宏观理论与基于晶格动力学及密度泛函理论的微观挠曲电理论模型之间存在较大差异。难以将两者结合用以跨尺度地研究材料中的挠曲电效应。针对该现状,本文基于前人提出的原子场理论,建立了一种新的多尺度挠曲电模型。并在该多尺度模型框架下解释了应变梯度诱发极化的微观机理。一方面,与基于连续介质力学的唯象理论不同,本文从材料微结构演化的角度推导了原子位移与极化的关系。另一方面,与通过晶格波假设原子位移的微观理论不同,本文得到的极化表达式更加真实和广义地解释了挠曲电效应。其能够适用于材料边界存在机械力作用,材料内部存在缺陷等复杂的情况。本文所建立的多尺度挠曲电模型能够为后续多尺度挠曲电效应的研究提供一些思路。 相似文献
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近年来,非线性力学国家重点实验室(LNM)在坚持固体与流体的非线性力学行为和规律的学术方向下,突出了多尺度力学和跨尺度关联的研究.这既与国际上近年来出现的对多时空尺度演化和斑图的非线性科学问题的重视相互呼应,又反映了LNM在科学前沿和重大需求的交叉点上长期探索所形成的发展特点.实际上,多个时间/空间尺度非线性耦合的行为,是非线性复杂系统中至今尚未阐明的一个关键科学问题. 相似文献
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在全球气候变化和双碳政策的大背景下,多孔介质中固体的变形和流体的输运问题变得尤为重要。然而,在多孔介质中建立流固耦合模型仍面临的挑战之一是需要考虑跨越宏观尺度到纳米尺度的耦合作用。本文利用基于非平衡热力学的混合耦合理论,提出了一个弹塑性多孔介质流固耦合新模型,在同一个理论框架内研究了弹性变形、塑性变形和液体渗流之间跨尺度的耦合,考虑了耗散过程中的熵产,并利用Helmholtz自由能来连接宏观尺度上的力学变形和纳米尺度上的液体输运之间的相互作用。在应力-应变关系中采用了弹塑性刚度系数以反映塑性的影响。同时,经典的达西定律扩展为考虑固体的塑性变形。通过与文献中模型的比较,验证了该模型的有效性。最后,数值分析表明在多孔介质的流固耦合中塑性变形具有比较显著的影响。 相似文献
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Problems involving coupled multiple space and time scales offer a real challenge for conventional frame-works of either particle or continuum mechanics. In this paper, four cases studies (shear band formation in bulk metallic glasses, spallation resulting from stress wave, interaction between a probe tip and sample, the simulation of nanoindentation with molecular statistical thermodynamics) are provided to illustrate the three levels of trans-scale problems (problems due to various physical mechanisms at macro-level, problems due to micro-structural evolution at macro/micro-level, problems due to the coupling of atoms/ molecules and a finite size body at micro/nano-level) and their formulations. Accordingly, non-equilibrium statistical mechanics, coupled trans-scale equations and simultaneous solutions, and trans-scale algorithms based on atomic/molecular interaction are suggested as the three possible modes of trans-scale mechanics. 相似文献
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Yilong Bai Mengfen Xia Haiying Wang Fujiu KeState Key Laboratory of Non-Linear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing P. R. China Author to whom correspondence should be addressed. E-mail: Baiyl@lnm.imech.ac.cn 《中国颗粒学报》2003,(1)
Multi-scale modeling of materials properties and chemical processes has drawn great attention from science and engineering. For these multi-scale and rate-dependent processes, how to characterize their trans-scale for-mulation is a key point. Three questions should be addressed:How do multi-sizes affect the problems?How are length scales coupled with time scales?How to identify emergence of new structure in process and its effect?For this sake, the macroscopic equations of mechanics and the kinetic equations of the microstructural transforma-tions should form a unified set that be solved simultaneously.As a case study of coupling length and time scales, the trans-scale formulation of wave-induced damage evolution due to mesoscopic nucleation and growth is discussed. In this problem, the trans-scaling could be reduced to two inde-pendent dimensionless numbers: the imposed Deborah number De=(ac)/(LV) and the intrinsic Deborah num-ber D = (nNc5)/V* ,where a. L, c, V and nN are wave speed, sample size, micr 相似文献
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大型土木结构多尺度模拟与损伤分析——————从材料多尺度力学到结构多尺度 总被引:3,自引:0,他引:3
从阐述重大土木工程结构安全运营面临的挑战性课题------结构多尺度力学问题开
始, 对多尺度力学中的材料多尺度模拟和结构多尺度模拟的工程背景、多尺度特征和关键研
究内容进行比较性评述;在此基础上, 重点介绍了对研究大型土木结构多尺度力学问题可能
有参考价值的材料多尺度模拟和分析方法如周期性异质材料问题的平均化与渐进分析方法、
单位分解法和多尺度重构核函数法, 以及大型土木结构多尺度模拟与分析领域的研究现状,
由此引出结构多尺度力学研究中亟待解决的关键问题并加以评述;通过认识与比较结构多尺
度与材料多尺度问题的共性与个性, 文中综述了在大型土木结构多尺度问题的研究进程中可
供参考的理论与方法, 提出了这类结构多尺度力学问题研究的几个关键科学问题为: 结构多
尺度模拟中的连接与跨越问题、多尺度模型的修正和验证、结构损伤的时间多尺度模拟与分
析、结构强度和损伤失效过程中多尺度分析的跨尺度敏感性与随机性因素, 以及适用于大型
土木结构多尺度模拟和计算分析的实施策略与技术. 相似文献
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We present the basic principles of physical mesomechanics of structurally inhomogeneous media; the theory is developed on
the basis of common approaches of nonequilibrium thermodynamics, gauge theory of defects, and mechanics of structured media.
Within a multilevel approach, the plastic deformation evolution is considered in the entire hierarchy of structure-scale levels:
at the nano, micro, meso, and macro level. Fracture is treated as the final stage of increasing disequilibrium of a solid,
when the nonequilibrium thermodynamical Gibbs potential becomes zero and the structure-phase decay of the crystal occurs. 相似文献
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压痕标度律是对通过压痕试验方法测定固体材料力学性能参量问题所给出的一般性结论, 具有重要的理论意义, 是探寻材料力学性能潜在规律的方法论研究. 本综述论文系统而简要地介绍如下主要内容: 采用传统理论对传统固体材料压痕标度律的研究回顾; 采用跨尺度力学理论对先进固体材料的跨尺度压痕标度律的研究回顾. 总结并得到了如下主要结论: 传统固体材料压痕标度律可由一空间曲面完整描绘, 若进一步已知某类无量纲独立参量的取值范围, 则该空间曲面可退化为系列平面曲线族; 先进固体材料(新材料)的跨尺度压痕标度律可由一个三维函数关系完整描绘, 若存在某类独立无量纲参量取值范围已知, 则该三维函数关系将退化为系列空间曲面族. 压痕标度律的未来研究发展仍将重点集中在建立新材料的跨尺度压痕标度律上, 以试图从根本上解决新材料力学性能标准规范难以建立的理论问题. 除此之外也将重点关注建立各类功能新材料的多尺度及跨尺度压痕标度律规律. 相似文献
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Synchronous multi-scale observations on rock damage and rupture 总被引:2,自引:1,他引:1
X.H. Xu S.P. Ma M.F. Xia F.J. Ke Y.L. Bai 《Theoretical and Applied Fracture Mechanics》2005,44(2):146-156
This paper reports a multi-scale study on damage evolution process and rupture of gabbro under uniaxial compression with several experimental techniques, including MTS810 testing machine, white digital speckle correlation method, and acoustic emission technique. In particular, the synchronization of the three experimental systems is realized for the study of relationship of deformation and damage at multiple scales. It is found that there are significant correlation between damage evolution at small and large length scales, and rupture at sample scale, especially it displays critical sensitivity at multiple scales and trans-scale fluctuations. 相似文献
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A novel efficient hybrid DSMC–dynamic collision limiter algorithm for multiscale transitional flows 下载免费PDF全文
A new 2D parallel multispecies polyatomic particle–based hybrid flow solver is developed by coupling the Direct Simulation Monte Carlo (DSMC) method with a novel Dynamic Collision Limiter (DCL) approach to solve multiscale transitional flows. The hybrid DSMC‐DCL solver can solve nonequilibrium multiscale flows with length scales ranging from continuum to rarefied. The DCL method, developed in this work, dynamically assigns different number of collisions in cells, which is based on the local value of K‐S parameter such that the number of collisions per time step is limited in near‐equilibrium flow regions. Present hybrid solver uses the Kolmogorov‐Smirnov statistical test as the continuum breakdown parameter, based on which, the solution domain is decomposed into near‐equilibrium and nonequilibrium flow regions. Direct Simulation Monte Carlo is used where nonequilibrium flow regions are encountered, while the DCL method is used where flow regions are found to be in near‐equilibrium state. In this work, we have studied hypersonic flow of nitrogen over a blunt body with an aerospike and supersonic flow of argon through a micronozzle. The results obtained by the hybrid DSMC‐DCL solver are compared and shown to agree well with the experimental data and with those obtained from DSMC, with significant savings in the computational cost. 相似文献
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压电介质损伤、断裂力学研究的现状 总被引:10,自引:1,他引:9
压电介质的损伤与断裂力学是现代固体力学的重要课题.本文简要地综述了压电介质损伤与断裂力学研究的现状,集中讨论了:(1)裂纹面电边界条件的不同模型及其求解的结果;(2)宏观连续力学与细观力学用于压电介质的损伤与断裂的静力学分析;(3)压电介质动态断裂分析的某些新结果.文末,指出了今后在压电介质损伤与断裂研究的某些有吸引力的研究方向 相似文献
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Multiscale models are designed to handle problems with different length scales and time scales in a suitable and efficient manner. Such problems include inelastic deformation or failure of materials. In particular, hierarchical multiscale methods are computationally powerful as no direct coupling between the scales is given. This paper proposes a hierarchical two-scale setting appropriate for isothermal quasi-static problems: a macroscale treated by continuum mechanics and the finite element method and a microscale modelled by a canonical ensemble of statistical mechanics solved with molecular dynamics. This model will be implemented into the framework of the heterogeneous multiscale method. The focus is laid on an efficient coupling of the macro- and micro-solvers. An iterative solution algorithm presents the macroscopic solver, which invokes for each iteration an atomistic computation. As the microscopic computation is considered to be very time consuming, two optimisation strategies are proposed. Firstly, the macroscopic solver is chosen to reduce the number of required iterations to a minimum. Secondly, the number of time steps used for the time average on the microscale will be increased with each iteration. As a result, the molecular dynamics cell will be allowed to reach its state of thermodynamic equilibrium only in the last macroscopic iteration step. In the preceding iteration steps, the molecular dynamics cell will reach a state close to equilibrium by using considerably fewer microscopic time steps. This adapted number of microsteps will result in an accelerated algorithm (aFE-MD-HMM) obtaining the same accuracy of results at significantly reduced computational cost. Numerical examples demonstrate the performance of the proposed scheme. 相似文献