大理岩瞬时及流变力学特性与本构模型研究

发布时间：2018-06-27 04:38

本文选题：瞬时 + 流变　；参考：《长安大学》2014年博士论文

【摘要】：本文通过对大理岩进行不同应力加载速率下的常规单轴压缩试验与不同初始加载应力下的单轴蠕变试验，研究了大理岩瞬时及流变力学特性，并在其力学特性基础上分别研究了考虑应力加载速率的瞬时本构模型与大理岩流变本构模型。在瞬时力学研究中，作者设计了五个级别的应力加载速率并对大理岩实施了各应力加载速率下的单轴压缩试验，分析了不同应力加载速率下大理岩变形特征、强度特征、破坏特征及能量交换特征。分析结果表明，应力加载速率的提高对大理岩的力学性质具有增强效应。当应力加载速率增大时，，大理岩变形模量增大，强度增大，脆性增强。基于应力加载速率对大理岩力学性质增强效应，应用统计损伤力学与BP神经网络技术分别构建考虑应力加载速率影响的瞬时本构模型。两种模型各自具有相应的优点。统计损伤模型不仅考虑了应力加载速率效应，同时从损伤的角度展示了大理岩破坏的机制。而BP神经网络模型则具有快速建模且较强的工程实用性特点。在大理岩流变力学研究中，作者首先设计并实施了不同初始加载应力，相同加载应力增量与相同单级持续时间的单轴分级加载蠕变试验。蠕变曲线反映了大理岩作为脆性岩石具有的非线性流变特征。通过对蠕变曲线的深入分析，总结了四种具有代表性的大理岩变形方式，并提出了“加速临界应力区间”、“负蠕变”及“等速临界应力”等概念，同时对其进行了初步探讨。在对大理岩蠕变变形的速率特征、长期强度计算与特征、破坏特征分析的基础上总结了不同的初始加载应力对其变形及破坏具有的影响。其次对蠕变破坏大理岩断口与切片进行了微细观观察试验，对破坏断口的微观花样与切片裂纹的展布及形态进行了分析，并在此基础上对大理岩蠕变破坏机制进行了探讨，得出大理岩蠕变破坏遵循原始裂纹缺陷的加载损伤试样内部非协调变形损伤加剧裂纹扩展壮大宏观劈裂伴生剪切破坏的发展模式。再次，基于分数阶微积分理论的数学优势，用分数阶微积分构建了大理岩流变模型，并应用损伤力学及非线性粘滞理论对模型进行了改进，得到了可反映大理岩非线性流变特征的变参数蠕变损伤模型。基于大理岩加速蠕变阶段的特点，提出了两个非线性粘滞元件，将其与分数阶微积分元件联合建模，得到了两个可反映大理岩整体流变特征的四元件模型。基于流变本构模型实用性原则，本文从改进一种弹塑性体元件入手，联合分数阶微积分元件，构建了一种新的、实用的及简洁的三元件模型。模型经过验证其具有较好的模拟精度与推广性。最后，基于支持向量机学习技术的发展优势，将其引入岩石流变本构模型研究中。在简述了支持向量机特点的基础上构建了分别加载下岩石流变的支持向量机模型。模型经过验证具有较高的模拟精度与快速工程应用特性。
[Abstract]:In this paper, the instantaneous and rheological properties of marble are studied by uniaxial compression tests under different stress loading rates and uniaxial creep tests under different initial loading stresses. On the basis of its mechanical properties, the instantaneous constitutive model and the rheological constitutive model of marble considering the stress loading rate are studied respectively. In the study of instantaneous mechanics, the author designs five levels of stress loading rates and carries out uniaxial compression tests on marble under different stress loading rates, and analyzes the deformation and strength characteristics of marble under different stress loading rates. Damage characteristics and energy exchange characteristics. The results show that the increase of stress loading rate can enhance the mechanical properties of marble. When the stress loading rate increases, the deformation modulus, strength and brittleness of marble increase. Based on the enhancement effect of stress loading rate on the mechanical properties of marble, the statistical damage mechanics and BP neural network technique are used to construct the instantaneous constitutive model considering the effect of stress loading rate respectively. The two models have their respective advantages. The statistical damage model not only considers the effect of stress loading rate, but also shows the mechanism of marble failure from the point of view of damage. The BP neural network model has the characteristics of fast modeling and strong engineering practicability. In the study of rheological mechanics of marble, the author first designed and carried out the creep tests under uniaxial loading with different initial loading stress, the same loading stress increment and the same single stage duration. The creep curve reflects the nonlinear rheological characteristics of marble as brittle rock. Through the deep analysis of creep curves, four typical deformation modes of marble are summarized, and the concepts of "accelerated critical stress interval", "negative creep" and "isokinetic critical stress" are put forward and discussed preliminarily. Based on the analysis of creep deformation rate, long-term strength calculation and failure characteristics of marble, the effects of different initial loading stress on its deformation and failure are summarized. Secondly, the micro-observation tests on the fracture and slice of the creep failure marble are carried out, and the microcosmic pattern of the fracture surface and the distribution and morphology of the crack in the section are analyzed, and the creep failure mechanism of the marble is discussed. It is concluded that the creep failure of marble follows the development model of internal uncoordinated deformation damage in the specimens with original crack defects which exacerbates the crack growth and macrofracturing accompanied by shear failure. Thirdly, based on the mathematical advantages of fractional calculus theory, the rheological model of marble is constructed by fractional calculus, and the damage mechanics and nonlinear viscosity theory are applied to improve the model. The creep damage model with variable parameters can reflect the nonlinear rheological characteristics of marble. Based on the characteristics of accelerated creep stage of marble, two nonlinear viscous elements are proposed, which are combined with fractional calculus element to model two four-element models which can reflect the rheological characteristics of marble as a whole. Based on the principle of practicability of rheological constitutive model, a new, practical and concise three-element model is constructed by improving an elastoplastic element and combining fractional calculus element. The model is proved to be accurate and extensible. Finally, based on the advantages of support vector machine (SVM) learning technology, it is introduced into the study of rock rheological constitutive model. A support vector machine model for rock rheology under loading is constructed on the basis of a brief description of the characteristics of support vector machine (SVM). The model has been proved to have high simulation accuracy and rapid engineering application characteristics.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU452

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