基于混合高阶非连续变形分析的刚性伺服数值试验方法

Stiff servo-controlled numerical test method based on mixed higher order discontinuous deformation analysis

相对于传统的力学试验而言,数值试验具有成本低和灵活方便的优点,且不受试验机性能和岩石试样自身离散性等因素的影响;通过对岩石细观结构及其参数的敏感性分析可以方便地实现对其变形破坏细观机制的研究。作为宏观力学试验的有益补充,细观数值试验方法近年来逐渐发展成为研究岩石力学特性的重要手段。基于非连续变形分析方法,建立能够同时实现刚性试验机的理想刚性和电液伺服试验机的伺服控制机制的细观数值试验方法。在混合高阶非连续变形分析框架下,组成岩石试样部分的块体单元根据需要可采用常应变单元或高阶多项式位移模式,模拟加载框架部分的块体单元则采用刚体位移模式,从而实现加载系统的理想刚性。通过对加载速率及其量值的实时反馈控制实现了对电液伺服试验机闭路循环控制机制的数值模拟;"加载步回撤"和"二分法搜索"等计算策略的应用使得数值试验中的加载速率及其量值能够始终与岩石试样自身的承载能力相适应,从而能够得到更为接近真实的的峰后曲线。采用两块体简化模型对伺服数值模拟程序的有效性进行验证;之后,利用研发的程序开展了单轴压缩数值试验,获得应力–应变全过程曲线。基于混合高阶DDA的伺服数值试验方法为岩石基本力学特性的细观数值试验研究提供了全新的研究手段。

Compared with the traditional mechanical test,the numerical test method has the advantages of low cost,flexibility and convenience,and is not affected by the performance of test machines and the dispersion of rock samples. The meso-mechanism of rock deformation and failure can be conveniently studied by analyzing rock meso-structure and parameter sensitivity. As a useful supplement to the macroscopic mechanical test,the mesoscopic numerical test method has gradually developed into an important means to study the mechanical properties of rocks in recent years. Based on the discontinuous deformation analysis method,a numerical micromechanical test method was established to realize the ideal rigidity of a rigid testing machine and the servo control of an electro-hydraulic servo testing machine. Under the framework of mixed high-order discontinuous deformation analysis,the block elements that make up the rock sample can adopt the displacement mode of constant strain element or higher-order polynomial,and the block elements that simulate the loading frame adopt the rigid-body displacement mode,so as to achieve the ideal rigidity of the loading system. The numerical simulation of the closed-loop control mechanism of the electro-hydraulic servo testing machine is realized by the real-time feedback control of the loading rate and its magnitude. The application of calculation strategies such as"loading step withdrawal"and"binary search"makes the loading rate and its magnitude in the numerical test always adapt to the bearing capacity of the rock sample,so as to get a more realistic post-peak curve. The validity of the servo numerical simulation program was verified by two simplified models. After that,uniaxial compression test was carried out with the developed program,and the stress-strain whole-process curve was obtained. The servo numerical test method based on mixed higher order DDA provides a new research method for the numerical micromechanical study of basic mechanical properties of rock.