准脆性材料损伤演化的实验力学研究

发布时间：2018-03-27 21:35

本文选题：准脆性材料　切入点：岩石　出处：《天津大学》2014年博士论文

【摘要】：岩石类准脆性材料的力学性能和损伤失效是地下空间开发、水利水电建设、岩石隧道掘进、矿产资源开采等领域所关注的基础科学问题。与此同时，从实验的角度测量和表征损伤是研究岩石各种损伤破坏过程的基础性和关键性工作。本文围绕准脆性材料损伤失效问题，在数字图像相关全场测量与实验数据统计分析的基础上，对岩石材料的损伤演化规律及失效机制开展研究，论文选题具有重要的工程背景与科学意义。本文通过数字图像相关技术（DIC）对岩石压缩失效过程中的损伤演化与局部化进行系统的实验研究，实时给出了不同载荷水平下岩石表面的变形位移场和应变场。在实验结果分析的基础上，本文将最大拉应变1作为描述损伤的力学参量，进一步对实验给出的所有的实验数据进行统计。统计分析结果表明，全场所有测点的应变平均值基本随压力载荷呈线性增长，反映大部分测点在加载过程中处于均匀变形状态；其中前10%左右的较大应变点的平均值在损伤局部化及裂纹萌生阶段表现为非线性快速增长，表明这些点主导了岩石的损伤演化和裂纹扩展。在DIC全场测量与实验数据统计分析的基础上，首次提出了损伤演化双因子实验表征方法。以实时测量的最大应变1作为损伤演化的关键参量，进行实验数据统计与归一化分析，提出了损伤局部化因子Lf，描述损伤的空间局部化程度，提出了损伤程度因子Df，描述损伤的程度，并给出了双因子曲线随压力载荷的变化。本文还将双因子方法应用于巴西圆盘、压头压入、循环加卸载等不同工况与不同试件的损伤演化测量，实验结果发现，双因子曲线均在损伤局部化阶段发生交汇之后曲线出现拐点，，表明损伤的汇聚串接已导致裂纹基本形成，验证了这一方法对准脆性材料损伤演化定量表征的适用性。论文开展了岩石在压头载荷、加卸载、三点弯等不同工况作用下的损伤断裂实验研究。分析了压头载荷作用下岩石裂纹扩展的机理，给出了压头载荷与裂纹长度之间的关系。实验发现加卸载过程中存在能量耗散，残余变形随循环载荷的增加而增大，并对加卸载过程中的裂纹行为进行了分析。DIC结合声发射技术研究了岩石三点弯实验损伤断裂问题，综合声发射振铃计数率与实验位移、应变场分析发现，裂纹起裂载荷约为峰值载荷的80%。利用DIC位移场分析得到了裂纹张开位移以及裂纹扩展全过程。
[Abstract]:The mechanical properties and damage failure of rock quasi brittle materials are the basic scientific problems in the fields of underground space development, water conservancy and hydropower construction, rock tunneling, mineral resource mining and so on. Measuring and characterizing damage from the point of view of experiment is the basic and key work to study the damage and failure process of rock. This paper focuses on the damage failure problem of quasi brittle materials. On the basis of digital image correlation full-field measurement and statistical analysis of experimental data, the damage evolution law and failure mechanism of rock materials are studied. This paper has important engineering background and scientific significance. In this paper, a systematic experimental study on damage evolution and localization during compression failure of rock is carried out by means of digital image correlation technique (DICs). The deformation displacement field and strain field of rock surface under different load levels are given in real time. Based on the analysis of experimental results, the maximum tensile strain 1 is taken as the mechanical parameter to describe the damage. The results of statistical analysis show that the average strain of all the measured points increases linearly with the pressure load, which shows that most of the measured points are in a uniform deformation state during the loading process. The average values of the first 10% of the large strain points show nonlinear and rapid growth during the damage localization and crack initiation stages, indicating that these points dominate the damage evolution and crack propagation of rocks. On the basis of DIC field measurement and statistical analysis of experimental data, a double factor experimental characterization method for damage evolution is proposed for the first time. The maximum strain 1 measured in real time is taken as the key parameter of damage evolution. Based on the statistics and normalization analysis of experimental data, a damage localization factor (LF) is proposed to describe the degree of damage localization in space, and a damage degree factor (Df) is proposed to describe the degree of damage. The change of double factor curve with pressure load is also given. The method is also applied to the damage evolution measurement of Brazilian disc, head indentation, cyclic loading and unloading under different working conditions and different specimens, and the experimental results show that, The curve inflection points appear after the intersection of the two-factor curves in the damage localization stage, which indicates that the convergence and serial connection of the damage has led to the basic formation of the crack, which verifies the applicability of this method to the quantitative characterization of the damage evolution of brittle materials. In this paper, the damage and fracture experiments of rock under different working conditions, such as head load, loading and unloading, three point bending, are carried out, and the mechanism of rock crack growth under pressure head load is analyzed. The relationship between head load and crack length is given. It is found that there is energy dissipation during loading and unloading, and the residual deformation increases with the increase of cyclic load. The crack behavior during loading and unloading is analyzed. DIC combined with acoustic emission technique is used to study the damage and fracture of rock in three-point bending experiment. The crack initiation load is about 80 parts of the peak load. The crack opening displacement and crack propagation process are obtained by DIC displacement field analysis.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU45

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