Theoretical and experimental analysis on the mechanism of the Kaiser effect of acoustic emission in brittle rocks

The Kaiser effect is formally described as the absence of detectable acoustic emission （AE） events until the load imposed on the material exceeds the previous applied level and is usually used to estimate geostress. By focusing on the heterogeneity of rock material, the mechanism of the Kaiser effect under cyclic loading is analyzed based on statistic damage mechanics. Two groups of granite specimens have been cyclically loaded with two different loading paths to verify the theoretical results. The heterogeneity of rock is the real reason that causes irrecoverable damage on the Kaiser effect of acoustic emission in cyclic loading. The Kaiser effect reflects the damaged state in rocks rather than the previous stress imposed on it. Applications for using the Kaiser effect to estimate geostress were discussed here. It is shown that the commonly used uniaxial loading method for estimating geostress is not in accor- dance with the theoretical and experimental results. The analysis is of importance to use the Kaiser effect correctly for estimating geostress or in other fields. 2008 University of Science and Technology Beijing. All rights reserved.     

基于Kaiser效应的地应力测试研究

通过分析Kaiser效应测量地应力时参数的选取,研究Kaiser点测试时表现的模式,得出了重复加载条件下Kaiser点的确定方法,分析了Kaiser点的误差。所得结果与其他方法得出的结果有较好的一致性,从而验证了Kaiser效应测试地应力的可靠性。     

含砖粒再生粗骨料混凝土损伤性能试验研究

用废弃砖部分取代废弃混凝土(取代率r=0%、10%、20%、30%)作为再生粗骨料制成再生混凝土。采用超声波检测再生混凝土的损伤,以超声波波速的衰减来衡量损伤,对单轴受压持荷状态下再生混凝土试件进行超声试验。通过试验研究,得出不同废弃砖取代率下单轴压应力系数对再生混凝土损伤的影响规律。试验结果表明废弃砖粗骨料取代率对单轴受压条件下再生混凝土的损伤影响很大。针对再生混凝土损伤的主要影响因素—单轴压应力系数,建立了含砖粒再生粗骨料混凝土的损伤关系模型。     

单轴受压下再生混凝土的损伤特性研究

利用超声检测技术,以超声波波速的衰减来度量损伤,对单轴受压条件下不同再生粗骨料取代率再生混凝土的损伤进行实时超声试验。通过试验研究了不同再生粗骨料取代率下再生混凝土损伤随单轴压应力的变化规律.试验结果表明再生粗骨料取代率对单轴压应力下混凝土损伤影响显著,且不应忽视混凝土在极限压应力以前的损伤。在考虑单轴压应力、再生混凝土初始强度影响因素下,建立了再生混凝土损伤关系模型。     

粗集料中心质效应的一些探讨

本文从中心质效应理论角度，利用弹性力学初步分析探讨了单轴受拉，受压时粗集料的一些中心质效应问题。     

岩石单轴压缩端部效应的数值实验研究

通过应用岩石破裂过程分析系统RFPA2D,模拟了不同刚度垫板下的岩石单轴压缩实验,对比刚性与柔性垫板,确认了端部效应的存在,通过不同刚度垫板下的岩石单轴压缩实验,分析了端部效应对试件的测试强度和破坏模式的影响。     

轻集料混凝土局部受压试验及动力本构分析

为探究轻集料混凝土单轴局部受压动力特性,采用试验机对轻集料混凝土单轴局部受压本构关系进行相关试验研究.考虑了5种不同加载应变率和4种不同加载面积,在位移控制下,得到轻集料混凝土单轴局部受压应力-应变曲线.根据应力-应变曲线特征点的峰值应力、峰值应变和弹性模量,分析不同加载应变率与加载面积对特征点的影响.同时根据混凝土黏弹塑性损伤本构模型,考虑不同加载应变率和加载面积的影响修正模型参数,并通过试验数据验证理论模型的合理性.研究结果表明:加载应变率和加载面积对轻集料混凝土应力-应变曲线影响明显;不同加载面积对轻集料混凝土弹性模量、峰值应力及峰值应变有较大影响;所提出的理论模型能够准确描述轻集料混凝土材料局部动力荷载作用下的应变率效应和非线性行为.     

Shape ratio effects on the mechanical characteristics of rectangular prism rocks and isolated pillars under uniaxial compression

Isolated pillars in underground mines are subjected to uniaxial stress, and the load bearing cross-section of pillars is commonly rectangularly shaped. In addition, the uniaxial compression test (UCT) is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress. The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks. Therefore, it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress. In this study, granite, marble and sandstone rectangular prism specimens with various height to width ratios (r) and width to thickness ratios (u) were prepared and tested. The study results show that r and u have a great influence on the bearing ability of rocks, and thin or high rocks have lower uniaxial compressive strength. Reducing the level of r can enhance the u effect on the strength of rocks, and increasing the level of u can enhance the r effect on the strength of rocks. The lateral strain on the thickness side of the rock specimen is larger than that on the width side, which implies that crack growth occurs easily on the thickness side. Considering r and u, a novel strength prediction model of isolated pillars was proposed based on the testing results, and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.     

混凝土率相关单轴塑性损伤本构的开发及应用

为了对爆炸作用下钢筋混凝土(reinforced concrete,RC)构件动力响应进行简化分析,需要合理描述混凝土和钢筋的应变率效应,而LS-DYNA中缺乏能够考虑混凝土应变率效应的单轴本构模型,因此,结合Faria单轴塑性损伤模型,通过黏性规则化方法调整率无关模型的损伤阈值演化律以考虑应变率效应,并利用LS-DYNA将该模型编制为用户材料子程序VUMAT.以单个单元测试了高应变率下材料的基本性能;基于纤维模型模拟了RC梁在爆炸、冲击作用下的动力响应.结果表明:该本构模型能反映混凝土受拉应变率效应高于受压应变率效应的事实,同时也能较准确地模拟爆炸与冲击作用下RC梁的动力响应.     

Statistical damage constitutive model for concrete materials under uniaxial compression

According to the damage mechanism of concrete material during the uniaxial compressive failure process,this paper further establishes the statistical damage constitutive model of concrete subjected to uniaxial compressive stress based on the statistical damage model under uniaxial tension. The damage evolution law in the direction subjected to pressure is confirmed by the tensile damage evolution process of lateral deformation due to the Poisson effect,and then the compressive stress-strain relationship is defined. The peak nominal stress state and the critical state occurring in the macro longitudinal distributed splitting cracks are distinguished. The whole loading process can be divided into the even damage phase and the local breakage phase. The concrete specimen is divided into the failure process zone and the resting unloading zone. The size effects during the local breakage phase under the uniaxial monotonic compressive process and the hysteretic phenomenon under the cyclic compressive loading process are analyzed. Finally,the comparison between theoretical results and experimental results preliminarily verifies the rationality and feasibility of understanding the failure mechanism of concrete through the statistical damage constitutional law.     

基于不可逆热力学的形状记忆合金相变塑性统一本构模型研究

为了获得能够描述形状记忆NiTi合金相变和塑性行为的本构关系,基于不可逆热力学,假设两个内变量,分别推导了相变演化规律和塑性演化规律,以及NiTi合金本构模型的主控方程。将导出的本构方程写成一维的增量形式,编制FORTRAN程序,将本构模型进行了程序实现。结合单轴加载的实验曲线、非线性拟合的方法确定该本构模型的相关参数。比较实验结果,验证了该本构模型的合理性。该模型能很好地描述随着载荷不断增加,NiTi合金表现出的母相弹性、马氏体相变、马氏体弹性以及马氏体塑性流动行为,同时,对于应变率效应也能够较为理想地描述。所建立宏观唯象本构模型,参数易确定,为NiTi合金在更加苛刻、极端的环境下的工程应用打下基础。     

颗粒增强脆性基复合材料的尺寸效应

在材料细观非均匀性的基础上研究了含粒径不同颗粒的脆性基复合材料的宏观力学性质和破坏过程的尺寸效应。采用材料破坏过程分析数值模拟软件，对多颗粒增强脆性基复合材料在单轴拉伸荷载作用下经变形、损伤直至破坏的全过程进行模拟研究。结果表明当脆性基体分别复合体积分数相同而大小不同的柔性颗粒时复合材料具有不同的破坏机制，颗粒的尺寸会显著影响材料的破坏及失稳方式，材料的宏观强度随颗粒粒径的增加而降低：但颗粒的尺寸对复合材料线弹性阶段的刚度却影响甚微。     

虑侧壁-土体脱离影响的桶基承载力

当桶基发生平动或转动，其侧壁可能与土体发生脱离，形成空隙，土体破坏模式由"双侧式"变为"单侧式"，承载力降低。建立桶基与黏性土相互作用的三维有限元模型，设置允许脱离和不允许脱离两种接触类型，改变土体强度和桶基长径比，确定桶基与土体发生脱离的条件，探讨脱离对桶基承载力的影响，总结单向与复合加载的承载力公式。结果表明：当允许桶基与土脱离时，土体强度越高，单向与复合承载力降低越严重，但长径比对承载力降低程度影响不大。对于单向承载力，建议通过折减系数量化脱离的影响；对于复合加载，提出了同时适用于允许和不允许脱离的归一化包络面表达式。     

Failure mechanism of full-size concrete filled steel circle and square tubes under uniaxial compression

In this paper, the failure mechanisms of full-size concrete filled steel tubes(CFST) under uniaxial compression were investigated with nonlinear finite element method. Existing experimental results were employed to verify the validity of the finite element models of CFST specimens. Then, the numerical analysis was further conducted to study the mechanical behaviors of full-size CFST columns with circular and square cross sections under uniaxial compression. The simulation results indicate that the distribution of the contact pressure between circular steel tube and core concrete is much more uniform than that between square steel tube and concrete, resulting in much higher confinement and more efficient interaction between steel tube and core concrete in circular CFST columns, as well as ultimate load capacity and ultimate displacement. Extensive parametric analysis was also conducted to examine the effect of various parameters on the uniaxial compression behaviors of circular and square CFST columns.     

高强混凝土框架节点非线性有限元分析

混凝土采用等效单轴应变的增量式正交异性分析模型，考虑裂面效应的反复加载本构关系并做了适当的修改。钢筋的应力应变关系中考虑了反复荷载下的Baushinger效应且做了相应的简化。在粘结滑移模型中引用了斜压杆单元和反复荷载下的粘结——滑移关系，并做了局部的变化。在此基础上编制了二维非线性有限元程序，并应用所编程序对四榀高强混凝土框架边节点进行了分析，研究框架节点的滞回曲线、延性、屈服强度、极限强度等性能。结果表明，计算结果与实测结果符合良好。     

断裂电磁辐射Kaiser效应的实验研究

在大型模拟巷道中研究了巷道变形破坏过程中的电磁辐射。结果表明，模拟巷过在变形破坏过程中产生电磁辐射，电磁辐射具有记忆效应，即Ｋａｉｓｃｒ效应。在实验的基础上讨论了电磁辐射记忆效应的机理和应用。     

碾压混凝土单轴抗压强度尺寸效应的数值模拟

碾压混凝土与混凝土一样也存在着尺寸效应.采用随机骨料模型模拟碾压混凝土的细观结构,利用有限元方法数值模拟碾压混凝土试件单轴抗压的细观损伤断裂,并重点对单轴抗压强度尺寸效应进行了研究.     

A composite material model for investigation of micro-fracture mechanism of brittle rock subjected to uniaxial compression

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声发射凯塞效应结合岩体结构分析测量地应力的新进展

本文论述了用岩体结构分析结合声发射Kasier效应试验测量地应力的问题。通过和传统现场地应力测量方法比较,说明该方法具有更为简单、更为经济、准确度高等优点,便于大量测量,以寻求区域性应力变化规律。     

次生扭矩对双弯构件抗剪强度的影响

在8根R．C．双向受弯构件的试验基础上,借鉴单向受弯有腹筋构件弯剪扭联合作用下弯剪扭强度无量纲相关关系,分析了次生扭矩对均布荷载下R．C．有腹筋双弯构件抗剪强度的影响。