人工制备结构性土力学特性试验研究

通过对结构性土的研究可以掌握天然土受荷过程中的变形破损过程, 从而为考虑土结构性的结构物设计、地基加固等提供依据。本文尝试了一种简单可行的结构性土样的人工制备方法, 通过在原状土料中加入少量水泥和盐粒以形成颗粒间的胶结作用和大孔隙组构以模拟天然黏土的结构性。然后进行了室内压缩试验和不同胶结强度土样在排水和不排水条件下的三轴剪切试验,分析结构性土样的力学特性,以探讨结构性土的破损过程和变形机理。     

基于微观力学机制的各向异性结构性砂土的本构模型研究

在岩土破损力学基础上,基于微观破损机制,提出了考虑各向异性的结构性砂土本构理论。采用Lade-Duncan强度准则考虑中主应力对抗剪强度的影响;采用考虑颗粒排列组构的各向异性状态变量A反映各向异性对土体强度和变形的影响;通过相似扩大重塑土的屈服面反映结构性对土性的影响;通过引入非相关联流动法则考虑各向异性和结构性对土体塑性变形的影响。同时,将基于微观力学机制的损伤演化规律引入结构性土的硬化规律;该硬化规律同时考虑了塑性体积应变和剪切应变对各向异性结构性土强度的影响。然后将该模型用于模拟室内三轴压缩试验,初步验证了该模型的合理性和适用性。     

结构性土压缩曲线的数学模拟

在总结结构性土压缩特点的基础上,以岩土破损力学理论中的弹塑性元（软弱带）为参照状态,通过引入一个可以表征土体结构影响的结构状态参数 ,建立了结构性土压缩曲线的数学表达式。通过结构性土的单轴压缩试验和等向压缩试验,验证了建议的模型可以较好地模拟结构性土的压缩变形特性。由于建议的表达式可以反映结构性土的压缩曲线在 - 坐标中的非线性,对于结构性土的沉降计算有一定的理论意义。     

初始应力各向异性结构性土的二元介质模型

天然岩土材料具有结构性和各向异性。在岩土破损力学的理论框架下,建立了初始应力各向异性结构性土的二元介质模型。岩土破损力学把结构性岩土材料抽象成由胶结强的胶结块（胶结元）和无胶结的软弱带（摩擦元）组成的二元结构体,变形过程中胶结块逐步破损并向软弱带转化。假定胶结块为横观各向同性的理想弹脆性体,胶结块破损后转化成的软弱带为可用邓肯-张模型描述的非线性弹性体。通过引入考虑各向异性影响的破损率和局部应变系数,建立了初始应力各向异性结构性土的二元介质本构模型,并给出了模型参数的确定方法。最后给出了模型的表现,且通过人工制备初始应力各向异性结构性土的三轴压缩试验结果验证了模型的适用性。计算结果表明,所提出的本构模型可以较好地模拟初始应力各向异性结构性土的应力-应变和体积变形特性。     

循环荷载下非饱和结构性黏土的弹塑性双面模型

非饱和黏土的结构性能够显著影响其力学特性。基于非饱和土经典模型BBM（Barcelona basic model）和一种可描述循环塑性的硬化法则,引入体积破损率的作为标准土体结构破损的参数,建立了一个描述常吸力下非饱和结构性黏土静态及动态力学特性的弹塑性双面模型。模型在应力空间中包含与重塑非饱和土屈服面几何相似的结构性边界面和加载面,采用径向映射法则和可移动的记忆中心原理,通过结构性边界面和加载面在应力空间中的演化来反映循环加载过程中非饱和结构性黏土的循环塑性特征和结构损伤过程。通过与相关非饱和黏土控制吸力试验数据的比较,表明该模型能够较好地反映静态加载下非饱和结构性黏土的力学特性,而模型预测的循环荷载下的应力?应变特征也具有一定的合理性。     

上海软粘土微观特性及在土体变形与地面沉降中的作用研究

对上海软粘土的颗粒及集合体成分、孔径分布、微结构、孔隙溶液与阳离子交换性作了分析 ,对固结前后的孔径变化与人工回灌对土体性质可能带来的影响作了探讨 ,从物理化学角度阐述了软粘土微观特性对土体固结变形及地面沉降的影响.     

湿陷性黄土变形的微结构突变模型研究

根据湿陷性黄土的湿陷特点,分析了其主要影响因素,包括外部因素：水、荷载与内部因素微结构及其力学性质。从湿陷性黄土的湿陷性影响出发,建立了湿陷性黄土结构失稳突变模型,并从模型基本假定、微结构模型应力特性和湿化于微结构失稳的突变关系3个方面进行了理论分析研究,在一定程度上揭示出湿陷性黄土变形机制和规律。通过微结构突变失稳理论发现：当应力状态满足孔隙微结构失稳判别式时,微结构元的变形状态将诱发微结构失稳崩塌。微结构的稳定性与结构刚度 和受力状态 密切相关。地下水不仅改变了颗粒的受力情况,更重要的是使颗粒间连接刚度降低,从而导致微结构失稳。     

结构性粘土的边界面砌块体模型

把天然粘土的变形看作是由结构的破坏引起的。总的变形由结构性粘土的弹性变形、结构面的滑移塑性变形和结构体破损引起的的损伤塑性变形组成。把滑移屈服面看作可以扩大、旋转的运动硬化面,并作为边界面,通过内插塑性模量来描述滑移塑性变形。采用损伤边界面,通过规定加荷或反向加荷产生损伤变形,卸荷不产生损伤变形来描述损伤塑性变形。建立了结构性粘土的边界面砌块体模型,并用试验进行了验证。     

黄土的湿载结构性本构模型研究

土结构性是土结构空间排列几何特征和联结特征所表现出的力学性质,是影响土力学特性的重要内在因素。它与土的密度、粒度、湿度相联系,能够综合反映土的强度、变形等力学特性的变化和发展。从综合反映增湿导致土结构内在主动变化和加载变形导致土结构被动变化两个方面出发,沿用土综合结构势的应力比结构性参数,首先建立压缩、剪切及增湿作用下黄土的结构性演化规律;其次,通过压剪湿作用下黄土的应力-应变特性、屈服破坏特性及其与结构性之间的关系,揭示结构性变化对土力学性质的影响;进而,建立了反映压剪湿作用下黄土结构性发展演化的湿载结构性本构模型。最后通过与试验数据、修正剑桥模型的比较分析,初步验证该模型的准确性。     

超固结粘土的二元介质模型

为了分析超固结粘土边坡的变形和稳定的需要,在岩土破损力学的框架内建议了一个适用于这类土的二元介质模型。该模型考虑了土体内在的不均一性,把它看作由结构块和结构带组成的复合体,两者共同分担外荷载,模型包含10参数,并拟定了这些参数的测定方法。通过模拟三轴试验的计算表明,该模型可以反映London粘土的应力-应变特征。     

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

粗粒料颗粒破碎数值模拟研究

粗粒料在外力作用下存在明显的颗粒破碎特性,研究颗粒破碎过程是当前研究的热点问题之一。基于粗粒料单颗粒破碎机制,考虑单颗粒破碎强度与直径的变化规律,采用非线性接触H-Z模型和密度控制法建立了粗粒料颗粒破碎数值模型。开展粗粒料双轴剪切试验数值模拟研究,并与室内试验结果进行对比分析。研究表明：建立的粗粒料颗粒破碎数值模型能够较好地模拟粗粒料偏应力与轴向应变和体积应变与轴向应变的关系;数值模拟获得的粗粒料颗粒破碎率与室内试验结果基本一致;去除试样制备过程和固结过程引起的颗粒破碎,不同围压条件下的颗粒破碎率归一化后基本重合,且可以近似地采用双曲线函数进行拟合。颗粒破碎率随着围压的增大,逐渐增大,试验级配趋于Einav提出的颗粒破碎的最终级配（分维数等于2.6）     

Scale up of lifters in ball mills

Liner design and lifter geometry in tumbling mills are very important in comminution kinetics and energy consumption. In terms of the parameters of the batch grinding model, the breakage rate function decreases as lifter size increases while the breakage distribution function is independent of the lifter size. However, the specific energy consumption is not a function of lifter size. Reducing the lifter height from 2.54 cm to 0.32 cm increases the production from this mill by 37%. When the mill is operated without any lifters, the charge apparently slips inside the shell resulting in lower breakage kinetics and higher energy consumption.     

Relationship between breakage parameters and process variables in ball milling — An industrial case study

The performance of the secondary ball mill at the New Broken Hill Consolidated Ltd. concentrator is analysed using the perfect mixing model and an ore-specific breakage distribution function. This function was determined from single-particle breakage tests using a computer-monitored twin pendulum apparatus.The ratio of the breakage rate to the normalized discharge rate, r/d^*, determined for the ball mill using the ore-specific breakage distribution function for a range of grinding conditions is related to the mill power consumption. The mill power consumption is related to the percentage of mill volume occupied by the ball charge and to the percentage of solids in the mill feed.     

Implicit integration of simple breakage constitutive model for crushable granular materials: A numerical test

In the context of the recently developed breakage mechanics that is based on thermodynamics principles, this paper presents a mathematical modelling procedure to implement the simple (i.e., linear elastoplastic) breakage constitutive model using finite element analysis (FEA) with illustrations by engineering applications. More informative mathematical derivation procedures of energy dissipations, plastic potential, yield function and non-associated flow rules are presented. In contrast, the existing relevant publications often lack sufficient elaboration, leaving knowledge gaps in the full understanding the model. This is followed by a series of numerical simulations in ABAQUS to test the model at the constitutive level. Various isotropic and triaxial shear tests in drained or undrained conditions are tested to illustrate the key features of the breakage model, which seem to be overlooked in the literature. Finally, a few numerical results are compared with experimental shear tests to demonstrate the ability of the simple breakage model in reflecting mechanical responses of crushable granular aggregates.     

考虑颗粒破碎影响的粗粒土本构关系

粗粒土在较大的应力条件下容易产生颗粒破碎现象,而现有的大多数模型都没有考虑剪切过程中的颗粒破碎。模型将塑性功引入土体受力变形过程的能量方程中,推导得到土体流动法则。采用直线型屈服轨迹和非相关联流动法则,利用不排水应力路径计算得到硬化函数,建立了一个考虑颗粒破碎的粗粒土本构模型。对比分析表明：该模型对粗粒土在各种围压下的应力-应变和体应变计算结果与试验曲线吻合较好。     

Modelling the performance of industrial ball mills using single particle breakage data

Ball milling is an energy-intensive unit operation and usually consumes a major proportion of the power drawn by a typical mineral processing plant. Hence, substantial economic benefits can be achieved by optimal design and by operating ball milling circuits under optimum process conditions. This requires an accurate ball mill modelling technique.In the multi-segment ball mill model, the size-dependent material transport within the mill varies systematically with the amount of coarse particles present in each segment. The ore-specific breakage distribution function can be determined from single particle breakage tests conducted using a computer-monitored twin pendulum apparatus. When the ore-specific breakage distribution function is used in the multi-segment, a constant relationship between the breakage rate parameters and mill diameter is observed. Thus, the performance of an industrial ball mill can be adequately described using the ore-specific breakage distribution function together with the systematic variation of the material transport and the breakage rate functions with process conditions and mill diameter, respectively.This ball mill modelling technique is illustrated using a case study on the design of a ball milling circuit for a particular grinding requirement and another case study on modelling the performance of an industrial ball milling circuit.     

DEM investigation of the effect of intermediate principle stress on particle breakage of granular materials

This study investigates the influence of the intermediate principle stress on the particle breakage of granular materials. The crushable agglomerate method is applied to model soil particles and numerical true triaxial tests were carried out. The results show that particle breakage increases with increasing b value, the relationship of which follows an exponential function and agrees well with previous experimental results. More importantly, the study found that the relationship between particle breakage and total energy input is independent of the intermediate principle stress, which provides a good basis for the constitutive modeling of granular materials.     

考虑颗粒破碎的钙质砂修正邓肯-张E-B模型

在常规应力水平下颗粒发生破碎是钙质砂有别于其他砂土的重要性质之一,且由于颗粒破碎的存在,使用传统的本构模型无法很好地模拟钙质砂的力学行为。因此本文以最为普及的本构模型之一--邓肯-张E-B模型为基础,对其进行颗粒破碎方面的修正以得到一个能用于钙质砂的本构模型。具体方法为:首先本文采用Hardin提出的相对破碎Br这一指标来度量颗粒破碎的大小。之后研究分析得出了颗粒破碎对邓肯-张模型参数(内摩擦角φ、割线模量E50及体积模量B)的影响规律。然后通过颗粒破碎与输入能量之间的关系将各状态下无法直接确定的相对破碎Br与可确定的应力-应变状态联系起来。最终得到了一个考虑颗粒破碎的钙质砂修正邓肯-张E-B模型。为验证模型的准确性及适用性,本文还使用该模型对4种不同粒径范围且试验围压不同的钙质砂的三轴排水行为进行了模拟。结果表明拟合效果较好,模型能适用于各种不同粒径范围的钙质砂,并且在颗粒破碎较大的情况下明显优于传统邓肯-张模型。     

Validation of a model for impact breakage incorporating particle size effect

Investigation of a breakage probability model published by Vogel and Peukert [Vogel, L. and Peukert, W., 2004. Determination of material properties relevant to grinding by practicable labscale milling tests. Int. J. Miner. Process., 74S, 329–338.] has led to a modification of their model to describe the degree of impact breakage, t₁₀. The modified model takes a form similar to the JKMRC prior art breakage model, but with particle size and breakage properties incorporated explicitly in the model.