复合地层盾构刀盘掘进速率及受力特性分析

为探究复合地层中盾构刀盘的掘进速率及受力特性,基于连续-非连续单元法(CDEM),建立盾构-岩土体这一完整系统的数值计算模型。通过在CDEM中引入简单有限体积法、虚拟质量法、单元溶蚀算法等系列算法,实现盾构刀盘掘进全过程的三维模拟。建立5种刀盘面花岗岩占比的刀盘破岩数值模型,并对不同刀盘面花岗岩占比下的刀盘进尺、掘进速率、平均转矩、平均倾覆力矩等进行详细分析。数值模拟结果表明:1)在某一特定复合地层中掘进时,随着掘进时间增加,刀盘进尺基本呈线性增大的趋势,但进尺曲线中平缓段及速升段交替循环出现; 2)刀盘面花岗岩占比由0增大至100%,掌子面处拉伸破坏单元增加,剪切破坏单元减少,且刀盘的掘进速率呈指数衰减趋势,掘进速率降低88. 7%; 3)刀盘面花岗岩占比由0增大至100%,平均转矩值逐渐增大,增大比例为117. 5%,平均倾覆力矩值则呈现先增大后减小的趋势,且在花岗岩占比为50%时最大

改进型铜基甲醇合成催化剂NC208的DTA研究

对改进型铜基催化剂进行了研究，活性评价结果表明，改进型铜基甲醇合成催化剂ＮＣ２０８（Ｃｕ－Ｚｎ－Ａｌ－Ｍ１２）初始活性比工业催化剂Ｃ２０７（Ｃｕ－Ｚｎ－Ａｌ）提高约１８％；耐热试验后比Ｃ２０７提高约４６％。两种催化剂的ＤＴＡ对比试验显示，工作态ＮＣ２０８催化剂热稳定性明显优于Ｃ２０７；ＮＣ２０８催化剂前驱体含Ｃｕ（ＮＯ３）２·３Ｃｕ（ＯＨ）２、Ｚｎ５（ＯＨ）６（ＣＯ３）２和（ＣｕＺｎ）（ＯＨ）２ＣＯ３等成分比Ｃ２０７多，其分解温度小于３５０℃；ＮＣ２０８催化剂还原最高温度为２３５℃

改进型铜基甲醇合成催化剂NC208的DTA研究

对改进型铜基催化剂进行了研究，活性评价结果表明，改进型铜基甲醇合成催化剂ＮＣ２０８（Ｃｕ－Ｚｎ－Ａｌ－Ｍ１２）初始活性比工业催化剂Ｃ２０７（Ｃｕ－Ｚｎ－Ａｌ）提高约１８％；耐热试验后比Ｃ２０７提高约４６％。两种催化剂的ＤＴＡ对比试验显示，工作态ＮＣ２０８催化剂热稳定性明显优于Ｃ２０７；ＮＣ２０８催化剂前驱体含Ｃｕ（ＮＯ３）２·３Ｃｕ（ＯＨ）２、Ｚｎ５（ＯＨ）６（ＣＯ３）２和（ＣｕＺｎ）（ＯＨ）２ＣＯ３等成分比Ｃ２０７多，其分解温度小于３５０℃；ＮＣ２０８催化剂还原最高温度为２３５℃

Progressive damage induced damage-aggravation effect and an energy dissipation model of brittle materials

渐进破坏广泛存在于岩土工程、国防工程和建筑结构等领域，与此同时，能量在渐进破坏过程中扮演重要角色。依据能量的来源，可大体分为内部能量演化诱发破裂和外界输入能量诱发破裂。因此，开展渐进破坏对力学响应特征的机理研究，建立渐进破坏过程中不同类型能量的统计算法，构建描述裂纹生成的能量耗散模型，对于准确评估模型的宏观强度和获取能量演化特征具有重要意义。 本文首先针对渐进破坏对力学响应特征的影响机理，提出了渐进破坏的&ldquo;破裂加剧效应&rdquo;和量化指标渐进破坏比Kt。随后，基于连续-非连续算法的基本概念和本构模型特点，建立了准确统计所有能量类型的能量统计算法。接着，根据岩石的多尺度模型、兰纳-琼斯势和范德华力，建立了基于岩石微观破裂机理的能量耗散模型。最后，探讨了车载导弹发射期间冲击荷载作用下道路结构的沉降、变形、破裂和能量演化特征。主要内容和结论如下： （1）提出渐进破坏的&ldquo;破裂加剧效应&rdquo;和量化指标渐进破坏比Kt，解释了渐进破坏对模型力学响应特征的影响机理。当模型发生渐进破坏时，因为应力重分布的存在，破坏将出现&ldquo;破裂加剧效应&rdquo;，导致模型宏观承载强度降低。在边坡稳定性分析中，理论分析和数值模拟结果均表明，基于渐进破坏比Kt对整体抗滑力修正后，依据极限平衡法得到的边坡安全系数更能准确反映边坡的稳定性。 （2）建立准确统计模型从连续介质转变为非连续介质过程中所有能量类型的能量统计算法。基于连续-非连续算法的基本概念，首先将模型的能量划分为单元变形能WEE、单元动能WEV、弹簧变形能WPE、弹簧断裂能WPC、摩擦耗能WR和阻尼耗能WD，随后依据本构模型特征，分别建立了每种能量的统计算法。数值案例验证了能量统计算法具有很好的自洽性和鲁棒性。 （3）建立基于岩石微观破裂机理的能量耗散模型，用于准确表征裂纹生成和扩展过程中的断裂能量和力学行为。基于岩石的多尺度模型（RVE尺度&mdash;颗粒尺度&mdash;分子尺度）、兰纳-琼斯势和范德华力，建立了拉伸过程与剪切过程中能量耗散模型的力方程和势能方程。最后，通过数值模拟结果与理论推导结果和室内实验结果的对比分析，验证了能量耗散模型的准确性。 （4）探究车载导弹发射期间冲击荷载作用下道路结构沉降、变形、破裂和能量演化特征。计算结果表明：荷载中心点沉降量时程曲线与冲击荷载时程曲线的变化趋势一致，沉降量最大值与冲击荷载的峰值点相对应，且道路结构的变形量主要产生于路基上部。破裂主要产生于冲击荷载急剧增大时期，破坏类型包括拉伸破坏和剪切破坏。不同能量类型的时程曲线存在差异，但均与冲击荷载的变化趋势密切相关。</p

基于连续-非连续单元法的三维脆性颗粒冲击破碎特性分析

通过在连续-非连续单元法（CDEM）中引入考虑应变率效应的断裂能本构以及能量统计算法，实现了球体冲击破碎过程中损伤破裂程度及能量演化的定量分析。计算结果表明，冲击破碎过程分为接触蓄能阶段、损伤破碎阶段和碎块飞散阶段。首先，颗粒的部分动能转化为单元弹性变形能，随后这部分变形能和动能迅速转化为摩擦消耗、阻尼消耗及弹簧断裂能，破碎基本完全后碎块继续飞散。不同冲击速度下，颗粒分别出现了反弹、开裂、破碎和粉碎的现象。随冲击速度的增加，D50的变化速率逐渐放缓，破碎块度逐渐趋于稳定；破裂度、损伤度以及平均损伤因子的变化速率先增加后放缓，颗粒破坏以拉伸破坏为主。以上结论可为脆性材料冲击破碎工艺的优化设计提供依据

基于渐近破坏模型的震前“静音期”数值分析与思考

在国内两次地震中某地震应变仪测量数据显示,地震发生前期约几个月的时间,有5天没有观测到压性脉冲及阶跃应变异常信号。而在这5天之外,压性脉冲及阶跃应变异常信号频繁。在岩石力学应力应变实验中,也有较多的文献表明,在应力峰值附近,灾变前也有一个时间段声发射信息较少。为叙述方便,我们将这个时间段称为"静音期"。鉴于这种现象在汶川8级大地震及之后的芦山7级地震中皆出现过,我们认为静音期很有可能是大地震的前兆

A strain-rate cohesive fracture model of rocks based on Lennard-Jones potential

To characterize the dynamic mechanical response of rocks during the initiation and propagation of cracks at a high strain rate, a strain-rate cohesive fracture model is established based on the Lennard-Jones potential and multi-scale model of rocks. The newly proposed model explains the micro-mechanism of strain rate effect from the molecular scale and establishes the potential energy function and force function. First, it is proposed that the strain rate effect arises due to the change of microscopic properties of molecules at a high strain rate. Thereafter, the potential energy function and force function of the strain-rate cohesive fracture model corresponding to the dynamic tensile and shear processes are established. Finally, the accuracy of the strain-rate cohesive fracture model is verified through numerical simulations. The results indicate that the strain-rate cohesive fracture model can accurately simulate the dynamic tensile failure and shear failure of rocks at different strain rates. The dynamic tensile strength, dynamic compressive strength, and dynamic tensile fracture energy obtained by numerical simulations and laboratory tests are similar

Quantitative characterization of damage-aggravation effect caused by progressive damage

Aiming at the progressive damage phenomenon in geotechnical field, it attempts to study the effect of progressive damage on the macro-bearing capacity. Firstly, based on the theoretical analysis of a two-dimensional plane inside representative volume element, it is proposed that progressive damage will occur if the bearing capacity of microplanes is different. Besides, "damage-aggravation effect" is proposed according to the difference between the macro-bearing capacity of entire plane and the sum of bearing capacity of all microplanes when progressive damage occurs. Secondly, progressive damage ratio K-t is proposed to quantify "damage-aggravation effect". Finally, based on the rod model, the correspondence between K-t and some influence factors is studied by theoretical analysis and numerical simulation. The results show that "damage-aggravation effect" does exist, and the macro-bearing capacity of entire plane is less than the sum of bearing capacity of all microplanes when progressive damage occurs. If the bearing capacity of rods in the rod model obeys uniform distribution, as the minimum of bearing capacity increases linearly, the macro-bearing capacity increases linearly, and K-t decreases inversely

Cohesive fracture model of rocks based on multi-scale model and Lennard-Jones potential

With the aim of modelling the energy dissipation phenomenon during the initiation and propagation of cracks, a novel cohesive fracture model is proposed in this study based on the multiscale model of rocks and the Lennard-Jones potential between non-bonding molecules. The proposed model establishes the corresponding relationship of deformation in the multi-scale model of rocks and suggests that the fracture energy is essentially the manifestation of the transformation of deformation energy into potential energy between molecules. First, the multiscale model of rocks is established based on the structural characteristics and fracture characteristics of rocks, and the corresponding relation of deformation at different scales is analysed. Thereafter, the force and potential energy equations of the cohesive fracture model corresponding to the tensile and shear processes are established. Finally, the accuracy of the cohesive fracture model is verified through three numerical simulations. The results indicate that the cohesive fracture model can accurately fit the theoretical values and experimental results in the Mode-I and Mode-II tests. In the uniaxial compression test, the cohesive fracture model can accurately simulate the uniaxial compressive strength and fracture pattern of rocks

Simulation-based personal fatality risk assessment due to the fragmentation hazard

In the military and chemical industry, modeling the fragmentation hazard field is of great significance in conducting the fatality risk assessment and calculating the safety distance for person. Although the ballistic methodology achieves the simulation of fragmentation flight trajectory, the acquisition of accurate initial projection data of fragmentation is a challenge. By coupling continuum-discontinuum element method and particle discrete element method, the fragmentation power algorithm is established, which achieves the integrated simulation of the initial projection data of fragmentation and the flight process of fragmentation. First, continuumdiscontinuum element method is adopted to simulate the detonation products-driven fragmentation acceleration process by introducing the explosive detonation model, which achieves the acquisition of initial projection data of fragmentation. Then, the particle discrete element method is adopted to simulate the flight trajectory and power data of fragmentation. Based on the numerical and experimental result, the accuracy of fragmentation power algorithm is verified. In conjunction with the personal vulnerability model, a systematic numerical simulation framework is established to conduct the simulation-based personal fatality risk assessment when the metal-cased munition detonates accidentally, and the results indicate that the personal fatality risk due to the fragmentation becomes severer with the increase of munition curvature