基于横观各向同性模型的片岩隧洞稳定性研究

以四川大渡河丹巴水电站引水隧洞为研究对象,结合三轴试验和自主研发的空间多角度片理抗拉强度测试技术,对不同片理夹角下石英云母片岩的力学参数进行测定,得出石英云母片岩的弹性模量、c和φ与围压之间的关系,并分别给出干燥和饱和条件下各力学参数围压敏感性排序。通过表征各向异性的参数k_1、k_2,对不同片理夹角下石英云母片岩的各向异性与围压的关系进行评价,并进一步指出不同高度岩样抗拉强度随片理角度的变化规律。采用横观各向同性本构模型,通过设定材料主轴空间方位,可模拟片理空间任意角度展布的岩体。针对大区域模型存在的不足,提出一种主应力构造精细应力场的新方法,避免了大模型的应力边界效应,可方便快捷对局部区域进行精细应力构造。根据片理走向及不同倾角选定15个不同片理空间展布模型进行计算分析,分别得出应力、位移、塑性区随片理角度的变化规律,并指出不同片理展布条件下的最不利工况。     

等规聚丙烯注塑成型冷却固化分子机制研究

针对等规聚丙烯(iPP)在注塑成型冷却过程中的液-固相变与大分子形构问题,采用分子模拟实验的方法,研究了iPP材料在注塑冷却过程中的分子固化与形态演化的分子机制。建立了聚合度依次为24、36、51、72、120,链数为36、24和16的iPP胞元体系,基于Smart Minimizer与SA算法实现了能量初始化;基于周期性边界并引入COMPASS力场及Velocity-Verlet算法,实现了体系冷却固化过程的分子模拟实验。结果表明:不同模拟体系的T_g结果符合Flory自由体积理论;固化前后iPP大分子链主链键长、键角等结构参数均呈高斯分布,温度越低键长与键角分布越集中,符合无外力加载条件下的缠结大分子链的冷却松弛过程;〈h〉和〈R_g〉均随聚合度的增大而增大,降温过程中〈h〉呈高斯分布状态,而〈R_g〉分布趋于集中,一方面表明冷却固化过程中大分子链由初始取向排布逐步恢复至缠结状态,另一方面体现了固化结晶过程;材料聚合度越大,降温过程中分子迁移或固化速率越小,且当温度高于T_g时,聚合度越小,降温过程体系扩散系数下降梯度越大,而温度下降至T_g以下则无明显规律。     

横观各向同性复合材料激光超声检测的数值模拟

为了分析横观各向同性复合材料的内部材料属性 ,结合激光超声理论,使用仿真软 件Comsol Multiphysics 建立了复合材料在激光热弹下激发出超声波的等效模型,通过设置 完美匹配层、低反射边界等方法消除了边界回波。采用有限元法模拟了横观各向同性材料中 激发超声波的物理过程,对缺陷回波信号进行了时域分析。结果表明:平板厚度的增加会使 超声波逐渐转变为高阶模态,且随着平板厚度的增加,模态的截止频率会逐渐降低,同时在横观 各向同性复合材料中传播的超声波将逐渐失去Lamb波的特征,转而表现出表面波特征,将 Lamb波向表面波转化激发出Rayleigh波。本次模拟为进一步研究复杂介质中超声波的产生 和缺陷定位奠定了基础。     

体积噪声矢量场空间相关特性研究的一种方法

确定噪声场的相干结构对分析矢量水听器阵信噪比增益非常重要.建立了一个三维的噪声源在球面上均匀分布的各向同性噪声模型,研究了噪声场中声压与质点振速3个正交分量的自相关和互相关特性,推导得到了窄带噪声场空间相关系数的解析表达式以及单矢量水听器接收噪声的协方差矩阵.基于三维噪声场的空间相关函数,讨论了矢量水听器线阵的某些应用及其输出信噪比增益.数值算例表明,该三维噪声场空间相关特性模型可方便地应用于任意形状的基阵在任意姿态下的信噪比输出的获取.     

The effect of a Gaussian distribution of chain-lengths on the phase-behaviour of a model system of rod-like macromolecules in solution

The calculations of Flory and co-workers for the formation and composition of isotropic, bi-phasic and anisotropic systems composed of rod-like macromolecules in solution have been extended to include a Gaussian distribution of rod-lengths. The critical concentrations for the beginning and end of the bi-phasic range $\text{v}{}^{\mathrm{<mtext>o</mtext><mtext>1</mtext>}}{}_{\mathrm{p}}$ and $\text{v}{}^{\mathrm{<mtext>o</mtext><mtext>7</mtext>}}{}_{\mathrm{p}}$ respectively, the volume fraction of anisotropic phase Φ_A, the compositions and average molecular weights of isotropic and anisotropic phases, and the order parameter S of the anisotropic phase are calculated as a function of polymer concentration v^o_p for rod-length x_o in the range 30 to 70 and for a Gaussian distribution half-width $\text{Δ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in the range 10 to 70. The extent of the bi-phasic range and the composition of the two components is found to be strongly dependent on the breadth of the distribution and average rod-length. The applicability of the calculations to data for poly(alkylisocyanates) in solution is briefly considered.     

混凝土在双向受压下力学性质的试验研究

采用大吨位等刚度双向加载系统,对混凝土立方体试块进行了双向和单向加载的试验研究。实验结果表明：在双向加载条件下,混凝土的破坏强度远大于单轴破坏强度;由于中间主应力的增加,约束了试件的横向变形,使1：l加载破坏强度大于双轴2：1加载破坏强度;总结了在最小主应力σ3=0的情况下,试件双向σ1—σ2关系。     

Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons: III. Powders based on an iron-catalyzed mesophase synthesis

A spherulitic mesophase pitch with about 50 vol% mesophase has been synthesized by an iron-catalyzed pyrolysis of a coal tar pitch. The isotropic pitch is removed to various extents by solvent extraction. The thermoplasticity of the resulting raw mesophase powders is adjusted by treatment with oxygen with respect to optimum sintering properties. After milling of these powders to a particle size d 10 μm they were compacted with various molding pressures, sintered and graphitization-treated with various heating programs. The individual process steps and intermediate products were analyzed. Carbons sintered at 1300 °C show flexural strengths up to 225 MPa and strains-to-failure up to 1.25%. After graphitization treatment at 2400 °C, carbons with a flexural strength of about 170 MPa and a strain-to-failure of about 1% were obtained.     

一个椎间盘生物力学模型

椎间盘在脊柱运动中起着重要的作用,根据椎间盘的生物力学特点建立力学模型.采用复合材料力学中的弹性嵌入体解,建立了椎间盘的一个横观各向同性圆柱体力学模型.求出了腰椎间盘在直立位、弯曲及扭转作用下的应力应变和位移解.得出结论椎间盘在受复合载荷的作用下更易被破坏.     

Spatially isotropic configuration of Stewart platform-based force sensor

This paper studies isotropic configuration of the Stewart platform-based force sensor using an analytic approach. The conditions leading to spatially isotropic configuration are introduced. The isotropic performance of the classical Stewart platform-based force sensor is studied, the result indicates that it is impossible to realize spatial isotropy in theory. A modified Stewart platform-based force sensor which can achieve spatial isotropy is proposed. In order to obtain spatially isotropic configuration, the analytic relations of key structural parameters leading to spatially isotropic configuration are derived. Classes of spatially isotropic configurations can be easily obtained from the analytic results.     

二维各向同性介质地震波全波场的有限差分模拟

对地震波场的有限差分方程进行了详细的推导,采用改进的中心线算法对有限差分方程中的大型稀疏线性方程组进行求解,并对算法的稳定性进行了分析。通过对二维双层弹性介质中的地震波全波场的模拟,获得了清晰的地震波波场特征,包括面波及体波波场特征。