Computer simulated experiments on fracture toughness of particle-dispersed composites

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边界元法的边界效应问题

本文采用两种新方法来处理边界元法的边界效应问题。首先,用线性元的降低高次奇异性法。与一般边界元相比,使边界效应大为缓和。其次,用抛弃基本解的插值法。它能得到一般边界元法无法求得更靠近边界的内点值。将两种方法结合起来的混合法,则可得到更为满意的结果。作者编制了线性元降低高次奇异性法程序。用它对工程实例进行计算,结果证明了本文方法的优越性。     

Numerical simulation on borehole breakout and borehole size effect using discrete element method

Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries, although there are critical research gaps that remain unfilled. In this paper, numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect, including temperature influence. The discrete element method(DEM) model shows that the borehole breakout angular span is constant after the initial formation,whereas its depth propagates along the minimum horizontal stress direction. This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation. The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking. This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock.In addition, the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells. Based on the results, the higher temperature led to lower breakout initiation stress with same borehole size, and more proportion of shear cracks was generated under higher temperature. This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries. Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions, suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.     

考虑骨料粒径影响的BFRP筋混凝土梁剪切破坏及尺寸效应

粗骨料是混凝土材料的组成之一,其粒径变化会影响混凝土梁中骨料咬合作用对抗剪承载力的贡献。为了系统地考虑最大粗骨料粒径对玄武岩纤维增强聚合物（Basalt Fiber Reinforced Polymer,BFRP）筋无腹筋混凝土梁剪切破坏的影响,采用细观尺度数值模拟方法,建立BFRP筋无腹筋混凝土梁数值模型,模拟分析构件尺寸和粗骨料粒径对BFRP筋混凝土梁剪切破坏模式和抗剪强度的影响规律。结果表明：BFRP筋无腹筋混凝土梁的抗剪强度存在尺寸效应,同时,随着最大粗骨料粒径的增大,BFRP筋混凝土梁的抗剪承载力提高,梁的剪切尺寸效应被削弱。根据最大粗骨料粒径的影响机制与规律,结合断裂力学尺寸效应律,建立了BFRP筋混凝土梁抗剪强度尺寸效应理论公式,并与模拟结果和试验数据进行对比,验证了公式的准确性和合理性。     

模拟准脆性材料热开裂的热力耦合格构离散单元法

针对准脆性材料的热传导与热开裂问题,基于格构离散单元法（LDEM）提出新的热力耦合数值模型. 通过格构离散体系与连续体传热过程的等效换算,结合格构单元的线膨胀公式,在LDEM中实现温度传导与裂纹扩展的数值模拟. 以平板的热传导与热弹性应力问题、由温度梯度与热失配引起的开裂问题为例,验证所提模型. 将所提模型应用于细观混凝土温度?应力试验的数值模拟中. 结果表明,LDEM热力耦合模型能够有效模拟准脆性材料的热传导过程、在温度影响下的裂纹萌生与扩展,是研究准脆性材料热开裂过程与机理的有力工具.     

运用插值法解决边界层效应的研究

本文分析了边界层效应产生的原因，提出了运用插值函数解决边界层效应的方法，给出插值节点选取的方法，其特点是插值节点的选取与边界单元的划分密切相关。数值算例表明，这些方法是完全正确的，且既简单又有很高的精度。     

边界轮廓法的若干进展

介绍了作者在边界轮廓法方面的一些研究新成果,内容包括基于等价边界积分方程的边界轮廓法,基于面力边界积分方程的边界轮廓法,以及边界轮廓法在裂纹、薄板弯曲等问题中的应用。     

Application of fractal theory to size effect of disordered materials

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ZnO超微粒子的量子尺寸效应和光催化性能

利用Raman激光光谱、XRD、TEM、BET、SPS和UV-Vis等手段研究了ZnO超微粒子的量子尺寸效应和光催化性能,结果发现,前驱物碱式碳酸锌在320、430和550℃经热处理制得的ZnO超微粒子的粒径分别为13.5、19.3和26.1nm,属六方晶系纤锌矿结构;随着热处理温度的降低,ZnO粒子的粒径减小,Raman激光光谱、SPS和UV-Vis吸收峰均发生蓝移,表现了量子尺寸效应;在光催化降解苯酚的过程中,ZnO超微粒子比商品ZnO的光催化活性高,且随着热处理温度的升高,其光催化活性下降。     

线弹性静力学中的另一类边界积分方程

讨论一类新的边界积分方程，它与经典的Ｒｉｚｚｏ型边界积分方程“共轭互补”探讨了该类边界积分方程数值方法的实现，可望它与经典的Ｒｉｚｚｏ型边界积分方程的恰当组合能导致更有效的边界元法。     

弹塑性力学问题的边界元——虚边界元耦合解法策略

采用边界元－虚边界元耦合解法对弹塑性问题进行了分析,并指出了处于弹塑性状态区域应使用边界元法,其它部分采用虚边界元法,进而提出了求解这一类问题的方案。     

Effect of rock mass structure and block size on the slope stability--Physical modeling and discrete element simulation

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.     

考虑材料参数随机分布的边界元计算方法

根据概率理论,将岩土力学材料参数看成呈高斯型空间正态分布的随机变量,提出了一种新的考虑材料参数随机分布的边界元计算方法,推导出了材料参数按空间呈高斯型正态分布时边界元基本计算公式,利用这些公式可以计算出每个单元的位移,从而求出结构的可靠度。     

分析永磁电机磁场的边界轮廓法

利用传统边界元积分方程的被积函数的散度等于零的特性，使用了一种新型的边界元法——边界轮廓法，使求解问题的维数再降一维，不但简化了计算，而且避免了求解奇异积分．针对永磁电机的磁场问题，选择双线性函数求得相应标量磁位，并对60kVA永磁电机的磁场进行了计算．实例计算表明，该方法具有较高的精度，为计算电机电磁场开辟了一个新的计算方法．     

考虑温度效应下轴对称问题的边界元法

利用边界元法计算在温度效应下轴对称的弹性问题，推出相应的边界积分方程，并给出算例。     

方孔分支裂纹的一种边界元分析

方孔分支裂纹是一个很复杂裂纹问题.本文利用笔者最近提出的边界元方法来研究内部压力作用下方孔分支裂纹问题.数值算例与文献报道的结果进行比较,发现这种数值方法无论对无限大板还是对有限大板中复杂裂纹的应力强度因子计算都非常有效.另外本文报道的方孔分支裂纹的应力强度因子数值结果可以揭示裂纹体几何对应力强度因子的影响.     

单向复合材料分析的三维横观各向同性边界单元法

对于象单向复合材料的典型横观各向同性弹性体,本文引入了三个位移势函数,求出了问题的基本解,根据弹性力学的Betti定理,建立了三维横观各向同性二次等参单元的边界单元法。最后,计算了两个算例,特别是使用该方法研究了单层纤维复合板在拉伸时的孔边应力集中。     

Monte Carlo simulation for simultaneous particle coagulation and deposition

The phenomena of simultaneous particle coagulation and deposition are of great ubiq- uity and of key importance in nature and various engineering applications, including the precipitation and downfall of rain, ice, snowflakes, fog and hail, the scavenging of fly ashin electrostatic precipitator of power plant, the transplantation of fume in smoke flue of pulverized coal-fired plant, nuclear reactor analysis modeling aerosol’s diffusion and deposition when blasting, the suspension and sedimenta…     

混凝土不同骨料粒径对声发射检测的影响

利用声发射技术对不同骨料粒径的混凝土试件进行断铅试验。探究不同骨料粒径对声发射检测混凝土材料定位精度、声速标定、时间参数设定的影响和最优传感器布置方式的选取。结果表明: 骨料是影响声发射检测精度的主要因素之一, 骨料粒径每增大5 mm, 声速下降7.5%;骨料粒径每增大5 mm, 上升时间下降3.5%左右, 且最大上升时间不超过200 μs; 进行“多次多点”测试能合理的确定最优传感器布置方式并有效减小定位误差, 但不能消除误差。     

Size effect of fracture characteristics for anisotropic quasi-brittle geomaterials

Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture toughness, effective fracture energy and fracture process zone(FPZ) size of geomaterials were first analyzed by systematic size effect fracture experiments. The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclin...