脆性岩石各向异性损伤和渗流耦合细观模型

采用细观力学方法提出一个岩石各向异性损伤和渗流耦合的细观模型。其中,岩石的损伤由裂纹的状态变量来表示,损伤演化通过裂纹扩展准则来定义,并采用细观力学的分析方法由含裂纹材料的自由熵推导出裂隙岩石的本构方程。同时可以假设：由于裂纹表面的粗糙不平,在裂纹扩展的同时将引起法向开度的产生,这是材料渗透系数变化的主要原因,根据上述假设及达西定律和微观层流理论,推导出岩石特征体积单元的渗透系数表达式,从而建立岩石各向异性损伤和渗流耦合的细观模型。模拟分析表明,提出的模型与试验结果吻合很好。     

楔入劈拉试验下钢纤维混凝土断裂试验研究

钢纤维混凝土是在普通混凝土中掺入乱向分布的短钢纤维所形成的一种新型的多相复合材料,在混凝土中加入钢纤维制成钢纤维混凝土,这些乱向分布的钢纤维能够有效地阻止钢纤维内部微裂缝的扩展及宏观裂缝的形成,显著的提高了混凝土的抗拉、抗弯、抗冲击和抗疲劳性能等。     

Tensile properties of as-deformed 2A50 aluminum alloy in semi-solid state

Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between 500 °C and 530 °C, and the maximum tensile stress decreases rapidly when the temperature is above 532 °C. The ductility decreases with increasing temperature and has an obvious fall when the temperature is above solidus temperature. This alloy almost has no ductility above 537 °C, and cannot sustain tensile stress above 550 °C. A brittle temperature range in which this alloy is prone to form microcracks was derived. The relation between microstructure, fraction solid and tensile properties were also investigated by examining the metallograph and fracture surface morphology of tested specimens, which could provide reference for forecasting the microcracks in this alloy occurring in semi-solid processing.     

聚碳酸酯在沸水中的老化研究

研究了聚碳酸酯(PC)在沸水中的吸水规律和冷热水循环老化对PC结构和性能的影响.结果表明,PC在冷热水循环老化过程中发生了脆韧转变,在48 h内其冲击强度降低了90%.老化后,PC的玻璃化转变温度有所降低,并出现反常比热峰.冷热水循环老化后的PC试样出现了光散射现象,利用光学显微镜观察到该PC试样中存在圆盘状微孔,经热处理后发现该PC试样中出现的缺陷是不可恢复的.     

粉砂岩三轴压缩条件下细观损伤特征的定量研究

首先利用RMT-150B岩石伺服试验系统，以不同围压(2，4，6，8，10 MPa)分别对大坦沙工程粉砂岩试样进行三轴压缩试验。然后，利用扫描电镜(SEM)拍摄得到的大量细观损伤图片，运用数字图像技术获取微裂纹的细观几何信息，从方位角、长度、宽度、面积和数量对不同围压条件相应的粉砂岩细观尺度微损伤特征进行统计分析。研究结果表明：三轴压缩条件下粉砂岩微裂纹的方位角、长度和宽度基本服从广义极限分布；微裂纹的方位角主要集中在与σ1作用方向成35°附近；随着围压的增长，仅有小部分微裂纹在长度尺寸上出现较大幅度的增长，而绝大部分微裂纹在宽度尺寸上基本不发育；经历三轴压缩试验的粉砂岩试样的能量耗散方式，主要以数量和长度两个方式进行。     

Critical linkages of coalescing microcracks under stress loading

ABSTRACT The fracture process of brittle materials with randomly orientated microcracks critically depends on strong interactions among microcracks and the coalescence path that leads to a fatal crack. In this paper, a model based on the coalescence process for planar orientated microcracks is presented. An energy ratio is defined as the competition between the potential energy release and the new crack surface energy in each coalescence step, which is a token of the excessive driving force for microcrack propagation. A critical linkage dictates the coalescence of microcracks under stress loading. Probabilities of microcrack coalescence dominated by the first linkage and subsequent linkages are analysed for collinear and wavy microcrack arrays in detail.     

Ultrasonic Vibration Turning of Ceramic Materials 一An Experimental Study

进行了超声振动车削与普通车削、磨削加工陶瓷材料的对比试验研究。结果表明，振动车削可明显地提高陶恣加工表面的质量，有效地消除普通车削，磨削中所形成的表面微裂纹，因此是陶瓷精密加工的一种新方法。     

Relationships between multiaxial stress states and internal fracture patterns in sphere-impacted silicon carbide

Internal fracture patterns developed in silicon carbide cylindrical targets as a result of dynamic indentation (63–500 m/s) by tungsten carbide spheres are defined. Microscopy of recovered and sectioned targets delineate into three regions, each associated with distinct cracking modes, i.e., shallow cone macrocracking at and near the impact surface, steep interior cone macrocracks that radiate into the target from the impact region and local grain-scale microcracking directly underneath the impact region. The observed fracture patterns are found to maintain a noticeable degree of self-similarity upto the impact velocity of 500 m/s. Linear elastic analysis of the full (surface and interior) stress field developed under static (Hertz) contact loading delineate the target into four regions, based on the number of principal stresses that are tensile (none, 1, 2 or all 3). A strong correlation is found between the principal stress conditions within each region and the forms of cracking, their locations and orientations present therein. This correlation has a number of implications, including non-interaction of crack systems, which are discussed. Illustrative linear elastic fracture mechanics analyses are performed for three regions, and calculated and observed macrocrack lengths are found to be in reasonable agreement.     

Particle simulation of the failure process of brittle rock under triaxial compression

In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simulated results were compared with those of the experiment. The numerical simulation results, such as fracture propagation, microcrack distribution, stress-strain response, and damage patterns, were discussed in detail. The simulated results under various confining pressures (0-60 MPa) are in good...