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...     

Stress-dilatancy of Zipingpu gravel in triaxial compression tests

Experimental investigations of the dilatancy and particle breakage of gravelly material from the Zipingpu concrete-faced rockfill dam, which was subjected to high-intensity seismic load during the 2008 Wenchuan earthquake, were conducted through a series of large-scale drained triaxial compression tests. A hyperbolic relation between the input plastic work and the degree of particle breakage was found for Zipingpu gravel, independent of the initial void ratio and confining pressures. The stress-dilatancy for Zipingpu gravel was analyzed and compared with data from two rounded alluvial and three angular quarried gravelly and rockfill materials in the literature. A nearly linear relationship between the dilatancy D~p and the stress ratio η was found at medium-to-large stress ratios before the peak stress ratio. The slope of the stress-dilatancy line before peak had slight dependence on the void ratio and confining pressure of the gravel. After peak, the stress-dilatancy relation shifts down compared with that before peak for the gravel specimen. The phase-transformation stress ratio decreased with increased confining pressure, with the exception of sub-rounded gravel with little particle breakage. A nearly linear relationship was found between the phase-transformation stress ratio M_f and the state parameter y for the Zipingpu gravel, regardless of the void ratio and confining pressure of the specimens.     

纤维混凝土三轴抗压强度及破坏特征的试验研究

利用伺服试验机对纤维混凝土和普通高强混凝土试样进行不同围压下轴向压缩试验,基于试验结果,研究了两种混凝土的单轴与三轴压缩强度,探讨了两种混凝土试样的破坏特征.结果表明,两种混凝土单轴压缩强度都达到80 MPa以上,普通高强混凝土单轴与三轴强度略高于与之配合比相同的混杂纤维混凝土;当围压达到20 MPa以上时,纤维混凝土峰值应力不显著,加载后期具有更大的塑性变形特征,说明掺入适量纤维可以提高混凝土的韧性,降低脆性;纤维混凝土试样加载结束后试样不断裂、不剥落,具有良好的整体性能.     

三轴受压状态混凝土当量损伤本构模型

本文根据Ｈ－Ｔ－Ｃｈｅｎ的多轴受压状态下的破坏准则,引用了混凝土损伤力学的概念,提出了在多轴受压状态下的当量损伤模型。可以模拟混凝土在多轴受压状态下的应力应变关系,得到等效单轴受压的应力应变全过程曲线,并且可求得在不同侧压力情况下混凝土的极限抗压强度。本模型不仅可模拟混凝土多轴受力的应力应变过程,并为拱坝非线性全过程分析了依据。     

砂岩三轴常规压缩物理和数值实验分析

基于曹窑东井采空区砂岩试件的超声波测试实验,选出了岩性较好的试件,并在RMT-150 B岩石力学实验机上对砂岩试样在不同围压条件下进行常规三轴压缩物理实验;利用RFPA系统,研究了不同围压对岩石试样承载能力的影响.数值试验和物理实验表明,在较低围压条件下,试样的承载能力与围压大致成线性关系,即试样的承载能力随着围压的增高而增大.     

焦作矿区含瓦斯煤体电阻率变化规律研究

在低频率（100～10000Hz）条件下测试了煤体在吸附瓦斯过程中和含瓦斯煤在三轴压缩条件下的电阻率变化规律．实验结果表明,煤体在吸附瓦斯过程中和含瓦斯煤三轴压缩条件下,电阻率值分别随着吸附时间和应力的增加,出现先大幅度减小后小幅度增大的变化规律．运用电介质物理学理论对含瓦斯煤体导电机理分析表明,电子和离于在煤孔隙表面上的迁移、游离瓦斯对煤颗粒的挤压作用和正负电荷在外电场作用下产生移动,三者共同造成煤体在吸附瓦斯过程和含瓦斯煤体受载过程中电阻率的降低．     

Electronic band Gap of ZnO under triaxial strain

The effect of triaxial strains on the band gap of wurtzite ZnO has been investigated by the first principles calculations. The results indicate that, after application of triaxial strain, the wurtzite ZnO is still a direct band gap semiconductor with conduction-and valence-band minima remains at the Γ point. Comparing with the unstrained ZnO, the Eg at Γ point increases under compressive strain but decreases under tensile strain. This triaxial strain model is in better agreement with the experimental results than the widely-employed in-plane biaxial strain model, thus providing a more accurate explanation on the behaviors of ZnO thin film under three-dimensional strain.     

阿刀亥煤矿掘进巷道煤壁瓦斯涌出规律的研究

针对阿刀亥煤矿1203炮掘巷道,通过现场实测掘进巷道煤壁瓦斯涌出量,建立了掘进巷道煤壁瓦斯涌出强度随时间的变化规律方程,确定出掘进巷道煤壁瓦斯涌出量与巷道长度、掘进速度及煤壁暴露时间的关系,给出了煤壁瓦斯涌出枯竭极限时间、掘进巷道煤壁最大瓦斯涌出量以及掘进巷道煤壁达到最大瓦斯涌出量时巷道长度的计算方法.该研究结果,对于指导矿井的通风设计和采掘部署,采取有针对性的防治煤巷掘进瓦斯灾害措施,具有重要的理论意义和实用价值.     

真三轴加载条件下混凝土的力学特性

采用真三轴设备对100mm×100mm×100mm的立方体混凝土试块进行静态加载。首先,保持三个轴向的应力相同,施加应力到设计值p。然后,在保持最小主应力(Z轴)恒定并且X轴应变速率与Y轴应变速率之比也恒定的条件下,单调地增加Y轴应变。通过这种复杂加载试验,研究了混凝土的强度和体积特征。结果表明:在应力-应变混合路径加载的真三轴试验下,混凝土的抗压强度随着最小主应力的增大而增大,随着加载应变速率比的增大而线性递减,都大于单轴抗压强度,最高可达单轴抗压强度的3.4倍;混凝土试块在只经历静水压的加载历史时,初始剪切模量不受影响,不同组剪应力-剪应变关系曲线初始段都存在重合现象。峰值体积应变随着最小主应力和应变速率比的增大而增大,体积先减小后增大,出现扩容现象;当最小主应力为10MPa时,混凝土的峰值强度和峰值体积压应变几乎同时出现,并随着最小主应力的增大,两者出现的时间间隔增大,峰值体应变滞后。     

含不同缺陷的金属材料声发射特性

根据声发射测试原理,利用信号峰值电压与材料形变过程中释放能量的关系建立了裂纹开裂的声发射参数与应力关系的数学模型,提出了声发射总计数和声发射计数率的一般表达式,研制了声发射装置,并在拉伸试验条件下对具有不同缺陷的ZG25试件进行了声发射检测。实验结果表明:无缺陷的ZG25材料与有气孔、疏松、夹渣和微裂纹缺陷的该材料具有不同的声发射AE事件特征,这对金属材料声发射无损检测具有实际意义。     

燃煤过程中汞的析出规律试验研究

在试验台架上进行了加热时间、反应条件、煤种等因素影响煤中汞析出规律的试验研究，首先利用马弗炉和管式炉两个试验台对各种煤样进行还原性气氛和氧化性气氛条件下汞的析出试验。然后在管式炉试验台上和小型煤粉燃烧实验台架上分别进行煤粉层燃和悬浮燃烧后汞的形态转化规律试验研究，研究表明，烟气中的汞主要以气态二价汞（Hgg^2 ）的气态零价汞（Hgg^0）形式存在，而颗粒态汞（Hgp）在20%以下，而且表的形态分布与反应条件和煤种有关，随着燃烧温度升高，烟气中的零价汞（Hgg^0）质量分数逐渐降低，二价汞（Hgg^2 ）质量分数逐渐升高，煤粉悬浮燃烧时，烟气中气态汞在10～15μg/Nm^3，二阶汞和零价汞占气态总汞的比例随燃烧反应条件变化而变化，另外较低的烟气冷却速率可促进零价汞向二价汞的转化。     

Buckling analysis of the shell of a refuge chamber in a coal mine under uniform axial compression

A stiffened cylindrical shell is normally used in refuge chambers of a coal mine.Based on the method of application and shape characteristics of a refuge chamber,we simplified its shell as an orrhotrop...     

钢-聚丙烯混杂纤维混凝土的真三轴强度试验研究

考虑纤维种类、长径比、体积掺量3个主要影响因素,设计制作25组纤维混凝土试件,通过真三轴压缩试验,研究钢-聚丙烯混杂纤维混凝土(HyFRC)在不同围压条件下的强度及破坏模式.研究结果表明,在不同侧向围压作用下,HyFRC试件的破坏模式均为斜剪破坏.与相同配合比的素混凝土试件相比,随着钢纤维特征参数的增加,HyFRC试件的三轴峰值强度有显著提升,而聚丙烯纤维特征参数的变化对峰值强度影响较小.基于试验结果,提出了基于W-W 5参数模型的HyFRC破坏准则,能够很好地预测纤维混凝土在多轴压缩状态下的强度.     

单轴压缩下不同层理方向对片麻岩声发射特征影响的试验研究

为探究不同层理方向岩体的损伤演化规律和变形破坏中的声发射特征,选用具有明显层理构造的片麻岩试样开展单轴压缩条件下的声发射试验,分析轴向平行和垂直层理片麻岩试样失稳破裂、声发射时序参数和声发射空间定位演化特征。结果表明:不同层理方向对岩石破裂影响显著,轴向平行层理片麻岩试样峰值载荷稍高于轴向垂直层理的,裂纹起裂应力水平较高,声发射定位点由加载初期离散无序分布转为向沿层理聚集,破裂时主裂隙沿层理面贯通上下端或沿层理扩展形成垮落区,最终表现为典型的张拉破坏,岩石达到峰值载荷后瞬间失稳,呈突发式破坏特征;轴向垂直层理试样起裂应力水平较低,进入声发射剧烈期参数波动更为显著,事件点在试样中部聚集产生倾斜带状剪切裂纹密集区,破裂时出现多种破裂模式,主要以剪切滑移破坏为主。岩石达到峰值载荷后应力发生多次跌落,呈渐进式破坏特征。     

液体雾化效果的检测及流体力学模拟

为获得一种快速灵敏的液体雾化效果检测方法,利用置于挡板后方的声发射传感器,采集液体喷雾撞击挡板产生的声信号并进行多次扫描累加的快速傅里叶变换,得到不同流量下的声能量值和功率谱图.通过对实验结果的分析,提出临界良好雾化状态的声能量判据,即随着流量的增加,当液滴撞击挡板产生的声能量趋于平稳并开始缓慢上升,雾化准数由缓慢增加转变为迅速增大以及声能量均方差开始上升并趋于平稳时,液体喷雾处于良好雾化的临界状态,进一步增大流量,雾化效果的提升不明显.同时,对雾化效果采用摄像法测定和基于Eulerian-La-grangian耦合算法的计算流体力学(CFD)模拟,结果与声发射实验的结果吻合很好,由此说明采用声发射方法对液体雾化效果进行定性检测具有较强的可行性与准确性.     

混凝土三轴受压等幅疲劳力学性能试验研究

为研究混凝土在多轴疲劳应力作用下的性能,进行了0.0fc、0．1fc、0．25fc、0．4fc4个不同初始定侧压级别下的混凝土三轴压静载试验和0．1c、0．25fc两个不同初始定侧压级别下的混凝土三轴压等幅疲劳试验,疲劳试验中最小应力水平均为0．1fc,最大应力水平为1．6fc-2．5fc．根据初始定侧压下混凝土三轴压本构特征,试验中将侧压变化的拐点作为其多轴疲劳破坏的判据．试验分析表明,三轴压疲劳荷载作用下混凝土纵向最大、最小应变表现出同单轴和双轴疲劳一样的三阶段规律,而变形模量则衰减不大．由各侧压级别下的S-N曲线得到混凝土在相应工况下的疲劳强度折减系数,其研究成果可为混凝土结构疲劳设计提供参考．     

Characteristics of acoustic emission signals in damp cracking coal rocks

A uniaxial load experiment on coal rocks at different stress rates was carried out, based on the characteristics of acoustic emission (AE) signals in cracking coal rocks, decomposition, de-noising and reconstruction for the AE signals through wavelet packet transform for solving the current problems created by the presence of noise in AE signals and the existing problems in AE signal processing. The results show that the various characteristics of AE signals in coal rocks cracking under different situations can be clearly reflected, after the AE signals are de-noised by the wavelet packet. Compared to dry coal rocks, the number of AE occurrences in damp coal rocks was significantly reduced, as well as the average amplitude. The number of AE occurrences in damp and dry coal rocks clearly increased with increases in the loading rate, but the largest amplitude of the AE signals in damp coal rocks has been reduced. There is no clear evidence of change in dry coal rocks.     

Study on primal CO gas generation and emission of coal seam

The main method of casting coal spontaneous combustion is prediction of index gases, with carbon monoxide(CO) commonly used as an index gas. However, coal spontaneous combustion is not the sole source of CO evolution; primal CO is generated through coalification, which can lead to forecasting mistakes. Through theoretical analysis, primal CO generation and emission from coal seams was determined.In this study, six coal samples were analyzed under six different experimental conditions. The results demonstrated the change in coal seam primal gas and concentration as functions of time, different coal samples, occurrence, various gas types and composition concentration, which are in agreement with the previous study on primal CO generation. Air charging impacts on primal gas emission. Analysis of the experimental data with SPSS demonstrates that the relationship between primal CO concentration and time shows a power exponent distribution.