岩石力学动态实验系统研制

该系统是基于落锤加载的岩石力学动载实验装置,主要由落锤加载,压力本体,泵压和测试四部分组成。由于设备采用了落锤加载方式,系统的加载速率将更接近于水力振荡、电脉冲、地震波、高能气体等强动载波作用于地下地层岩石的速率。系统采用先进的数据采集处理系统,同时采集位移、围压、应变等信号,保证了数据的一致性。对于进行动载下的岩石力学特性研究提供了必要的手段,特别是对掌握动载作用下的油气层岩石破坏和变形规律,开     

损伤石灰岩单轴再加载力学特性及破坏机理

为研究卸荷损伤破坏围岩力学特性及破坏机理,选用RMT-150岩石力学试验系统进行三轴岩石加载-卸载过程,制备损伤岩石。结合AEwin声发射系统开展损伤石灰岩单轴再加载试验,测试应力-时间-能量累计值关系曲线,分析阐述岩石宏观破坏特征。结果表明:随着卸荷点的增加,损伤石灰岩破坏程度与破坏形式均发生较明显的变化。石灰岩破坏形式从脆性破坏向延性破坏转化,扩容现象越来越不明显;低于70%峰值强度卸荷点的损伤岩石单轴加载过程中声发射能量累计值增长规律趋于一致,可分为平稳阶段、稳定增长阶段、二次平稳3个阶段;岩石内部微裂纹分布方式对宏观破坏特征影响明显,岩石细观力学响应决定其宏观力学破坏特征。     

等围压条件下岩石本构模型及损伤特性

为了揭示岩石变形破坏的全过程,将连续损伤理论与非平衡统计方法相结合,建立了等围压作用下岩石的损伤本构模型,推导了模型参数与岩石变形破坏特征参量的理论关系,分析了砂岩以裂纹为主导的变形破坏过程.结果表明:岩石损伤细观上表现为原始微裂纹的扩展贯通,其宏观力学特性取决于岩石内部的细观力学响应;随着轴向应变的增加,岩石损伤经历演化、稳定扩展、损伤加速,直至产生破坏;随着围压的增加,砂岩的损伤劣化程度减小,损伤演化率逐渐降低,宏观上表现为岩石平均强度的增大和塑性的增强.通过试验结果验证,损伤本构模型合理可行.     

井壁稳定性的断裂损伤力学分析

为了研究石油工程中的井壁失稳问题,将断裂力学和细观力学相结合,给出了一种新的计算方法.根据断裂力学和微观损伤力学原理,研究了脆性岩石中含微裂纹的扩展条件、扩展方向和变形机理.由井壁附近的应力状态和岩石破坏准则,建立了井壁坍塌和地层破坏的力学计算模型,并对井壁稳定性的问题中的井壁坍塌和地层破坏进行了定量的分析,确定了钻井液密度的范围.所给出的计算结果与传统的油井工程中采用的摩尔-库仑准则所得出的结论相同.同时通过细观力学分析和考虑岩石断裂韧性的影响,提出了岩石的内禀断裂应力的概念.此概念将揭示岩石变形机理的本质,并为钻井工程设计提供理论参考依据.     

冲击荷载下岩石动态损伤演化研究

I型裂纹破坏为岩石材料在冲击荷载作用下的主要破坏方式.通过假设岩石材料宏观上是一个均匀连续体,而细观上其内部则包含了大量随机分布的微裂纹等损伤缺陷;研究了岩石材料在冲击荷载下裂纹的成核、发展以及内部损伤演化规律;借助于宏细观相结合的理论建立了表征岩石材料细观结构及其损伤演化过程中的某种特征参量与宏观力学参数之间的关系方程.     

水分及冻融效应对页岩力学特性影响的试验研究

将页岩试样干燥后进行饱水及冻融循环试验,并对各种状态下的岩样进行力学特性试验,研究了岩石的遇水软化性、冻融劣化及变形破坏规律,分析其损伤扩展特性。结果表明:水分及冻融循环对页岩的力学效应有重要影响。岩石结构弱化,摩擦特性增强,力学性质产生劣化,但经历20次冻融循环后冻融损伤趋于稳定。     

冻融受荷岩石唯象损伤扩展特性探讨

针对工程地质和岩土工程中所涉及到的冻害问题,从细观力学机理出发,将冻融循环次数及应变和岩石的损伤变量联系起来,得到宏细观相结合的冻融受荷岩石损伤演化方程及损伤扩展本构关系;对冻融荷载作用后的岩石进行唯象损伤扩展特性分析.研究发现:岩石的冻融损伤是一个疲劳损伤破坏过程,在寒区岩体工程设计和施工中,必须考虑冻融损伤的影响;寒区工程结构受荷岩石的岩性、初始损伤状态及力学性质的不同,造成冻融循环和荷载对损伤扩展的影响差别非常大,并表现出终态的宏观差异.     

饱和岩石各向异性弹塑性损伤模拟

自然界岩石是各向异性的,其破坏性也是非均匀的,岩石各向异性力学特性研究非常必要.提出了一种弹塑性破坏模型,该模型可以描述弹性变性、损伤不可逆变形和塑性变形,以二阶张量来描述损伤的扩展,损伤演化相关于微裂纹扩展标准.并以应变自由能获得有效弹性刚度矩阵,推导出了损伤参数限制范围,提出了以室内试验决定损伤参数的相应表达式.模拟了不同加载路径情况下的岩石力学行为,数值结果和试验结果较为一致.该模型被推广应用于不同加载路径的岩石水力学行为的模拟之中,数值结果显示该模型能模拟岩石孔隙水力学基本特征.     

基于统一强度理论的岩石弹塑性损伤模型研究

基于统一强度理论,建立了岩石弹塑性损伤本构模型,该模型不仅考虑了岩石在拉伸和压剪两种情况下其损伤不同,还反映了在动载作用下岩石的应变率效应.采用Fortran语言通过LS-DY-NA的用户自定义材料接口(Umat)对该本构模型进行编程,并把该程序生成求解器以达到对该模型进行应用的目的.采用该模型分别对岩石单轴压缩试验、巴西圆盘劈裂试验和单孔爆破试验进行了数值模拟,同时把数值模拟结果分别与试验数据、经典模型(HJC模型)的数值结果和理论计算结果相对比.结果表明:由该模型所得出的结果与试验数据、经典模型(HJC模型)的数值结果和理论计算结果均比较吻合;该模型能够很好地反映岩石在动载和静载2种情况下的力学行为.     

损伤灰岩动态压缩力学特性的实验研究

在Hopkinson压杆上采用改进的实验技术对灰岩材料进行了高应变率动态压缩实验，有效地解决了横向惯性效应对岩石类脆性材料实验精度的影响，对完整灰岩和损伤灰岩的动态压缩力学特性进行了对比实验研究。结果表明，灰岩表现出应变率硬化效应和损伤软化效应，完整岩石的极限动态破坏压应力高于损伤岩石约30％。     

Damage and fragmentation of rock under experiencing impact load

1 INTRODUCTIONThe dynamic fragmentation of brittle materialsexperiences an extremely complex process ,invol-ving micro-cracks nucleation,propagation and coa-lesce , which breaks the solid into fragments . Butthe process canfall into two successive phases gen-erally : damage stage and fragmentation phase .The most widely applied theoretical models of theprocess , such as those based on the pioneeringstudies of Grady[1], Glenn et al[2],involve sometype of relatively si mple global energy ba…     

The dynamical loading on rock with different loading wave shapes conventional SHPB

Since loading wave shapes are very important in the study of rock dynamical properties, a new procedure for obtaining a variety of wave shapes using equi-diameter impact hammer of conventional SHPB device is proposed based on theoretical analysis. Experiment shows that different loading wave shapes can be obtained through varying the radius at impact end of hammer. Experiment results are quite consistent with the theoretical analysis. Project supported by the National Natural Science Fundation of China Synopsis of the author Xu Jichen, senior engineer, born in January 1951. Major research fields: Rock fracture mechanics and modern experimental method and technique in rock impact dynamics.     

Experimental research on influence mechanism of loading rates on rock pressure stimulated currents

The study of pressure stimulated current (PSC) changes of rocks is significant to monitor dynamic disasters in mines and rock masses. The existing studies focus on change laws and mechanism of currents generated under the loading of rocks. An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs. The results indicated that PSC curves of different rocks had different change laws under low/high loading rates. When the loading rate was relatively low, PSC curves firstly changed gently and then increased exponentially. Under high loading rates, PSC curves experienced the rapid increase stage, gentle increase stage and sudden change stage. The compressive strength could greatly affect the peak PSC in case of rock failure. The loading rate was a key factor in average PSC. Under low loading rates, the variations of PSCs conformed to the damage charge model of fracture mechanics, while they did not at the fracture moment. Under high loading rates, the PSCs at low stress didn’t fit the model due to the stress impact effects. The experimental results could provide theoretical basis for the influence of loading rates on PSCs.     

冲击载荷下脆性岩板损伤断裂演化的实验模拟研究

在矿山运输系统中,井壁围岩冲击损伤破坏对经济和安全效益的影响是至关重要的,因为动态冲击载荷对井壁围岩和支护结构会产生严重的削弱破坏作用,室内研究表明,岩石样品如岩板在动态载荷的冲击作用下会失效。为研究在低速冲击载荷作用下,脆性岩石损伤断裂的演化过程,利用分离式霍普金森压杆(SHPB)装置中压缩气体发射球体子弹对脆性岩板进行变角度冲击损伤实验,岩板受到冲击后,边缘出现凹坑,表面裂纹从撞击凹坑直达岩板边缘,实验中样品的表面裂纹能有效代表试样内部的开裂状况,能有效反映冲击能量的耗散、破裂区面积与裂纹表面积随入射能量呈非线性增长趋势,同时与入射角度相关,但当破裂区面积急剧下降时,裂纹表面积反而急剧上升,表明裂纹的发生发展有明显的孕育期,在入射能量达到临界值前,主要表现为裂纹孕育增长,在达到临界值后,发生宏观断裂破坏,裂纹面积呈负增长,破裂区面积增大。实验结果分析表明在实际工程中,围岩和支护结构的抗冲击的最优化设计角度范围在15°～30°。     

盐岩损伤测试中卸载模量研究

利用MTS815 Flex Test GT岩石力学试验系统,对盐岩和大理岩进行了单轴压缩下的7级加卸载试验和低周循环加卸载试验测试,对盐岩和大理岩的卸载模量进行了探讨。低周循环试验加载波形采用正弦波,频率1Hz,循环应力幅值小于其平均抗压强度,单级应力幅值为30个振动循环。通过试验,得到了盐岩应力应变滞回环均为条带状,大理岩则均为尖叶状;盐岩在加卸载部位具有较大不可逆变形,对应弹性响应较慢,大理岩则反之;盐岩卸载模量变化趋势受加载测试方法影响较大,而大理岩在2种试验条件下得到的卸载模量变化趋势相似;加载应力幅值比加卸载循环数对盐岩不可逆变形增量影响更加显著。损伤变量研究结果表明,利用低周循环加卸载方法测试具有显著时间效应变形岩石的损伤弹性模量,能更真实反映其损伤特征。     

强冲击载荷下岩石损伤特性实验研究

通过在一级轻气炮驱动的平板碰撞实验台进行冲击损伤实验 ,对软回收样品进行超声波测试 ,研究了强冲击载荷下两种典型岩石损伤特性 .结果表明 ,岩石的动态损伤与冲击速度和超声波衰减系数α有关 ,后者较好地反映了岩石的损伤程度 ,可作为构造岩石损伤模型的主要参量     

损伤岩石周边控制爆破分析

应用损伤力学的理论与方法,对崩落眼爆破经起光爆层岩石损伤因子与光面爆破参数的关系进行了分析,导出了相应在的光爆参数计算式,并与不考虑岩石损伤的光面爆破参数进行了对比,指出了目前低强度岩石中光爆效果往往较差,原因是没有考虑损伤因子对光面爆破参数的影响,造成炮孔装药过量所致,由此认为研究崩落眼爆破对光爆层岩石的损伤规律及损伤岩石的光面爆破参数计算方法,是未来深入研究岩石学面爆破理论与技术的方向。     

Theoretical and experimental analysis on the mechanism of the Kaiser effect of acoustic emission in brittle rocks

The Kaiser effect is formally described as the absence of detectable acoustic emission （AE） events until the load imposed on the material exceeds the previous applied level and is usually used to estimate geostress. By focusing on the heterogeneity of rock material, the mechanism of the Kaiser effect under cyclic loading is analyzed based on statistic damage mechanics. Two groups of granite specimens have been cyclically loaded with two different loading paths to verify the theoretical results. The heterogeneity of rock is the real reason that causes irrecoverable damage on the Kaiser effect of acoustic emission in cyclic loading. The Kaiser effect reflects the damaged state in rocks rather than the previous stress imposed on it. Applications for using the Kaiser effect to estimate geostress were discussed here. It is shown that the commonly used uniaxial loading method for estimating geostress is not in accor- dance with the theoretical and experimental results. The analysis is of importance to use the Kaiser effect correctly for estimating geostress or in other fields. 2008 University of Science and Technology Beijing. All rights reserved.     

Rock-breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock

The rock-breaking mechanism and effect of confined blasting were analysed by blasting and impact dynamic mechanics, fluid dynamic mechanics, fracture mechanics as well as blasting experiment. The results showed that the fracturing of surrounding rock in confined blasting condition is the result of coaction of rock pre-cracking by shock wave and stress wave and the continuing expanding crackenhancement of confined medium, and the model of crack development of borehole surrounding rock in confined blasting condition was established. This study acquired the damage range of surrounding rock under the action of shock wave and stress wave, as well as the crack development characteristics of surrounding rock after the wedge-in confined medium into the crack space. Deep-hole confined blasting experiment on large rock showed that the high-efficient utilisation of in-hole explosive was achieved and the safety of rock blasting operation was ensured. Safe static rock-breaking under the action of high-efficient explosive blasting was achieved as well as the unification of super dynamic load of explosive blasting and static rock-breaking of water medium.