用正弦波加载和超声实验研究饱和砂岩弛豫特征和衰减峰

采用Metravib分析仪在-50℃~100℃温度条件及300~400Hz的正弦波作用下进行泵油饱和砂岩应力应变实验,获得了虚模量温度峰与对应实模量的剧烈亏损规律,显示出饱和砂岩有别于由衰减峰引起的典型粘弹性行为。利用超声法对饱和大理岩与花岗岩样品进行波速和衰减特性测试,获得了大理岩的Biot衰减峰变化规律。该研究对岩石物理理论模型的发展具有重要意义,可以利用岩层的衰减和波速频散特性进行油气藏的预测,降低勘探风险。     

岩石对冲击波的非线性动态响应

对干燥、饱水、饱泵油大理岩和饱和砂岩进行了SHPB冲击压缩实验,得到了干燥岩石和饱和岩石的应力波衰减规律。在应力波传播过程中,其幅值有较大的衰减,干燥岩石的衰减最大,且孔隙度越大衰减越大,饱和岩石还存在较强的波弥散效应。在小于岩石屈服强度时,多次冲击加载下获得随冲击加载次数的增加,加载模量增大,残余应变减小的压实效应。这一结果可用于大型地震工程和防护工程的设计和建造。     

岩石时频效应的实验研究

对饱和泵油南京砂岩和饱水大理岩在MTS上进行了单轴压缩实验和正弦波加载实验,求得两种饱和岩石的单轴抗压强度和屈服强度,并获得随正弦波频率的提高,饱和泵油南京砂岩的杨氏模量、纵横波速度增大,具有较明显的频散效应.饱和岩石中的微细观缺陷在正弦波加载中引起滞后,导致瞬时杨氏模量与应力成不对称"X"形,获得随正弦波频率增高,"X"交点在模量轴上的位置增高,杨氏模量增大,模量的频散增强.本文揭示了岩石的非线性时频响应的一些物理机理,对于岩石介质中的非线性波动研究以及地震、工程等理论研究和应用都具有重要意义.     

饱水对煤层顶板砂岩单轴压缩破坏能量影响的分析

为研究饱水对砂岩力学参数和能量特征的影响,利用RMT-150B岩石力学系统对煤层顶板砂岩自然和饱水试样进行单轴压缩试验。试验结果表明:饱水对砂岩试样的强度和变形参数均有不同程度的影响,软化系数为0.79,弹性模量降幅为5.25%,变形模量降幅为5.92%;饱水后砂岩试样峰值前吸收能量、可释放弹性能和耗散能均有不同程度降低,吸收能量降幅36.8%,可释放弹性能降幅为34.4%,耗散能降幅为57.7%;饱水后砂岩储蓄能量的能力有较大减弱,脆性减弱,塑性明显增强;饱水砂岩试样压缩过程中积蓄可释放能难以使试样滑移破坏,仍需要吸收部分能量使试样逐步失稳破坏;饱水对砂岩试样压缩过程吸收能量、可释放能量比例关系的影响较小,而对耗散能比例关系的影响较大;自然状态下砂岩试样峰值前相同应变条件下吸收能量、可释放能均明显高于饱水试样对应能量值;深部巷道位置确定和支护设计时应充分考虑水对巷道围岩弱化的影响,对于完整坚硬围岩采用高压注水软化可有效防止冲击地压发生和减缓灾害程度。     

干燥和饱水砂岩孔隙度对应力波能耗的影响

为探讨应力波穿越干燥、饱水砂岩时孔隙度对能耗的影响规律,开展了孔隙砂岩的SHPB试验,并采用核磁共振分析了SHPB试验前后孔隙的变化特征。结果表明:(1)砂岩冲击试验前后T2谱波峰数没变,但对应小孔径孔隙的波峰峰值有所增加。这说明,砂岩结构内部仍停留在微裂纹形成阶段,应力波能量仅能够促使新的微裂纹形成,而不足以撕裂扩展孔隙使其孔径更大。(2)相同孔隙度时,饱水砂岩比干燥砂岩能耗小;随着孔隙度增加,前者能耗相应减小,后者能耗反而增加。这一现象可分别解释如下:(a)由断裂力学理论可知,水的表面张力和Stefan效应使裂纹扩展受到很大阻力,因而,相对干燥砂岩,相同孔隙度的饱水砂岩更难产生新表面耗散应力波能量。(b)冲击加载时饱水砂岩处于不排水状态,饱水砂岩变形可近似等于砂岩和水的压缩变形之和。由于水比砂岩压缩变形小,随着孔隙度增大,即含水量增加,饱水砂岩变形量减小,出现塑性变形和新裂纹的概率减小,能耗值也随之减小。(c)随着孔隙度增大,干燥砂岩的动态强度相应降低,加载时更易出现新裂纹以表面能形式耗散应力波能量,因而孔隙度越大则能耗越大。     

单轴荷载下饱水岩石静态和动态抗压强度的细观力学分析

由于单轴荷载下饱水岩石的动态力学特性与静态力学特性存在很大差异,从宏观上进行力学分析 存在局限性。根据岩石受压全应力应变曲线的细观机制,分析了静态及动态单轴荷载条件下孔隙水影响饱水 岩石裂纹扩展的情况。在静态单轴压缩条件下,初始裂隙受压使自由水产生孔隙水压力,自由水对翼裂纹有 向外挤压的应力,促进裂纹扩展。在动态单轴压缩条件下,自由水会产生粘结力,抑制裂纹扩展。根据翼裂纹 受压扩展原理,推导出饱水单轴条件下动态抗压强度、静态抗压强度的计算公式,在相同断裂韧度下,饱水岩 石静态抗压强度风干岩石静态抗压强度饱水岩石动态抗压强度。对自然风干和饱水砂岩进行单轴静态、 动态压缩实验,结果与理论模型的结果相符。     

含水率对砂岩渐进破裂过程影响的试验研究

为了研究含水率对砂岩渐进破裂过程的影响,采用MTS-815岩石力学试验系统,考虑不同围压及含水率条件下砂岩的三轴试验,对其渐进破裂坏过程进行试验研究,分析不同含水率条件下砂岩的渐进破裂指标及其扩容特性的演化规律。研究结果表明,含水率对砂岩的渐进破裂过程存在促进作用;随着含水率的增加,砂岩的闭合应力、起裂强度、损伤强度和峰值强度均逐渐减小;且当砂岩饱水系数在0.7左右时,岩石损伤强度和峰值强度减少量超过20%;砂岩含水率对岩石强度的弱化作用较明显,而砂岩含水率的变化对扩容速率影响不明显,但随着含水率的增大,岩石压缩极限减小,扩容提前发生。     

大理岩非分叉断裂的随机分形模型

本文建立了大理岩沿晶、穿晶及沿晶穿晶偶合断裂的随机分形模型，该模型能与大理岩的整体晶态结构自洽，且模型的分维值与测量值有很好的吻合。     

高低温加载对大理岩力学特性影响的试验研究

许多工程（如采矿、隧道掘进、地热开采等）都涉及到岩石损伤及破碎问题．传统的岩石损伤破碎技术，如爆破法、水射流法、机械掘进法等均面临着一系列问题，利用岩石的热损伤性质辅助机械破岩有望实现安全、高效破岩的目的．大理岩是一种典型的硬岩，常见许多工程之中，因此本文以大理岩为研究对象，首先将均质性较好的大理岩试样加热至不同温度(20~1000 °C)后放入液氮中进行急速冷处理，然后对其进行了系列的物理力学性质测试．试验结果表明：处理后密度、纵波波速、抗拉强度、单轴抗压强度(UCS)和弹性模量整体上都随温度的上升而下降；当加热温度在100 °C之前，大理岩表现出一定的热硬化现象，即随着温度升高，其UCS、纵波波速以及弹性变形模量均增大；UCS变化的阈值温度为400 °C左右，一旦温度超过400 °C，UCS迅速下降，其速率达到了9 MPa/100 °C，当温度超过500 °C弹性模量迅速下降，其速率达到7.00 GPa/100 °C，表明岩样抵抗变形能力减弱．整体上，热加载降低了大理岩的脆性，使其在单轴作用下的破坏模式由脆性破坏逐渐转化为弹塑性破坏．     

SHPB冲击加载下四种岩石的复合型动态断裂实验研究

分别用绿砂岩、黄砂岩、灰砂岩、大理岩制作了三种几何相似的(φ80mm、φ122mm、φ155mm)中心直裂纹平台巴西圆盘(CSTFBD)试样;利用分离式霍普金森压杆加载,进行了I型和I-II型复合动态断裂实验,并由实验结合有限元分析得到了四种岩石材料的I、II型动态断裂韧度KId、KIId。研究表明:动态断裂韧度均存在尺寸效应,试样尺寸对I-II型复合比和纯II型加载角均会产生影响,复合比随尺寸的增大而减小,大尺寸试样II型加载的加载角比小尺寸试样的小。同时,由于负值的T应力显著减小了裂纹的起裂角,用广义最大拉应力准则预测的起裂角更符合实验结果。     

Coupled extensional and bending motion in elastic waveguides

A variety of different linear elastic waves propagate in long slender rods. These waves do not interact in straight rods; however, extensional and bending waves do interact in slightly curved rods. If curved rods are used as waveguides for extensional waves, wave energy is exchanged between extensional and beding waves. The result has the superficial appearance of viscous attenuation.

The petroleum and geothermal industries have an interest in using drill pipe as a waveguide to transmit data by acoustic waves. Attempts have been made to transmit data from transducers in the vivinity of a drill bit to the drill rig at the surface. These efforts have not been successful. Poor signal strenght is a major problem. Historically,the observed reduction in signal strength is attributed to viscous dissipation. This paper proposes an alternative model-mode conversion from extensional waves to bending waves. This model is analyzes both as an eigenvalue problem and a transient finite-difference problem. The results predict measured attenuation levels, and account for many anomalous observations.     

金属圆管内爆轰波相互作用效应的数值模拟研究

采用动力学有限元程序,针对大变形带来的网格扭曲造成计算的锁死现象进行了ALE技术处理,结合高速摄影和X光照相实验结果,对金属圆管内爆轰波的相互作用效应进行数值模拟,给出了爆轰波对碰作用下金属圆管运动计算结果,复现了金属圆管对碰区鼓包现象,计算结果与实验吻合较好。可以预见,基于该方法能够初步分析影响金属圆管运动规律的诸多因素。     

The estimate and measurement of longitudinal wave intensity

Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending waves. In a two-dimensional quasi-longitudinal wave field, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities and in the measurement, it is measured by a pair of two-transducer arrays. In a onedimensional quasi-longitudinal wave field, the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves. The project supported by the National Natural Science Foundation of China     

激波驱动的气固两相流的动态压力测量

利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究.利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响.试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波,其强度与驱动气源、颗粒大小、颗粒装载比等参数有关;激波衰减率随着装载比、马赫数的增大而减小. 研究指出,在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用.      

Studies of reactive triple shock collision

Experimental studies have been performed on two-dimensional reactive blast waves in a diverging nozzle. Both blast and reaction wave loci have been measured and the results compared with numerical calculations.With the inclusion of additional wedges into the channel reactive Mach reflections were generated and the subsequent interactions of these waves have been observed and modelled using a full chemistry scheme. The results are in excellent agreement and the technique shows great promise for the study of the coupling between chemistry and gas dynamics under conditions similar to those obtaining within a single cell of a gaseous detonation.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Propagation of acoustic surface waves on a phononic surface investigated by transient reflecting grating spectroscopy

We present a study of surface acoustic waves (SAW) propagation on a 1D phononic surface (PS) by mean of an heterodyne-detected transient reflecting grating experiment. We excited and detected coherent stationary SAWs characterized by variable wave-vectors. The measured SAW frequencies enables the characterization of the band diagram of this PS sample beyond the first Brillouin zone (BZ). Four different SAW frequencies have been revealed, whose band diagram show articulated dispersion phenomena. In order to address the nature of the investigated SAWs, the experimental results are compared with a numerical simulation of elastic modes based on a finite element model. The observed SAWs are addressed to four Bloch waves characterized by different frequencies and surface energy localization. Moreover, we measured the SAW propagation on a flat non-phononic part of the sample surface and compared it with results from the PS.     

THE ESTIMATE AND MEASUREMENT OF TRANSVERSE WAVE INTENSITY

Transverse waves are a type of structural waves and should be considered in the analy-sis of high frequency vibration because the energy carried by transverse waves increases with the in-crease of frequency and becomes important at high frequencies. This paper studies the estimate theoryand measuring technique of the transverse wave intensity in two dimensional homogeneous structures.In general, the intensity vector is the sum of the effective intensity vector and the intensity variationvector. Each axial intensity component is proportional to two imaginary parts of cross spectral densitiesand its estimate is complicated. For the special case where transverse waves propagate in one direction,the intensity variation is zero and the estimate of the intensity is simplified. The intensity technique isformed based on the finite difference principle. Transverse wave intensity can be measured using a pairof two-transducer arrays lying in the orthogonal direction for the general case or a two-transducer ar-ray lying in the propagating direction for the special case. In order to assess the measurement accuracyof transverse wave intensity, the coupling loss factors from bending to transverse waves in buildingstructures were measured using the intensity technique and compared with the results predicted andmeasured using the conventional method. It is shown that the agreement between the results measuredusing the intensity technique and that by the conventional method is good.     

爆炸地震波模拟研究

基于能够描述爆炸地震波的非平稳随机过程模型进行爆炸地震波的模拟研究。基于爆炸地震能量守恒以及经验关系,提出了能够考虑装药量和爆距影响的爆炸地震波功率谱密度和幅值包络线模型,并且利用实测的爆炸试验数据,对模型参数进行标定,给出单点、两点（微差）和多点（微差）爆炸地震波实用模拟方法。结果表明模拟得到的爆炸地震波时程能够很好地再现爆炸地震波的一些特性。     

Elevated-temperature elastic moduli of 2024 aluminum obtained by a laser-pulse technique

Elastic waves were generated in slender polycrystalline 2024 aluminum rods by the deposition of laser energy into the ends of the rods with a Q-switched laser. The propagation velocities of the waves were measured in the temperature range of 22° to 500°C. The elastic moduli of the material determined from these wave-propagation measurements are compared with previously reported single-crystal and polycrystalline aluminum data at elevated temperatures. Elastic moduli for polycrystalline 2024 aluminum agree with other reported data below about 200°C. Above this temperature, the 2024 aluminum moduli were found to decrease more rapidly with temperature than did those for single-crystal aluminum, although not as drastically as has been previously reported for polycrystalline aluminum.     

Generation and propagation of pressure waves in supersonic deep-cavity flows

The mechanism behind cavity-induced pressure oscillations in supersonic flows past a deep rectangular cavity is not well understood despite several investigations having been carried out. In particular, the process by which the pressure wave is generated and the path of the pressure wave propagating inside the cavity remains unclear. In the present study, the pressure waves around a deep rectangular cavity over which nitrogen gas flows at a Mach number of 1.7 are visualized using the schlieren method. The length of the cavity is 14.0?mm. The depths of the cavity are selected as 20.0?and 11.7?mm, corresponding to length-to-depth ratios of 0.70 and 1.2, respectively. The pressure waves propagating inside as well as outside the cavity have been successfully visualized using a high-speed camera, and the propagation pattern of these waves is found to be different from that previously predicted by numerical simulation and from those expected in previous oscillation models. In addition, the pressure oscillation near the trailing edge of the cavity is also measured using semiconductor-type pressure transducers simultaneously with the capture of the schlieren images. As a result, the relationship between the shear-layer motion, pressure-wave generation, and pressure oscillation at the trailing edge of the cavity is clarified experimentally.