金属丝网橡胶压缩力学性能研究

对金属丝网橡胶进行了静态压缩试验。利用控制变量法研究了压缩量、相对密度、金属丝丝径、丝材和承压面积对金属丝网橡胶压缩力学性能的影响,并对平均刚度和能量耗散系数随压缩量和相对密度的变化关系进行了研究。试验结果表明:随着压缩量的增加,金属丝网橡胶非线性力学特性逐渐增强;相对密度越大,金属丝网橡胶承压能力越强;金属丝的丝径和丝材主要影响金属丝网橡胶非线性阶段的力学特性,丝径越大,丝材越硬,承压能力越强;承压面积越大,金属丝网橡胶的承压和耗能性能越好;随着压缩量的增加,平均刚度增大,承压能力增强,能量耗散系数减小,减震性能降低;随着相对密度的增加,平均刚度和能量耗散系数均增大,承压能力和减震性能均增强。     

动力荷载对围压卸载下岩石动态变形模量的影响

利用SHPB岩石动静组合加载实验系统,研究在不同轴压水平下围压以1 MPa/s速率卸载至预加值50%时矽卡岩受频繁冲击作用的动态变形模量变化规律。实验结果表明：高轴压促使岩石内部微裂纹萌发与扩展,降低了岩石抵抗外部冲击的能力。围压的侧向约束阻碍岩石内部裂纹的横向扩展,但在围压卸载时会加剧岩石内部的损伤,这是由于高轴压下,围压卸载导致岩石内部应力重新分布。轴压与围压卸载共同影响着冲击作用下的岩石动态变形模量,通过岩样在冲击荷载下的能量耗散分析岩石动态变形模量的变化规律,有助于了解深部岩体开挖的破坏机制。

     

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.     

基于能量耗散的岩石脆性评价方法

脆性评价是页岩气钻井以及压裂工艺设计的重要环节.然而,现今对于脆性的定义十分模糊,且脆性评价的方法没有成熟的理论作为支撑.本文以岩石应力应变关系为基础,采用能量法来进行储层岩石脆性评价.根据断裂力学裂纹尖端的非线性场理论,以前端区作为尖端特殊的屏蔽构型,来描述储层岩石在断裂过程中能量的耗散. 通过计算本征内聚力与前端区稳态阻力比值来表征储层岩石的脆性指数. 研究表明,能量耗散相对越大,岩石的脆性指数越低,其塑性特征表现得越明显. 基于能量耗散的储层岩石脆性评价是分析岩石力学特性的重要内容,也为压裂选层提供了重要依据.      

基于强夯实测夯沉量的地基变形模量反演分析

在运动方程法和能量法等强夯理论基础上,采用位移反分析方法建立二者反演格式,利用易于测量的夯沉量等数据反算地层变形模量,结合北京园博园强夯实验数据,计算并分析了变形模量随夯击次数的变化情况. 研究表明,地基变形模量随夯击次数逐渐增大,增幅逐渐减小,变形模量最终趋于稳定;反演得出该实验地基的初始变形模量在5～8MPa 之间,夯击7 次后在18～22MPa 之间,提高幅度约为3～4 倍;能量法反演过程相对简便,可在类似工程中推荐采用.     

不同围压下C60混凝土三轴压缩过程能量分析

针对复杂应力状态下高强混凝土受压变形破坏过程中的能量演化机制问题,开展不同围压下C60高强混凝土试样三轴压缩试验,分析其在受力全过程中的变形与破坏特征。根据试验结果,探究了不同围压下高强混凝土三轴压缩过程能量演化机制。研究结果表明:围压越大,混凝土试样破坏时,其峰值应力与峰值应力对应的轴向应变越大,破坏形式由张拉破坏向剪切破坏过渡;峰值应力前,混凝土试样主要以弹性应变能储存为主,峰值应力对应的输入能密度和耗散能密度均随围压的增大而增大,且均与围压满足指数函数关系,其形状改变系数FX与轴向应力呈正比关系,体积改变系数FV与轴向应力呈反比关系;达到峰值应力时,体积改变系数FV小于形状改变系数FX;峰值应力后,主要以弹性应变能释放为主,并随着混凝土试样的破坏转化为各种形式的能量耗散。研究结果可为今后从能量角度研究高强混凝土本构关系提供有益参考。     

泡沫铜对密闭管道内合成气爆炸特性影响的实验研究

为研究泡沫铜孔隙密度和H₂体积分数对合成气爆炸特性的影响,在封闭的管道中安装了孔隙密度为15、25和40 ppi的泡沫铜,实验分析了当量比为1的合成气-空气在不同H₂体积分数时的火焰结构、尖端速度和超压等参数变化规律。实验结果表明：火焰在泡沫铜上游的行为是受“郁金香”火焰形成过程的影响,泡沫铜对其没有影响。但是孔隙密度和H₂体积分数的改变不仅会影响“郁金香”火焰的形成时间,还会影响变形“郁金香”火焰的形成。泡沫铜将火焰分割促使其从层流向湍流转化,对爆炸火焰传播起到加速作用。泡沫铜会引起管道内超压和火焰尖端速度的极大提升,且孔隙密度越小,H₂体积分数越大,火焰穿过泡沫铜后的最大火焰尖端速度越大,压力上升幅度越大,超压峰值越高。

     

参变量变分原理求解土的变形模量与压缩模量间的关系

运用参变量最小势能原理推导了弹性及塑性状态下的土的变形模量与压缩模量间的关系,认为两者比值与土的内摩擦角φ、泊松比μ及粘聚力c等土性指标有关.提出了塑性影响因子α及临界应力p*的概念,指出当试验时土体应力大于土体的临界应力值时,变形模量与压缩模量的理论关系式应引入塑性影响因子α,从而克服了以往基于弹性理论得出的变形模量理论值远小于试验值的不足.     

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。     

加载速率影响的单裂隙类岩石试样能量演化规律

为了研究加载速率对单裂隙类岩石试样破坏过程中能量演化进程的影响规律,分析裂隙类岩石试样在不同加载速率下的能量响应特征,以预埋金属薄片方法制作的裂隙类岩石试件为研究对象,基于RMT-150B对单裂隙类岩石试样进行四级加载速率下的单轴压缩试验,获得四级加载速率下裂隙类岩石试样力学性能。试验结果表明:单裂隙类岩石试样峰值强度与加载速率呈正相关性,但增长速率随加载速率的增加而减小;当加载速度不断增大时,峰值处试样弹性应变能积聚能力增强,但是耗散应变能随加载速率的增大而逐渐减小;裂隙试样在峰值后会累积弹性应变能,但其积聚能力随加载速率的增大而有所削弱;裂隙试样耗散应变能转化速率在峰值前处于较低水平,在峰值后伴随宏观破裂面的贯通而骤增,表明单裂隙类岩石试样内部能量演化进程与其破坏规律之间具有内在联系。     

Dynamic bulk and shear moduli due to grain-scale local fluid flow in fluid-saturated cracked poroelastic rocks: Theoretical model

Grain-scale local fluid flow is an important loss mechanism for attenuating waves in cracked fluid-saturated poroelastic rocks. In this study, a dynamic elastic modulus model is developed to quantify local flow effect on wave attenuation and velocity dispersion in porous isotropic rocks. The Eshelby transform technique, inclusion-based effective medium model (the Mori–Tanaka scheme), fluid dynamics and mass conservation principle are combined to analyze pore-fluid pressure relaxation and its influences on overall elastic properties. The derivation gives fully analytic, frequency-dependent effective bulk and shear moduli of a fluid-saturated porous rock. It is shown that the derived bulk and shear moduli rigorously satisfy the Biot-Gassmann relationship of poroelasticity in the low-frequency limit, while they are consistent with isolated-pore effective medium theory in the high-frequency limit. In particular, a simplified model is proposed to quantify the squirt-flow dispersion for frequencies lower than stiff-pore relaxation frequency. The main advantage of the proposed model over previous models is its ability to predict the dispersion due to squirt flow between pores and cracks with distributed aspect ratio instead of flow in a simply conceptual double-porosity structure. Independent input parameters include pore aspect ratio distribution, fluid bulk modulus and viscosity, and bulk and shear moduli of the solid grain. Physical assumptions made in this model include (1) pores are inter-connected and (2) crack thickness is smaller than the viscous skin depth. This study is restricted to linear elastic, well-consolidated granular rocks.     

裂隙岩体损伤局部化破坏分岔模型及其应用

采用概率统计方法分析节理裂隙岩体的几何特征，定义了反映裂隙岩体几何特征的组构张量．基于不可逆热力学理论，通过裂纹扩展的细观分析，得出了损伤的发展机理和演化方程，把损伤演化和裂隙的几何特征的变化联系起来，建立了弹塑性损伤本构关系．为分析含有节理裂隙岩体在发生局部化破坏时的特征，通过对发生局部化时的裂隙岩体的分析。构造了适用于节理裂隙岩体局部化分析的不连续分岔模型．利用非线性规划数值解法，可以得出局部化破坏的方向特征．在有限元方法中，根据该模型给出了节理裂隙岩体相关的算例，分析表明该模型用于分析裂隙岩体的局部化破坏是有效的．     

三点弯曲试样幂硬化材料裂纹撕裂扩展的实验研究

本文应用三点弯曲试样和撕裂模量理论对弹塑性裂纹撕裂扩展的稳定性进行了实验研究,得出了适用于三点弯曲试样的施加撕裂模量T_(app)的计算公式。结果说明了材料硬化和系统柔度等因素对裂纹扩展稳定性的影响。实验中采用多层高柔度组合梁系统,得到了随加载系统柔度增加,裂纹扩展从慢稳定到失稳发展的过程。证明了撕裂模量理论的有效性。实验结果与理论预测相符。     

An Area Modulus of Elasticity: Definition and Properties

A new modulus of elasticity is defined to be the ratio of an equibiaxial stress to the relative area change in the planes in which the stress acts. This area modulus of elasticity is intermediate in properties between Young's modulus and the bulk modulus. Expressions for the area modulus are computed in isotropic elasticity. A simple, convenient expression for the compliance tensor of transverse isotropy is found in terms of, amongst others, the longitudinal (axial) area modulus and this leads to a new, concise condition for positive definiteness of the compliance tensor. The limits of incompressibility, inextensibility and constant area are briefly considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

同轴气流式液体射流分裂液滴粒径研究

针对同轴气流式液体射流分裂液滴粒径预测模型缺乏的现状,结合射流线性稳定性理论,建立了基于临界模数的同轴气流式黏性液体射流分裂液滴粒径表达式,在此基础上,分别研究了气流旋拧(气流同时存在轴向和周向运动)及流体物性(气体可压缩性、液体黏性、气液密度比和表面张力)对液滴粒径的影响规律.研究发现:周围气流轴向引射作用和同轴旋转...     

Squirt-Flow in Fluid-Saturated Porous Media: Propagation of Rayleigh Waves

Propagation of attenuated waves is studied in a squirt-flow model of porous solid permeated by two different pore regimes saturated with same viscous fluid. Presence of soft compliant microcracks embedded in the grains of stiff porous rock defines the double-porosity formation. Microcracks and pores respond differently to the compressional effect of a propagating wave, which induces the squirt-flow from microcracks to pores. Elastodynamics of constituent particles in porous aggregate is represented through a single-porosity formulation, which involves the frequency-dependent complex moduli. This formulation is deduced as a special case of double-porosity formation allowing the wave-induced flow of pore-fluid. This squirt-flow model of porous solid supports the attenuated propagation of two compressional waves and one shear wave. Superposition of these body waves, subject to stress-free surface, defines the propagation of Rayleigh wave. This wave is governed by a complex irrational dispersion equation, which is solved numerically after rationalising into an algebraic equation. For existence of Rayleigh wave, a complex solution of the dispersion equation should represent a leaky wave, which decays for propagation along any direction in the semi-infinite medium. A numerical example is solved to analyse the effects of squirt-flow on phase velocity, attenuation and polarisation of the Rayleigh waves, for different combinations of parameters. Numerical results suggest the existence of an additional (second) Rayleigh wave in the squirt-flow model of dissipative porous solids.     

P- and S-wave velocity and anisotropy in saturated rocks with aligned cracks

Rocks in the Earth’s crust contain cracks in variable amounts and on variable scales. Depending on the in situ stress level, cracks are always distributed in a common normal direction (so-called aligned cracks). In this study, we focus on the velocity and anisotropy of perfectly aligned cracks (parallel cracks). The theoretical model is introduced to calculate the elastic properties of cracked rocks based on solid matrix properties, crack parameters, and fluid properties. The theoretical results using high- and low-frequency limits and intermediate frequency for velocities and anisotropy are compared with experimental data measured in the laboratory, where rocks are saturated with water and air. We used four synthetic rocks with different crack densities (0.0, 0.0243, 0.0486, and 0.0729) in this study. The comparison shows that the results for high, low, and intermediate frequencies provide good predictions of the shear velocities and anisotropy for saturated cracked rocks. Quantitatively, the results of the P-wave velocity and anisotropy for intermediate frequency fit the measured data better than that for the high- and low-frequency limits. Compared with water saturation, dry cracks with high compliance have a strong influence on the total compliance of rock. The water saturation results in high P-velocities and a low P-anisotropy, while dry cracks induce much lower P-velocities and a high P-anisotropy. The shear wave anisotropy is fluid-independent, theoretical results fit the measured data well in both water saturation and the dry case.     

P-wave velocity prediction in porous medium with liquid-pocket patchy saturation

It becomes increasingly clear that non-uniform distribution of immiscible fluids in porous rock is particularly relevant to seismic wave dispersion. White proposed a patchy saturation model in 1975, in which spherical gas pockets were located at the center of a liquid saturated cube. For an extremely light and compressible inner gas, the physical properties can be approximated by a vacuum with White's model. The model successfully analyzes the dispersion phenomena of a P-wave velocity in gas-watersaturated rocks. In the case of liquid pocket saturation, e.g., an oil-pocket surrounded by a water saturated host matrix, the light fluid-pocket assumption is doubtful, and few works have been reported in White's framework. In this work, Poisson's ratio, the bulk modulus, and the effective density of a dual-liquid saturated medium are formulated for the heterogeneous porous rocks containing liquid-pockets. The analysis of the difference between the newly derived bulk modulus and that of White's model shows that the effects of liquid-pocket saturation do not disappear unless the porosity approaches zero. The inner pocket fluid can no longer be ignored. The improvements of the P-wave velocity predictions are illustrated with two examples taken from experiments, i.e., the P-wave velocity in the sandstone saturated by oil and brine and the P-wave velocity for heavy oils and stones at different temperatures.     

Determination of elastic moduli of composite medium containing bimaterial matrix and non-uniform inclusion concentrations

Reservoir porous rocks usually consist of more than two types of matrix materials,forming a randomly heterogeneous material.The determination of the bulk modulus of such a medium is critical to the elastic wave dispersion and attenuation.The elastic moduli for a simple matrix-inclusion model are theoretically analyzed.Most of the efforts assume a uniform inclusion concentration throughout the whole single-material matrix.However,the assumption is too strict in real-world rocks.A model is developed to estimate the moduli of a heterogeneous bimaterial skeleton,i.e.,the host matrix and the patchy matrix.The elastic moduli,density,and permeability of the patchy matrix differ from those of the surrounding host matrix material.Both the matrices contain dispersed particle inclusions with different concentrations.By setting the elastic constant and density of the particles to be zero,a double-porosity medium is obtained.The bulk moduli for the whole system are derived with a multi-level effective modulus method based on Hashin's work.The proposed model improves the elastic modulus calculation of reservoir rocks,and is used to predict the kerogen content based on the wave velocity measured in laboratory.The results show pretty good consistency between the inversed total organic carbon and the measured total organic carbon for two sets of rock samples.