压力敏感材料中的空洞长大研究及其在页岩及高分子材料中的应用（英文）

主要研究压力敏感材料中含内压的空洞长大,如页岩或者高分子材料。采用数值方法研究含内压空洞的对称和非对称球形和柱形胞元的宏观力学行为。结果表明,压力敏感性及其空洞内压将极大影响空洞的形核与长大。在球形胞元情形中未出现柱形胞元的单轴拉伸现象。将胞元有限变形的数值计算结果与基于近期提出的考虑压力敏感材料中空洞长大的塑形力学模型的分析结果进行了对比。     

空洞敏感材料有限变形中的横向变形系数

讨论了空沿敏感韧性及超塑性材料由于变形损伤引起的体积膨胀，提出了弹塑性有限变形下表征体积膨胀特性的横向主形系数在各向同性损伤条件下的解析表达式。     

图像相关法在高分子材料拉伸性能研究中的应用

本文对聚碳酸酯(PC)和丙烯腈丁二烯苯乙烯(ABS)的合金(PC/ABS)高分子材料不同环境温度下的拉伸性能进行了试验研究。根据图像相关分析法编制了图像法位移测量分析软件,并对该分析软件的适用性进行了分析。系统研究了PC/ABS高分子材料拉伸试验时三个方向的位移场和应变场。根据测得的位移场研究了该高分子材料拉伸过程中应变和应变率的变化以及应力应变变化规律,并对试验结果进行了详细分析。结果表明,文中采用的图像法位移测量系统具有较高的测试精度;拉伸过程中,试件厚度方向的收缩变形大于宽度方向的收缩变形;颈缩过程区具有非常高的应变率,颈缩后的平直颈缩区的应变率快速下降到一个很低的应变率继续缓慢变形;尽管载荷位移曲线出现了较大的载荷下降现象,PC/ABS拉伸时的真应力应变曲线没有明显的应力下降现象出现,因此,载荷下降现象主要由颈缩时的截面减小引起;高分子材料PC/ABS的屈服应力随环境温度的升高而降低。     

1GPa压力脉冲发生器的研究及锰铜压阻技术在低压宽脉冲测量中的应用

本文阐述了新研究的一种在甘油介质中可产生0～1 GPa 压力宽脉冲的加载装置,以及用于该装置测量的相应锰铜计测试系统。同时对锰铜计在1 GPa以下的压阻系数进行了动态标定。实验结果表明,所研制的装置可产生脉宽10微秒以内,压力脉值为0～1 GPa的脉冲,与理论设计基本相符。     

微小电容检测技术在重力敏感器中的应用研究

对几种微小电容检测的方法进行了探讨，详细地阐述了交流电桥法微小电容检测的原理，分析了测量误差和相应的解决方法，为重力敏感器中的微小电容检测技术的实现奠定了基础。     

应变式压杆压力传感器在冲击波载荷测试中的应用

在近区爆炸冲击波载荷测量中,压电式压力传感器因上升时间短且强度高的高频压力脉冲作用而可能产生疲劳和过载失效。本文根据应力波在细长圆柱弹性杆中的传播特性,设计了一种应变式压杆压力传感器,当圆柱杆的一端受到压力波作用时,产生的弹性应力波沿杆轴向传播,通过测量杆的轴向应变可计算出杆中传播的应力波,从而得到作用在杆端的压力波。为了检验压杆压力传感器的性能,采用一个厚壁圆柱形爆炸容器,并将传感器安装在容器壁面不同位置上,测量中心装药产生的爆炸冲击波载荷,经反复试验,结果表明这种传感器性能是稳定可靠的。     

数字梯度敏感方法及其在航空透明件断裂力学中的应用

本文将数字梯度敏感方法用于航空透明件断裂力学问题研究。首先,基于透明材料的弹性-光学效应,建立了透明件应力状态与光线穿过透明件后的偏转角之间的关系。在平面应力假设下,利用最小二乘拟合建立了I型裂纹尖端应力强度因子与光学偏转角的关系。其次,通过数字梯度敏感方法搭建非接触光学测试平台,开展了带单边裂纹的航空有机玻璃试件三点弯曲实验,应用数字梯度敏感方法提取了I型裂纹尖端应力强度因子。最后,通过选择不同计算子区域和步长大小,分析了数字梯度敏感方法中的子区域和步长选择对计算结果的影响。研究结果表明,数字梯度敏感方法实验所得应力强度因子与经验公式计算所得结果偏差小于10%,通过增加最小二乘拟合项数以及合理的子区域和步长选择可以减小数字梯度敏感方法计算应力强度因子误差。     

EH4电磁成像系统在高速公路长大深埋隧道勘察中的应用研究

EH4电磁成像系统是一套双源型电磁法数据自动采集和处理的物探系统,它是CSAMT和MT的结合体。本文介绍了EH4的原理、特点、工作方法和资料处理。该系统首次运用于高速公路长大深埋隧道勘察中,结合其他手段,成功解译出了隧道的软弱层、地下水及断层破碎带的位置,为划分隧道围岩类别提供了较好的依据,同时也为高速公路长大深埋隧道提供了一种新的勘察方法。     

圆环式压力传感器的研究与应用

本文通过解圆环挠曲线微分方程及圆环面内振动微分方程，给出圆环式压力传感器理论设计方法．在设计实例中给出材料的选取、工艺处理、电测方法及其标定结果、结论     

相干梯度敏感(CGS)干涉测量技术及其应用研究

首先介绍了相干梯度敏感(CGS:Coherent Gradient Sensing)光学干涉测量技术的最新研究进展;其次,详细介绍了透射CGS方法和反射CGS方法的基本原理及实验技术;最后给出了CGS技术在各种断裂力学研究中的应用,不仅给出了各向同性均匀聚合物材料I型、混合型、V型裂纹及梯度材料I型裂纹尖端奇异场的控制方程,而且给出了对应各自情况下的CGS光学条纹模拟与实验图像。研究结果将为实验断裂力学研究提供基础性理论和实验应力分析手段。     

Void growth and cavitation in nonlinear viscoelastic solids

This paper discusses the growth of a pre-existing void in a nonlinear viscoelastic material subjected to remote hydrostatic tensions with different loading rates. The constitutive relation of this viscoelastic material is the one recently proposed by the present authors, which may be considered as a generalization of the non-Gaussian statistical theory in rubber elasticity. As the first order approx-imation, the above constitutive relation can be reduced to the “neo-Hookean” type viscoelastic one.Investigations of the influences of the material viscosity and the loading rate on the void growth, or on the cavitation are carried out. It is found that: (1) for generalized “inverse Langevin approximation” nonlinear viscoelastic materials, the cavitation limit does not exist, but there is a certain (remote) stress level at which the void will grow rapidly; (2) for generalized “Gaussian statistics” (neo-Hookean type) viscoelastic materials, the cavitation limit exists, and is an increasing function of the loading rate.The present discussions may be of importance in understanding the material failure process under high triaxial stress.     

密闭空间油页岩粉尘爆炸特性研究

为探究油页岩粉尘的爆炸特性,以龙口（Longkou, LK）、茂名（Maoming, MM）、桦甸（Huadian, HD）和抚顺（Fushun, FS）4种油页岩粉尘为研究对象,采用20 L球形爆炸装置,对这4种油页岩粉尘样品开展系统的爆炸实验,探讨油页岩粉尘的粉尘云质量浓度、粒径、挥发分、灰分、氧含量等对其爆炸特性的影响。结果表明:挥发分含量越高,油页岩粉尘的最大爆炸压力p_max、最大压力上升速率(dp/dt)_max越高,爆炸下限越低;挥发分和灰分对油页岩粉尘云爆炸分别有显著的促进和抑制作用。在37.52～106.43 μm粒径范围内,这4种油页岩粉尘样品的p_max和(dp/dt)_max均随其粉尘粒径的增大而降低,且到达最大爆炸压力的时间逐步缩短,说明小粒径油页岩粉尘较高的脱挥发速率能提高爆炸的反应程度。当粉尘质量浓度在400～2 500 g/m3范围内时,p_max和(dp/dt)_max均随粉尘云质量浓度的升高呈现先升高后降低的变化趋势,高于最佳粉尘云质量浓度（1 000 g/m3）时略有下降,但维持在较高水平,表明超过最佳质量浓度的粉尘云引燃后仍有较强的破坏力;LK样品的p_max和(dp/dt)_max均最高,分别为0.61 MPa和29.32 MPa/s,与挥发分含量相当的褐煤在同一水平,其爆炸下限为200 g/m3,在4种样品中最低,高于挥发分含量相当的褐煤;在N₂惰化条件下,LK样品的p_max和(dp/dt)_max均随环境氧含量的降低而降低,当氧含量降至15%时,系统不再发生爆炸,极限氧含量为16%。     

A physical model for nucleation and early growth of voids in ductile materials under dynamic loading

Spall fracture and other rapid tensile failures in ductile materials are often dominated by the rapid growth of voids. Recent research on the mechanics of void growth clearly shows that void nucleation may be represented as a bifurcation phenomenon, wherein a void forms spontaneously followed by highly localized plastic flow around the new void. Although thermal, viscoplastic, and work hardening effects all play an essential role in the earliest stages of nucleation and growth, the flow becomes dominated by spherical radial inertia, which soon causes all voids to grow asymptotically at the same rate, regardless of differences in initial conditions or constitutive details, provided only that there is the same density of matrix material and the same excess loading history beyond the cavitation stress.These two facts, initiation by bifurcation at a cavitation stress, at which a void first appears, and rapid domination by inertia, are used to postulate a simple, but physically realistic, model for nucleation and early growth of voids in a ductile material under rapid tensile loading. A reasonable statistical distribution for the cavitation stress at various nucleation sites and a simple similarity solution for inertially dominated void growth permit a simple calculation of the initiation and early growth of porosity in the material.Parametric analyses are presented to show the effect that loading rate, peak loading stress, density of nucleation sites, physical properties of the material, etc. have on the applied pressure and distribution of void sizes when a critical porosity is reached.     

The growth of the void in a hyperelastic rectangular plate under a uniaxial extension

In the present paper, the finite deformation and stress analysis for a hyperelastic rectangular plate with a center void under a uniaxial extension is studied. In order to consider the effect of the existence of the void on the deformation and stress of the plate, the problem is reduced to the deformation and stress analysis for a hyperelastic annular plate and its approximate solution is obtained from the minimum potential energy principle. The growth of the cavitation is also numerically computed and analysed.Project supported by the National Natural Science Foundation of China     

Coupled modeling of damage growth and permeability variation in brittle rocks

This paper presents a coupled model for anisotropic damage and permeability evolution by using a micro–macro approach. The damage state is represented by a second order tensor. The evolution of damage is determined from a crack propagation criterion. The free enthalpy function of cracked material is obtained by using micromechanical considerations. It is assumed that cracks exhibit normal aperture which is coupled with the crack growth due to asperities of crack faces. By using Darcy’s law for macroscopic fluid flow and assuming laminar flow in microcracks, the overall permeability of the RVE is obtained by a volume averaging procedure taking into account crack aperture in each orientation.     

The non-isothermal rheological behaviour of molten polymers: Shear and elongational stress growth of polyisobutylene under heating

Summary Data of stress growth under both shear and elongational kinematics have been taken in presence of heating temperature ramps on a commerical polyisobutylene.The experimental results have been analysed on the basis of a generalized Maxwell model already proved to be very accurate in predicting the isothermal behaviour. A good agreement is observed between the theoretical predictions and the experimental results.Also the features usually observed in volume-temperature curves by effect of cooling acrossT _g are qualitatively reproduced by the model.With 6 figures     

Modeling of crack growth in ductile solids: a three-dimensional analysis

A population of several spherical voids is included in a three-dimensional, small scale yielding model. Two distinct void growth mechanisms, put forth by [Int. J. Solids Struct. 39 (2002) 3581] for the case of a two-dimensional model containing cylindrical voids, are well contained in the model developed in this study for spherical voids. A material failure criterion, based on the occurrence of void coalescence in the unit cell model, is established. The critical ligament reduction ratio, which varies with stress triaxiality and initial porosity, is used to determine ligament failure between the crack tip and the nearest void. A comparison of crack initiation toughness of the model containing cylindrical voids with the model containing spherical voids reveals that the material having a sizeable fraction of spherical voids is tougher than the material having cylindrical voids. The proposed material failure determination method is then used to establish the fracture resistance curve (J–R curve) of the material. For a ductile material containing a small volume fraction of microscopic voids initially, the void by void growth mechanism prevails, which results in a J–R curve having steep slope. On the other hand, for a ductile material containing a large volume fraction of initial voids, the multiple voids interaction mechanism prevails, which results in a flat J–R curve. Next, the effect of T-stress on fracture resistance is examined. Finally, nucleation and growth of secondary microvoids and their effects on void coalescence are briefly discussed.     

Impact of texture on stress growth in thermotropic liquid crystalline polymers subjected to step-shear

The Landau-de Gennes tensor order parameter equations of nemato-dynamics are formulated, solved and used to find the impact of textural transformation on stress growth in thermotropic liquid crystalline polymers subjected to shear start-up flow. The simulated textural transformations include nucleation and annihilation of twist inversion walls. Coarsening processes include wall-wall annihilation, wall pinching and wall-bounding surface reactions. In the absence of defect-related effects, the stress growth is characterized by an early stress plateau, intermediate power law growth, and a late stage stress plateau. As the Deborah number (De) increases, flow-induced textural transformations affect the late stage and then the intermediate stress growth stage. Defects are found to be stress sinks, and so removal of defects increases stress. At lower Deborah numbers, few defects arise and coarsening rates are low, so the main texture effect in this regime is in the late stage plateau region, causing localized step increases. At Deborah numbers close to one, nucleation and coarsening rates increase, and textural effects appear closer and closer to the intermediate stress growth regime. As De increases further, coarsening by pinching processes overcomes nucleation, and all defects disappear in the intermediate stress growth regime, causing the stress growth to exhibit a smooth staircase shape. Strain and amplitude scaling is not observed. Simulated textural transformations show that smooth staircase stress growth is the result of defect annihilation processes. The non-monotonic stress growth is consistent with experimental observations. Simulated textures provide specific knowledge important to the eventual understanding of the rheologies of textured liquid crystal polymers.     

Hydrodynamics of two-phase flow in vertical up and down-flow across a horizontal tube bundle

Flow patterns, void fraction and friction pressure drop measurements were made for an adiabatic, vertical up-and-down, two-phase flow of air–water mixtures across a horizontal in-line, 5×20 tube bundle with a pitch-to-diameter ratio of 1.28. The flow patterns in the cross-flow zones were obtained and flow pattern maps were constructed. The data of average void fraction were less than the values predicted by a homogenous flow model and showed a strong mass velocity effect, but were well-correlated in terms of the Martinelli parameter X_tt and liquid-only Froude number Fr_LO. The two-phase friction multiplier data could be well-correlated with the Martinelli parameter.     

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.