The constitutive equations of finite strain poroelasticity in the light of a micro-macro approach

After recalling the constitutive equations of finite strain poroelasticity formulated at the macroscopic level, we adopt a microscopic point of view which consists of describing the fluid-saturated porous medium at a space scale on which the fluid and solid phases are geometrically distinct. The constitutive equations of poroelasticity are recovered from the analysis conducted on a representative elementary volume of porous material open to fluid mass exchange. The procedure relies upon the solution of a boundary value problem defined on the solid domain of the representative volume undergoing large elastic strains. The macroscopic potential, computed as the integral of the free energy density over the solid domain, is shown to depend on the macroscopic deformation gradient and the porous space volume as relevant variables. The corresponding stress-type variables obtained through the differentiation of this potential turn out to be the macroscopic Boussinesq stress tensor and the pore pressure. Furthermore, such a procedure makes it possible to establish the necessary and sufficient conditions to ensure the validity of an ‘effective stress’ formulation of the constitutive equations of finite strain poroelasticity. Such conditions are notably satisfied in the important case of an incompressible solid matrix.     

Condition Monitoring of Ground Anchorages by Dynamic Impulses: GRANIT System

The GRANIT system operates by applying an impulse of known force by means of an impact device that is attached to the tendon of the anchorage. The vibration response signals resulting from this impulse are complex in nature and require analysis to be undertaken in order to extract information from the vibrational response signatures that is relevant to the condition of the anchorage. In the system, the complicated relationship that exists between characteristics of an anchorage and its response to an impulse is identified and learned by a novel artificial intelligence network based on artificial intelligence techniques.The results presented in this paper demonstrate the potential of the GRANIT system to diagnose the integrity of ground anchorages at a site near Stone, England, by using a trained neural network capable of diagnosing the post-tension level of the anchorage. This neural network was used for the diagnosis of load in a second ground anchorage adjacent to the original anchorage used for the training of the neural network. Further tests were taken with a different anchor head configuration of the anchorage and a different relationship between the signature response of the anchorage to an applied impulse and its post-tension level was found.Problems encountered during the diagnosis of this second set of test signatures by the trained neural network are investigated with the use of a lumped parameter dynamic model. This model is able to identify the parameters in the anchorage system that affect this change in response signature. The results from the investigation lead to a new form of classification for the installed anchorages, based on their anchor head configuration.Laboratory strand anchorage tests were undertaken in order to compare with and validate the results obtained from the field tests and the lumped parameter dynamic model.     

A centrally cracked thin circular disk, Part I: 3D Elastic–plastic finite element analysis

A full field solution, based on small deformation, three-dimensional elastic–plastic finite element analysis of the centrally cracked thin disk under mode I loading has been performed. The solution for the stresses under small-scale yielding and lo!cally fully plastic state has been compared with the HRR plane stress solution. At the outside of the 3D zone, within a distance of rσ_o/J=18, HRR dominance is maintained in the presence of a significant amount of compressive stress along the crack flanks. Ahead of this region, the HRR field overestimate the stresses. These results demonstrate a completely reversed state of stress in the near crack front compared to that in the plane strain case. The combined effect of geometry and finite thickness of the specimen on elastic–plastic crack tip stress field has been explored. To the best of our knowledge, such an attempt in the published literature has not been made yet. For the qualitative assessment of the results some of the field parameters have been compared to the available experimental results of K, gives a fair estimate of the crack opening stress near the crack front at a distance of order 10⁻² in. On the basis of this analysis, the Linear Elastic Fracture Mechanics approach has been adopted in analyzing the fatigue crack extension experiments performed in the disk (Part II).     

用地面模拟试验识别卫星太阳电池翼伸展运动的各种阻尼参数

本文利用Lagnrange方程建立了卫星太阳电池翼伸展运动的数学模型.这是一个包含摩擦阻尼、结构阻尼和空气阻尼参数的非线性微分方程组.在用气垫消除了重力影响但存在空气阻尼的地面环境中,对实尺太阳电池翼模型进行了伸展运动的模拟试验并用频闪摄影技术记录了运动的时间历程.再利用最小p乘优化方法识别出该系统的各个阻尼参数.通过对系统运动方程进行数值积分求得的太阳电池翼的伸展运动历程与实测值相当吻合.取空气阻尼等于零,得出了太阳电池翼在无空气阻尼的太空中的伸展运动规律.     

基于光学和扫描显微平台的微尺度实验力学检测技术和装置研究

本文基于光学和扫描显微平台,介绍了本研究组在微尺度实验力学检测技术和设备方面的最新研究成果。在检测技术方面涉及显微散斑干涉技术、微标记阵列检测技术、晶粒变形分析技术、光学探针动静态变形分析技术;在检测系统和装置方面介绍了新近开发的双视场薄膜检测系统、散斑微干涉系统、微标记检测平台、AFM和SEM单轴拉伸装置、三维微定位与加载系统、微力传感器及其标定装置、微动平台驱动装置等。探讨了微尺度实验力学检测中的问题和新的检测技术,给出了一些典型的应用和相关装置。     

岩石加卸荷破坏细观机理CT实时分析

利用与CT(computerizedtomography)机配套的专用岩石三轴加载试验设备 ,采用CT实时试验的手段对连续加载试验条件下和卸围压应力作用下砂岩破坏细观机理进行了对比研究。结果表明 ,岩石的卸荷损伤演化破坏具有突发性 ,卸围压破坏导致的扩容比连续加载破坏时大.     

磁粉法检测表面裂纹概率曲线的测定

本文介绍了利用实物零件测定裂纹检出概率的方法，并作出了用磁粉法检测表面裂纹的检测概率曲线，为大型构件检测周期的确定提供了可靠数据，为结构损伤容限设计，可靠性设计提供了重要的依据。     

损伤和断裂的统一

本文讨论了连续损伤力学基础的缺陷,从微裂纹随机演化出发给损伤概念作出新的普适的统计定义,导出了损伤断裂几率的动力学方程,使损伤、断裂、统计、微观机理及宏观特性五者有机地相结合,从而有可能形成一个统一的损伤断裂微观统计理论。     

不同围压实验变形物质中的微观滑移方式标志研究

通过不同围压条件下岩石破裂粘滑或稳滑实验样品的微观对比观测研究，分析了压力对滑移方式标志的可能影响，提出在不同围压条件下，变形物质中赋存的微观粘滑或稳滑的识别标志，为类似围压条件下形成的天然样品微观滑移方式标志的识别提供了实验判据。     

An engineering approach to blade designs for low to medium pressure rise rotor-only axial fans

Low to medium pressure rise axial fan equipment of the arbitrary vortex flow rotor-only type is widely used in industrial and commercial applications, with many of the installations and rotor designs being far from optimum. Complex computational methods exist for analyzing flows in, for example, high-speed axial flow compressors with multistage blade rows; however, the designers and manufacturers of low-speed, general-purpose axial flow fan equipment have been reluctant to embrace this technology. A simpler yet reliable design technique is presented that allows this category of ducted axial fan rotors, in the presence of swirl-free inlet flow, to be designed to achieve a specified duty with sufficient accuracy for engineering purposes. Practical blade design recommendations and limits, similar to those that exist for free vortex flow axial rotors, have been established for the arbitrary vortex flow rotor-only case.

The technique employs a straightforward engineering approach to arbitrary vortex flow axial fan rotor design, and the equation set can be solved by using relatively simple numerical methods. Estimates of pressure rise and shaft power characteristics for a proposed fan/rotor design can be computed and the design loop iterated until an acceptable set of blade parameters is identified. It is also possible to analyze the performance of an existing axial fan installation as a prelude to the design of a more efficient and effective replacement rotor.

Experimental data used in validating the design and analysis techniques are also presented. These data include comprehensive Cobra pressure probe surveys of local flow parameters downstream of three different low boss ratio, low solidity, arbitrary vortex flow rotors (all with circular arc camber line type blades) as well as fan performance characteristics for one of the experimental rotors configured as a direct-exhaust fan unit. Installation-dependent factors such as direct-exhaust losses and tip clearance effects are also examined. The analytical technique is shown to provide acceptable estimates of fan/rotor pressure rise performance and shaft power characteristics over a moderately wide range of blade angles and operating conditions.