Laboratory investigation of boundary effect on pressure-settlement behavior of foundation soil with limited thickness involving geosynthetics

Plate loading tests were conducted to investigate the effect of a bottom boundary condition on the pressure-settlement behavior of a footing on sand with a limited thickness involving geosynthetics. Seven boundary materials including geosynthetics were used to create different boundary conditions at the bottom of the sand. Interface direct shear tests were conducted first to determine the interface friction angles between these boundary materials and sand, followed by plate loading tests to determine their pressure-settlement curves. Test results show that the sand with a limited thickness by a rigid bottom boundary had a higher bearing capacity than that with a larger thickness. The ultimate bearing capacity of the footing on the sand with a limited thickness generally increased with the increase of the interface friction angle. Geosynthetics provided better lateral restraint than other materials. An equation was developed to describe the relationship of the bearing capacity ratio of the sand with a limited thickness to that with a large thickness versus the soil thickness and the interface interaction coefficient. The effect of the boundary material on the back-calculated modulus of the sand was also evaluated.     

水轮机过流部件磨蚀机理的研究

分析了水轮机过渡部件磨蚀的特点,总结出过流部件的磨蚀主要是冲蚀磨损,气蚀破坏及它们的联合作用。决定冲磨损的关键因素是材料的弹性模量,影响气蚀破坏的主要因素是材料的硬度,提出了提高过流部件抗磨蚀性能的方法。     

基于Hermite插值的小波模极大值重构滤波的肌电信号消噪方法

为了消除混杂在肌电信号中的噪声,该文提出了基于Hermite插值的小波模极大值重构滤波的肌电信号消噪方法。该方法先对肌电信号进行小波分解;其次,根据小波系数的奇异性,利用信号与噪声模极大值在小波尺度上的不同变化特性,分离出信号与噪声;再次,用Hermite插值法重构小波系数;最后从重构的小波系数恢复成去噪后的信号。实验结果表明,Hermite插值的小波模极大值重构能有效地去除噪声,提高信噪比,且保留了肌电信号的细节信息,为肌电信号的特征提取和模式识别创造了良好的条件。     

The influence of indenter bluntness on the apparent contact stiffness of thin coatings

In the present paper, the influence of punch tip sharpness on the interpretation of indentation measurements is considered.Firstly, in order to obtain analytical insight into the nature of the problem, closed form solutions are presented for the indentation of a homogeneous elastic half-space by an axisymmetric indenter of arbitrary shape, including Hertzian, conical, and conical indenter with a rounded tip.Next, a fast and efficient numerical implementation of a semi-analytical approach to the solution of problems about frictionless axisymmetric indentation of an elastic layer on a dissimilar substrate is described. The approach allows rapid determination of the load-displacement curves for an arbitrary punch shape.The aim of the study was to explore the implications of a finite indenter tip radius for the problem of property identification of thin films. The variation of the apparent substrate stiffness with indentation depth was established for several generic indenter shapes, namely for flat, conical and parabolic punches, and for a conical punch with a rounded tip. It is demonstrated that in each of these cases the depth variation can be described by a simple curve belonging to a family of two-parametric functions. On the basis of these findings we assess the efficiency of using different punch shapes for property determination. A procedure is proposed for this purpose which relies on the use of the depth variation profiles established here. Finally, the influence of imperfect punch shape on the accuracy of analysis is considered.     

Molecular Dynamics Simulations of Polymer‐Bonded Explosives (PBXs): Modeling,Mechanical Properties and their Dependence on Temperatures and Concentrations of Binders

Two models, i.e. “covering” and “cutting” models, for the polymer‐bonded explosives (PBXs) were proposed for different researching aspects. Used for choosing polymeric binders, the “covering” models are mainly applied to find the relations of temperatures and concentrations respectively with elastic properties of the PBXs. The “cutting” model is especially used to describe the highly anisotropic behavior of 1,3,5‐triamino‐2,4,6‐trinitrobenzene crystals (TATB). These models were realized by using molecular dynamics methods. It is found that the ductility of crystalline TATB can be effectively improved by blending fluorine‐containing polymers in small amounts. The moduli for the PBXs decrease with increase in temperature and concentration of binders. Different crystalline surfaces interacting with the same polymer binder have different modulus‐decreasing effects due to the highly anisotropic behavior of TATB. The modulus‐decreasing effect for different crystalline surfaces ranking order is (010)≈(100)>(001).     

Quality Evaluation of RDX Crystalline Particles by Confined Quasi‐Static Compression Method

A confined, quasi‐static uniaxial compression method, named as the compressive stiffness test (CST), is promoted to evaluate the quality of different RDX crystalline particles which are obtained from commercial and reprocessed lots. This method is based on the fact that the fragmentation or fracture behavior in the compression process could be correlated to the external/internal defects of targeted crystalline particles. The quality difference between the commonly used RDX and reprocessed RDX can be easily discriminated by compaction curves and the defined initial secant modulus can be used as a quantitative parameter to grade RDX particles. The results show that the RDX recrystallized from mixed solvents and spheroidized by treatment with solvent is of much higher quality than the commonly used RDX, and the particle size as well as external characteristics exert limited effects on the compaction curves, but the key factor is internal defects, which affect the coherence strength of RDX crystalline particles. Qualitative optical image analysis and quantitative particle apparent density measurements by liquid density gradient tubes also give consistent results with those from the CST.     

输电线路暂态电压行波的故障特征及其小波分析

分析了电压行波的基本故障特征 ,给出了电压行波故障特征的新的数学描述———小波表示。建立起了电压行波的故障特征和小波变换模极大值之间的联系 :通过有限个具有明确物理意义的小波变换模极大值 ,完整、清晰地刻划了暂态电压行波的故障特征。为构造性能优良、可靠的行波测距和行波保护奠定了重要的数学基础。     

Young's Modulus Extraction Methods for Soft Tissue from Ultrasound Measurement System

Abstract

Young's Modulus of soft tissue is a key index to evaluate the biomechanical features of the soft tissue; it has a close relationship to the force and deformation of the soft tissue. In order to measure the force and the deformation of soft tissue, a specially designed device is used to link ultrasound and force transducers by mounting them in series. The combined transducers can simultaneously sense the compressive force and the deformation of the soft tissue. The measurement system is calibrated, before it is used, to collect the data. Based on the measured force and the measured deformation of the soft tissue, the analytics biomechanical model of the soft tissue can be obtained by data fitting.

In this paper, the biomechanical model of the soft tissue is assumed to be linear and possess viscous elasticity; when the model of the soft tissue is a linear model, the derived Young's Modulus of the soft tissue is a constant; when the model of the soft tissue is a viscoelastic model, the derived Young's Modulus is a function of the deformation of the tissue. Calibration data show that the maximal error of the measurement system is less than 1.9 µm, non‐linearity error γ_T is ±0.06%, and the static error band γ is ±0.07%. The measurement system can be used to diagnose the pathology of soft tissue.     

筵席：中国古代早期建筑模数研究

文章对中国古代以“筵席”作为建筑设计尺度中的基本计量单位从而确立了最早的模数制度进行了研究。