论高强度钢压杆稳定计算中的屈服强度因数

《钢结构设计规范》(GB 50017-2003)关于压杆稳定计算的规定一般以Q235钢为基础,并通过引入屈服强度因数ξ=(fy/235)^(1/2)使其适用于高强度钢压杆。但是,这一因数的运用在很多情况下过于简单化,致使高强度钢压杆承载潜力不能充分发挥。本文对轴压构件的板件进行的综合分析表明,中等和大长细比构件的板件宽厚比限值只有一部分需要和因数ξ挂钩。此项分析同时采取了两种准则,并考虑了构件初弯曲的影响。格构式轴压构件剪力分析表明,现行规范的公式(5.1.6)的因数ξ可以删去。此外,单边连接的单角钢压杆简化为轴压构件时,等效长细比只要部分乘以因数ξ即可。

东营凹陷陈南断层构造正反转及其油气成藏关系

济阳拗陷正反转构造存在与否一直存在争议.以东营凹陷陈南断层为例,通过地震资料及录、测井资料分析证实了陈南断层东营期末正反构造的存在,并进一步对陈南断层的反转特征、反转选择性及其与油气成藏关系进行了研究.结果表明:陈南断层反转区段按其走向分为3段,反转构造样式存在单一型和取直型;陈南断层反转强度因数平均为1.25,多数区段完全反转,北北西走向段反转强度最大;构造正反转对先存断层具有选择性,在相同的应力条件下,边界控盆断层优先发生反转,而反转断层是否发生取值则与先存断层倾角有关.陈南断层的反转时期与生烃高峰期的有效匹配及构造反转形成的良好圈闭环境为油气运移、聚集提供了有利条件.

Properties of W/DLC/W-S-C composite films fabricated by magnetron sputtering

A kind of W/DLC/W-S-C composite film was fabricated by magnetron sputtering method.Effects of WSx content on the structure and the adhesion of the composite films were investigated.In addition,tribological behavior of the composite films was studied in the conditions of the ambient air and N2 gas atmosphere by ball-on-disk tester.The results indicate that the composite films show dense and amorphous microstructure.The WCx and WSx compounds are found in amorphous diamond like carbon matrix in the top layers of W-S-C.A proper WSx content is beneficial for improving the adhesion of the composite films.In air atmosphere,the composite films with high C content have better wear resistance and the friction coefficients range from 0.15 to 0.25.In N2 condition,high WSx content is benefit for the wear resistance and the friction coefficients of the composite films range from 0.03 to 0.1.

Closing law and stress intensity factor of elliptical crack under compressive loading

The solution of surface displacement of an elliptical crack under compressive-shear loading was obtained by using the complex function method. The closing mode was established by analyzing the geometrical condition of closing crack, and the corresponding critical stress was solved. The result corrects the traditional viewpoint, in which there exist only open or close states for an elliptical crack, and points out that the local closing is also one of crack states. Based on them, the effect of the closed crack on stress intensity factor was discussed in detail, and its rational formulae are put forward.

选择坐标计算的最佳路线

本文介绍了用图的理论来解决三角网和导线网坐标计算最佳路线的方法，通过举例，说明方法的正确性。

Experimental study on dimension-form effect for compressive strength of coal

The uniaxial compression tests of cylinder standard specimens and different dimension cube specimens of No.13 coal seam of Jianxin Colliery were carried out using MTS, and the basic mechanics parameters of Jianxin Colliery 13 coal were studied. The dimension-form effect of uniaxial compression strength was analyzed. The exponent formula σc=6.928＋130.269 8 exp（-0.105 95D）of dimension effect was fitted. While the side length of specimen reaches 80 mm, its unaxial strength tends to a stable value which is called to be the strength of coal mass. Studies indicates that since the cube specimen suffered more shake than the cylinder one during machining and processing and the stress is centralized at four corners of cube during compressive experiment, the coal strength of standard cylinder specimen is higher than that of cube one.

Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks

In this paper, numerical method is used als. A typical unit of masonry is selected to serve merical model of RVE is established with detailed to study the strain rate effect on masonry materias a representative volume element （RVE）. Nudistinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor （DIF） of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results.

Feasibility analysis for monitoring fatigue crack in hydraulic turbine blades using acoustic emission technique

In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.

Interaction of a circular cavity and a beeline crack in right-angle plane impacted by SH-wave

The problem of scattering of SH-wave by a circular cavity and an arbitrary beeline crack in right-angle plane was investigated using the methods of Green's function,complex variables and muti-polar coordinates.Firstly,we constructed a suitable Green's function,which is an essential solution to the displacement field for the elastic right-angle plane possessing a circular cavity while bearing out-of-plane harmonic line source load at arbitrary point.Secondly,based on the method of crack-division,integration for solution was established,then expressions of displacement and stress were obtained while crack and circular cavities were both in existence.Finally,the dynamic stress concentration factor around the circular cavity and the dynamic stress intensity factor at crack tip were discussed to the cases of different parameters in numerical examples.Calculation results show that the crack produces adverse engineering influence on both of the dynamic stress concentration factor and the dynamic stress intensity factor.

Wing crack model subjected to high hydraulic pressure and far field stresses and its numerical simulation

By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length lcq of wing crack, two terms make up the stress intensity factor K1 at wing crack tip： one is the component K（1） for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K1^（2） due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method （FEM）. In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.

反复张力下V形切口圆条的表面裂纹的疲劳扩展(英文)

研究目的:在相同的反复张力下,研究V形切口圆条表面裂纹的疲劳扩展规律。研究方法:1.构建V形切口圆条模型(图1),基于线性二次元将模型表面离散成一个个网格点(图2);2.以AZ-6A-T5镁合金为例,利用J积分计算应力强度因数,利用NASGRO裂纹增长率模拟裂纹的疲劳扩展;3.通过研究不同的裂纹纵横比和对应的应力强度因数之间的相关性来研究裂纹的扩展。重要结论:1.在裂纹扩展时裂纹纵横比的初始值对断裂形状的发展有重要影响;2.裂纹纵横比对疲劳负荷寿命的作用比缺口半径更加明显;3.当裂纹前缘演变成一条直线形时可观察到不稳定的裂纹扩展;4.裂纹深度一定时,断裂纵横比越小,疲劳负荷寿命越短;5.当裂纹纵横比为0.6–0.7时,出现了不稳定的裂纹扩展。

A novel enriched CB shell element method for simulating arbitrary crack growth in pipes

In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness varia- tion and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the 'equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum en- ergy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.

剪切速率对平直节理摩擦行为的影响及其机制研究

认识平直岩石节理的摩擦行为是研究起伏、粗糙节理剪切力学性能的基础,对预防洞室失稳、边坡滑坡也具有重要意义。为探究平直节理的摩擦行为与剪切速率的相关关系,首先对类岩石人工节理进行5种剪切速率下的直剪试验,分析剪切强度、摩擦因数、剪切刚度、节理面磨损随剪切速率的变化;然后,结合颗粒离散元模拟,方法,从节理接触的角度分析了剪切速率对节理摩擦因数的部分影响机制。试验结果表明,随着剪切速率的增大,节理剪切强度和刚度均呈现减小的趋势,且减小的幅度逐渐减弱;不同法向压力作用下,剪切强度和剪切刚度随剪切速率的变化趋势基本一致;节理摩擦因数与剪切速率的对数呈负相关,拟合得到相应的经验模型;节理面的摩擦划痕深度随剪切速率的增大而减小,磨损面积受剪切速率的影响较小。模拟结果表明,随着剪切速率的增大,节理接触的中心点位置出现偏移,颗粒的接触重叠量减小,从而引起接触剪切力减小,宏观表现为节理剪切强度和摩擦因数的降低。剪切速率的增大,导致节理表面微凸体磨损深度减小,这是剪切速率对节理摩擦行为的一个重要影响机制。

Brittle-Ductile Transition of Ferroelectric Ceramics Induced by Thermally Activated Dislocation Emission

Thermally activated dislocation emission in high-temperature ferroelectric ceramics is investigated through an assumption of thermal stability and a novel analytical method. The stress intensity factor (SIF) arising from domain switching is evaluated by using a Green's function method, and the critical applied electric field intensity factor (CAEFIF) for brittle fracture at room temperature is obtained. Besides, the lowest temperature for single dislocation emission before brittle fracture is also obtained by constructing an energy balance. The multi-scale analysis of facture toughness of the ferroelectric ceramics at high temperature is carried out. Through the analysis, the CAEFIF for crack extension is recalculated. The results show that the competition and interaction effects between dislocation emission and brittle fracture are very obvious. Besides, the higher critical activation temperature, the more columns of obstacles will be overcome. Additionally, the shielding effect arising from thermally activated dislocations is remarkable, thus, the brittle-ductile transition can promote the fracture toughness of high-temperature ferroelectric ceramics.

The Action of Structure and Efficiency on Energy Intensity Variation in China- An Empirical Analysis Based on AWD

This paper discusses the factors influencing Chinese energy intensity from 1980 to 2003 based on adaptive weighting Divisia index method and the analyzing results are different in different phase. In period of 1980～1990, both the structure factor and the technology factor effected positively Chinese energy intensity＇s fall but the former became inefficacy and even turned out to be negative in 1991～2001 meanwhile the later factor strengthened its function. After 2001, the two factors promoted Chinese energy intensity＇s rising together. The conclusion is given in the end.

Massive heat transfer enhancement of Rayleigh-Benard turbulence over rough surfaces and under horizontal vibration

We carried out direct numerical simulations of turbulent Rayleigh-Benard convection(RBC)with accounting for both the roughness and the external vibration over the Rayleigh number range 10^(7)≤Ra≤10^(11) and the vibration frequency range 0<ω<1400.The triangular rough elements are uniformly distributed over the top and bottom surfaces,and the vibration is applied in the horizontal direction.It is shown that under the combined action of roughness and horizontal vibration,with increasing the vibration frequency ω,the heat transfer is initially decreased a little and then greatly enhanced after ω exceeds the critical value.The physical reason for massive heat-transfer-enhancement is that high frequency vibration destabilizes thermal boundary layers(BL)over rough surfaces,triggers abundant emissions of thermal plumes,and strengthens the motion of large-scale circulation(LSC),which consequently thins the thickness of thermal BL and heightens the convective transport.In addition,it is shown that vibration-induced heat-transfer-enhancement can obviously affect the scaling behavior between the heat flux and the Rayleigh number,and the scaling exponent increases with increasing ω,whereas the influence of vibration on the scaling behavior between the intensity of LSC and Ra is very weak.