金属非对称循环下的匀变速加载问题

由损伤力学理论可知,疲劳是由材料内部的损伤演化导致的,但其损伤演化的机理并不清楚。为此,我们将高分子物理中断裂的分子理论推广应用于金属的疲劳损伤,认为金属的断裂是一个松驰过程,宏观断裂是微观原子键断裂热活化的结果。以Q235钢为例,在CMT5105万能电子试验机上进行拉压非对称循环疲劳试验。从原子键离解的视角出发并结合试验数据,讨论并推算诸多因素影响下匀、变速加载时非对称循环疲劳损伤演化律的具体形式。再将速率作为重点考虑因素提出了新的疲劳损伤演化律,分别讨论了匀、变速情况下损伤演化律的基本形式,并对速率相关参数因子进行了修正。结果表明,新的疲劳损伤演化律形式简单、参数少、应用广泛且与试验结果贴合较好。     

砼构件线差温度应力测试

按照砼结构设计规范第五批课题的要求，我们对砼结构因钢筋与砼之间的线膨胀系数差异引起的温度应力问题进行了研究。本文介绍对称配筋构件在均匀受热条件下，因线膨胀系数差异引起的温度应力的测试。     

面向RC结构损伤演变的位移相关型阻尼模型及参数识别

针对目前阻尼模型不能充分反映钢筋混凝土结构阻尼与损伤之间关系的不足,提出位移相关型非线性阻尼模型,该模型既能反映结构振动过程中的粘滞阻尼耗能又能反映与结构损伤相关的内摩擦耗能。将内摩擦阻尼分解为残余应力效应和粘结滑移效应。基于能量守恒原理提出模型中阻尼参数的识别方法,并进行数值验证。对一钢筋混凝土简支梁进行损伤加载和动力测试,基于位移相关型非线性阻尼模型和相关动力学模型识别各损伤状态下的阻尼参数,分析其变化规律及非线性阻尼与损伤之间的内在联系。结果表明位移相关型阻尼模型不仅能反映阻尼比随位移峰值的增大而增大的现象,还能反映阻尼比随损伤程度的演变规律。     

煤炭科学开采新理念与技术变革研究

煤炭产业作为我国重要的传统能源支柱产业,在经济发展新常态下也必将发生重大变化,以智能、安全、绿色为特征的科学开采成为趋势。本文基于煤炭科学开采新理念,提出了煤炭技术变革战略路线,论述了2016—2030年不同阶段、不同层次的煤炭变革技术,包括升级与换代技术、拓展与变革技术、引领与探索技术,提出了不同阶段需要重点研发的理论与技术。     

Temperature and Time Dependence on Recovery Stress Relaxation in Nickel Titanium Wire during Isothermal Holding at High Temperatures

In this study, the influence of kinematically constrained thermal cycling (heating, isothermal holding and cooling) on the recovery stress in annealed nickel titanium wire was investigated. A 4% pre‐strained nickel titanium wire was heated to temperatures (150, 200, 250 and 300 °C) much higher than the austenite finish temperature. It was observed that the maximum recovery stress obtained at different conditions decreases significantly after the first thermal cycle and reduces gradually with further increasing the number of thermal cycles. It was also seen that the recovery stress increases with time during isothermal holding at 150 °C. During isothermal holding at other temperatures, the recovery stress shows an exponential decrease, and the decrease rate of the recovery stress depends on the isothermal holding temperature. The higher isothermal holding temperature is the more the recovery stress decreases. The decrease rate reduces with increasing the number of thermal cycles.     

岩石冲击损伤演化规律数值流形方法模拟

采用应力波衰减损伤模型对仅适用于模拟基于线性本构关系和恒定载荷作用下物体变形规律的数值流形程序进行了扩展;利用扩展后的程序对岩石长杆在冲击载荷作用下的损伤演化规律进行了模拟,得出了不同位置点处的损伤演化曲线和材料总体的损伤演化曲线。模拟结果表明,损伤的增加主要集中在冲击载荷作用的初始阶段,随着时间的推移,应力波强度衰减,损伤将不再明显增加。     

Thermo-mechanical evolution of multilayer thin films: Part I. Mechanical behavior of Au/Cr/Si microcantilevers

MEMS microcantilever test structures were utilized to examine the microstructural evolution of Au/Cr/Si thin films subject to annealing. Curvature evolution of the micron-sized structures was measured in response to anneals at various times and temperatures. Particular emphasis was placed on the accelerated annealing condition of 225 °C for 24 h. The thermo-mechanical response of the microcantilevers consisted of both linear-elastic and inelastic regimes. The temperature at which the thermo-mechanical profile deviates from linear thermo-elasticity is influenced by the stress, curvature and/or the microstructure of the specimens. Stress analysis suggests that microstructural evolution, not plastic yielding, controls the inelastic portion of the thermo-mechanical profile. Maximum stress increases of 146.3 and 202.9 MPa (i.e. 500% relative to the as-deposited state) were observed in the gold layer of the microcantilevers of different silicon thickness, as the result of the inelastic strain at elevated temperature. Increasingly greater curvature change is observed for specimens as annealing temperature is increased up to 150 °C, whereas the magnitude of curvature change is diminished as annealing temperature is increased above 150 °C. A complex curvature evolution is observed at 225 °C over a 24-h timeframe. Curvature evolution during isothermal hold occurs in response to the development of intrinsic stress within the metals. Use of a nitrogen atmosphere or nano-thickness alumina surface coatings was seen to alter the stability of the curvature evolution at 225 °C. The critical thickness for a protective alumina passivation occurs between 6.5 and 32.5 nm. Thermo-mechanical behavior is discussed here, while the corresponding microstructural evolution is discussed in the second part of this paper.     

The Multiaxial constitutive law for concrete structures subjected to impact loading

Abstract

This paper aims to provide a constitutive law for describing the rate depedent triaxial behavior of concrete subjected to impact loading. The proposed damage‐plastic loading surface model is characterized by normality, continuity, convexity and associatedness. It utilizes two loading surfaces, of which the slanted ellipse loading surface describes the behavior associated with damage due to inelastic volume change and the other plasticity of no inelastic volume change. The smeared crack model is used for analysis. The contact‐impact relation is formulated based on the law of mass conservation, the law of linear momentum and the law of conservation of energy. The proper treatments are taken to modify the coalescence condition, release condition and maintained contact condition for two impact subjects. To calibrate the material constants of this constitutive law, one only needs to know the results of the uniaxial tensile test, the uniaxial compressive test, the biaxial and triaxial compressive test and the test which gives the rate dependent information of concrete.     

数字化矿山体系结构模型及其应用

分析国内外数字化矿山的概念及其研究现状,从3个层次给出数字化矿山基本内涵,从业务层面、数据层面、技术层面提出数字化矿山的应用模式和构成体系结构。设计了一个三层四级网络体系结构,并对每一层牵涉的关键技术都给出详细阐述。在此体系结构基础之上,结合试验煤矿给出了试验煤矿的具体实施方案、实施现状和实施效果。     

基于微博社区的大学生情绪语义网络结构挖掘

目的探讨新媒体时代下的大学生情绪风险管理对策。方法选取大学生在微博社交平台上的发言、回复等作为样本数据,通过UCINET构建出大学生情绪语义网络,再从整体网网络密度、中心性和情绪、行为、结构的对比分析对语义网络进行结构挖掘。结果 (1)在大学生情绪语义网络中,影响因素主要分为学习与考试。学业、毕业与社会、手机控、集体与人际关系四个派系。(2)四大派系的情绪传染与发散、行为表现与结构均存在差异性。结论本研究对于大学生情绪管理与把控有一定启示意义,对于加强社会安全风险管理和大学生教育的发展提供了一定程度的理论指导。     

TRIZ中技术进化定律、进化路线及应用

对发明问题解决理论（TRIZ）中的技术进化定律系统进行了分类及简单介绍,以实例说明进行路线是从结构进化的特点出发描述产品核心技术所处的状态序列,提出了基于TRIZ的问题求解搜索过程。用一工程实例说明了进化定律及进化路线的应用。     

Data mining and accelerated electronic structure theory as a tool in the search for new functional materials

A highly accelerated electronic structure implementation and data mining algorithms have been combined with structural data from the inorganic crystal structure database to generate materials properties for about 22,000 inorganic compounds. It is shown how data mining algorithms employed on the database can identify new functional materials with desired materials properties, resulting in a prediction of 136 novel materials with potential for use as detector materials for ionizing radiation. The methodology behind the automatized ab initio approach is presented, results are tabulated and a version of the complete database is made available at the internet web site <http://gurka.fysik.uu.se/ESP/> (Ref. [1]).     

U形板件模压各区应变演化规律研究

目的 探究U形件模压的应变演化规律,为U形件大塑性变形提升材料性能提供理论指导。方法 基于有限元仿真软件DEFORM对U形件进行了限制性模压仿真研究,分析了应变分布规律并对其进行了量化的讨论。结果 试样经过单道次挤压后,直齿区域应变呈现波动式分布,受到剪切作用的位置均呈现中心处应变较大并向两侧逐渐减小,在靠近齿拐角的区域应变最小。扇形齿区域应变分布规律为齿面跨度越小,应变越大,齿面跨度越大,应变越小。从两道次模压变形来看,随着变形道次的增加,整体应变显著增加。应变分布曲线的波动程度随着变形道次的增加有所降低,应变均匀性有所改善。结论 通过对直齿、扇形齿及其多道次的应变演化规律来看,减小齿宽及增加变形道次有助于累积应变。     

Thermal Evolution of Alumina Prepared by the Sol-Gel Technique

The thermal evolution of an alumina gel synthesized by hydrolysis of aluminium alkoxide (sol-gel technique) was studied by thermal analysis (DTA and TGA), X-ray diffraction, FTIR and NMR spectroscopies, and specific surface area measurements. Between 400 and 900°C, - and -aluminas were formed showing aluminium vacancies preferentially located in tetrahedral sites. The atomic rearrangements produced during -alumina formation are oriented to the progressive elimination of tetrahedral aluminium in the ultimate phase. The evolution of the specific surface area during heating is explained by changes in structure and microstructure.     

Experimental study on dynamic damage evolution of concrete under multi-axial stresses

The effect of stress state on the dynamic compressive strength and the dynamic damage evolution process of concretes are investigated by use of a Spilt Hopkinson Pressure Bar (SHPB) and the ultrasonic technique. The columned concrete specimen is encircled by a steel sleeve. The multi-axial loading includes the axial and the radial loadings. The axial loading is supplied by the incidence bar, and the radial ones are produced by the steel sleeve. Analysis of the dynamic damage evolution of the samples is based on the measurement of the changes of ultrasonic wave velocities before and after the impact tests. The waveforms in the test bars, the stress strain curves, the confining pressure of the specimen, the dynamic compressive strength and other information about the samples are obtained during the SHPB experiments. The results of the tests show that the loading rate and stress states of the specimen apparently influence the damage evolution process in concretes. The dynamic damage evolutions are accelerated with the increase of the strain rate and are delayed significantly under the confined pressure.     

TiC／Ni3Al系梯度材料的残余应力与工作应力计算及结构优化

测定了TiC／Ni3Al复合材料的物性参数．对TiC／Ni3Al系梯度材料在制备过程中产生的残余应力以及在隔热使用时产生的工作应力,进行了热弹性假设下的有限元模拟在综合考虑热应力最小、应力强度比值最小以及纯TiC侧应力状态的基础上,完成了FGM的热应力缓和设计与结构优化结果表明,按线性组成分布设计是体系的最佳设计．     

The Effect of the Stress-Relative Displacement Law on Failure Predictions Using the Cohesive Zone Model

Barenblatt has pioneered the use of the cohesive zone model to quantify the effect of material non-linearity on the fracture behaviour of materials. As a tribute to his outstanding contributions in the fracture field, the paper appraises the effect of the stress-relative displacement law on failure predictions using the cohesive zone model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical study of bluff body flow structures

Our recent progress in numerical studies of bluff body flow structures and a new method for the numerical analysis of near wake flow field for high Reynolds number flow are introduced. The paper consists of three parts. In part one, the evolution of wake vortex structure and variation of forces on a flat plate in harmonic oscillatory flows and in in-line steady-harmonic combined flows are presented by an improved discrete vortex method, as the Keulegan-Carpenter number (KC) varies from 2 to 40 and ratios ofU _m toU ₀ are ofO(10⁻¹),O(1) andO(10), respectively. In part 2, a domain decomposition hybrid method, combining the finite-difference and vortex methods for numerical simulation of unsteady viscous separated flow around a bluff body, is introduced. By the new method, some high resolution numerical visualization on near wake evolution behind a circular cylinder at Re=10², 10³ and 3×10³ are shown. In part 3, the mechanism and the dynamic process for the three-dimensional evolution of the Kármán vortex and vortex filaments in braid regions as well as the early features of turbulent structure in the wake behind a circular cylinder are presented numerically by the vortex dynamics method. This study was supported by the National Natural Science Foundation of China and the Laboratory for Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, as well as by the National Basic Research project “Nonlinear Science”.