Expansion of spherical cavity of strain-softening materials with different elastic moduli of tension and compression

An expansion theory of spherical cavities in strain-softening materials with different moduli of tension and com-pression was presented. For geomaterials,two controlling parameters were introduced to take into account the different moduli and strain-softening properties. By means of elastic theory with different moduli and stress-softening models,general solutions cal-culating Tresca and Mohr-Coulomb materials' stress and displacement fields of expansion of spherical cavity were derived. The effects caused by different elastic moduli in tensile and compression and strain-softening rates on stress and displacement fields and development of plastic zone of expansion of cavity were analyzed. The results show that the ultimate expansion pressure,stress and displacement fields and development of plastic zone vary with the different elastic moduli and strain-softening prop-erties. If classical elastic theory is adopted and strain-softening properties are neglected,rather large errors may be the result.

Application of the Zisman Critical Surface Tension Technique to Textile Materials Using Contact Angle Measurements

This is the first one that applies the Zisman critical surface tension technique successfully to textile materials. It was accomplished by carefully determination of the contact angle of fabric. The deviation caused by the porous structure of the fabric will be taken into account. To do so, a Jens equation is applied, and the measured contact angles can be corrected. The surface porosity was determined by measurement and approximate calculation, and the chemical composition of the surface was characterized by means of attenuated total reflection Fourier-transform infrared(FTIR/ATR).

A Bionic Approach for Topology Optimization for Tension-only or Compression-only Design

A new bionic approach is presented to find the optimal topologies of a structure with tension-only or compression-onlymaterial based on bone remodelling theory.By traditional methods,the computational cost of topology optimization of thestructure is high due to material nonlinearity.To improve the efficiency of optimization,the reference-interval with material-replacement method is presented.In the method,firstly,the optimization process of a structure is considered as bone remodellingprocess under the same loading conditions.A reference interval of Strain Energy Density (SED),corresponding to thedead zone or lazy zone in bone mechanics,is adopted to control the update of the design variables.Secondly,a material-replacement scheme is used to simplify the Finite Element Analysis (FEA) of structure in optimization.In the operation ofmaterial-replacement,the original tension-only or compression-only material in design domain is replaced with a new isotropicmaterial and the Effective Strain Energy Density (ESED) of each element can be obtained.Finally,the update of design variablesis determined by comparing the local ESED and the current reference interval of SED,e.g.,the increment of a relativedensity is nonzero if the local ESED is out of the current reference interval.Numerical results validate the method.

EFFECTIVE ELASTIC MODULUS OF BONE-LIKE HIERARCHICAL MATERIALS

A shear-lag model is used to study the mechanical properties of bone-like hierarchical materials. The relationship between the overall effective modulus and the number of hierarchy level is obtained. The result is compared with that based on the tension-shear chain model and finite element simulation, respectively. It is shown that all three models can be used to describe the mechanical behavior of the hierarchical material when the number of hierarchy levels is small. By increasing the number of hierarchy level, the shear-lag result is consistent with the finite element result. However the tension-shear chain model leads to an opposite trend. The transition point position depends on the fraction of hard phase, aspect ratio and modulus ratio of hard phase to soft phase. Further discussion is performed on the flaw tolerance size and strength of hierarchical materials based on the shear-lag analysis.

Molecular design and applications of a nanostructure green Tripodal surface active ionic liquid in enhanced oil recovery: Interfacial tension reduction, wettability alteration, and emulsification

Surface active ionic liquids (SAILs) are considered as prominent materials in enhanced oil recovery thanks to their high interfacial activity. This study reports the preparation and applications of a nanostructure Tripodal imidazolium SAIL as an environmentally-friendly substitute to the conventional surfactants. The product has a star-like molecular structure centered by a triazine spacer, namely [(C_(4)im)_(3)TA][Cl_(3)], prepared by a one-step synthesis method and characterized with FT-IR, NMR, XRD, and SEM analysis methods. The interfacial tension of the system was decreased to about 78% at critical micelle concentration of less than 0.08 mol·dm^(−3). Increasing temperature, from 298.2 to 323.2 K, improved this capability. The solid surface wettability was changed from oil-wet to water-wet and 80% and 77% stable emulsions of crude oil–aqueous solutions were created after one day and one week, respectively. Compared to the Gemini kind homologous SAILs, the superior effects of the Tripodal SAIL were revealed and attributed to the strong hydrophobic branches in the molecule. The Frumkin adsorption isotherm precisely reproduced the generated IFT data, and accordingly, the adsorption and thermodynamic parameters were determined.

MATERIALS FOR RETENTION OF LIQUID CRYOGENS CONTAINED IN SPACE QUALIFIED COOLER

A new kind of material used in liquid cryogen cooler has been found and investigated in our group It is anticipated that the materials can be applied in the conditions of launching, rotation in any orientation and weightlessness. The mechanism on which the material relies is similar to 'sponge' trapping the liquid cryogens within its micro-pores with surface tension. Preliminary tests have been performed on wicking. Also,we apply the materials to the cryogenic optical cooler whjch needs to be maintained within the temperuture range of 80-100 K. The results are satisfactory.

Finite element method simulation for tensile process of sintered iron-base material

Different material properties leads to different metal fracture behaviors. Even if the powder material is composed of plastic metal, the fracture still does not show macroscopic plastic deformation characteristics if the material contains a large number of voids. Eight node isoparametric elastic plastic finite element method was used to simulate the tensile process of sintered powder material. By setting a number of voids in the analyzed metal cuboid, the initial density was taken into consideration. The material properties of the three dimensional solid for the tensile simulation were defined with reference to the known pure iron material parameters. The load displacement curves during elongation were obtained with a universal testing machine, and then the simulated curves were compared with the experimental results. The factors that cause the stress concentration and strength decrease were analyzed according to the simulated equivalent von Mises stress distribution.

炔属二醇表面活性剂在环氧树脂灌浆材料中的作用

通过在CW环氧树脂灌浆材料浆液中加入2种不同结构的非离子表面活性剂炔属二醇,制备了2种改性环氧树脂灌浆材料,并开展了黏度、表面张力、接触角、渗透性和浆材固化物力学强度的研究。结果表明:加入表面活性剂对浆液的黏度、浆材固结体抗压强度、抗拉强度无明显影响,但可以提高浆材的粘接强度和抗剪强度,降低浆液的表面张力和接触角,提高浆液在黏土中渗透性。其中,加入表面活性剂S 1对浆液的粘接强度、拉伸剪切强度和在黏土中的浸润渗透高度提升更为显著,分别提高了23.6%、37.5%和109.4%。基于以上试验,初步探讨了表面活性剂提高浆液渗透性的机理。

三种新型钢结构体系研究

传统粗放型建造方式存在环境污染、耗能过大等问题。近年来,建筑行业正向绿色节能方向转型,推动钢结构建筑的发展是实现这一转型的重要方法和必由之路。钢结构具有自重轻、强度大、易于安装等优点,根据社会现阶段发展的需求,各种钢结构体系应运而生。为促进新型钢结构体系的发展及其工程应用,结合笔者课题组近年来相关的研究方向和成果,对装配式钢结构、自适应索杆张力结构、不锈钢材料结构三种结构体系的研究进行了详细的总结与介绍。

灌浆插筋式模块钢结构连接节点力学性能试验研究

针对模块钢结构建筑间的连接问题,提出了一种新型的由钢筋与CGM灌浆料组成的灌浆插筋式模块钢结构连接节点形式,并采用试验和理论分析的方法,对节点柱的轴压性能、轴拉性能和抗弯性能进行了深入研究,提出了相应的承载力计算方法.研究结果表明:①在轴向压力作用下,此节点上下两侧空钢管发生屈曲破坏,轴压承载力约为钢管截面屈服承载力的97%,表明此节点具有较好的抗压承载能力;不同钢筋直径试件的荷载-位移曲线基本一致,表明节点的抗压承载力与钢筋直径无关;②在轴向拉力作用下,试件在节点的连接缝隙处发生分离,灌浆料表面呈现了斜向裂缝;在钢筋直径为14~18 mm的范围内,构件的极限抗拉承载力为钢管极限承载力的28%~32%,并且随着钢筋直径的增大,试件的极限抗拉承载力增大、延性减小;③在弯矩作用下,试件一侧受拉、另一侧受压,在节点的连接缝隙处钢管发生分离,受拉区灌浆料形成斜向裂缝;在钢筋直径为14~18 mm的范围内,构件的抗弯承载力为钢管承载力的37%~47%,并且随着钢筋直径的增大,试件的极限抗拉承载力增大、延性减小,试件的屈服位移和极限位移均增大.

历史与政治的张力:马克思政治哲学思想的独特意蕴——俞吾金教授历史与政治哲学研究方法探微

与各种超历史和纯观念论的政治哲学思想不同,马克思的政治哲学思想是建立在历史唯物主义的科学性与规律性的基础之上的,但与对历史唯物主义线性、机械化的理解不同,马克思将历史理解为有政治实践张力和弹性的历史,从而为政治行动的能动性与主体性留下了足够的空间。这意味着马克思政治哲学是充满张力的政治哲学,其是内在的和历史的,而不是外在的和抽象的,既给政治行动与实践足够的空间与场域,又为其规定了不得不直面的难题与困局。

STFE膜材力学试验与材料本构研究

STFE膜材是一种新型建筑膜材料,它具有良好的透光和透景性能,并且有较高的抗拉强度,可用于大跨度张拉结构中。本文针对这种新式膜材料,基于国内检测标准改进了单、双轴力学试验方法,并测定了其弹性模量、泊松比、剪切模量、徐变伸长率等力学参数。进一步地,提出了描述STFE膜材应力-应变关系与短期时变(徐变、应力松弛现象)力学性能的材料本构模型。试验结果表明,STFE膜材相对于传统织物涂层膜材,拥有更高的弹性模量和同等水平的徐变伸长率,相对于同样透光透景的ETFE膜材,STFE膜材的强度为其6~7倍,弹性模量为其6倍以上,且徐变伸长率不到其15%。综上所述,STFE膜材具有优异的建筑表现效果和力学性能,适合作为透明张拉膜结构的建筑材料。

模拟爆炸冲击加载下岩石破裂行为的改进JH2模型

JH2模型广泛应用于模拟脆性材料的动态力学行为,但是其强度准则和损伤定义存在一定不足,因此本文针对爆炸冲击荷载作用下的岩石材料提出了一个改进JH2模型.首先为强度模型增加了初始屈服面和非线性损伤尺度因子,对拉伸和压缩损伤分别进行拉压不对称处理,并将体积塑性应变引入到压缩损伤中.将该模型嵌入LS-DYNA材料子程序后,开展一系列单元测试、分离式霍普金森压杆(Split Hopkinson Pressure Bar, SHPB)动态劈裂试验和岩石爆破试验的数值模拟.数值模拟结果表明:改进后的JH2模型克服了原始JH2模型在损伤演化的拉压不对称特性、非线性应变硬化行为、洛德角效应和体积行为等方面的不足,证明了本文所提改进JH2模型的预测精度和应用潜力.

大连梭鱼湾专业足球场罩棚膜结构设计

大连梭鱼湾专业足球场罩棚膜结构采用张拉膜结构体系,膜结构沿屋盖两个对称轴1/4对称,主膜内环外环间共336个三角形膜单元,各膜以上斜索为谷索,屋盖设置五圈环向膜拱。屋盖覆盖材料采用PTFE膜材,内挑棚区域采用ETFE气枕。依据风洞试验和风致雪漂移数值模拟报告,对罩棚膜结构进行计算分析得出,在第一类荷载组合和第二类荷载组合作用下,罩棚膜结构经纬向应力均满足规范要求,标准组合下变形满足规范要求,结构设计指标均满足结构设计性能目标要求。另外,对膜面较大的单元设置膜面索可有效提高膜单元刚度及承载力,主拱间合理设置次拱可减小膜承载面积,提高膜单元刚度及承载力。

物性与张力:黄焕义实验陶艺的媒介观

对物性的不同探讨是现代陶艺与传统陶瓷艺术的显著差异。物性是指事物如其所示的样子。陶瓷媒介不再成为道德比附与他者意义的载体,其自身就成为独立的语言与价值所在。实验陶艺将陶瓷媒介的创造性、实验性、不确定性发挥到极致,这无不建立在对物性探讨的基础之上。论文从对陶瓷物性的探讨入手,结合黄焕义教授近年来的实验陶艺创作,从物性之思、张力之态、生态之意论述其对陶瓷媒介的观念与认知。

弹性体改性沥青防水卷材拉力测量不确定度的评定

文章通过对弹性体改性沥青防水卷材(SBS防水卷材)检测标准的学习与梳理,严格按照检验检测要求进行拉力试验,通过试验得到15组拉力(纵向)检测结果。通过分析影响防水卷材拉力测量不确定度结果的分量,根据JJF1059.1—2012《测量不确定度评定与表示技术规范》,采用测量不确定度A类和B类评定,得到拉力的合成标准不确定度结果。拉力测量不确定的评定,对于日常检验检测的严谨性以及临界值的判定具有指导意义。

Analysis for the residual prestress of composite barrel for railgun with tension winding

Based on the elastic theory of cylindrical shells and the theory of composite laminates,a prediction model for the residual prestress of the simplified round composite barrel for railgun is established.Only the fibre pretension is considered in this model.A three dimensional numerical simulation for the residual prestress in the railgun barrel is carried out,by combining the temperature differential method with the element birth and death technology.The results obtained by the two methods are compared.It reveals that the distribution trends of residual prestress are consistent.And the difference for residual prestress in the filament wound composite housing of barrel is relatively small.The same finite element method is used to analysis the residual prestress in the non-simplified composite barrels for railgun,which are under different control modes of winding tension.The results mean that the residual prestress in barrel will increase while the taper coefficient for winding is decreasing.Therefore,the sealing performance in bore is improved,but the strength of the filament wound composite housing drops.In addition,the axial and circumferential residual prestress in the filament wound composite housing with constant torque winding are close to the ones in iso-stress design for barrel.

The mathematic model of tension straightening process of magnesium alloy and experimental validation

The stress-strain curve of bending bar and the stress relax curve of AZ31 was obtained by a tension test using Gleeble-1500.The tension straightening process mainly consisted of the elastic loading-I and unloading stage,the elastic loading-II and unloading stage,and the elastic-plastic loading stage,which were based on the stretch force change during straightening.The circular bar straightening under one-dimensional bending was investigated and assumed to be linear strain-hardening elastic-plastic material.According to the elastic-plastic mechanics theory,the mathematical displacement-force model of a tension straightening process established,on which was based,the predicted displacement of tension straightening for various original deflection was calculated.The tension straightening experiment for AZ31 magnesium was conducted under the guidance of the predicted displacement.The experiment results present good straightness when there is a stress relaxation phenomenon or the temperature of tension straightening is 25℃.

Effect of wire tension on different output responses during wire electric discharge machining on AISI 304 stainless steel

WEDM is used in machining conductive materials where it is required to obtained complicated and intricate shapes with high accuracy.Various applications are in the field of automobile,medical industries,aerospace etc.WEDM is an economical machining option with short product development cycle.Surface roughness,kerf width,Material removal rate,Recast layer hardness and surface microhardness in WEDM are most important responses.In this paper,effect of varied Wire tension on SR,KW,MRR,RCL hardness and surface microhardness on AISI 304 have been investigated.Pulse on time,pulse off time,current and dielectric fluid are taken as fixed parameter.Results show that Wire tension influences the SR,MRR and Surface microhardness and has no effect on kerf width in case of Stainless steel304.

Fracture Analysis of Composites in High-speed Tension

In this paper the results of a high-speed tension experiment of the SiC_w/Al composite have been reported and a simplified theoretical model has been developed to study the fracture mechanism of composites in high-speed tension. This theoretical model provides a new explanation for the increase of dynamic fracture strength of composites in high-speed tension.