晶格失配应变对铁电薄膜铁电性能的影响

采用与时间有关的Ginzburg-Landau方程,在考虑表面效应的条件下研究了晶格失配应变对外延铁电薄膜铁电性能的影响,通过外推长度考虑表面效应。获得了不同应变情况下的铁电薄膜电滞回线及蝶形应变迟滞回线。结果表明,剩余极化强度和矫顽场与压应变和张应变密切相关,其值强烈依赖于晶格失配应变。

塑性应变比各向异性度与制耳率之间关系探讨

采用成形试验机和万能材料试验机,对DC01、DC06、HC340LA、HC420LA钢进行了制耳试验和室温拉伸试验,获得了其制耳率和不同计算条件下的塑性应变比各向异性度Δr,并分析了Δr与Z的关系。分析结果表明,采用单点法测定塑性应变比r值时,r值与应变的路径特征干扰了试样结果的测定,试样结果间的离散性较大,塑性应变比各向异性度Δr与制耳率Z无对应关系。采用回归方法测定r值时,可以有效消除r值与应变的路径特征的干扰,塑性应变比各向异性度Δr与制耳率Z成比例关系。

纳米催化剂Pt/C的X射线衍射线形分析

X射线衍射线形与晶体材料的微观结构密切相关.在晶粒尺寸衍射线形和微应变衍射线形可由Voigt函数近似描述的前提下,本文较详细地论述了由X射线衍射线形分析获取晶粒尺寸和位错等微观结构信息的方法.采用这种方法,对乙二醇还原法制备的Pt/C催化剂进行了X射线衍射线形分析.样品晶粒尺寸分布的对数正态均值为0.95 nm,对数正态方差为0.37.X射线衍射线形分析所得晶粒尺寸分布与透射电镜的测试结果符合较好.对样品的衍射线形积分宽度进行细致的比较,发现存在各向异性展宽现象.如果衍射线的各向异性展宽主要是由伯格斯矢量为1/2〈110〉的位错引起,可进一步计算位错密度值.结果表明,位错组态无论是螺型位错还是刃型位错,位错密度值的量级均约为1015/m2.

Strain anisotropy models for refined diffraction line profile analysis in cubic metals

The present work examined the anisotropy magnitudes obtained from different elastic models of cubic metals(Cu,5383 Al alloy,FCC austenite steel and BCC steel)to explore the origin of strain anisotropy.The results showed that stable intersections were observed from the modeled and experimental plots of the reciprocal elastic modulus(1/Ehkl)and orientation parameter(Γ).The effectiveness of quasi elasto-plastic model based method in correcting strain anisotropy was further verified in cold-worked specimens.For the important input parameters in dislocation model based diffraction line profile analysis methods,the average diffraction contrast factors(■)of dislocations were observed to depend on elastic constants.Interesting intersections were found from linear dependence of■onΓ.The conventional input■values indicated distinct dependencies on given elastic constants in diffraction line profile analysis.Accordingly,a refined approach was proposed by adopting the optimized intersections as input values,by which more reliable results could be obtained in practical applications.

Evolution of anisotropy during sandstone rockburst process under double-faces unloading

Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility.P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus.The P-wave velocities were calculated in both two directions to analyze their patterns.To find a characteristic precursor for rockburst,the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k,defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes.The results show that rockburst occurs on the two free surfaces asynchronously.The rockburst failure occurs in the following order:crack generation,rock peeling,particle ejection,and rock fracture.In the process of rockburst under double-face unloading,the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy.The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one,i.e.,isotropy.The rocks with horizontal bedding planes will reach the isotropic state before rockburst,which could be considered as a characteristic precursor of this kind of rockburst.

Redistribution and magnitude of stresses around horse shoe and circular excavations opened in anisotropic rock

In this paper numerical analysis of underground structures, taking account the transverse isotropy system of rocks, was done using CAST 3M code by varying the shape of excavation and the coefficient of earth pressure k. Numerical results reveal that the anisotropy behavior, the shape of hole and the coefficient of earth pressure k have significant influence to the mining induced stress field and rock deformations which directly control the stability of underground excavation design. The magnitude of horizontal stress obtained for the horse shoe shape excavation(25.2 MPa for k = 1; 52.7 MPa for k = 2)is lower than the magnitude obtained for circular hole(26.4 MPa for k = 1; 59.5 MPa for k = 2).Therefore, we have concluded that the horse shoe shape offers the best stability and the best design for engineer. The anisotropy system presented by rock mass can also influence the redistribution of stresses around hole opened. Numerical results have revealed that the magnitude of redistribution of horizontal stresses obtained for transverse isotropic rock(12.1 MPa for k = 0.5; 25.2 MPa for k = 1 and52.7 MPa for k = 2) is less than those obtained in the case of isotropic rock(27.6 MPa for k = 1;48.6 MPa for k = 2 and 90.81 MPa for k = 2). The more the rock has the anisotropic behavior, the more the mass of rock around the tunnel is stable.

Equivalent strain hardening exponent of anisotropic materials based on spherical indentation response

Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel method was proposed to estimate the equivalent strain hardening exponent of anisotropic materials based on an equivalent energy method. By performing extensive finite element (FE) simulations of the spherical indentation on anisotropic materials, dimensionless function was proposed to correlate the strain hardening exponent of anisotropic materials with the indentation imprint parameters. And then, a mathematic expression on the strain hardening exponent of anisotropic materials with the indentation imprint was established to estimate the equivalent strain hardening exponent of anisotropic materials by directly solving this dimensionless function. Additionally, Meyer equation was modified to determine the yield stress of anisotropic materials. The effectiveness and reliability of the new method were verified by the numerical examples and by its application on the TC1M engineering material.

Softening response under undrained compression following anisotropic consolidation

Experimental evidence has indicated that clay exhibits strain-softening response under undrained compression following anisotropic consolidation.The purpose of this work was to propose a modeling method under critical state theory of soil mechanics.Based on experimental data on different types of clay,a simple double-surface model was developed considering explicitly the location of critical state by incorporating the density state into constitutive equations.The model was then used to simulate undrained triaxial compression tests performed on isotropically and anisotropically consolidated samples with different stress ratios.The predictions were compared with experimental results.All simulations demonstrate that the proposed approach is capable of describing the drained and undrained compression behaviors following isotropic and anisotropic consolidations.

Effect Analysis of High Strain Rate and Anisotropy on Tension⁃Compression Asymmetry of Aluminum Alloy 7050

Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.

Anisotropic Lattice Strain of Composite Materials of LiMnO2 and H/D-Substituted Chiral Cyanide-Bridged Ni（Ⅱ）-Fe（Ⅲ） Coordination Polymers

Composite materials composed of LiMnO2, a typical electrode material for lithium ion battery, and a chiral cyanide-bridged Ni（Ⅱ）-Fe（Ⅲ） coordination polymer [NiL2][Fe（CN）6]·4H2O （Ni-Fe, H-form） （L = （1R,2R）-（-）-1,2-cyclohexane-diamine） or its deuterium isomer, [NiL2][Fe（CN）6]·4D2O （Ni-Fe, D-form） have been prepared by the various ratios （w/w） of Ni-Fe：LiMnO2 = 10：0 （pure Ni-Fe）, 9：1, 8：2, 7：3, 6：4, 5：5, 4：6, 3：7, 2：8, 1：9 and 0：10 （pure LiMnO2）. Gradual shift of IR （infrared） spectra by changing the ratios and losing difference between H-form and D-form of Ni-Fe due to isotope effects revealed adsorption of Ni-Fe onto LiMnO2 to form composite materials. Formation of composite materials of Ni-Fe and LiMnO2 could be also proved losing ferromagnetic behavior of LiMnO2 on increasing of the ratios of Ni-Fe in each composite. In contrast to smoothly positive thermal expansion of pure LiMnO2 along the crystallographic b axis, variable temperature powder XRD （X-ray diffraction） patterns at 100-300 K of the composite materials exhibited thermally-accessible lattice distortion along the b axis with different ratios. It is also proved deviation of ideal linear correlation of an evaluation function, In K = a/T ＋ b （where, K = （d（T） - d（0））/d（T）, d（T） denotes nλ/（sin 2θ） at T （K））.

Formability of the AMS 5596 Sheet in Comparison with EDDQ Steel Sheet

Some materials form better than others, moreover, a material that has the best formability for one stamping may behave very poorly in a stamping of another Configuration. The forming limit of a metal sheet is generally given in terms of the limiting principal strains under different loading conditions and represented by the so-called FLD （forming limit diagram）. In view of the difficulty to experimentally determine the forming limits, many researchers have sought to predict FLD. The formability of sheet metal has frequently been expressed by the value of strain hardening exponent and plastic anisotropy ratio. The stress-strain and hardening behaviour of a material is very important in determining its resistance to plastic instability. For these reasons, extensive test programs are often carried out in an attempt to correlate material formability with value of some mechanical properties. In this study, mechanical properties and the FLD of the AMS 5596 sheet metal was determined by using uniaxial tensile test and Marciniak＇s flat bottomed punch test respectively.

以猪肉为基准高水分组织化植物蛋白的工艺优化

组织化植物蛋白作为肉类替代品,存在质构单一、保水性不佳等亟待解决的问题,制约了组织化植物蛋白产品的商业化。其中,质构的仿真度是最大的壁垒,该论文研究了仿猪肉高水分组织化植物蛋白的生产工艺,以猪肉的应变各向异性为基准,对高水分组织化植物蛋白进行工艺优化。结果表明:影响高水分组织化植物蛋白应变各向异性大小的顺序为:加油量>淀粉含量>谷朊粉含量,优化的最佳原料配比为谷朊粉含量10.00%、加油量3.54%,淀粉含量20.45%。经过工艺优化,得到高水分组织化植物蛋白的品质指标为:硬度(12.94±0.17)kg、组织化度1.92±0.03、应变各向异性1.57,与猪肉的质地基本一致。

Remarkable anisotropic phonon response in uniaxially strained few-layer black phosphorus

Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on cry- stallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane A1 mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B2g and A2 modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.