黑磷的力学及摩擦学性能研究进展

归纳了黑磷在力学和摩擦学方面的理论计算和实验研究进展,重点总结了黑磷因其独特的褶皱结构而导致的负泊松比及力学性质的各向异性,关注了厚度、缺陷、预应变以及环境降解等因素对其力学性能的影响。黑磷优异的力学性能为运动传感器、柔性器件、安全装备以及微机电系统等的设计与开发提供了新的选择。应变以及缺陷对其力学性能的调控可以为黑磷的应用推广提供新的思路。大气环境条件下,黑磷的表面降解是阻碍其应用的一大瓶颈,但其化学活性可以在摩擦学领域中加以利用,实现超润滑。同时重点概述了近年来对黑磷的微观摩擦学研究,主要集中在黑磷摩擦性能的各向异性、厚度和载荷的影响,以及表面降解对润滑的贡献。黑磷纳米片、黑磷量子点等纳米材料在油基润滑、水基润滑以及聚合物复合材料方面的摩擦学研究表明,高载下黑磷的润滑性能优异,有望推动工程领域超润滑的实现。最后,对二维纳米材料黑磷未来的研究与发展做了进一步的展望。     

再制造电弧喷涂成形层的残余应力分析

阐述了热喷涂涂层中残余应力的产生原因,并利用XRD残余应力测试仪、纳米压痕仪、扫描电镜和X射线衍射仪研究了不同厚度和热处理温度下电弧喷涂7Cr13涂层的残余应力、弹性模量及涂层微观结构.结果表明,涂层的残余应力与厚度成正比关系.适当的热处理工艺能够释放涂层的残余拉应力,当热处理的温度在200～300 ℃之间时,涂层由拉应力转变为压应力,并随着温度的升高,压应力逐渐增大;涂层的弹性模量和热处理温度之间成正比关系.通过对涂层残余应力分布的研究,为喷涂成形较厚涂层提供了一定的理论依据和方法.     

The flow stress of PcBN cutting tool materials at high temperatures

The onset of plastic deformation has serious implications when predicting the useable life of a cutting tool material. Through simulation of the tool/workpiece interface it is possible to determine the combination of mean pressure and temperature that would produce plastic deformation in these materials. This paper describes the effects of temperature and mean pressure on the plastic deformation characteristics of a range of polycrystalline cubic boron nitride cutting tool materials. Using a novel soft impressor technique, the brittle–ductile transition temperatures for a range of polycrystalline cubic boron nitride materials has been identified. It will also be shown that the minimum mean pressure to cause plastic deformation is greatest in the polycrystalline cubic boron nitride aggregate materials but decreases with the addition of the volume fraction of titanium and with an increase in temperature.     

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研究了扬氏模量(E)、切变模量(G)和泊松比(μ)的关系,介绍了悬丝耦合弯曲共振法的优点,简单阐述了悬丝耦合弯曲共振法的原理,用悬丝耦合弯曲共振法测量金属试样的弹性模量。     

Study of metal injection molding of highly porous titanium by physical modeling and direct experiments

The prospects of metal injection molding (MIM) technique for manufacturing of highly porous titanium parts was studied by physical modeling, based on feedstock warm compaction experiments. The space holder method and typical MIM binder were used in all cases of the study. The influence of the starting powder (dehydrided and atomized) in feedstock on resulting properties of porous titanium was investigated. The size of space holder particles and space holder amount were adjusted to obtain porosity and pore size desired for medical implants application. NaCl and KCl were studied and compared as prospective space holder materials. The porous samples were characterized regarding their microstructure, uptake of interstitial contents and mechanical properties. For comparison, same investigations have been conducted on samples, which were prepared by established space holder technology based on cold isostatic pressing (CIP) and sintering. Finally, first direct MIM experiments and attempts of feedstock optimization were carried out. The peculiarities and problems of metal injection molding of highly porous titanium have been discussed.     

金属纤维多孔材料力学性能研究现状

详细论述了金属纤维多孔材料的拉伸性能、剪切性能、压缩性能和冲击性能等力学性能的研究进展,并简要叙述了应力波在多孔材料内部传播的研究现状,最后指出未来应加强金属纤维多孔材料的动态冲击性能及应力波在多孔材料内部的传播、衰减机制研究,从而进一步扩大金属纤维多孔材料的应用领域。     

Cooling rate effect on Young's modulus and hardness of a Zr-based metallic glass

It is known that cooling rate can affect the atomic structure and thus may possibly affect the mechanical properties of metallic glasses (MGs). In spite of the considerable efforts on the cooling rate, its effect on the mechanical properties is controversial at the present time. In this study, we present a micromechanical study of the cooling-rate effect on Young's moduli and hardness of the cast bulks and melt-spun ribbons for a Zr₅₅Pd₁₀Cu₂₀Ni₅Al₁₀ metallic glass. Using the classic nanoindentation method, the Young's moduli of the ribbon samples obtained at higher cooling rates were measured which appeared to be much lower than those of the bulk samples. However, through further experiments on slice samples cut from the as-cast bulks and finite-element (FE) analyses, we have clearly demonstrated that the measured difference in elastic moduli was mainly caused by the sample thickness effect in nanoindentation tests. To overcome such a confounding effect, microcompression experiments were performed on the as-cast and as-spun MG samples, respectively. Being consistent with the findings from nanoindentation, the microcompression results showed that the cooling rate, as ranging from ∼10² to ∼10⁶ K/s, essentially has no influence on the Young's modulus and hardness of the metallic glasses.     

Relating tensile, bending, and shear test data of asphalt binders to pavement performance

Eight different asphalt binders representing a wide range of applications for pavement construction were tested in uniaxial tension, bending, and shear stresses. Theoretical analyses were performed in this study to convert the data from the three engineering tests to stiffness moduli for predicting pavement performance. At low temperatures, high asphalt stiffness may induce pavement thermal cracking; thus, the allowable maximum stiffness was set at 1,000 MPa. At high temperatures, low asphalt stiffness may lead to pavement rutting (ruts in the road); master curves were constructed to rank the potential for rutting in the asphalts. All three viscoelastic functions were shown to be interchangeable within the linear viscoelastic region. When subjected to large deformation in the direct tension test, asphalt binders behaved nonlinear viscoelastic in which the data under bending, shear and tension modes were not comparable. The asphalts were, however, found to exhibit linear viscoelasticity up to the failure point in the steady-state strain region.     

IMPROVEMENT ON THE CALCULATION OF PLASTIC STRAIN RATIO IN BCC MONOCRYSTALS

Two improvements have been made on the calculation of plastic strain ratio(r value)inBCC monocrystals by considering the differences in the critical shear stresses among thethree slip systems and the rotation of crystal lattice.It is found that the results calulatedby the improved method are more rational.     

钢材切割现状及Fast切割软件的应用

现代切割技术有别于传统手工切割技术．它是基于现代计算机信息技术．针对不同的切割下料设备。对传统切割技术加以改进提高，发展成为以优化套料技术、钣金展开技术和数据库管理技术为代表的计算机辅助切割生产和管理软件。以有效提高钢材综合利用率，提高切割效率和切割质量．加强切割生产管理。     

Percussion capacitor discharge welding with a magnetic-pulsed drive

A mathematical model of the stress–strain state in drawing flux-cored wire, which takes into account the actual distribution of geometrical parameters, mechanical properties, and the conditions of contact friction at the bottom of the deformation zone, is developed. The model also takes into account the possibility of plastic deformation of the sheath.     

Determination of Young's modulus and yield stress of porous low-k materials by nanoindentation

In the present study, the concept of the ‘effectively shaped indenter’ was used to analyse nanoindentation data of rather soft films on hard substrates. This approach was introduced for monolithic materials by Pharr and co-workers some years ago [G.M. Pharr, A. Bolshakov: J. Mater. Res. 17 (2002) 2660, A. Bolshakov, W.C. Oliver, G.M. Pharr, MRS Symp. Proc 356 (1995) 675]. Substrate to layer moduli ratios range from nearly 60 to 160. With such soft and brittle materials (Young's modulus nearly 3 GPa or smaller, yield strength around 100 MPa), no completely elastic measurements can be performed even at low loads. Hence, an established method for the determination of yield stresses by means of nanoindentation, namely that of loading-partial-unloading [N. Schwarzer: ASME J. Tribology 122 (2000) 672, T. Chudoba, N. Schwarzer, F. Richter: Thin Solid Films 355-356 (1999) 284, T. Chudoba, N. Schwarzer, F. Richter: Surf. Coat. Technol. 127 (2000) 9] was not applicable. However, the ‘effectively shaped indenter concept’ allows one to separate the elastic stresses due to the penetration from the residual stresses caused by the inelastic deformation, assuming that their influence on the elastic stress field is small. Thus, by using this approach critical yield stresses of soft porous materials have been obtained. Additionally, the Young's modulus of these materials has also been determined by means of laser-generated surface acoustic wave (LSAW) measurements and the Oliver and Pharr method. In the latter case, a special extrapolation method for the indentation modulus had to be applied to correct for the substrate influence. The results by the different methods are compared and their deviations are discussed. As there is no complete solution available for the correction of the substrate influence on Young's modulus of the film when plastic deformation occurs during indentation, the authors are searching for an approach to approximate the elastic properties of a soft film on a hard substrate. It seems that the determination of the Young's modulus of very soft films cannot be separated from the determination of the yield stress. As an example for a low-k material actually of interest, porous silica xerogel films on silicon with porosities of 38 up to 51 vol.% were investigated.     

套裁排样在数控切割优化过程中的应用

板材下料问题是许多机械加工企业的实际问题,受加工车间生产模式、管理水平、人员素质、工艺手段等诸多因素限制,手工设计套裁方案不能对全局统筹把握.而套裁排样软件作为一种辅助工具,利用其特有的数据库系统,经过复杂运算,能够准确地辅助工程技术人员从复杂的工作中解脱出来,并使材料达到合理利用,以降低原材料的制造成本.     

Effect of moisture on hammer-milled glass-fiber-reinforced polyurethane

The effect of moisture on the dynamic properties of hammer-milled glass-fiber-reinforced polyurethane was investigated. Similar investigations were also made on an unfilled polyurethane matrix for comparison. Moisture was found to increase the shear modulus at lower temperatures due to the formation of ice. At higher temperatures, however, shear modulus decreased due to the plasticizing effect of water. Moisture also modified the damping properties of the material.     

光致弯曲聚合物的材料特性测试

一种具有双向形变记忆功能的光致弯曲聚合物材料,在光驱动型执行器中应用潜力较大。材料的力学性能及光致弯曲特性,是执行器结构设计和分析的必要依据。通过拉伸实验,了解到材料具有线弹性材料类似的力学性能,并得到了其弹性模量。通过对材料光致弯曲效应的分析,推导出光致弯曲曲率的表达式。利用该公式,对光致弯曲实验观测到的数据进行非线性拟合,得到材料的光致弯曲特性参数。计算曲率较好地符合了实验数据,证明了公式和参数的合理性。     

φ407mm冷轧圆盘剪切机间隙和重合度对剪切质量的影响分析

针对国内某钢铁企业冷轧线上φ407 mm双边圆盘剪切机剪切厚度为2.82 mm的带钢时出现切边不齐现象,本文利用有限元分析软件对该剪切系统(剪刃和带钢)进行了CAE分析,以此得出了带钢在被剪切位置的应力分布情况,并根据得出的仿真数据结合力学知识,分析了剪刃间隙和重合度对剪切力大小变化的影响以及剪切过程所产生的边界应力对剪切质量的影响.最后通过经验公式证明了数据的可靠性,并提出了改进剪切质量的措施.     

用超硬刀具材料制造刀具的方法及应用效果

介绍了陶瓷、金刚石、立方氮化硼三种超硬刀具材料制作刀具的方法以及切削加工中的应用效果.     

Thermal treatment effect on structural and mechanical properties of Cr–C coatings

In the present study, the effect of thermal treatment on the mechanical and structural properties of chromium carbide coatings with different thicknesses is evaluated. The coatings were deposited by cathodic magnetron sputtering on XC100 steel substrates. Samples were annealed in vacuum, at different temperatures ranging from 700 to 1000°C for 1?h, resulting in the formation of chromium carbides. X-ray diffraction (XRD), microanalysis X/energy-dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy analysis were used to characterise the samples. Mechanical properties were evaluated by nano-indentation tests and the residual stress was calculated with the Stoney formula. The XRD analysis suggests the formation of the Cr₇C₃, Cr₂₃C₆ carbides at 900°C. For thin films, they transformed totally to ternary (Cr, Fe)₇C₃ carbides and their partial transformation has been observed in the case of thick films at 1000°C, without the formation of Cr₃C₂. The EDS and XPS showed the diffusion mechanism between the chromium film and the steel substrate for the Cr, Fe, C, O elements during the annealing treatment. The increase of chromium film thickness from 0.5 to 2.64?µm, contributed to the significant enhancement of mechanical properties such as hardness (H) (from 12 to 26.3?GPa) and Young's Modulus (E) (from 250 to 330?GPa), respectively.     

单一尺寸矩形毛坯下料问题的一种确定性算法

针对单一尺寸矩形毛坯下料问题,讨论了如何用最少的库存板材切割出一定数量的单一尺寸矩形毛坯。提出1种切割工艺简单的5块排样方式,该排样方式将板材划分成5块区域,每块区域中矩形毛坯按照相同方向排列。设计了1种确定性算法求解下料方案,首先构造1种基于隐式枚举思想的算法确定整张板上的最优5块排样方式;然后对该算法进行扩展,使其能够求解部分板上的最优5块排样方式。采用算例将文中下料算法和文献中递归下料算法、拼合下料算法进行比较,数值模拟分析结果表明,文中的下料算法在切割工艺和板材利用率两方面均较为有效。